Preparation and Investigation of Complex Halides and Thiocyanates of Chromium(II).

Many new compounds of chromium(II) have been prepared under anaerobic conditions, and their properties investigated by spectroscopic, magnetic and X-ray powder techniques, also carried out in the absence of air. An effective method of filling glass capillaries for X-ray powder photographs of air-sensitive compounds, without the use of a nitrogen box, has been developed. The new compounds obtained were M2 CrCl4(H2O)2, (where M = Cs or PyH), M2CrCl4, (where M = Cs, PyH, EtNH3, MeNH3 or Me2NH2), MCrCl3, (where M= Me4N or Me2NH2), (enH2)CrCl4, (dienH3)CrCl5 and (trienH4)CrCl6. The dihydrates are magnetically normal while the anhydrous compounds are ferromagnetic except for the trichiorochromates(II) and the pyridinium and dimethyl-ammonium tetrachlorochromates(ll) which are antiferromagnetic. The structures of most of these compounds, as well as the known dihydrates, have been deduced by comparison of their powder photographs with those of corresponding copper(II) compounds of known structures. A new series of compounds of the type M2CrBr4(H2O)2, (where M = Cs, PyH, Rb or NH4) and M2CrBr4, (where M = Cs, PyH, Rb, NH4, EtNH3 or Et4N) has been prepared. These compounds have also been investigated by spectroscopic and magnetic techniques, and,when possible, their structures have been compared with those of the corresponding chlorochromates(II) or bromocuprates(II) by X-ray powder photography. The dihydrates, which are similar to or isomorphous with the corresponding chlorochromates(II) or bromocuprates(II), are magnetically dilute while the anhydrous compounds are antiferromagnetic except for the caesium and ethyl-ammonium compounds which show ferromagnetic behaviour. From spectral and X-ray results it has been found that in all compounds the chromium(II) ion is situated in a distorted octahedral environment , and polymeric structures have been assigned to these compounds except for the dihydrates which are mononuclear. A brief investigation of thiocyanato-complexes of chromium(II) has shown that the known compound, Na3Cr (NCS )5. 9H2O has the unusual stoichiometry previously assigned to it although the degree of hydration is uncertain. The compound, Na3Cr(NCS)5. CH3COCH3. 6H2O, has also been prepared. Infra-red, reflectance and magnetic studies show that the first compound contains N-bonded thiocyanate while the second appears to contain bridging thiocyanate as well. Considerable difficulties were encountered during preliminary attempts to prepare complex iodides and some new complex fluorides because chromium(ll) has little affinity for the iodide ion, and the glass apparatus was not suitable for use with hydrofluoric acid