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 o btained under various experimental conditions that favour volatilizati on 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, charact erized by one-dimensional infinite metaphosphate chains and isolated M O(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 geometr y [d(ave)(Cr-O) = 1.96 (2) Angstrom] were observed. Within the two ind ependent 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].