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).

The transition metal orthophosphate CaNi2Fe(PO4)3 adopts the α-CrPO4 structure type. The structure is built up from two types of sheets, resulting in an open three-dimensional framework that delimits two types of channels in which the CaII cations are located.

Single crystals of sodium copper(II) indium bis[phosphate(V)], NaCuIn(PO4)2, were grown from the melt under atmospheric conditions. The title phosphate crystallizes in the space group P21/n and is isotypic with KCuFe(PO4)2. In the crystal, two [CuO5] trigonal bipyramids share an edge to form a dimer [Cu2O8] that is connected to two PO4 tetrahedra. The obtained [Cu2P2O12] units are interconnected through vertices to form sheets that are sandwiched between undulating layers resulting from the junction of PO4 tetrahedra and [InO6] octahedra. The two types of layers are alternately stacked along [101] and are joined into a three-dimensional framework through vertex- and edge-sharing, leaving channels parallel to the stacking direction. The channels host the sodium cations that are surrounded by four oxygen atoms in form of a distorted disphenoid.

Crystals of the new compound, AgSr4Cu4.5(PO4)6, were grown successfully by the hydrothermal process. The asymmetric unit of the crystal structure of the title compound contains 40 independent atoms (4 Sr, 4.5 Cu, 1 Ag, 6 P and 24 O), which are all in general positions except for one Cu atom, which is located on an inversion centre. The Cu atoms are arranged in CuO n (n = 4 or 5) polyhedra, linked through common oxygen corners to build a rigid three-dimensional motif. The connection of these copper units is assured by PO4 tetrahedra. This arrangement allows the construction of layers extending parallel to the (100) plane and hosts suitable cavities in which Ag+ and Sr2+ cations are located. The crystal-structure cohesion is ensured by ionic bonds between the silver and strontium cations and the oxygen anions belonging to two adjacent sheets. Charge-distribution analysis and bond-valence-sum calculations were used to validate the structural model.

A new potassium-nickel iron phosphate, K3Ni6Fe(PO4)6, has been synthesized by solid-state reaction and structurally characterized by single-crystal X-ray diffraction and qualitative energy dispersive X-ray spectroscopy (EDS) analysis. The structure is built up by [FeO6], [PO4], and [NiO6] coordination polyhedra, which are linked to each other by edge and corner sharing to form zigzag layers parallel to the ab plane. These layers are interconnected by [PO4] tetrahedra and [NiO6] octahedra via common corners, leading to a three-dimensional framework delimiting large channels running along the [100] direction in which the K+ cations are localized.