No abstract

The transition metal orthophosphates Na2 M 2Fe(PO4)3 (M = Co, Ni) crystallize in an alluaudite-type structure. The chains characterizing the alluaudite structure are then built up from [M 2O10] units alternating with [FeO6] octa­hedra.

The title compound, Cd2V2O7, was obtained under hydro­thermal conditions. Different from the known monoclinic form, the new polymorph of Cd2V2O7 has triclinic symmetry and is isotypic with Ca2V2O7. The building units of the crystal structure are two Cd2+ cations, with coordination numbers of six and seven, and two V atoms with a tetra­hedral and a significantly distorted trigonal–pyramidal coordination environment, respectively. Two VO5 pyramids share an edge and each pyramid is connected to one VO4 tetra­hedron via a corner atom, forming an isolated V4O14 8− anion. These anions are arranged in sheets parallel to (-211) and are linked through the Cd2+ cations into a three-dimensional framework structure.

The transition metal orthophosphates SrM 2Fe(PO4)3 (M = Co, Ni) crystallize in an α-CrPO4-type structure. The chains characterizing this structure are then built up from [Ni2O10] units alternating with [PO4] tetra­hedra and [FeO6] octa­hedra. The structure is nearly the same as that observed in MMnII 2MnIII(PO4)3 (M = Pb, Sr, Ba).

NaMg3(PO4)(HPO4)2 crystallizes in the alluaudite-type structure. Two types of [MgO6] octa­hedra, one [NaO10] polyhedron, one orthophosphate and one hydrogenphosphate tetra­hedron form the structural set-up.