The crystal structure of manganese(II) hexacyanochromate(III), Mn₃[Cr(CN)₆]₂·xH₂O

Abstract

The crystal structure of Mn₃[Cr(CN)₆]₂·xH₂O has been determined from three dimensional X-ray diffraction data measured by counter methods. The cubic face centered unit cell with space group O₃F432 or H_h⁵Fm3m has a = 10.761(4) Å and contains 1$\text{1}\text{3}$ formula units, the measured and calculated densities are 1.50 and 1.48 g/cm³, respectively. The structure was determined by application of a general structural model for Prussian Blue analog compounds. Least squares refinement of the positional and individual isotropic thermal parameters led to a final R value for the observed reflections of 0.054.

The crystal structure is very closely related to the structures of other Prussian Blue analog compounds. Manganese and chromium atoms occupy the positions 4a (0 0,0) and 4b (0.5, 0.5, 0.5), respectively, of the unit cell. Carbon and nitrogen atoms are situated at positions 24e (x,0,0) and two different kinds of oxygen atoms (O(1) and O(2)) are distributed in general positions with O(1) (coordinated water) close to the nitrogen position and O(2) (zeolitic water) close to the special position Sc (0.25, 0.25, 0.25). One third of all Cr(CN)₆ groups are statistically absent so that each manganese atom has a mixed coordination, its average composition being MnN₄O₂. All cyanide groups are bridged between chromium and manganese atoms, with the carbon atoms bonded to chromium. The Cr-C, C-N, Mn-N, and Mn-O(1) distances are 2.06(1), 1.12(2), 2.20(1), and 2.36(4) Å respectively.