Abstract
Single-crystal X-ray crystallographic investigations have been carried out in order to determine the crystal structures of several chromium(II) complex halides and thiocyanates. The magnetically-dilute complexes [C(NH[2])[3]] [2]CrBr[4] (MeCOOH)[2] and [NMe[2]H[2]][2]CrBr[4](MeCCOH)[2] have been shown to have structures which consist of discrete, planar [CrBr[4](MeCOOH)2][2-] units which are separated by the relevant cation. The structure of the complex [HPy] [2]CrBr[4] (OH[2])[2] that of discrete diaquadibromochromium(II) units and bromide ions and is better formulated as [CrBr[2](OH[2])[2]].[2](Hpy)Br. Of the chromium(II) complex thiocyanates studied, the red form of [Bu[4]N][2]Cr(NCS)[4] has a structure in which square-planar, N-bonded [Cr(NCS)[4]][2-] units are separated by [Bu[4]N] cations. The structure of the blue form of [Bu[4]N][2]Cr(NCS)[4], which is antiferromagnetic, was found to contain [Cr[2](NCS)[8]][2-] dimers which allow "superexchange" to occur between two adjacent chromium(II) ions and are separated by [Bu[4]N] cations. The magnetically dilute [Et[4]N][2]Cr(NCS)[4]. EtOH has a structure which consists of discrete, square-pyramidal [Cr (NCS)[4]. EtOH][2-] anions separated by tetraethylammonium cations. Cr (tu)[2](NCS)[2] is shown to consist of seemingly discrete square-planar Cr(tu)[2](NCS)[2] units and the antiferromagnetic interaction found in this complex is probably due to direct interaction between the chromium (II) atoms in adjacent units. The ternary halides [HPy] CrCl[3], [HPy] CrClxBr[3-x] and [(CH[3])[2]NH3]CrClxBr3-x have been shown to be essentially isostructural, with structures consisting of one-dimensional anionic chains which are separated by cations. [EtNH[3]] [2]CrCl[4] and [EtNH3]2CrClxBr[4-x] have also been shown to be isostructural, consisting of two-dimensional layer structures in which square-planar [CrX[4]][2-] (x = Cl- or Pr- ) units have their octahedral coordination completed by halide ions from neighbouring [CrX4]2-units. The layers are intercalated by the ethylammonium ions. An attempt was made to determine the structure of Cs2CrBr4 from neutron powder diffraction data using the Rietveld refinement technique.