Abstract
Many new compounds of chromium(II) have been prepared under anaerobic conditions, and their properties investigated by spectroscopic and magnetic techniques, also carried out in the absence of air. The hydrated complex chlorides of chromium(II) M[2]CrCl[4](H[2]O)[2], where M = NH[4], Rb and Cs, and CsCrCl[3](H[2]O)[2] have been prepared for the first time, and shown, except for CsCrCl[3](H[2]O)[2] which is binuclear with bridging chlorine atoms, to be normal, high-spin chromium(II) compounds. A simple method for the preparation of their anhydrous analogues has been developed, and, although the corresponding hydrated compound was unstable, K[2]CrCl[4] has been obtained. Anhydrous complex chlorides of the type M[4]CrCl[4] are ferromagnetic, whilst CsCrCl[3] is antiferromagnetic. These are the first ferromagnetic complexes of chromium(II) to be reported. Although slight ferromagnetic interactions have been observed for compounds of other metal, these compounds exhibit the largest interactions so far reported. Reflectance spectra of all the complex chlorides indicate that they have tetragonally distorted, octahedral structures. New complexes of 1,3-propanediamine and C-alkyl and N-alkyl substituted ethylenediamines have been prepared. These are of two types: Cr(bidentate amine)[2]X[2], where X = halide, and Cr(bidentate amine) Cl[2]. The former are high spin, tetragonally-distorted chromium(II) chelates: the latter are halide-bridged polymers in which antiferromagnetic interactions occur. It has been shown that the degree of substitution influences complex formation, in that no tris (amine) compounds and few compounds of N-substituted ligands have been obtained. Investigations of complex formation of chromium(II) with the cyclic quadridentate amine, 1,4,8,11-tetraazacyclotetradecane (cyclam), have been carried out. CrcyclamCl[2], CrcyclamBr[2], and Crcyclaml[2] have been prepared for the first time. Since very little ligand was available only the iodide was extensively investigated, and it was shown to contain tetragonally-distorted octahedral chromium(II) species. Its reflectance spectrum at liquid nitrogen temperature provides the first resolution of all three expected transitions of chromium(II) in D[4]h symmetry.