Complexes of bivalent chromium with nitrogen donor ligands

• Main Author: Tabatabai, Javad M.
• Published: University of Surrey 1976
• Subjects: 547.05
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.474437

The new chromium(II) complexes: [Cr(NH[3])[6]]X[2], [Cr(NH[3])[5]]X[2] (X = CL,Br or I), [Cr(NH[3])[2]X[2]] (X = Cl or Br), [Cr(NH[3])[4]H[2]O]SO[4], [Cr(NH[3])[2]SO[4]] , [Cr(CH[3]CO[2])[2](NH[3])] and Cr(NH[3])[4] (CH[3]CO[2])[2] have been isolated and investigated in the absence of air. The hexammines, obtained by bubbling ammonia through ethanolic solutions of the chromium(II) halides, were handled in an atmosphere of ammonia because they lost ammonia readily and reversibly to form pentammines. Thermal decomposition of the pentammines gave the diammine halides. The sulphates and the chromium(II) acetate monoammine have been obtained by similar procedures. Tetramminechromium(II) acetate was obtained by the action of liquid ammonia on the monoammine acetate. From magnetic, spectroscopic and X-ray powder investigations (which frequently showed isomorphous relationships with analogous copper (II) complexes of known structure), the hexammines and pentammines have been assigned tetragonal and square-pyramidal structures respectively, and the diammines anion-bridged, six-coordinate structures. The complexes [Cr(NH[3])[4]H[2]O]SO[4] and Cr(NH[3])[4] (CH[3]CO[2])[2] are believed to have square-pyramidal and distorted octahedral structures respectively, although the latter lost ammonia to form the monoammine [Cr(CH[3]CO[2])[2](NH[3])] so readily that infra-red spectra and X-ray powder photographs could not be obtained. The monoammine was found to be essentially diamagnetic, like the acetate-bridged dimer [Cr(CH[3]CO[2])[2]H[2]O][2], and to have a similar powder pattern, so it is thought to be a dimer with NH3 replacing H[2]O. Preliminary investigations showed that [V(NH[3])[6]]Br[2] can be obtained by similar preparative methods to the chromium(II)-ammines, but attempts to prepare chromium(II) salen (salen is the di-anion of NN'-ethylenebis(salicylideneimine)) from [Cr(NH[3])[5]]l[2] were unsuccessful. Several other, mostly new chromium(II) complexes have also been prepared. These are Cr(iz)[4]X[2], Cr(py)[2]I[2], Cr(gly)[2].H[2]O, Cr(Smc)[2] and Cr(his)Cl.H[2]O, in which iz is imidazole and py is pyridine, X is Cl, Br, I, or 1/2 SO4, and gly, meth, Smc and his are respectively the anions of glycine, DL-methionine, S-methyl-L-cysteine and L-histidine. Magnetic measurements showed the imidazole complexes to be high-spin, and their reflectance spectra indicate trans-octahedral structures, with tetragonal distortion increasing in the order SO[4] < Cl < Br < I. The sulphate and iodide are isomorphous with analogous copper(II) complexes of known trans-structures. The iodide Cr(py)[2]I[2] was found to be antiferromagnetic and possesses a polymeric iodide-bridged structure. The first three amino-acid complexes exhibited minor antiferromagnetic interaction. Their reflectance spectra indicate that the environment of the chromium(II) ion is similar in each case, and polymeric, carboxyl-bridged structures are likely. The histidine compound showed considerable antiferromagnetism and is believed to be chloride-bridged.