Synthesis, Spectroscopic Studies and X-Ray Crystal Structure Analysis of Cobalt Nitroprusside, Co[Fe(CN)5NO]·5H2O

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Abstract
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, O5 h), a = 10.28 I (2)Å, with three formula units per cell. D m = 1.67(1) Mg m−3 and D x = 1.673 Mg m−3. Final full-matrix least-squares refinement of 102 unique reflections converged to R = 0.020 and R w = 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.

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