Our data indicate that this action cannot be explained by an increased agonist-induced IP3 production or an overloaded SR Ca2+ pool in smooth muscle cells from guinea pig urinary bladder. The incubation of these cells with three different PKC inhibitors, such as Go6976, Go6983, and BIM 1, resulted in a higher SR Ca2+ leak revealed by inhibition of the SERCA pump with thapsigargin. This SR Ca2+ leakage was sensitive to protein translocation inhibitors such as emetine and anisomycin. Since this increased SR Ca2+ leak did not result in a depleted SR Ca2+ store, we have inferred there was a compensatory increase in SERCA pump activity, resulting in a higher steady-state. This new steady-state increased the frequency of Spontaneous Transient Outward Currents (STOCs), which reflect the activation of high conductance, Ca2+-sensitive potassium channels in response to RyR-mediated Ca2+ sparks. This increased STOC frequency triggered by PKC inhibition was restored to normal by inhibiting translocon-mediated Ca2+ leak with emetine. These results suggest a critical role of PKC-mediated translocon phosphorylation in regulating SR Ca2+ steady-state, which, in turn, alters SR Ca2+ releasing activity.PKC inhibitors stimulate Ca This action results in a chemical gradient that provides a driving force for Ca2+ discharge upon activation of Ca2+ release channels  and ryanodine receptor (RyR)  . The leaRCA pump . These cgulation . Despitechannels . In othechannels . Translochannels . This ch channel , reducinanslocon . Moreoveanslocon .2+ leak   . Agonisteceptors  or PLCβ eceptors , resulti2+ release in smooth muscle cells, particularly Go6976 because this inhibitor stimulates Ca2+ release while inhibiting the carbachol-induced IP3 response. This apparent paradox was clarified by showing that PKC inhibitors trigger SR Ca2+ leak that seems to be occurring via translocon, and SERCA pumps compensate for this leak. This new steady-state in the luminal SR Ca2+ level facilitates agonist-induced Ca2+ release. Our results suggest that PKC activity might be modulating translocon-mediated SR Ca2+ leak, which modifies SR Ca2+ releasing activity.We have studied the mechanism used by inhibitors of PKC to facilitate agonist-mediated Caad libitum. Precautions were implemented to minimize animal use and reduce pain and distress.All animal care and experimental procedures were performed according to the Mexican Official Norm for the Use and Care of Laboratory Animals (NOM-062-ZOO-1999). The protocol was reviewed and approved by the local Ethics Committee on Animal Experimentation  with 0306–06 and renewed with the reference number 0131–15. Animals were bred and housed in the Cinvestav Animal facility with clean air and controlled light and temperature. Food and water were given Single smooth muscle cells were isolated using the previously described method . The uriSmooth muscle cells were loaded with 2 μM Fura-2/AM in the dark for 1 h at room temperature. Fura-2 loaded smooth muscle cells were placed on the stage of an inverted microscope and dually excited with a PTI DeltaRamV attached to a Nikon Diaphot TMD inverted microscope. Fluorescence excited at 340 and 380 nm were recorded at 510 nm in response to the addition of 20 mM caffeine, 100 μM carbachol, or 10 μM thapsigargin dissolved in recording saline solution and applied using a puffer pipette placed 10 μm away from the cell. These compounds were applied to the cell with a WPI PV830 pico pump .2+]i , single muscle cells were patched in the whole-cell configuration and held at 0 mV. The frequency of STOCs was determined for 1 min. Digitized ion current data was stored to be analyzed offline. The frequency of STOCs was determined using the peak detector tool of the Origin program using a threshold ≥20 pA .3 production, we followed a procedure previously described , EDTA (50 mM), and KOH (1.5 M). The amount of IP3 produced was calculated using the fraction of labeled IP3 released from cerebellar IP3R microsomes with the equation: IP3 = k (1-b)/b, where the k value was obtained for each determination using 75 and 150 pmol of IP3 standards. The b value was obtained with the equation b = (sample-NS)/(Bo-NS), where Bo was one of the standards, and NS was the nonspecific binding signal . The recording saline solution contained (in mM): 137 NaCl, 5 KCl, 4 NaHCO3, 2 CaCl2, 2 MgCl2, 0.42 KH2PO4, 10 glucose, and 10 HEPES, pH 7.4 (NaOH). The pipette internal solution contained (in mM): 80 glutamic acid, 80 KOH, 5 NaCl, 40 KCl, 2 MgCl2, 2 Na2ATP, 0.1 GTP, 20 HEPES, pH 7.2 (KOH). The internal solution also contained 100 μM of Fura-2 acid in experiments where SR and cytosolic calcium were measured simultaneously. The Li solution contained (in mM): 120 NaCl, 10 LiCl, 4 KCl, 2 NaHCO3, 2 CaCl2, 1 MgSO4, 10 glucose, and 10 HEPES, pH 7.4 (NaOH).The dissociation solution contained (in mM): 55 NaCl, 6 KCl, 5 MgClMag-Fluo4/AM, Fura-2/AM, and Fura-2-free acid were purchased from Molecular Probes . Thapsigargin was purchased from RBI. All other chemicals were from Sigma-Aldrich. Fura-2/AM, Mag-Fluo4/AM, Go6976, Go6983, BIM1, and Thapsigargin were dissolved in a DMSO 1000x stock solution and stored before use. Fura-2-free acid and carbachol were dissolved in water, and aliquots were stored separately at -20°C before being used. Daily freshly dissolved caffeine was prepared in the recording saline solution. All experiments were performed at room temperature (24°C).3 [Ca2+]i, luminal SR Ca2+ level, and STOCs are reported as mean ± SEM, where n represents either the number of cells studied or the number of independent experiments to determine IP3 production. Statistical analysis was carried out with Student`s t-test or ANOVA using Dunnett or SNK posthoc analysis. The differences were considered significant when p < 0.05.Data for IP3) and diacylglycerol (DAG). The incubation with carbachol (100 μM) for only 5 s significantly increased more than double the IP3 production . Although the presence of lithium should be inhibiting 1IP phosphatase in our assay conditions  and 200 nM Go6976 for 30 min before the stimulation of IP3 production with carbachol  to 718 ± 67 nM (n = 19), the peak rate of rise (n = 11) to 919 ± 105 nM/s (n = 19) while the rising time (n = 11) to 1.96 ± 0.18 s (n = 19) by the inhibition of PKC with Go6976. Since Go6976 did not promote a larger carbachol-induced IP3 production, we studied the possibility that the incubation with Go6976 could result in an overloaded SR Ca2+ store. The smooth muscle SR is endowed with the IP3 receptor and Ryanodine Receptor (RyR); these receptors share the same SR Ca2+ store in this cell type  to 233 ± 25 nM  in cells incubated with 200 nM Go6976. A saturating concentration of caffeine (20 mM) that activates all RyR at once can be used as an indirect indicator of the size of the SR Ca2+ store. In this case, caffeine-induced [Ca2+]i response did not display any difference between cells incubated with Go6976 (n = 8) and control (n = 8). These data show that inhibition of PKC potentiates both the carbachol- and caffeine-induced [Ca2+]i responses, but it seems unlikely that this was due to an overloaded SR Ca2+ store.Despite the strong reduction in the carbachol-induced IPresponse  went fro of rise  increaseing time  was signell type . The app2+ level, we simultaneously recorded changes in Mag-fluo4 and Fura-2 fluorescence to measure modifications in the luminal SR (2+]i (2+ store does not present an evident Ca2+ leak under our recording conditions (2+]i because this pump no longer buffers the plasma membrane Ca2+ entry (2+ leak for the recorded time (2+ availability to release channels in smooth muscle cells (2+]i response was significantly diminished (2+]i response was 159 ± 15 nM (n = 7). However, the same protocol but in cells incubated with 200 nM Go6976 resulted in a clear reduction in the SR Ca2+ level in response to the inhibition of SERCA pumps with thapsigargin . The third application of carbachol-induced no further reduction of the luminal SR Ca2+ level nor any increase in the [Ca2+]i  was not different  when cells were incubated with 200 nM Go6976. If Go6976 had induced a Ca2+ overloaded SR, a smaller Ca2+ leak should be expected since a less leaky SR would be easier to overload with Ca2+. Nevertheless, Go6976 increased the SR Ca2+ leak.To study the effect of Go6976-induced PKC inhibition on the luminal SR Canditions . Indeed,le cells . Accordi [Ca2+]i . These o2+ leak similar to the one caused by Go6976 /sec), n = 4) was similar to the one obtained with only Go6976. These data imply that the effect of Go6976 was due to the inhibition of PKCs.Go6976 inhibits classic PKCs and PKD . To deteeduction , red bareduction . We decieduction . The slo2+ leak, implying the activation of release channels (IP3Rs or RyRs) or some other type of Ca2+-permeable channel in the SR. 2 mM MgCl2 inside the pipette solution inhibits the RyR-mediated SR Ca2+ leak. Yet, this condition did not interfere with the Go6976-induced SR Ca2+ leak  did not increase the BKCa current, while caffeine activated the BKCa current with the same increase in the [Ca2+]i. The frequency of STOCs increases with a higher RyR activity (n = 5), suggesting that the inhibition of PKC increased the spontaneous activation of RyRs. Moreover, the inhibition of IP3Rs with 5 mg/ml of heparin in the pipette solution did not modify the effect of Go6976 (n = 5). However, the presence of emetine (10 μM) fully inhibited the Go6976-induced increased STOCs frequency (n = 6) without interfering with the STOCs amplitude. Collectively, these data suggest that the inhibition of PKC in smooth muscle cells induces a translocon-mediated SR Ca2+ leak that appears to be compensated by an increase in the SERCA pump activity. This new steady-state seems to facilitate the spontaneous activation of RyRs.Spontaneous transient outward currents (STOCs) are potassium currents carried out by Ca of RyRs . Figure activity . The inc2+ release from the SR in response to carbachol and caffeine in smooth muscle cells isolated from guinea pig urinary bladder. However, we could not find evidence of an overloaded Ca2+ store to explain this effect. Moreover, PKC inhibition reveals a translocon-mediated SR Ca2+ leak without reducing the agonist-induced [Ca2+]i responses. We have inferred that this situation reflects increased compensatory SERCA pump activity. This new steady-state facilitates Ca2+ release by both IP3Rs and RyRs. The latter resulted in a higher STOCs frequency. Overall, these data point to the SR Ca2+ leak role in determining the steady-state luminal SR Ca2+ level, particularly the participation of translocon in defining the SR Ca2+ leakage.We have found that PKC inhibition stimulated Ca2+ level upon inhibition of the SERCA pump. This SR Ca2+ leak was not inhibited by MgCl2 or heparin in the pipette solution, arguing against RyRs or IP3Rs being the SR Ca2+ leak channels responding to the inhibitors of PKC. However, emetine and anisomycin inhibited this SR Ca2+ leak supporting the idea that Sec61 translocon participates in this SR Ca2+ leak.The inhibition of PKC with different inhibitors such as Go6976, Go6983, and BIM1 resulted in a reduction of the luminal SR Ca2+ leak in different cell types , Sec62, and Sec63 proteins, oligosaccharyltransferase complex , TRAM, and the TRAP protein complex  . Puromycll types . Howevera2+ leak . A resul2+ pool depletion. Accordingly, an extensive account of molecular mechanisms reduces translocon Ca2+ leak activity  have preferential access to Ca2+ trapped in luminal proteins (2+ release event. While the leak channels control SERCA pump activity by modifying the free luminal ER/SR [Ca2+], implying much smaller Ca2+ fluxes than when the total Ca2+ capacity of the ER/SR is involved. This separation between Ca2+ release channels and leak channels allows the ER/SR to function as a Ca2+ source without triggering ER stress by Ca2+ depletion or other activities that require an elevated free luminal [Ca2+]ER.The calcium release from internal stores is organized in discrete units , resultior IP3Rs . The ER/behavior . There aproteins , making 2+ leak activity of translocon, which appears to be compensated by a higher SERCA pump activity to avoid SR Ca2+ depletion. This increased steady-state results in accelerated Ca2+ release in response to activation of either IP3Rs or RyRs. These results point to the scenario where the translocon Ca2+ leak modulates the Ca2+-releasing activity of the SR Ca2+ store.Altogether, our results indicate that PKC inhibitors increase the Ca


