Abstract
Many new complexes of chromium(II) and vanadium(II) with thiocyanate and heterocyclic ligands have been prepared under anaerobic conditions. The structures of the compounds have been investigated by spectroscopic, magnetic susceptibility and X-ray powder methods. Some complexes of chromium(II) with the macrocyclic tetradentate amine 1,4,8,11-tetrazacyclotetradecane (cyclam) have been prepared before but only the iodide, Cr(cyclam)I[2], was investigated in any detail. A series of such complexes Cr(cyclam)X[2] (X = Cl[-], Br[-], 1/2SO[4][2-] and NCS[-]) has been investigated further. The chloride and bromide are weakly antiferromagnetic while the thiocyanate appears to be low-spin, although the compound was not obtained pure. The sulphate group is ionic and as the complex is a monohydrate it may be five coordinate. The reflectance spectra of the complexes do not show the usual anion-dependence of tetragonal six-coordinate chromium(II) complexes and five and six coordinate structures are possible. Attempts to obtain similar vanadium(II) complexes were unsuccessful. Another new class of complexes obtained comprises the thiocyanato-chromate(II) salts of organic cations: (Cat)[2] [Cr(CNS)[4]] in which Cat = pyH, Me[4]N, hexH (protonated hexamine), Et[4]N, Pr[4]N and Bu[4]N; and (Cat)[Cr(CNS)4] where Cat = double charged trans [14]dienium and ethylene-diammonium ions. Most of the complexes have polymeric tetragonal structures with bridging and terminal thiocyanate groups, as judged from their magnetic behaviour, and infrared investigations of the thiocyanate bonding. All except the ethanol adducts of the Et[4]N and Pr[4]N compounds, one form of the Bu4N compound, and Cr (SCN)2.2 (hexH. SCN), are antiferromagnetic. The last compound is the only one previously known and it was formulated as written. It is now believed to contain coordinated hexaminium and N-bonded thiocyanate ions in the solid and has been assigned the formula Cr(hexH)[2](NCS)[4]. Amine thiocyanato-complexes of chromium (II): CrL2 (CNS)2, (L = pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine and thiourea), and Cr(LL)2(NCS)2, (LL = 1,10-phenanthroline and 2,2'-bipyridyl) have also been isolated for the first time. The complexes with the pyridines and thiourea are all anti ferromagnetic and have thiocyanate bridged polymeric structures. The complexes Cr(py)2(CNS)2 and Cu(py)2(CNS)2 have similar X-ray powder patterns. The phenanthroline and bipyridyl complexes are low-spin and have a cis-octahedral structure. The first thiocyanate complexes of vanadium(II) have also been prepared. These are the thiocyanatovanadate(II) salts: (Cat)2[V(NCS)6] , (Cat = pyH, Me4N, Et4N, Bu4N and hexH), and the amine thiocyanato-complexes VL4(NCS)2 (L = pyridine, 3-methylpyridine, 4-methylpyridine and 4-cyanopyridine) and V (LL) 2 (NCS)2 (LL = 1,10-phenanthroline and 2,2'-bipyridyl). The thiocyanatovanadates have regular octahedral structures with N-bonded thiocyanate groups while the amine thiocyanates, VL4(NCS)2, have four equatorial amine molecules and two axial N-bonded thiocyanate groups. These complexes have been found to be isomorphous with the corresponding nickel(II) complexes. The phenanthroline and bipyridyl complexes have cis-octahedral structures like the chromium(II) complexes.