Refinement of the superstructure of C-type chromium(III) tris(metaphosphate), Cr(PO3)(3)

Single crystals of Cr(PO3)(3) suitable for X-ray investigations were obtained under various experimental conditions that favour volatilization of the phosphate and its recrystallization from the gas phase. The compound belongs to the series of phosphates M(PO3)(3) (M(3+) = Al, In, Sc, Ti, V, Fe, Mo, Rh, Ru) which adopt the C-type structure, characterized by one-dimensional infinite metaphosphate chains and isolated MO(6) octahedra. Associated with the superstructure generally found for this structure type, in which the monoclinic b axis is tripled, three crystallographically different CrO6 octahedra of almost ideal geometry [d(ave)(Cr-O) = 1.96 (2) Angstrom] were observed. Within the two independent metaphosphate chains distinctly different bond distances from P to bridging and terminal O atoms were found [d(ave)(P-O-b) = 1.58 (1), d(ave)(P-O-t) = 1.49 (1) Angstrom].