Quite unexpectedly, the apical atom in the paddlewheel structure belongs to the carbamate carbonyl oxygen atom. Such extra coordination by the propargyl carbamate groups drastically reduces the MOF porosity, a feature that was also confirmed by BET measurements. However, the MOF functionality is retained at the external crystal surface where 2% of active terminal alkynes is located.A copper-based metal–organic framework (MOF) was prepared using a new linker, a 5-substituted isophthalic acid bearing a propargyl carbamate group, intended to provide a terminal alkyne function protruding from the material surface to generate supported gold species for potential catalytic applications. The novel material was fully characterized by spectroscopic analyses of different kinds: FTIR, Raman, EDX, and XPS, as well as by thermal and surface area measurements. Synchrotron X-ray diffraction data analysis, in particular, revealed that this MOF, labelled [Cu]· A copper-based metal–organic framework with a novel 5-substituted isophthalic linker bearing a propargyl carbamate group protruding from the material surface. As denticity and other stereochemical preferences make the different organic ligands prone to the formation of archetypal frameworks , it should not surprise that specific classes of ligands have received much more attention than others: benzene dicarboxylates , imidazolates, bis-pyrazolates, and topologically analogues with extended cores.8 Thus, a rational design of the network topology, with predictable size and shapes of the pores, has reached its maturity. Jointly with structural prediction, exemplified by the isoreticular chemistry approach, also thermal inertness, chemical stability in harsh conditions and, to some extent, the functional properties of the prepared MOFs can be rationally outlooked.9–11 However, when flexible residues are protruding from the ligand cores, the availability of a large “empty space” within the crystal makes prediction capability fail. In these conditions, a systematic study of the sample properties, which heavily depend on the actual “stable” structure, is required.Metal–Organic Frameworks (MOFs), also known as Porous Coordination Polymers (PCPs), are one of the most studied classes of crystalline solids, with a wide range of potential applications as functional materials in different advanced technological fields.3(BTC)2(H2O)3] compound ,12 one of the most extensively studied 3-dimensional porous coordination polymers, is a highly porous material  in which {Cu2} units are coordinated to four carboxylate groups to give the well-known paddle-wheel unit.6,13–17 Simpler ligands, like benzene-dicarboxylates (BDC), thanks to their structural rigidity  centers), have also been widely employed, as they can bear an additional, pendant and chemically tailored, functionality on the benzene ring.18–20As anticipated, benzene-polycarboxylato ligands are frequent choices for the construction of stable and performing metal–organic networks. One of the most common organic linkers is benzene-1,3,5-tricarboxylic acid (BTC). The related 3D- group anchored on different oxide supports  is capable of straightforwardly reducing Au(III) to Au(0), yielding supported gold nanoparticles (AuNPs) without the addition of any external reducing and/or stabilizing agent.21–23 The reactivity of the triple bond within this molecule has been additionally exploited to fabricate a novel amino-sulfide branched silica support by radical click thiol-yne (TYC) chemistry.24 Based on these results and taking into account that the chemical, structural, and functional behaviour of the gold nanoparticles reported above depend on the physico-chemical environment dictated by the support, we envisaged that the versatility demonstrated by the propargyl carbamate residue could be further exploited by anchoring it to different solid supports than oxides, for example within alkynyl-derivatized MOFs. Indeed, the isolation of a metal–organic framework starting from a suitably functionalized organic linker would ensure an even, dense, and possibly highly symmetric distribution of the reactive alkyne moiety in the material. Additionally, the material porosity and the presence of the metal nodes could affect the reactivity of the alkyne and induce different effects on the ensuing gold nanoparticles, than when the alkyne is attached onto the oxidic surfaces cited above.In recent years, our research group has shown that a propargyl carbamate [–N(H)C(O)O–CHi.e. 5-(2-{[(prop-2-yn-1-yloxy)carbonyl]amino}ethoxy)isophthalic acid , bearing a propargyl carbamate residue; we also discuss the optimized conditions for the synthesis of the novel Cu(ii)–MOF, [Cu]·xH2O derived therefrom, and, finally, we present a detailed, comprehensive multi-technique characterization by means of complementary analytical, structural and imaging tools.In this paper we report the synthesis of a new organic linker belonging to the substituted BDC class, 2.2.12YBDC, bearing a propargyl carbamate group, was prepared following the synthetic route depicted in The novel organic dicarboxylic linker 1,3-H2YBDC with Cu(NO3)2 · 2.5H2O in refluxing 2-propanol for 24 h employing a Cu : L molar ratio of 1.8 : 1 .As shown in 6 After filtration, a turquoise polycrystalline powder was obtained with yields above 90%. Thanks to the nearly quantitative formation of compound 6, the overall yield of the entire process approaches 90%, making the scale-up of this efficient synthesis highly viable.Employment of 2-propanol was found crucial: indeed the use of ethanol brought about partial esterification of the linker, hence causing erratic MOF yields and purity.2 and Cu2(OH)3NO3, in variable  amounts. Even by keeping them at a minimum, still a few percent  of these hydroxy-salts are always present and contaminate the MOF up to a maximum value of ca. 10 w/w%. X-ray powder diffraction, the most suitable technique for assessing the correct phase composition of the mixture, however, did not help in quantifying it, as the extreme texture of the contaminants made visible only a few  scale" fill="currentColor" stroke="none"><path d="M400 1000 l0 -40 -40 0 -40 0 0 -80 0 -80 -40 0 -40 0 0 -120 0 -120 -40 0 -40 0 0 -120 0 -120 -40 0 -40 0 0 -160 0 -160 80 0 80 0 0 40 0 40 40 0 40 0 0 40 0 40 40 0 40 0 0 40 0 40 -40 0 -40 0 0 -40 0 -40 -40 0 -40 0 0 -40 0 -40 -40 0 -40 0 0 120 0 120 40 0 40 0 0 40 0 40 40 0 40 0 0 40 0 40 40 0 40 0 0 40 0 40 40 0 40 0 0 120 0 120 40 0 40 0 0 120 0 120 -80 0 -80 0 0 -40z m80 -120 l0 -80 -40 0 -40 0 0 -120 0 -120 -40 0 -40 0 0 -40 0 -40 -40 0 -40 0 0 40 0 40 40 0 40 0 0 120 0 120 40 0 40 0 0 80 0 80 40 0 40 0 0 -80z"/></g></svg>) diffraction peaks. Indeed, crystal phase quantification by the Rietveld method25 relies on the experimentally determined scale factors and, if preferential orientation (texture) is present, on the accurate estimation of the so-called orientation distribution function.26 In the present case, where (00) diffraction peaks only were observed, neither the ODF nor the scale factor of the fully oriented (nanosized) crystal plates are accessible, as they mutually 100% correlate.X-ray evidences, shown in the ESIFinally, the target product is stable in water at r.t and at neutral pH and such stability was evaluated using XRD. After keeping the product in water for 24 h, no changes in the XRD pattern were observed ]·xH2O was first analysed by IR and Raman spectroscopy. As shown in the ESI file,−1 region of the ATR-IR spectrum of the Cu–MOF the very broad band due to the carboxylic acid OH stretching present in the ligand is totally absent, indicating that full deprotonation occurred, with the carboxylate ions involved in binding to the metal centres, very much as in similar compounds.27The coordination of the Cu−1 which are particularly diagnostic for the asymmetric and symmetric stretching mode of the carboxylate group (RCO2−). The difference Δν (213 cm−1) between the νas(1585 cm−1) and νs(1372 cm−1) stretching vibrations indicates that each carboxylate group is bonded to two different copper atoms in a bridging bidentate mode, whereas the band at 731 cm−1 can be attributed to bonding between copper and oxygen of YBDC.15,28–30 Another band, attributed to the ν scale" fill="currentColor" stroke="none"><path d="M0 440 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z M0 280 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z"/></g></svg>O) stretching of the carbamate residue, bound to the Chinese lantern in apical position , can be found at 1628 cm−1, i.e. at ca. 59 cm−1 lower frequencies than in the pristine ligand. This red shift is in line with previous observations reported for analogous fragments coordinating, through their carbonylic oxygen atoms, to Cu(ii) ions of molecular (mononuclear) complexes.31In addition, the IR spectrum Fig. S13 possessexH2O, 1,3-H2YBDC, and Cu(NO3)2 · 2.5H2O. The appearance of the Raman active band at 2135 cm−1, unobserved in the IR spectra, is assigned to –CC– stretching of the alkyne triple bond,28 and confirms that, during complexation, no changes in the structure of the organic linker have occurred nor is the triple bond involved in π–metal bond. The signals located at 1605 and 1004 cm−1 are associated with the benzene ring ν(CC) stretching modes, whereas the peaks at 807 and 745 cm−1 are ascribed to out-of-plane δ(C–H) and δ(CC) ring bending vibrations, respectively.32,33 In the low-frequencies region (600–200 cm−1 range), [Cu]·xH2O exhibits, in agreement with previous studies, two peaks at 495 and 276 cm−1, respectively assigned to the vibrational stretching modes of equatorial and axial Cu–O bonds.34,35Complementary information was gained by Raman spectroscopy; Fig. S14 in the ESIca. 