SYNTHESIS, SPECTROSCOPIC STUDIES AND X-RAY CRYSTAL-STRUCTURE ANALYSIS OF COBALT NITROPRUSSIDE, CO[FE(CN)5NO]5H2O

Slow diffusion of cobalt chloride with Na2[Fe(CN)5NO].5H2O in aqueous solution produced crystals of Co[Fe(CN)5NO]-5H2O suitable for analysis by three-dimensional, single-crystal_X-ray diffractometry. This polynuclear transition metal cyanide crystallized in the cubic space group Fm3m (No. 225, O5n, a = 10.281(2) A, with three formula units per cell. Dm = 1.67(1) Mgm−3and Dx = 1.673 Mgm−3. Final full-matrix least-squares refinement of 102 unique reflections converged to R = 0.020 and Rw= 0.019. The iron nucleus is octahedrally coordinated to five cyanide ligands and a nitrosyl group and the cobalt nucleus is octahedrally coordinated to five cyanide ligands and one water molecule. Cyanide bridging (Fe-C=N-Co) links the metal centers, providing a cubic framework within which uncoordinated water molecules occupy three crystallographically distinct environments. These uncoordinated water molecules are held in position by hydrogen bonding and/or van der Waals forces. The crystal lattice of cobalt nitroprusside is characterized by unique vacancies and a high degree of disorder, which can be described as a super- positioning of various ordered unit cells. Infrared, thermogravimetric and crystallographic data have led to the formulation of a plausible model for cubic nitroprussides. © 1991, Taylor & Francis Group, LLC. All rights reserved.