The europium–oxygen interaction in nine different europium(III) oxo-compounds (including C-type Eu2O3) was investigated on the basis of powder reflectance spectra (near-IR/vis/UV) and temperature-dependent magnetic measurements. Computation of the transition energies and of the effective Bohr magneton numbers for Eu3+ in the different ligand fields were performed within the framework of the angular overlap model (AOM) using the computer program BonnMag. These calculations show that all electronic transition energies in the optical spectra, the magnetic susceptibilities as well as their temperature dependence, are very well-accounted for by AOM. BonnMag provides a facile way to perform these calculations. Analysis of the obtained “best fit” AOM parameters eσ(EuIII–O) shows that these are significantly influenced by the further bonding partners of oxygen (“second-sphere ligand-field effect”). An increase of eσ, max(EuIII–O) from 404 cm–1 (EuPO4) to 687 cm–1 (EuSbO4), both normalized to d(EuIII–O) = 2.38 Å, is found. Correlation of this variation to oxide polarizability and optical basicity of the oxo-compounds is discussed.

Detailed experimental data on UPO4Cl comprising single-crystal UV/vis/NIR spectra and temperature-dependent magnetic susceptibilities form the basis for the investigation of the electronic structure of the U4+ cation in UPO4Cl. For modeling of the observed physical properties the angular overlap model (AOM) was successfully employed. The computations were performed using the newly developed computer program BonnMag. The calculations show that all electronic transitions and the magnetic susceptibility as well as its temperature dependence are well-reproduced within the AOM framework. Using Judd–Ofelt theory BonnMag allows estimation of the relative absorption coefficients of the electronic transitions with reasonable accuracy. Ligand field splitting for states originating from f-electron configurations are determined. Slater–Condon–Shortley parameters and the spin–orbit coupling constant for U4+ were taken from literature. The good transferability of AOM parameters for U4+ is confirmed by calculations of the absorption spectra of UP2O7 and (U2O)(PO4)2. The effect of variation of the fit parameters is investigated. AOM parameters for U4+ (5f) are compared to those of the rare-earth elements (4f) and transition metals (3d).

Emerald-green single crystals of U(PO4)Cl were grown by chemical vapor transport in a temperature gradient (1000 → 900 °C). The crystal structure of U(PO4)Cl (Cmcm, Z = 4, a = 5.2289(7) Å, b = 11.709(2) Å, c = 6.9991(8) Å) consists of a three-dimensional network of [PO4] tetrahedra and bicapped octahedral [UIVO6Cl2] groups. Polarized absorption spectra measured for two perpendicular polarization directions show a large number of well-resolved electronic transitions. These transitions can be fully assigned on the basis of a detailed ligand-field treatment within the framework of the angular overlap model. The magnetic behavior predicted on the basis of the spectroscopic data is in agreement with an f 2 system and perfectly matched by the results of temperature-dependent susceptibility measurements.

•In the quasi-binary system VVOPO4-WVOPO4 the new compound VIII(WVIO2)2(P2O7)(PO4) has been discovered.•Internal redox and Lux-Flood acid-base reaction lead to stabilization during solid solution formation.•VIII(WVIO2)2(P2O7)(PO4) represents the first anhydrous phosphate containing a tri- and a hexavalent transition metal.•Vanadium(III) can be substituted by a wide range of trivalent cations.•With titanium(III) the mixed ortho-pyrophosphate does not exist due to the redox reaction Ti3+ + W6+ → Ti4+ + W5+.The series of isotypic anhydrous ortho-pyrophosphates MIII(WVIO2)2(P2O7)(PO4) (M: Sc, V, Cr, Fe, Mo, Ru, Rh, In, Ir) was obtained via vapor phase moderated solid state reactions in sealed ampoules. The crystal structure of the phosphates MIII(WVIO2)2(P2O7)(PO4) (M: V, Ru, Rh) was solved from single crystal X-ray data (C2/c, Z = 16). Fairly regular MO6 and distorted WO6 octahedra share vertices with PO4 and P2O7 units to form a 3D network. For the ortho-pyrophosphates with M: V3+, Cr3+, and Fe3+ the oxidation state of M is confirmed by magnetic measurements. 31P-MAS-NMR spectra of the diamagnetic phosphates MIII(WVIO2)2(P2O7)(PO4) (M: Sc, In, Ir) show surprisingly different isotropic chemical shifts for the seven phosphorus sites. VIII(WVIO2)2(P2O7)(PO4) occurs as equilibrium phase in the quasi-binary system (V1–xWx)OPO4 at x = 0.67 and exhibits a small homogeneity range 0.60 ≤ x ≤ 0.67. The scandium compound shows a fully inverted occupancy of the M sites according to the formulation W(Sc1/2W1/2O2)2(P2O7)(PO4).VIII(WVIO2)2(P2O7)(PO4) is the first anhydrous phosphate containing a tri- and a hexavalent transition metal. Its formal composition (V1/3W2/3)OPO4 relates it to the quasi-binary system VVOPO4-WVOPO4. By internal redox and Lux-Flood acid-base reaction obviously a stabilization with respect to the crystal structures of the end members of the binary system is achieved. Vanadium(III) can be substituted by a wide range of trivalent cations (M3+: Sc, Cr, Fe, Mo, Ru, Rh, In, Ir).