1 . Thermogravimetric analyses (TGA) were carried out in air to determine the thermal stability of [Cu]·xH2O. The corresponding TGA profiles of 1,3-H2YBDC and [Cu]·xH2O are reported in vide infra) decompose at ca. 132 °C (Tonset for Cu(OH)2)36 and at ca. 175 °C (Tonset for Cu2(OH)3NO3)37 and are not evidenced in the TG trace, confirming their low percentage.The elemental analysis of the synthesized sample is in good agreement with the theoretical chemical composition, showing a Cu/N molar ratio of xH2O contains water molecules loosely bound to the framework (vide infra), very much as the prototypical channel hydrates found in zeolites and in molecular organic species of pharmaceutical interest, their amount can vary depending on the history of the sample and on the relative humidity conditions.38 Accordingly, the stoichiometry of this crystal phase is somewhat undefined, and may vary depending upon the external conditions.In the ideal absence of contaminants, TGA experiments can be safely used to estimate the amount of water content, but, as [Cu]·2YBDC  shows three main weight losses between 200 and 600 °C, due to organic material decomposition, and zero residual weight. The first two steps are interpreted by progressive loss of the propargyl fragments . Similarly, the copper-containing product  shows two decomposition steps in the 200–350 °C range , terminating at a temperature ca. 150 °C lower than in the pristine organic ligand. Such lower thermal stability of the organic skeleton within the MOF is tentatively attributed to assistance, during decomposition, of redox process(es) catalyzed by Cu(ii) ions. Furthermore, a residue of ≈26 wt% is present at 400 °C, with no significant variation up to 800 °C, which is presumably due to residual CuO. As a residual 21.6% only is calculated if the starting material were pure, the excess residue at high T speaks for the presence of carbonaceous residuals and only marginally to Cu-rich contaminants, the nature of which is presented in the Experimental section.The TGA plot for 1,3-H2.3xH2O (x ∼ 2) phase contains a complex network of 5-substituted isophthalate anions bound to Cu(ii) centers belonging to the common paddlewheel dimeric fragments  of Cu2(μ-COO)4(D)2 formulation, D being a neutral Lewis base, typically bound through a N or O atom 4(H2O)2 molecule. In line with previous data for analogous compounds,39 it shows a short Cu⋯Cu distance of 2.633(4) Å ·atom see . The dimT-1 ref. ] and simT-1 ref. ]. Unexpe.d's see . The pro2(μ-carboxylate)4 coordination sphere in apical positions. The complete structures (E and F panels) for the idealized and periodic a and b conformers (not including the weakly bound water atoms) show the terminal alkyne moieties pointing coherently into the same (tetrad axis-generated) crystal cavity. The remaining channels, accounting for ≈20% void space in both a and b models, are partially filled by water molecules, possibly disordered and of non-stoichiometric character. As powder diffraction of such complex material can provide only limited information on these guests, their amount and geometrical properties will not be discussed any further.The extended fragments shown in panels C and D highlight the location of the carbonyl oxygen atoms (O6a and O6b) completing the Cu5H5N)], where D = pyridine N atom.41 However, in [Cu]·xH2O, the layers are not disjointed, but are interlinked by the long propargyl carbamate residues (in both a and b conformations) completing the Cu2(μ-COO)4 coordination sphere with the apical O6a and O6b atoms.A simplified overall picture of the crystal structure is shown in 2.4xH2O species, while the tiny platelets are attributed to the layered nanosized copper hydroxide and hydroxy-nitrate evidenced in the XRD trace (see above). The compositional purity of the material under the electron beam was investigated by EDXS; the obtained spectrum , BE = 531.8 eV , due to O atoms bound to C and hydroxyl groups42,46,47 and (VII), BE = 533.3 eV, related to carboxylic oxygen atoms and/or a concurrent contribution from adsorbed water.42,43 The N 1s peaks , BE1s peaks  showed a3/2 and Cu 2p1/2 spin–orbit components  could be ascribed to Cu(ii) centers in the copper-containing metal–organic framework and in Cu(ii) hydroxides impurities.15,29,42,43,47 This attribution was in agreement with the presence of intense shake-up satellites centered at BE values ≈9.0 eV higher than the main spin–orbit components, that are considered as a finger-print for the predominant presence of d9 copper(ii) centers and are not detected in the case of Cu(i) .49,50The analysis of copper chemical state  required2.551 confirming the absence of flexibility of the Cu(ii)-isophthalate framework and of its many congeners.39Surface area and pore volume were determined by measuring the adsorption isotherm of nitrogen at 77 K after pre-treating the as made sample under vacuum; the (fully reversible) isotherm, shown in R2 = 0.99757, BET R2 = 0.99986); the Langmuir surface area was found to be 18.4 ± 0.9 m2 g−1, while the BET surface area was 14.5 ± 0.8 m2 g−1. The estimated pore volume was 46 mm3 g−1, while that derived from mercury52 was about two times larger (105 mm3 g−1).The BET model fits the isotherm slightly better than Langmuir in the low pressure region , a rather small specific surface area of the internal voids (of only 100 m2 g−1), accounting for 17.1% of the crystal volume. Given that this approach usually provides an estimate of an upper limit , our measurements are roughly in line with what expected, and possibly further lowered by the occluding effect of coprecipitated nanosized Cu hydroxide and hydroxonitrates lowering the channel accessibility. As a reference values for isostructural compound, we have taken the (pyridine free) copper isophthalate easily derived from the published coordinates of the MOF presented in literature; in this case, SSA = 1509 m2 g−1 and void percentage = 49.9%.57The reported BET for Cu–BTC MOFs are usually above 1000 m2 dumbbells in the structure of [Cu], the size of the MOF cavities, arranged in poly-hourglass shaped channels running along a and b, is only 141 Å3. However, taking into account the approximate volume of the tetrachloroaurate anion  and the tabulated size of a single Au atom [≈43(2) Å3],58 we hardly envisage that the MOF could be used for capturing gold species inside the material, particularly, due to charge-balancing effects by additional counterions and by the expected presence of a solvation sphere. Thus, Au species may bind primarily on the MOF external surface, which is covered by a dense and even array of protruding propargyl-carbamate residues. Considering the size of crystalline domain estimated by the XRD model (of the order of 100 nm for isotropic particles), nearly 2% of the ligands lie on the crystal surface, possibly acting as catalytic sites.Using these values and normalizing to the number of Cu3.xH2O in high yields. The novel material was fully characterized by many analytical techniques. Synchrotron X-ray diffraction data, in particular, revealed that [Cu]·xH2O contains a complex network of 5-substituted isophthalate anions coordinated to Cu(ii) centers belonging to the common paddlewheel dimeric structure with a short Cu⋯Cu distance of 2.633(4) Å. Quite unexpectedly, the apical atom in the paddlewheel structure belongs to the carbonyl atom of the propargyl carbamate functionality, which is present with two equally populated alternative chain conformations. Such extra coordination by the propargyl carbamate groups drastically reduces the MOF porosity, as also confirmed by BET measurements. Although this evidence suggests that the internal pores of the material are available only to a small extent to host reactive gold species, this material can nonetheless be envisaged to be used for generation and anchoring of reduced gold species on the MOF surface, due to its dense, even array of propargyl-carbamate residues branching out therefrom and acting as binding sites able to capture Au(iii) ions and subsequently forming Au(0) clusters.In summary, we showed that the reaction of the novel 5-substituted organic linker 5-(2-{[(prop-2-yn-1-yloxy)carbonyl]-amino}ethoxy)isophthalic acid, bearing a propargyl carbamate substituent, with copper nitrate in refluxing 2-propanol leads to a new copper-based MOF [Cu]·4.4.13)2 · 2.5H2O (98%) and all chemicals employed in the synthesis were of analytical reagent grade and purchased from Sigma-Aldrich. Details regarding the synthesis and characterization of the new dicarboxylic linker 1,3-H2YBDC described in †Cu(NO4.2xH2O phase (x ∼ 2) were collected in transmission mode on polycrystalline powders loaded into a G50 glass capillary (0.5 mm in diameter) at the high-angle resolution Material Science MS-X04SA beamline of the Swiss Light Source (SLS) of the Paul Scherrer Institute. The operational wavelength, calibrated with the use of a silicon standard (NIST SRM 640c), was 0.56377 Å. The beamline description and the available set of optics and the Si microstrip 1D Mythen detector, with nominal step-size of 0.0036°, are detailed in ref. 2(OH)3(NO3) and Cu(OH)2. Fractional atomic coordinates and crystal structure details of [Cu]·xH2O were deposited with the CCDC (CSD code 2054304).Synchrotron data for structure solution of the [Cu]·14H15CuNO9, fw = 404.82 g mol−1, tetragonal, P4/ncc, a = b = 18.5281(2), c = 19.2204(4) Å, V = 6598.2(2) Å3, Z = 16, ρcalc = 1.629 g cm−3, μ = 7.1 cm−1; Rp and Rwp, 0.070 and 0.085 respectively, for 7708 data collected in the 2.25–30.00° 2θ range. RBragg = 0.045.C4.3Detailed information regarding instruments and methods employed for Electron Spray Ionization Mass Spectrometry (ESI-MS), Nuclear Magnetic Resonance (NMR), Attenuated Total Reflectance Fourier Transformed Infrared spectroscopy (ATR-IR), Thermogravimetric (TGA) analyses, and Atomic Absorption Spectroscopy (AAS) are reported in the ESI file.Field emission-scanning electron microscopy (FE-SEM) analysis was carried out by means of a Zeiss SUPRA 40VP instrument equipped with an INCAx-act PentaFET Precision spectrometer (Oxford Instruments) for energy dispersive X-ray spectroscopy (EDXS) characterization. The used primary beam acceleration voltages were comprised between 1 kV (for imaging) and 20 kV .