Structure of pentaammineaquacobalt(III) hexacyanochromate(III), [Co(NH3)5(H2O)][Cr(CN)6], by time-of-flight neutron diffraction at 11.5 K

Msub(r)=370.2, rhombohedral, R anti 3, a=7.318 (8) A, ..alpha..=97,5(1)/sup 0/, V=381(1)A/sup 3/, Z=1, Dsub(m)(295 K)=1.593(5), Dsub(x)=1.613g cm/sup 3/, lambda=0.7-5.3 A, ..mu..(lambda)=1.82 + 0.0826lambda(..mu.. in cm/sup 1/),T=11.5 K, R=0.071 for 888 observed data. The highly regular nature of the cation and anion octahedra shown by a 120 K X-ray diffraction study was confirmed. The water molecule is disordered over the six 'ammine' sites of the cation with its hydrogen atoms approximately occupying two of three particular sites of the ammine protons. The N-H bonds average 1.01 (1)A. The strong hydrogen bonding involves only one of the three ammine hydrogen atoms, in a nearly linear system, with the cyanide ion of the anion (CN...H=1.933 (5) A). (orig.).