Crystal structure of ammonium octacyanomolybdate(IV) and rubidium octacyanomolybdate(IV)

The crystal structure of ammonium octacyanomolybdate(IV) and rubidium octacyanomolybdate(IV) has been determined by the single-crystal method on a Syntex P2/sub 1/ automatic diffractometer: ((NH/sub 4/)/sub 4/ Mo(CN)/sub 4/) 0.5H/sub 2/O (I) (space group Pma2, a = 15.550(3), b = 14.118(3), c = 7.438(1) A, Z = 4, R = 0.062) and Rb/sub 4/(Mo(CN)/sub 8/). 3H/sub 2/O (II) (space group P4/sub 1/2/sub 1/2, a = 9.300(10, c = 21.807(3) A, Z = 4, R = 0.065). The Mo atoms in structure I occupy two special positions (2(b) and 2(c)) and are each surrounded by eight CN ligands. The mean value of the Mo-C distances for Mo(1) is equal to 2.216 A, and the corresponding value for Mo(2) is 2.235 A. The mean Mo-N lengths are practically identical in both molybdenum anions and are equal to 3.353 A. The mean values of the C identical with N bond lengths in the Mo(1) and Mo(2) anions are 1.118 and 1.137 A, respectively. The MoCn angles vary from 175.0 to 178.4/sup 0/. The coordination sphere of the Mo(1) atom corresponds to a dodecahedron with a single twofold symmetry axis, and the coordination polyhedron of the Mo(2) atom in an antiprism of m symmetry. Inmore » structure II the Mo-C distances are within the 2.130-2.160-A range, and the Mo-N distances range from 3.290 to 3.307 A. The MoCN angles vary from 176.0 to 179.3/sup 0/, and the coordination polyhedron of (MoC/sub 8/) is a dodecahedron of 2 symmetry. The existence of two types of coordination of Mo in structure I is presently the only example among the structurally studied octahyanomolybdates(IV).« less