−8 mbar, using a standard AlKα excitation source (hν = 1486.6 eV) and an analysis area with a diameter of 800 μm. Survey scans were acquired in the 0–1300 eV range . Higher resolution scans for the single photopeaks were recorded using the following settings: 58.7 eV pass energy, 0.1 eV per step, 0.05 s per step. Binding energy values  were corrected for charging by assigning to the adventitious C 1s peak associated with adventitious hydrocarbons a value of 284.8 eV.60 After a Shirley-type background subtraction,61 curve fitting was carried out by the XPS peak software.62 Atomic percentages (at%) were evaluated from integrated peak areas using sensitivity factors supplied by Perkin-Elmer.42X-ray photoelectron (XPS) characterization was performed using a Perkin-Elmer Φ 5600-ci instrument, at an operating pressure <10Raman spectra were recorded using a HORIBA Jobin Yvon T64000 spectrometer equipped with three monochromators in double subtractive configuration. The spectrometer was coupled to an Olympus BX40 confocal microscope equipped with 100×, 50×, 20×, and 10× objectives, for a lateral resolution lower than 1 μm with the 100× objective. An Ar+ laser emitting at 514.5 nm was used in which its output power was limited in order to avoid sample damaging (70–100 mW) and with long times and accumulations (about 50–60 min for spectrum).2) was above the lowest measurable value (0.5 m2). The errors on SA were calculated by standard deviation on 5 consecutive measurements. The sample was degassed at 1 × 10−3 mbar at 323 K for 2 h prior the measurement and after this operation ca. 5% mass loss was observed, in according with TGA. The BET model is usually considered the reference for MOF,1 however, in order to obtain the highest agreement between the measured area and the effective geometrical area, the correct interval of pressure must be taken in account;63 in our case the optimal pressure range was between 0 and p/p0 < 0.075.The adsorption isotherm was measured by using a static volumetric apparatus . The absolute total surface area (SA) of the solid powder  and Cu(NO3)2 · 2.5H2O  in 2-propanol (15 mL) was refluxed at 83 °C under stirring (300 rpm) for 24 h and then cooled to room temperature. The precipitate was collected by Buchner filtration and washed with 2-propanol (2 × 10 mL). The turquoise microcrystalline powder was then dried in an oven at 70 °C for 24 h, successively kept under vacuum (0.02 bar) for 24 h and stored under nitrogen to give 0.142 g of [Cu]·xH2O (yield 90% based on the organic acid and considering the Cu–MOF dihydrate). The reaction can be easily scaled up to produce gram quantities. The elemental analysis of the synthesized sample  is in good agreement with the calculated composition of [Cu]·2H2O .In a 100 mL round-bottom flask, a suspension of 1,3-HThere are no conflicts to declare.RA-011-D1RA02686K-s001RA-011-D1RA02686K-s002RA-011-D1RA02686K-s003RA-011-D1RA02686K-s004


The diethylene glycol plays an important role in tailoring the particle size of LiCoPO4. It is found that using a ratio of water/diethylene glycol of 1 : 6 (v/v), LiCoPO4 is obtained with a homogenous particle size of ∼150 nm. The bare LiCoPO4 prepared after heating in Ar exhibits high initial discharge capacity of 147 mA h g−1 at 0.1C with capacity retention of 70% after 40 cycles. This is attributed to the enhanced electronic conductivity of LiCoPO4 due to the presence of Co2P after firing under Ar. The effects of carbon, TiN and RuO2 coating are also examined. Contrary to other studies, it is found that the solvothermally synthesised LiCoPO4 samples produced here do not require conductive coatings to achieve good performance.Olivine-structured LiCoPO 4, followed by thermal treatment under Ar, air, 5%H2/N2 or NH3 was investigated.Solvothermal water-diethylene glycol synthesis of LiCoPO Li/Li+) and high theoretical capacity (167 mA h g−1), making it a promising future cathode material for high-voltage LIBs.25–30 However, use of LiCoPO4 as a cathode in practical applications has been hindered by its unsatisfactory cycle stability and rate capability, which could be mainly attributed to its low electronic conductivity17,31–36 and poor Li+ ionic conductivity36–41 relating to the one-dimensional ion transport channels,42 as well as to the decomposition of electrolytes under high potentials.43Development of energy storage and conversion devices is vital to address the increasing energy crisis and ecological concerns in the 21st century.4 have included: (1) size reduction and morphology control, decreasing the particle size of LiCoPO4 or tailoring its crystal growth orientation along the a–c plane to decrease the diffusion length of lithium ions in the insertion/extraction process;44,45 (2) surface modification (e.g. carbon coating), to enhance the electronic conductivity of the composite electrode by forming a conductive network among the LiCoPO4 particles;42,46 (3) ion doping with cations on either Li or Co sites to enhance the intrinsic electronic/ionic conductivity of LiCoPO4 although the mechanism is still in controversy.29,47 Among these approaches, the combination of size reduction and conductive agent coating (e.g. carbon coating) is regarded as an effective method to enhance the specific capacity and rate capability of LiCoPO4 cathode.48 Reducing the particle size of LiCoPO4 to the nanometer size range can shorten the Li ion transport distance, and thus reduce the time required for Li ion diffusion within the bulk LiCoPO4 material. Carbon coating not only improves the surface electrical conductivity of LiCoPO4 composite, which alleviates electrode polarization, but also provides effective protection from chemical attack by HF produced via electrolyte decomposition at high potentials in LiPF6 based electrolytes.48 Metal oxides30,49–52 and metal nitrides53–56 have been combined with other electrode materials to form structured composites with improved conductivity and stability. TiN and RuO2 are suitable for this purpose as they have good electrical conductivity, and good chemical and thermal stability.53,57Efforts to overcome the low electronic and ionic conductivity of LiCoPO4 with good electrochemical performance.25 Various synthesis methods such as hydrothermal/solvothermal syntheses,42,44 sol–gel processes58,59 and solid-state reactions60,61 have been proposed. Hydrothermal/solvothermal synthesis is facile and easily scalable, with mild reaction conditions and advantages of producing nanomaterials with controllable particle sizes and morphologies.62 Mixing an organic solvent and water as a co-solvent has been employed in the solvothermal synthesis of LiCoPO4.44,45,62–64 The solvent mixture can be beneficial for effectively tailoring the particle size of LiCoPO4 due to the high viscosity of the organic solvent,62,63 and the water component can promote the dissolution of the reagents.62 However, optimisation of solvothermal conditions to achieve LiCoPO4 cathodes with good specific capacity and cycle performance is still challenging.It is important to develop facile, easily scalable and controllable, time and energy saving synthetic routes to produce LiCoPO4 at relatively low temperatures (180 °C) using diethylene glycol (DEG) as a co-solvent is presented, followed by thermal treatment under Ar, air, 5%H2/N2 or NH3. Surface modification of LiCoPO4 with conductive agents like TiN, RuO2 and carbon has been investigated. Unusually in this work the electrochemical performance of samples produced by this method does not require the use of conductive coatings (e.g. carbon) to achieve good electrochemical performance.Herein, a novel, simple and fast solvothermal approach towards high-performance LiCoPO4 was prepared under solvothermal conditions. We previously reported the phase behaviour during charging of a sample made in this way.65 LiOH  was dissolved/dispersed in 45 ml deionised water/diethylene glycol (H2O/DEG) mixture, then H3PO4 aqueous solution  was added. CoSO4·7H2O  was dissolved in 25 ml H2O/DEG mixture and added slowly to the LiOH solution with constant stirring, during which time a blue/purple suspension formed. The volume ratio of H2O/DEG was set as pure H2O, 6 : 1, 3 : 1, 1 : 1, 1 : 3, 1 : 6 and pure DEG. The precursor solution was heated in a Parr 4748 Teflon-lined autoclave (125 cm3) at 180 °C for 10 h. The precipitate was then washed with deionized water and ethanol, and dried at 80 °C for 5 h under vacuum. The resulting material was heated at 5 °C min−1 to 600 °C and maintained for 3 h under Ar, air, NH3 or 5% H2/N2 to crystallise LiCoPO4.LiCoPO2 coated LiCoPO4 the uncrystallised or pre-fired LiCoPO4,  was manually ground in a pestle and mortar with sucrose  or ruthenium(iii) chloride hydrate  to obtain a uniform mix that was then heated under Ar as described above. The products were black powders and were ground before further characterisation. TiN modified LiCoPO4 powders were prepared using a propylamine cross-linking sol–gel process53,66–68 under nitrogen using glove box or Schlenk line conditions. Ti(NMe2)4  was dissolved in dry THF , and added to 0.5 g dry LiCoPO4 powder. nPrNH2  was slowly added. The solution gradually changed colour from yellow to red-orange. The suspension was stirred at room temperature for ∼16 h and dried in vacuo to form a sticky powder. This was heated under Ar or NH3 as described above for LiCoPO4 samples.To obtain carbon or RuOα radiation, and data was fitted using the GSAS package.69 Scanning electron microscopy (SEM) used a JEOL JSM-6500F (30 kV). Transmission electron microscopy (TEM) used a FEI Tecnai T12 (120 kV). Brunauer–Emmett–Teller (BET) surface area and pore size distribution measurements via N2 physisorption analysis were carried out with a Micromeritics TriStar II analyser. Electrochemical testing used a Biologics VMP-2 multichannel potentiostat. X-ray photoelectron spectroscopy (XPS) was collected with a two chamber Thermo K-alpha spectrometer with a monochromated Al K-alpha X-ray source (1486.6 eV) in constant analyser energy mode. Sample charging was prevented by use of a dual beam flood gun. X-rays were focused to a 400 μm spot at the sample surface. High resolution core peak spectra were recorded at 50 eV pass energy. Spectra were analysed using Casa XPS software. The binding energy scale was calibrated from the carbon at 285.0 eV. Core peaks were analysed with a nonlinear Shirley-type background.70 The peak positions and areas were optimized using a weighted least-square fitting method with 70% Gaussian and 30% Lorentzian line shapes. Several spectral analyses were applied at different positions for each sample to ensure the results were statistically reliable. Electronic and ionic conductivity was determined from the current–voltage measurement and electrochemical impedance spectroscopy on gold-coated sintered LiCoPO4 disks (11 mm in diameter and ∼0.5 mm in thickness).31,71,72 Current–voltage plots were collected at 20 mV s−1 over the range of −0.3 to +0.3 V (or larger voltage ranges) at room temperature. Electrochemical impedance spectroscopies were collected at 500 mV in the frequency range of 0.1 Hz to 200 kHz at room temperature.Powder X-ray diffraction used a Bruker D2 Phaser with CuK4 or TiN/carbon/RuO2 coated LiCoPO4 