MULTICOMPONENT POLYANIONS - 54 - CRYSTAL-STRUCTURE OF TETRACAESIUM MONOHYDROGEN PHOSPHATO(PHOSPHITO)PENTAMOLYBDATE DIHYDRATE, CS-4[H(HP)PMO5O22]CENTER-DOT-2H(2)O

The crystal structure of tetracaesium monohydrogen phosphato (phosphit o)pentamolybdate dihydrate was determined by single-crystal X-ray diff raction. The compound crystallises in the triclinic space group P (1) over bar, a=10.284(2), b= 10.791(2) and c=13.047(3) Angstrom, alpha=10 9.34(2), beta=99.92(2) and gamma=102.85(2)degrees, V=1283.4(5) Angstro m(3) and Z=2. The final R-values are R=0.066, wR=0.039 and S=1.3667. T he H(HP)PMo5O224- anion has common features with the Strandberg X2M5-t ype heteropolyanion. The five MoO6 octahedra form a five-membered ring by one corner-sharing and four edge-sharing connections, and the trip odal phosphate and phosphite ligands protrude from each side of this r ing in opposite directions. This is the first example of the structure of the heteropolyoxometalate having both P-III and P-V as heteroatoms .