Vanadyl(V)–titanium–orthophosphate (VVO)TiIV6(PO4)9 is formed by solid state reactions in the temperature range 525≤ϑ≤780 °C. At higher temperature decomposition into V2O5 and the hitherto unknown solid solution Ti(P1−xVx)2O7 (0≤x≤0.23; 0.30≤x≤0.43) is observed. The process of phase formation has been monitored by MAS-NMR (31P, 51V) spectroscopy. Equilibrium phase relations in the quaternary system TiO2/VO2.5/PO2.5 have been determined.A structure analysis from X-ray single-crystal data (P63/mP63/m (No. 176), Z=2; a=8.4438(3) Å, c=22.215(1) Å, 14 independent atoms, 87 variables, 2066 unique reflections, R1=0.032, wR2=0.084) shows the relationship of (VVO)TiIV6(PO4)9 to the NASICON structure family. In marked contrast to the other members of this family [TiIV2O9] double-octahedra and strongly distorted tetrahedral [(VV=O)O3] groups are observed besides isolated [TiIVO6] octahedra and phosphate tetrahedra. The structure model is in agreement with the results from MAS-NMR (31P, 51V) spectroscopy.Graphical abstract(VVO)TiIV6(PO4)9 belongs to the NASICON structure family. Its structure contains [TiIV2O9] double-octahedra and unprecedented, strongly distorted tetrahedral [(VV=O)O3] groups, in stark contrast to other members of this family. The structure model is in agreement with the results from MAS-NMR (31P, 51V) spectroscopy.Highlights► Equilibrium relations for the subsolidus have been established for the system TiO2/V2O5/P2O5. ► Phase formation has been monitored by XRPD as well as by 31P- and 51-MAS-NMR. ► A solid solution Ti(P1−xVx)2O7 exists up to x=0.43 with a miscibility gap at 0.23≤x≤0.30. ► The crystal structure of the new NASICON-related phosphate (VVO)TiIV6(PO4)9 is reported. ► The crystal structure contains the unprecedented [(V=O)O3] group.

α-Li4Co(PO4)2 has been synthesized and crystallized by solid-state reactions. The new phosphate crystallizes in the monoclinic system (P21/a, Z=4, a=8.117(3) Å, b=10.303(8) Å, c=8.118(8) Å, β=104.36(8) Å) and is isotypic to α-Li4Zn(PO4)2. The structure of α-Li4Co(PO4)2 has been determined from single-crystal X-ray diffraction data {R1=0.040, wR2=0.135, 2278 unique reflections with Fo>4σ(Fo)}. The crystal structure, which might be regarded as a superstructure of the wurtzite structure type, is build of layers of regular CoO4, PO4 and Li1O4 tetrahedra. Lithium atoms Li2, Li3 and Li4 are located between these layers. Thermal investigations by in-situ XRPD, DTA/TG and quenching experiments suggest decomposition followed by formation and phase transformation of Li4Co(PO4)2:α-Li4Co(PO4)2⟹442°Cβ-Li3PO4+LiCoPO4⇌773°Cβ-Li4Co(PO4)2⟹quenchingto25°Cα-Li4Co(PO4)2According to HT-XRPD at ϑ=850°Cβ-Li4Co(PO4)2 (Pnma, Z=2, 10.3341(8) Å, b=6.5829(5) Å, c=5.0428(3) Å) is isostructural to γ-Li3PO4. The powder reflectance spectrum of α-Li4Co(PO4)2 shows the typical absorption bands for the tetrahedral chromophore [CoIIO4].Graphical abstractThe complex formation and decomposition behavior of Li4Co(PO4)2 with temperature has been elucidated. The crystal structure of its α-phase was determined from single crystal data, HT-XRPD allowed derivation of a structure model for the β-phase. Both modifications belong to the Li3PO4 structure family.Highlights► Li4Co(PO4)2 exhibits complex thermal behavior. ► The new phosphate belongs to the Li3PO4 structure family. ► A single-crystal structure analysis is provided for the metastable α-Li4Co(PO4)2. ► From HT-XRPD data a cation distribution model is developed for β-Li4Co(PO4)2. ► No electrochemical delithiation is observed up to 5 V.