powders (75 wt%) with acetylene black  and polytetrafluoroethylene  in a pestle and mortar. The resulting solid paste was hand rolled (Durston Rolling Mill) into a film of ∼90 μm thickness and cut into circular disks with diameter of 11 mm. The pellet was then dried at 120 °C in vacuo for 12 h to obtain the cathode with a typical mass of ∼0.022 g. Swagelok cells were assembled in an argon-filled glove box with lithium foil (Rockwood Lithium GmbH) anodes and glass microfiber filter  separators soaked in 8 drops (∼0.4 ml) of 1 mol dm−3 LiPF6 in ethylene carbonate/ethylmethyl carbonate (EC : EMC = 3 : 7 in weight) electrolyte . Galvanostatic testing was carried out at 25 °C at various rates of charge/discharge  within the voltage range of 3.5–5 V (vs. Li/Li+).Electrodes for use in lithium half cells were prepared by manually mixing the LiCoPO4 samples were prepared by a solvothermal method. First, we present a systematic study on the effect of the solvents and heating environment to optimise the solvothermal conditions. Then, LiCoPO4 samples were coated with TiN, carbon or RuO2 with a variety of processing conditions and thicknesses to determine whether the expected conductivity enhancement and increased surface stability improved the electrochemical behaviour of the materials.LiCoPO4 samples were produced using H2O/DEG solvent mixtures with various volume ratios, followed by firing at 600 °C in an Ar environment, to determine the effect of solvents on their morphologies. The volume ratio of H2O/DEG in solvothermal synthesis was set as pure H2O, 6 : 1, 3 : 1, 1 : 1, 1 : 3, 1 : 6 and pure DEG, which corresponds to samples defined as LCP-H2O(Ar), LCP-6 : 1(Ar), LCP-3 : 1(Ar), LCP-1 : 1(Ar), LCP-1 : 3(Ar), LCP-1 : 6(Ar), LCP-DEG(Ar), respectively. The heating temperature affects purity, crystallite/particle size distribution and specific capacity of LiCoPO4.53 Most successful previous studies produce LiCoPO4 samples at 550–700 °C,45,73–75 and in this study samples were fired at 600 °C.Uncoated LiCoPO4 samples obtained using various ratios of H2O/DEG. The particle size of LiCoPO4 decreased from ∼10 μm to ∼80 nm with increasing DEG content  synthesis.42,76–78 The pore size distribution of LiCoPO4 samples obtained using various ratios of H2O/DEG were investigated via N2 physisorption analysis  pore size distributions calculated from the adsorption curves reveal that the main pore sizes of LiCoPO4 samples are 4–20 nm. These mesopores are created by the interfaces between nonporous LiCoPO4 particles. The control of particle sizes in solvent mixtures has been attributed to the increased viscosity of the solvent mixture when increasing DEG concentration, which can reduce mass transport to growing crystallite surfaces, thus results in decreasing LiCoPO4 particle size.63,79 Also, the solubility of the precursors decreases as the solvent mix becomes less polar, which increases the nucleation rate during the solvothermal process.45 For a given amount of precursor, more nuclei means less matter for each nucleus.45,80 Therefore, larger nucleation rate in solvothermal process could result in smaller LiCoPO4 particle size.The SEM images  show the content , and itst  and LCP-DEG(Ar) showed homogeneous particle size distribution with nanoparticle of less than 200 nm. This small particle size can reduce the length of Li-ion migration paths, and facilitate easier Li-ion transfer in LiCoPO4 crystals, thus enhancing the rate performance of LIBs.45,79,82 However, nanosized LiCoPO4 particles with high surface area can enlarge the electrode/electrolyte interface area, which leads to undesirable electrode/electrolyte by-reactions, thus resulting in a poor cycle stability.20 Hence, sample LCP-1 : 6(Ar) with particle size of ∼150 nm and a relatively small surface area of 5.4 m2 g−1 (compared to LCP-DEG(Ar) with surface area of 22.6 m2 g−1) was chosen for the following studies.Our previous review on LiCoPO4, but the intrinsic role and effects of various heating gases on LiCoPO4 has still not been fully ascertained and remains controversial.25 NH3 and 5% H2/N2 are typical heating gases to coat TiN and carbon onto electrode materials.25,48,53 Thus, it is important to evaluate whether heating in NH3 or 5% H2/N2 caused a deterioration in the LiCoPO4 properties. In this section, uncoated LiCoPO4 samples were produced by using the 1 : 6 (v/v) H2O/DEG co-solvent optimised above, and fired at 600 °C in Ar, air, 5% H2/N2 or NH3 to determine the effect of heating environment on their behaviour. Ar or air are typical heating environments in thermal treatment to crystallise LiCoPO4 samples  as expected. Table S14 samples. The Rietveld fits83 to this XRD data  are detectable according to the microanalysis results  and LCP(NH3) had initial discharge capacities of 147, 130, 139 and 132 mA h g−1, respectively. The capacity of LCP(Ar) decayed gradually with continuous cycling, retaining 102 mA h g−1 after 40 cycles, and 88 mA h g−1 after 57 cycles. The low coulombic efficiency values in the first cycle for these samples are caused by the decomposition of the electrolyte during charge at high potentials.62,86 The coulombic efficiency of LCP(Ar), which improved upon cycling, was 92% in the second cycle and maintains values higher than 95% after five cycles. LiCoPO4 fired in air or in reducing gases had lower initial discharge capacities and lost capacity more rapidly on cycling. A comparison of relevant articles using a hydrothermal/solvothermal methodology in the synthesis of LiCoPO4 olivine phosphate cathodes is presented in 4 has been optimised with conductive coatings (e.g. carbon). Overall the results suggested that Ar firing was the most effective heat treatment to apply for the crystallisation of LiCoPO4, but since air firing is also common in this system,75,87–89 both samples as well as uncrystallised LiCoPO4 were carried forward to test the surface modification of LiCoPO4 with TiN, RuO2 and carbon.The electrochemical performance of LiCoPO4 were chosen for coating, the uncrystallised LiCoPO4 directly after solvothermal synthesis, with the advantage of a single heating step, and the LiCoPO4 already crystallised in Ar or air  together with LiCoPO4, then firing under Ar.45,57 This solid-state process proved to be an easy and effective method to achieve carbon coatings on LiCoPO4.25,45 TiN coating used a propylamine-crosslinked sol–gel method, then firing under Ar or NH3. This sol–gel process has been shown to be effective to achieve TiN coatings onto LIB cathode materials according to our previous research.53Three kinds of LiCoPOr or air . RuO2 an2 and C coated LiCoPO4 samples   , so the 4 , which retained 102 mA h g−1 after 40 cycles  sample is good enough to provide competitive specific capacity and cycle stability.A similar position was observed with the Ar-fired LiCoPO4 . The cap0 cycles . The coa4 powders fired in Ar and air was evaluated with current–voltage measurements and electrochemical impedance spectroscopy. LiCoPO4 samples were pressed, sintered and gold-coated to produce self-standing LiCoPO4 disks, which were dry contacted with two silver paste electrodes. The linear current–voltage plots  and 0.64 mm for LCP(air) sample), A is the area of the LiCoPO4 pellets (95 mm2), and R is the resistance (42.2 Ω for LCP(Ar) and 1.7 × 107 Ω for LCP(air) sample). The conductivities of LCP(Ar) and LCP(air) are calculated to be ∼10−3 S cm−1 and ∼10−9 S cm−1, respectively. Current–voltage plots with larger voltage ranges are shown in Fig. S7,The electronic and ionic conductivity of LiCoPOge plots  showed t4 pellets, as presented in Fig. S8.−3 S cm−1, estimated from the value of the resistance and taking into account the dimension of the pellet. On the other hand, the LCP(air) sample shows much higher values of impedance  Co2P phase in LiCoPO4 cathode led to improved electrochemical performance. As the amount of the Co2P phase increased to 4 wt%, the electronic conductivity increased to ∼10−4 S cm−1 with a maximum discharge capacity of ∼120 mA h g−1 obtained. However, for LiCoPO4 cathodes with higher concentrations of Co2P, the capacities dropped rapidly due to the electrochemically inert Co2P phase, which improves the electronic conductivity but tends to hinder the Li+ insertion/extraction. Similar phenomena were also observed by Xu99 and Indris et al.88 Ma et al. demonstrated that the presence of Co2P can accelerate the electrolyte decomposition at high voltage in the charge process for LiCoPO4 due to the catalytic property of Co2P.100 Dimesso et al. suggested that the formation of Co2P occurs due to reduction reactions at the grain boundaries of the LiCoPO4 crystalline phase during annealing at high temperatures.101–107 Brutti et al. synthesized LiCoPO4via a solvothermal synthesis followed by heating under Ar atmosphere. It was found that the heating promotes Co2P precipitation on the LiCoPO4 particles surface together with loss of organic by-products formed in the solvothermal synthesis.108 Nallathamby et al. confirmed that the presence of Co2P as a second phase enhanced the conductivity and electrochemical performance of LiCoPO4. It was found that the Co2P is achievable only in an inert atmosphere. The LiCoPO4 cathode showed a discharge capacity of 123 mA h g−1 at 0.1C with capacity retention of 89% after 30 cycles, and rate capability of 81 mA h g−1 at 5C.61Wolfenstine 4 heated in Ar was considered likely to be due to the presence of Co2P on the surface on LiCoPO4. X-ray photoelectron spectroscopy (XPS) of LiCoPO4 samples fired under Ar and air is shown in 4 fired under Ar, the Li 1s signal located at 55.7 eV is well in accordance with the value reported for LiCoPO4.61 The C 1s spectrum consists of three peaks, with the main component at 285.0 eV corresponding to C–C, and the other two peaks observed at 287.1 eV and 289.0 eV attributed to C–O and O PBM data was replaced with SVG by xgml2pxml:<glyph-data id="z.dbd" format="PBM" resolution="300" x-size="8" y-size="10" xml:space="preserve">00000000000000000000000000000000111111110000000011111111000000000000000000000000</glyph-data><svg xmlns="http://www.w3.org/2000/svg" version="1.0" width="13.200000pt" height="16.000000pt" viewBox="0 0 13.200000 16.000000" preserveAspectRatio="xMidYMid meet"><metadata>Created by potrace 1.16, written by Peter Selinger 2001-2019</metadata><g transform="translate scale" fill="currentColor" stroke="none"><path d="M0 440 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z M0 280 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z"/></g></svg>C–O environments of carbon.1094 fired under Ar, the O 1s spectrum with a binding energy of 531.6 eV is in agreement with the air-fired sample and with the (PO4)3− environment in LiCoPO4,61 but an additional weak peak at 529.1 eV demonstrates the presence of a small amount of metal oxide (e.g. Li2O with binding energy of 528.6 eV for O 1s spectrum).110–112 The P 2p spectrum (2p3/2 and 2p1/2 doublet) shows the main