Crystal structure of strontium dicobalt iron(III) tris-(orthophosphate): SrCo2Fe(PO4)3

Structural and Spectroscopic Studies of NaCuCr2(PO4)3: A Noncentrosymmetric Phosphate Belonging to the α-CrPO4-Type Compounds

An electron and joint neutron and X-ray diffraction study of the synthetic copper/chromium phosphate NaCuCr₂(PO₄)₃ (NaCuP) is reported. A noncentrosymmetric Imm2 space group belonging to the well-known α-CrPO₄ type is observed contrary to what is reported in NaMCr₂(PO₄)₃ (M = Co and Ni) phosphates. The structural model is validated by bond valence sum analysis and charge-distribution (CHARDI) calculations and supported by complementary infrared and Raman spectroscopy investigations. Both Raman spectroscopy and theoretical study by deformation density approach further suggest the presence of Cu²⁺ (3d⁹) and Cr²⁺ (3d⁴) Jahn-Teller polaron effects as a key factor to the centro Imma to noncentrosymmetric Imm2 phase change.

Crystal structure of SrCo4(OH)(PO4)3, a new hy-droxy-phosphate

Single crystals of strontium tetra-cobalt tris-(orthophosphate) hydroxide, SrCo4(OH)(PO4)3, were grown serendipitously under hydro-thermal conditions at 473 K. The crystal structure consists of undulating chains of edge-sharing [CoO6] octa-hedra that are linked into (010) layers by common vertices between chains. Adjacent layers are linked along [010] into a framework structure by tetra-hedral [CoO4] units and by PO4 tetra-hedra. The framework delimits channels extending along [100] in which the eleven-coordinate strontium cations are situated. Bifurcated O-H⋯O hydrogen bonds of weak strengths consolidate the crystal packing. The title compound was also characterized by infrared spectroscopy.

K1+2x Ni1-x Fe2(AsO4)3 (x = 0,125): un nouvel arséniate à structure de type α-CrPO4

A new arsenate K1+2x Ni1-x Fe2(AsO4)3 (x = 1/8) {potassium nickel diiron(III) tris-[arsenate(V)]} was synthesized using a flux method and its crystal structure was determined from single-crystal X-ray diffraction data. This material was also characterized by qualitative energy dispersive X-ray spectroscopy (EDS) analysis. The crystal structure belongs to the α-CrPO4-structure type, space group Imma. It consists of a three-dimensional-framework built up from FeO6 and Ni0.875□1.25O6-octa-hedra and AsO4-tetra-hedra that are sharing corners and/or edges, generating tunnels running along the [010] and [001] directions in which the potassium cations are located. The proposed structural model was validated by bond-valence-sum calculations, charge-distribution (CHARDI) and Madelung energy analyses.

Synthesis and crystal structure of calcium dizinc iron(III) tris-(orthophosphate), CaZn2Fe(PO4)3

Single crystals of the title compound, CaZn2Fe(PO4)3, were synthesized by conventional solid-state reaction. In the asymmetric unit, all atoms are located in fully occupied general positions of the P21/c space group. The zinc atoms are located on two crystallographically independent sites with tetra-hedral and distorted triangular-based bipyramidal geometries. Two edge-sharing triangular bipyramidal ZnO5 units form a dimer, which is linked to slightly deformed FeO6 octa-hedra via a common edge. The resulting chains are inter-connected through PO4 tetra-hedra to form a layer perpendicular to the b axis. Moreover, the remaining PO4 and ZnO4 tetra-hedra are linked together through common vertices to form tapes parallel to the c axis and surrounding a chain of Ca2+ cations to build a sheet, also perpendicular to the b axis. The stacking of the two layers along the b axis leads to the resulting three-dimensional framework, which defines channels in which the Ca2+ cations are located, each cation being coordinated by seven oxygen atoms.