The crystal structure of two nitroprussides: Mn[Fe(CN)5NO]·3H2O and Cd[Fe(CN)5NO]·3H2O

The crystal structures of manganese(II) and cadmium(II) nitrosylpentacyanoferrate trihydrate have been determined from three dimensional, single- crystal X-ray diffraction data. These polynuclear cyanides crystallize in the monoclinic space group P21/n (No. 14, C52h) with four formula units per cell. The lattice constants are a = 7.302(4), b = 14.783(6), c = 10.751(1) Å and β = 91.47(2)° for manganese nitroprusside and a = 7.425(2), b = 14.963(2), c = 10.848(3) Å and β = 91.64(2)° for cadmium nitroprusside. Dm = 1.86(1) Mg m−3, Dx = 1.864 Mg m−3 and Dm = 2.09(1) Mg m−3, Dx = 2.106 Mg m−3, respectively for manganese and cadmium nitroprusside. Final full-matrix least-squares refinement of 1881 unique reflections for Mn[Fe(CN)5NO] and 1958 unique reflections for Cd[Fe(CN)5NO] yielded R = 0.023 and 0.030, respectively. Both iron and divalent metal centers have distorted octahedral symmetries. The iron atom is coordinated by five cyanide ligands and one nitrosyl group, whereas the cation metal center is coordinated by five cyanide ligands and one water molecule. The metal atoms in both structures are linked by FeCNM bridging (M Mn or Cd). The two uncoordinated water molecules, O(2) and O(3), are hydrogen bonded to the coordinated water molecule, O(1), and occupy channels in the crystal lattice. Important mean bond lengths for manganese nitroprusside are: MnN = 2.226(19), FeC = 1.935(5) and CN = 1.140(2) Å. Other notable bond lengths include MnO(1) = 2.218(2), FeN = 1.659(2) and NO = 1.135(2) Å as well as the contact distances O(1)O(2) = 2.854(3) and O(1)O(3) = 2.759(3) Å. Important mean bond distances for cadmium nitroprusside are CdN = 2.314(18), FeC = 1.942(6) and CN = 1.135(7) Å. Other notable bond and contact distances include CdO(1) = 2.335(2), FeN = 1.667(3), NO = 1.125(3), O(1)O(2) = 2.856(4) and O(1)O(3) = 2.784(4) Å.