component at 133.5–134.4 eV in accordance with LiCoPO4,91 and a doublet at lower binding energy (130.9–131.8 eV) that corresponds to Co2P.113 A small shift in binding energy of P 2p in Co2P (expected at around 129 eV) is likely to be due to a differential charging effect resulting from the different electrical conductivities at the surfaces of LiCoPO4 and Co2P.113–115 Co2P formation in Ar fired LiCoPO4 is attributed to the carbon-containing organic solvent (DEG) chosen for the synthesis, which can decompose at high temperature and the resulting carbon can cause carbothermal reduction to reduce the LiCoPO4 surface layers to Co2P during heating under inert atmosphere.33,34,61,101,105,108 This process also explains the relatively low carbon content measured in these samples by microanalysis. The Co 2p spectra are not fitted due to the complexity of the 2p spectra resulting from peak asymmetries, complex doublet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies.116 For the LiCoPO4 fired under Ar, the 2p3/2 and 2p1/2 doublet in the Co 2p spectrum has binding energy values of 781.5 and 797.6 eV, respectively. In LCP(air) these peaks are observed at 782.1 eV and 798.1 eV (2p3/2 and 2p1/2). The shift to lower binding energy can be attributed to the presence of Co2P in LCP(Ar).113 The difference of binding energy between Co 2p3/2 and its satellite peak is in agreement with the Co2+ environment in LiCoPO4.91,116 For the LiCoPO4 fired under air, a new chemical environment corresponding to P2O5 is identified with additional peaks in the P 2p (135.3–136.1 eV) and O 1s (533.3 eV) spectra.117,118Based on the discussion above, the better conductivity of LiCoPO−1) and cycling performance of LiCoPO4 shown in −3 S cm−1) of LiCoPO4 due to the presence of Co2P after firing under Ar. Also, the nanosized LiCoPO4 obtained from DEG promoted solvothermal synthesis provides short Li-ion migration paths, and facilitates easier Li-ion transfer within the material. The LiCoPO4 fired in air showed relatively low initial specific capacity of 130 mA h g−1. This could be attributed to the poor electric conductivity of ∼10−9 S cm−1 , LiCoPO4 is obtained with a homogenous particle size of ∼150 nm. The LiCoPO4 prepared after heating in Ar exhibits high initial discharge capacity of 147 mA h g−1 at 0.1C with capacity retention of 70% after 40 cycles. This is attributed to the enhanced electronic conductivity of LiCoPO4 due to the presence of Co2P after firing under Ar. The specific capacity and cycle stability of carbon, TiN and RuO2 coated LiCoPO4 were also examined, but did not improve the performance of the material. Hence, under our solvothermal synthesis conditions, LiCoPO4 with good discharge capacity and cycle stability, without need for separate conductivity coatings, were produced.A facile solvothermal synthesis to prepare olivine-structured LiCoPOThere are no conflicts of interest to declare.RA-009-C8RA08785G-s001


A predominance of the divalent cations was found for low pH . Nonetheless, recent literature reports the existence of small titanium oxo-clusters in aqueous acidic media for large titanium(iv) concentration , as stable precursors for the formation of condensed titanium dioxide. The present paper reconsiders firstly previous knowledge about the speciation of titanium(iv) in non-complexing acidic media by giving evidence for the presence of polynuclear hydrolyzed species, even at very low Ti(iv) concentration . UV-visible absorbance spectra recorded for diluted nitric acid solutions (a model of non-complexing acidic medium) containing titanium(iv) were compared to time-dependent density functional theory (TD-DFT) predicted excitation energies. Experimental and predicted maximal absorbance wavelengths showed significantly improved matches when polynuclear species were considered in TD-DFT calculation. Then, 0.1–12.7 mol L−1 phosphoric acid solutions containing titanium(iv) were studied by means of spectroscopic techniques  in order to identify qualitatively the presence of titanium(iv) complexes and to link this speciation to the acid concentration. Two different titanium(iv) orthophosphate complexes, potentially polynuclear, were detected, and the presence of free titanium(iv) is also expected for low phosphoric acid concentration . A general complexation scheme for a large range of H3PO4 concentration was thus formulated.Titanium chemistry in aqueous acidic media has been extensively investigated over the last decades. Hydrolyzed species such as Ti(OH) iv) speciation in diluted nitric acid (model of non-complexing medium) and 0.1–12.7 mol L−1 phosphoric acid aqueous solutions. Evidence for the presence of polynuclear species is supported by molecular modeling.A spectroscopic study of titanium( This process is based on the leaching of the phosphate rock with concentrated sulfuric acid and a series of purification steps to reach the purity specification requested by the target application.1–3 The purification steps aim at removing inorganic anions such as fluorides, sulfates, chlorides and metal impurities including cadmium, iron or titanium. For this goal, the most appropriate technology at the industrial scale is solvent extraction.4–10 This technology relies on the use of an extraction solvent, which can efficiently extract phosphoric acid from the leach solution. However, most common solvents exhibit a lack of selectivity against several impurities including titanium(iv).11,12 In order to remove titanium from wet phosphoric acid, it is therefore mandatory to implement additional purification steps.The wet phosphoric process produces different grades of phosphoric acid  in concentrated phosphoric acid and its liquid–liquid extraction equilibria. UV-visible,12–14 Raman14 and NMR spectroscopies,15 liquid–liquid extraction,16 solubility measurements17,18 and potentiometric methods19 were used to investigate the speciation of titanium(iv) in various media such as nitric, perchloric, sulfuric, hydrochloric and phosphoric acids. The divalent titanium(iv) aquocation was generally found to be predominant in perchloric or nitric acid solutions in the absence of any complexing agents.13,16,18 The exact structure of this divalent cation is still debated as it was initially identified as a titanium oxocation (titanyl TiO2+)20 whereas more recent studies suggested an intramolecular rearrangement leading to the formation of titanium(iv) dihydroxide [Ti(OH)2]2+.15,21,22 According to the most recent literature, the hydrolysis equilibria of titanium(iv) in non-complexing acidic media can be written as follows:The design of extraction solvents selective of HThe corresponding hydrolysis constants are reported in iv) can form various complexes as described in m = 0 or 1 and n = 1 or 2, and the corresponding equilibrium constant is expressed as follows:In the presence of inorganic ligands in solution, titanium9.5]− anions at titanium(iv) concentrations ranging between 0.25 mol L−1 and 1 mol L−1. Likewise, other studies showed the presence of small titanium clusters whose size changed depending on the experimental conditions.29–32 Such polytitanates species with bridging oxo groups were also identified in anhydrous conditions in the case of titanium alkoxide compounds such as titanium ethoxide.33,34 Therefore, it cannot be excluded that polycondensation of titanium(iv) also occurs in phosphoric acid. However, only few studies concern the investigation of the speciation of titanium(iv) in phosphoric acid and the conclusions of these studies are still subject of controversies.19,35,36iv) chemistry in acidic aqueous media, we have decided to reinvestigate as a starting point the speciation of Ti(iv) in dilute nitric acid solution  as a model of non-complexing acidic media. For this goal, UV-visible spectroscopy was used and completed with time-dependent density function theory calculations (TD DFT). Then, the speciation of Ti(iv) was investigated at its turn in a large range of concentration of phosphoric acid  by 31P NMR spectroscopy and UV-visible spectroscopy coupled with chemometric analyses.To gain a better knowledge of titanium(2.2.14TiO4) used to prepare a mother solution of various Ti(iv) was obtained as follows. A volume of 5 mL of titanium tetraisopropoxide  was added dropwise to 25 mL of ethanol  at 0 °C under constant stirring. A white precipitate of orthotitanic acid was formed immediately.41 Afterwards, a mixture of 25 mL ethanol  and 3 mL of deionized water cooled at 0 °C (resistance = 18.2 Ω) was then added to the orthotitanic acid suspension. After 1 h of agitation in an ice bath, the suspension was filtered under vacuum by means of a fritted glass filter (cat. 4). The solid was dried for 1 h under vacuum at room temperature (the solid was regularly triturated during drying). A white powder (∼3 g) of titanium hydroxide was obtained.All work was carried under a fume hood. Orthotitanic acid (H−1 nitric acid prepared by dilution of 65% (vol) nitric acid  in deionized water. After 24 h under agitation, orthotitanic acid was almost completely dissolved in nitric acid. In order to complete the dissolution, 20 mL of 0.73 mol L−1 nitric acid was added again. Residual insoluble powder of orthotitanic acid was removed by filtration under vacuum with a fritted glass filter (cat. 4). The turbid solution was then filtered using an Acrodisc Supor syringe filter containing a PES membrane  previously conditioned by using 0.73 mol L−1 nitric acid. The titanium concentration in the filtrate was determined by using an Agilent Microwave-Plasma Atomic Emission Spectrometer (see below). Titanium concentration was found to be equal to 2.3 g L−1.All work was carried under a fume hood. Approximately 0.3 g of the orthotitanic acid was dispersed in 10 mL of 0.73 mol Liv) concentration was found to be equal to 8.0 g L−1.All work was carried under a fume hood. Approximately 2.7 g of orthotitanic acid was added under agitation to 30 mL of 85% (weight) phosphoric acid (Sigma-Aldrich). After one night of agitation, a small amount of deionized water was added to decrease the viscosity. The suspension was filtered under vacuum with fritted glass filter (Cat. 4) previously conditioned with deionized water. Titanium concentration in the filtrate was determined by using the Agilent Microwave-Plasma Atomic Emission Spectrometer (the filtrate was still slightly turbid). The titanium. The pH-meter used for the potentiometric titration was a pHenomenal pH 1100 L (VWR) equipped with a pHenomenal pH electrode. The pH electrode was calibrated by using two buffer solutions at pH = 4 and pH = 7 . The concentrations of phosphoric acid in the stock solution and in the titanium solutions were also determined by potentiometry with a fresh solution of 0.1 mol L−1 sodium hydroxide . The same pH-meter and the same electrode were used but three buffer solutions at pH = 4, pH = 7 and pH = 9 , respectively, were used to calibrate the pH electrode.The nitric acid