The Crystal and Molecular Structure of Strontium Nitroprusside Tetrahydrate

E. E. CASTELLANO; O. E. PIRO; B. E. RIVERO

Acta Cryst. B

IUCr

Año: 1977 vol. 33 p. 1725 - 1728

Sr[Fe(CN)sNO].4H20 crystallizes in the monoclinic system, space group C2/m, with a = 20.08 (2), b = 7.51 (4), c = 8-42 (2) , beta = 98.4(3)°, Z = 4. The structure was solved by the heavy-atom method and refined by least squares to R = 0.099 for 1014 reflexions. The nitroprusside ion is in a special position with site symmetry m; the water molecules can be grouped into three categories according to their chemical environments: in one category the molecule is at the van der Waals distance from its inversion symmetry-related molecule and also strongly hydrogen-bonded to a molecule of the second category. The third type belongs to the octahedral environment of the Sr ion. The nitrosyl groups of neighbouring nitroprusside ions are approximately parallel to the a-axis and are piled up along the C-axis at intervals of about 4 A, a distance short enough to allow a strong dipole--dipole interaction which is perhaps responsible for the broadness of the NO stretching band. The [Fe(CN)sNO]2- ions are highly distorted octahedra with a mean Fe-C distance of 1.94 and Fe-N of 1.64 A.