Single crystals of the oxidephosphates TiIIITiIV3O3(PO4)3 (black), CrIII4TiIV27O24(PO4)24 (red-brown, transparent), and FeIII4TiIV27O24(PO4)24 (brown) with edge-lengths up to 0.3 mm were grown by chemical vapour transport. The crystal structures of these orthorhombic members (space group F2dd ) of the lazulite/lipscombite structure family were refined from single-crystal data [TiIIITiIV3O3(PO4)3: Z=24, a=7.3261(9) Å, b=22.166(5) Å, c=39.239(8) Å, R1=0.029, wR2=0.084, 6055 independent reflections, 301 variables; CrIII4TiIV27O24(PO4)24: Z=1, a=7.419(3) Å, b=21.640(5) Å, c=13.057(4) Å, R1=0.037, wR2=0.097, 1524 independent reflections, 111 variables; FeIII4TiIV27O24(PO4)24: Z=1, a=7.4001(9) Å, b=21.7503(2) Å, c=12.775(3) Å, R1=0.049, wR2=0.140, 1240 independent reflections, 112 variables). For TiIIITiIVO3(PO4)3 a well-ordered structure built from dimers [TiIII,IV2O9] and [TiIV,IV2O9] and phosphate tetrahedra is found. The metal sites in the crystal structures of Cr4Ti27O24(PO4)24 and Fe4Ti27O24(PO4)24, consisting of dimers [MIIITiIVO9] and [TiIV,IV2O9], monomeric [TiIVO6] octahedra, and phosphate tetrahedra, are heavily disordered. Site disorder, leading to partial occupancy of all octahedral voids of the parent lipscombite/lazulite structure, as well as splitting of the metal positions is observed. According to Guinier photographs TiIII4TiIV27O24(PO4)24 (a=7.418(2) Å, b=21.933(6) Å, c=12.948(7) Å) is isotypic to the oxidephosphates MIII4TiIV27O24(PO4)24 (MIII: Cr, Fe). The UV/vis spectrum of Cr4Ti27O24(PO4)24 reveals a rather small ligand-field splitting Δo=14,370 cm−1 and a very low nephelauxetic ratio β=0.72 for the chromophores [CrIIIO6] within the dimers [CrIIITiIVO9].Single crystals of the oxidephosphates TiIIITiIV3O3(PO4)3 (black), CrIII4TiIV27O24(PO4)24 (red-brown, transparent), and FeIII4TiIV27O24(PO4)24 (brown) with edge-lengths up to 0.3 mm were grown by chemical vapour transport. The crystal structures of these orthorhombic members of the lazulite/lipscombite structure family were refined from single-crystal data.

The crystal structures of SrNiP2O7 (I) and SrNi3(P2O7)2 (II) have been refined from single crystal data [(I): P21/n, Z=4, a=5.2630(16), b=8.2605(10), c=12.6018(15) Å, β=90.224(19)°, 101 parameters, 1143 independent reflections, R/wR2=0.029/0.070; (II): P21/c, Z=2, a=7.4092(9), b=7.6594(8), c=9.4474(10) Å, β=112.216(9)°, 104 parameters, 1484 independent reflections, R/wR2=0.027/0.063]. SrNiP2O7 belongs to the α-Ca2P2O7 structure family with Ni2+ ions occupying isolated square-pyramidal sites, (Ni O) = 2.032 Å. SrNi3(P2O7)2 is isostructural to AM3(P2O7)2 (A = Ca, Pb and M = Fe, Co, Ni). Two crystallographically independent, slightly distorted [NiO6] octahedra ((NiO) = 2.083 Å) share edges, thus forming chains along the b-axis (d(NiNi) = 3.143 and 3.226 Å). The colours of SrNiP2O7 (orange-red) and SrNi3(P2O7)2 (greenish-yellow) are significantly different. Reflectance spectra in the UV/VIS/NIR region are reported for SrNiP2O7, SrNi3(P2O7)2, and the isotypic diphosphates CaNi3(P2O7)2 and BaNi3(P2O7)2. Angular overlap parameters for the NiO interaction are derived. The shift in d-electron energies of Ni2+ caused by the change in coordination from [NiO5] (C4v) to [NiO6] (Oh) is reproduced nicely by the model calculations.Graphic

The surprisingly complicated crystal structure of (bis(terpyridine))copper(II) tetraphenylborate [Cu(tpy)2](BPh4)2 (tpy = 2,2′:6′,2″-terpyridine) consists of six crystallographically independent [Cu(tpy)2]2+ complexes. At ambient temperature, five out of six [CuIIN6] chromophores appear to be compressed octahedra, while at 100 K, four exhibit elongated and only two compressed octahedral geometry. Temperature dependent single crystal UV/vis (100, 298 K) and EPR measurements (20, 100, 298 K) as well as AOM calculations suggest that the octahedra which show apparently compressed octahedral geometry (XRD) result from dynamic Jahn–Teller behavior of elongated octahedra [CuIIN6]. The detailed correlation of structural and spectroscopic data allows an understanding of the strongly solvent-dependent structures of the [Cu(tpy)2]2+ complex in solution.