concentration in the diluted nitric acid stock solution was determined by potentiometry with 0.1 mol L3PO4.Titanium concentrations in the samples were determined by using an Agilent Microwave-Plasma Atomic Emission Spectrometer . The mother standard solution containing 1000 ppm of titanium in 2% (vol) nitric acid  was diluted in 5% (vol) nitric acid to prepare five standards containing 1 to 10 ppm titanium. In order to minimize possible matrix effects, two different series of standards were prepared, without or with H−1 titanium. A 0.1 mm light path demountable cuvette  was used to analyze the solutions containing titanium at concentration greater than 1 mmol L−1.An Agilent Cary 60 UV-visible spectrophotometer was used to record spectra between 190 nm and 400 nm with a step of 0.5 nm. A 2 mm light path cuvette (Agilent) was used to analyze the solutions containing less than 1 mmol L−1 as the nitrate ion exhibits a broad absorption peak at 200 nm with a molar absorption coefficient approximately equal to 105 cm−1 L mol−1. Therefore, the titanium(iv) solutions were diluted and the [Ti]/[NO3] ratio was controlled by adding the requested amount of nitric acid in the solutions. The reference solutions were prepared by using the same protocol. The blank was 0.73 mol L−1 nitric acid, which was filtered by using a 0.2 μm syringe filter with PES membrane prior to UV-vis analyses.In nitrate media, a good signal-to-noise ratio was obtained providing that the nitrate concentration was lower than 2 mmol L31P NMR spectra were recorded at 161.975 MHz on a Bruker AVANCE III 400 spectrometer at 25 °C equipped with a 5 mm BBFO broad-band probe. Samples were introduced in a 5 mm NMR tube with a coaxial insert containing D2O as a lock solvent. The D2O is separated from the samples in order to avoid affecting the pH of the solution. Chemical shifts are referred to external H3PO4 (0 ppm). 31P NMR data were acquired with 128 scans, 64 k points, a repetition delay of 2 s and a spectral width of 16 164 Hz.2.242–44 It was used to determine the number of chromophores detectable within a given range of concentrations and wavelengths as reported by Meloun et al.45 This criterion relies on a component analysis calculated from the covariance matrix  PBM data was replaced with SVG by xgml2pxml:<glyph-data id="z.dstrS" format="PBM" resolution="300" x-size="10" y-size="12" xml:space="preserve">001111110001111111101010000110100100000001011100000100001100001100010000001100100000001010010000101001100011100111111100</glyph-data><svg xmlns="http://www.w3.org/2000/svg" version="1.0" width="13.666667pt" height="16.000000pt" viewBox="0 0 13.666667 16.000000" preserveAspectRatio="xMidYMid meet"><metadata>Created by potrace 1.16, written by Peter Selinger 2001-2019</metadata><g transform="translate scale" fill="currentColor" stroke="none"><path d="M160 920 l0 -40 -40 0 -40 0 0 -40 0 -40 -40 0 -40 0 0 -80 0 -80 40 0 40 0 0 -80 0 -80 40 0 40 0 0 -40 0 -40 80 0 80 0 0 -40 0 -40 80 0 80 0 0 -120 0 -120 -120 0 -120 0 0 40 0 40 -40 0 -40 0 0 40 0 40 -40 0 -40 0 0 -120 0 -120 280 0 280 0 0 40 0 40 40 0 40 0 0 160 0 160 -40 0 -40 0 0 80 0 80 -80 0 -80 0 0 40 0 40 -80 0 -80 0 0 40 0 40 -40 0 -40 0 0 40 0 40 160 0 160 0 0 -40 0 -40 80 0 80 0 0 80 0 80 -40 0 -40 0 0 40 0 40 -240 0 -240 0 0 -40z m0 -160 l0 -40 40 0 40 0 0 -80 0 -80 120 0 120 0 0 -40 0 -40 40 0 40 0 0 -40 0 -40 40 0 40 0 0 -120 0 -120 -40 0 -40 0 0 80 0 80 -40 0 -40 0 0 40 0 40 -80 0 -80 0 0 40 0 40 -80 0 -80 0 0 80 0 80 -40 0 -40 0 0 80 0 80 40 0 40 0 0 -40z"/></g></svg>T. The eigenvalue vector of this covariance matrix gives information about the components associated to independent signals in the UV-visible spectra. The Malinowski factor indicator function IND criterion is calculated by using k-values, which correspond to the number of chromophores in solution. The number of chromophores is equal to the value of k corresponding to the minimum value of IND.gj, n and m denote the j-th eigenvalue of the covariance matrix, the number of spectra used in the dataset and the number of wavelengths, respectively. The q parameter is equal to the highest value between n and m.The R2019b version of Matlab was used for chemometric analyses of the spectral dataset. This analysis relies on the determination of the Malinowski factor indicator function criterion.46 it was found efficient to identify the number of chromophores.To better identify the number of chromophores in solution from the spectral data, a common data analysis procedure was used. Numerical noise (jitter) was added to the recorded spectra in order to erase the contribution of the minor components and to distribute more uniformly noise in the considered wavelength range. Although jittering is usually used to reduce overplotting and better identify clusters in large datasets,47 The structures considered in this work were optimized geometrically with the PBE0 global hybrid functional48,49 and the 6-311+G basis set.50–52 The solvation of the first coordination sphere was described explicitly whereas the outer solvation sphere was described by using the PCM model.53,54 Frequencies were calculated on the optimized geometries. Excitation energies were then determined by TD-DFT with the same level of theory with a linear response non equilibrated PCM solvation model with water. Unless otherwise stated, a total number of 80 states were computed in order to get a representative range of the experimental wavelength where light absorption occurred. The same type of calculation was performed on a larger system, i.e. a titanium oxo-cluster denoted Ti18, and the procedure and parameters  used for this system is detailed in the ESI.†Time independent and time dependent density functional theory (DFT and TD-DFT) calculations were performed using the Gaussian package (version 16).55 molecular systems in complex environments56 as well as polyoxometalates.57 This scheme and the pitfalls of the implemented methods have been well-known for a decade.58 In the current state of the art, the computed excitation energies may thus be considered reasonably reliable as illustrated by our previous works using the same methodology.59–61The use of hybrid functionals as well as the implicit solvation model PCM was found to be efficient to obtain reliable estimations of the wavelengths of maximal absorbance for metal complexes,62The orbital transitions associated with the main predicted excitation energies were described by calculating natural transition orbitals (NTO).63 software and POV-Ray64 as post-treatment (ray-tracer).The structures of the optimized geometries and the representation of the Natural Transition Orbitals (NTOs) were generated using Avogadro3.3.13.1.1.−1 titanium(iv) in 0.73–2.2 mmol L−1 nitric acid were recorded in order to investigate the speciation of titanium(iv)  = 0.73–2.2 mmol L−1.UV-visible spectra of 0.05 mmol Lnium(iv) . It is e13,14,70 The strong band located between 180 and 220 nm (region 1) can be attributed to nitrate ions,71 and the band which appears in the range 220–350 nm (region 2) on iv) complexe(s). In coherence with the above statement, it is interesting that the intensity of the band located in region 1 strongly and almost linearly increases with the concentration of nitric acid whereas it does not depend on the presence or absence of titanium(iv). On the opposite, the intensity of the band located in region 2 (iv) in 0.73–2.2 mmol L−1 HNO3 in agreement with Szilágyi et al.44. The noise observed in region 2  is indepiv) complexes in solution or the presence of a unique titanium(iv) complex exhibiting several major possible electronic transitions.The large width of the absorbance peak for wavelengths between 230 and 275 nm suggests an asymmetry with respects to the region between 200 and 230 nm. This may result from the presence of several titanium(iv) species are written as [(TiO)μ]μ2 with μ = 1 for mononuclear species and μ >1 for polytitanate species as it is not possible to exclude the presence of polynuclear species in solution. For μ >1, as illustrated in 2+ ⇌ Ti(OH)22+ for mononuclear species might occur in the case of polynuclear species, leading to the formation of hydroxo bridging groups  species in non-complexing media, computed transition energies of several complexes were obtained by Time-Dependent Functional Density Theory (TDDFT) calculations.To get information about the chemical structure and the stoichiometry of the titanium.13,16,18,22 Both TiO2+ and Ti(OH)22+ cations as well as Ti(OH)3+ and Ti(OH)3+ were considered in order to figure out the predominant species in solution. The starting geometries were thus obtained by placing one to three hydroxyl groups (and oxo group for TiO2+) coordinated to titanium(iv) cation. The rest of the octohedra sites of the complexes were filled with water molecules (solvation shell). The outer solvation shells were described by an implicit model of water molecules (PCM) in accordance with other DFT works, which demonstrated that such kind of models are relevant to describe transition metal complexes in aqueous media.61,723+ and Ti(OH)22+ cis structures as shown in 2), Ti PBM data was replaced with SVG by xgml2pxml:<glyph-data id="z.dbd" format="PBM" resolution="300" x-size="8" y-size="10" xml:space="preserve">00000000000000000000000000000000111111110000000011111111000000000000000000000000</glyph-data><svg xmlns="http://www.w3.org/2000/svg" version="1.0" width="13.200000pt" height="16.000000pt" viewBox="0 0 13.200000 16.000000" preserveAspectRatio="xMidYMid meet"><metadata>Created by potrace 1.16, written by Peter Selinger 2001-2019</metadata><g transform="translate scale" fill="currentColor" stroke="none"><path d="M0 440 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z M0 280 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z"/></g></svg>(O) and Ti–(OH) bond distances of the final geometrically optimized structures reported in The structures used in the TD-DFT calculations were local potential energy minima, as the vibration modes were all associated with positive eigenvalues after geometry optimization. The octahedricity was conserved during the optimization even though an important distortion was observed for the Ti(OH)The excitation energies of the optimized complexes were calculated using TD-DFT (excited states are available in the ESIiv) [Ti(OH)2]2+ in acidic nitrate solutions cannot be supported by this study. In other words, the free titanium(iv) complex in non-complexing acidic solutions (perchloric or nitric acid) may not match with [Ti(OH)2]2+ cation as it was previously stated in the literature.13,15,16,18The oscillator strengths associated with the permitted transitions are shown in iv) atoms were considered. Two bridging oxygen atoms were inserted between the titanium atoms and their three different protonation states were chosen for calculations. The spectra of the dimeric structures showed a fair agreement with the experimental spectrum