The first example of a heteropolyoxomolybdate containing palladium(IV) was isolated and characterized by X ray crystallography The palladium(IV) hexamolybdate, K0 75Na3 75[PdMo6O24H3 (5)] 17H(2)O, was isolated from an aqueous solution at pH 4 5 in the space group P (1) over bar a 10 790(2) b 12 244(3), c 14 086(3) angstrom, alpha 113 77(1), beta 90 41(1) gamma 107 86(1)degrees and the structure was determined using X ray diffraction methods refining to a residual of 0 0301 for 5334 reflections A formal [PdMo6O24H3](5-) subunit exhibits the basic Anderson structure with two [PdMo6O24H3](5-) cluster anions in the structure bridged by a hydrogen atom (formally an H+) situated on a center of symmetry to give a [Pd2Mo12O48H7](9-) dimeric anion The palladium(IV) atom occupies a slightly distorted octahedral environment with Pd-O distances ranging from 1 968 to 2 009 angstrom.