obtained in diluted nitric acid (iv) atoms bonded via a mixed μ-(OOH) bridge. The first coordination spheres of the two titanium(iv) cations were completed with water molecule as for the monomeric complexes. However, the shape of the band between 230 nm and 340 nm is poorly reproduced. It is worth mentioning that a predicted transition associated with a non-negligible oscillator strength is present at 275 nm as depicted in The formation of polytitanate species is suspected even in acidic solutions. The computational cost of the level of theory chosen to perform the calculation (6-311+G**/PBE0) was a limiting factor to perform the geometry optimization on large oxoclusters. Thus, the excitation energies were obtained only for the dimeric form of titanium aquo-complexes. Different structures containing several hydroxyl groups coordinated to titanium an electron transfer from p-orbitals of the two bridging oxygens and of the oxygen atoms of coordinated water molecules to the d-orbitals of titanium atoms. The second excitation  was described by a similar transition, i.e. p-orbitals of bridging oxygen atoms to d-orbitals of titanium atom. Both these descriptions support the ligand-to-metal charge transfer character of the most intense transitions in the titanium(iv) complex.The main transitions located at 227 nm and 278 nm (the most intense in their respective wavelength domains) were described with the natural transition orbitals (NTO) method . The ideiv) complexes whose chemical structure remains close to the previous one: the first one in which a water molecule in the solvation shell was replaced by an hydroxyl group (iv) in nitric acid because of the existence of many structures whose calculated wavelengths match with experimental wavelengths.The same type of calculation has been performed for two other titanium atoms. The cartesian coordinates of the optimized geometries of [Ti2(μ-(O)2)]4+ and [Ti3(μ-(O)3)]6+ as well as the procedure used to obtain the excited states for Ti18 are given in the ESI.†Nevertheless, this study shows that the predicted position of maximal absorbance shifts toward higher wavelengths when the size of the polyoxometalate complex species increases. This tendency was confirmed for higher nuclearity as depicted in iv) in nitric acid reported in et al.28The comparison with the experimental spectrum of titanium(2(μ-(OOH)) (OH)]4+ and [Ti2(μ-(OOH))]5+ (2(μ-(OOH))]5+ and [Ti2(μ-(O)2)]4+ (iv) and the protonation state of bridging oxo-groups may influence the position of the absorbance band.However, the comparison between the results obtained for the [TiOOH))]5+  and 7 an(O)2)]4+  and 8 su3.2iv), it is expected that the [(TiO)μ]μ2 species identified above (with μ = 1 for mononuclear species and μ >1 for polytitanate species) will be converted into titanium-phosphate complexes. The goal of this part is to investigate the formation of such complexes by using 31P NMR spectroscopy and chemometric analyses of UV-visible spectra.When phosphoric acid is added to non-complexing solutions of titanium(3.2.1.31P NMR spectra of 6.9–12.7 mol L−1 phosphoric acid solutions containing 17 mmol L−1 titanium(iv). The peaks located between δ = −6.1 and −6.9 ppm may be attributed to a titanium–phosphate complex as the corresponding integration (after weighting) depends on the phosphoric acid concentration. In the region δ = −11 to −12.5 ppm, it is difficult to conclude if the two observed weak peaks correspond to (i) two different phosphorus complexes or (ii) a unique titanium–phosphate complex containing two non-equivalent phosphorus atoms characterized by two chemical shifts. Furthermore, the mean dynamic conformation could also depend on experimental conditions such as pH and viscosity correlated with phosphoric acid concentration. Previous works on the synthesis of amorphous titanium(iv) phosphate reported two peaks at similar chemical shifts obtained from the deconvolution of MAS-NMR spectra of synthesized materials (δ = −5.0 to −5.2 ppm and δ = −13.5 to −15.5 ppm).73 These peaks at δ = −5.0 to −5.2 ppm and δ = −13.5 to −15.5 ppm were attributed to the following types of phosphorous sites: P(OTi)x(OH)x4− where x = 1 or 2 (H3PO4 or H2PO4− environment) and P(OTi)3OH (HPO42− environment), respectively. Similar assignation, i.e. −4.5 to −7.3 ppm attributed to H2PO4− and −12.5 to −15.9 ppm attributed to HPO4− were made by Trublet et al.74 and Zhang et al.75 for amorphous titanium(iv) phosphates. The MAS-NMR spectra of a synthesized oxyfluorinated titanium(iv) phosphate76 led also to the conclusion that the peaks located at −7.0 ppm and −11.5 could be attributed to orthophosphates groups linked to 1 or 2 titanium(iv) centers, respectively. From these assignments, it can be assumed that the peak observed in this study between −6.18 and −6.95 ppm may correspond to a complex in which the orthophosphate group (in the form of H3PO4 or H2PO4−) is linked to one titanium(iv) atom. For the second region, i.e. −11.3 to −12.3 ppm, the peaks might be attributed to deprotonated orthophosphate groups (HPO42− form) in a titanium(iv) phosphate complex, possibly as bridging groups between two titanium(iv) centers.3.2.2.−1 titanium(iv) in 5.8–11.6 mol L−1 phosphoric acid (after baseline correction). These spectra were used to determine the number of chromophores detectable between 200 and 400 nm by using the Malinowski factor indicator function IND criterion.42–45 The calculation of the IND criterion allows to identify the number of independent chromophores k. The orange curve (bottom) in k without any external perturbation. This curve does not permit to determine the number of chromophores as it does not exhibit any minimum. Conversely, this curve reaches a plateau that can be explained by the presence of non-uniformly distributed noise as well as by the presence of species characterized by UV-visible signals of the same order of magnitude as the noise. After perturbing the signal by adding more noise, the curves exhibit a minimum value for k = 3, which corresponds to the number of chromophores in solutions.iv) in phosphoric acid, its contribution in the experimental spectra of The value of the Malinowski indicator function IND for the third chromophore without addition of noise is low in comparison to the value for the first and second species. Thus, even though this third species has to be taken into account to study the speciation of titanium(−1 titanium(iv) in 2.0–7.7 mol L−1 H3PO4. These spectra were used to find more accurately the location of the absorbance peaks of the chromophores. The first peak with a maximum located at λm,1 = 220 nm is attributed to the presence of a species quoted Tiλm,1 which might also be at the origin of the 31P NMR peak observed between δ = −6.1 and −6.9 ppm as both the UV-visible absorbance and the ponderate integration values of the 31P NMR signal exhibit a dependence versus the phosphoric acid concentration  attributed to the species Tiλm,2 by considering, as stated above, that the contribution to the total absorbance of third species detected by the Malinowski indicator function IND was negligible.A second band can be observed as a shoulder between 260 and 280 nm in the spectra of n) (titanium(iv) and phosphoric acid concentrations as reported for (n) = 1 to 4 in ελm,1Ti and ελm,2Ti denote the vectors of the molar extinction coefficients of the species Tiλm,1 and Tiλm,2 between 200 and 340 nm.The Beer–Lambert law was expressed by considering two chromophores and a set of wavelengths comprised between 200 and 340 nm:n = 1 ([Ti(iv)] = 0.3 mmol L−1 and [H3PO4] = 7.7 mol L−1), λm,2 was negligible. Therefore, under these experimental conditions, the contribution of Tiλm,2 in the expression of (1) can be neglected as well. The molar extinction coefficient between 200 and 340 nm for Tiλm,2 can thus be expressed as:For the set of experimental condition λm,2, it is therefore necessary to evaluate the ratio of the concentrations of the first species Tiλm,1 between the two different experimental conditions (n) and (1). This ratio may be expressed in λm,1 = 220 nm  = 1.4 mol L−1 (curve (5) in −1 (curves (8) and (9) in −1. Such an observation suggests that another chromophore, Tiλm,3, exists at low concentration of H3PO4.The two chromophores Tiλm,3 in the spectra of titanium(iv) in phosphoric acid and the peak observed in the spectrum of titanium(iv) in diluted nitric acid attributed to free titanium(iv) μ2 in solution as The absorbance at 310 nm for 0.3 mmol Liv) from non-complexing aqueous solution to concentrated solution of H3PO4 can be explained by considering the two following titanium orthophosphate complexes in addition to free titanium(iv), Tiλm,3, corresponding to [(TiO)μ]μ2.In summary, the variation of the speciation of titanium was not possible due to the multiplicity and similarity of corresponding structures.The use of UV-visible spectroscopy and molecular modeling techniques was found to be relevant to reinvestigate the speciation of titanium in non-complexing acidic solutions. Indeed, mononuclear species such as titanyl ion or titanium dihydroxide which were considered in previous studies to be predominant in non complexing acidic media were found not to be sufficient to correctly simulate UV-visible spectra by DFT calculations. On the opposite, taking into account the existence of small polytitanate clusters as dimeric or trimeric structures lead to a satisfactory match between experimental and DFT calculated UV-visible spectra. However, in spite of such a good fitting, the determination of the exact nature of the observed polytitanates  in a large range of phosphoric acid concentrations . Thus, it is concluded that titanium(iv) is present as mononuclear (μ = 1) or polynuclear (μ >1) free cation(s), [(TiO)μ]μ2, in diluted H3PO4 solutions  and then progressively forms orthophosphate complexes as the concentration of phosphoric acid is increased, namely [(TiO)μ(Hm3−PO4)γ]μ−γm2 and [(TiO)μ(Hm3−PO4)γ(Hn3−PO4)β]μ−γm−βn2 in moderate  and concentrated  H3PO4 solutions, respectively.UV-visible spectroscopy coupled with chemometric analyses and iv) in H3PO4 solution might be to perform TD-DFT calculation as the one reported above for diluted HNO3 solutions (non-complexing media). However, due to the large number of possible structures  and necessary long computing time, such calculations were beyond the scope of the present paper.A further step in the study of the speciation of titanium(This work was conceptualized by L. M., A. C., G. C. and H. H. The access to the calculation resources was made possible by A. M. The investigation process was performed by L. M., A. M. and S. L. The original draft of the manuscript was written by L. M., A. C. and G. C. All the authors contributed to edit and review the final version of the manuscript. G. C., H. H. and A. C. were involved in the funding acquisition and supervision of the project.There are no conflicts to declare.RA-011-D1RA04284J-s001