Some complexes of vanadium, cobalt and manganese

• Main Author: O'Donoghue, Michael William
• Published: University of Surrey 1977
• Subjects: 546.3
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.467478

Many new complexes of vanadium(II) and (III), manganese(II), and cobalt(II) and (III) have been synthesized and characterized. Difficulties were encountered in isolating most of these compounds due to their rapid oxidation on exposure to air. Certain vanadium(II) and cobalt(II) systems were found to be oxidized, apparently by traces of water or by the ligand, even in the absence of air. Experimental procedures were conducted in glass apparatus either under vacuum or nitrogen as all manipulations necessitated rigorous air-free conditions. Infra-red, ultra-violet and visible spectroscopy, magnetochemistry and X-ray powder diffraction have helped to determine the structures of the new compounds. The first part of this thesis is concerned with investigations of vanadium(II) chemistry. New vanadium(II) alcoholates, VBr[2]. 6EtOH, VI[2]. 6MeOH, VCl[2]. 4EtOH and VCl[2]. 2EtOH, have been prepared from the vanadium(II) salts VBr[2]. 6H[2]O, VCl[2]. 4H[2]O and VCl[2]. 2H[2]O, which were themselves obtained via electrolytic reduction. The alcoholates were prepared as they were expected to be more suitable than the hydrates for use as precursors for other synthetic work in non-aqueous solvents. From the vanadium(II) hydrates and alcoholates compounds containing pyrazole, imidazole, 2-methylimidazole, benzimidazole and isoquinoline have been prepared and characterized. Their structures were dependent on the nature and number of ligands bound to the metal ion. Complexes formulated as VL[4]X[2], where L = a heterocyclic amine and X = Cl, Br and I, have distorted octahedral stereochemistry whereas species of the type [VL[6]]X[2] have octahedral geometry. Attempts to prepare complexes of vanadium(II) with Schiff's bases such as N,N'-ethylenebis (salicylideneimine) from vanadium(II) salts in organic solvents in the absence of air were unsuccessful, vanadium(III) or (IV) compounds being obtained. Attempts to prepare vanadium(II) dithiocarbamates were similarly unsuccessful, but the new vanadium(III) dithiocarbamates, V(S[2]CNR[2])[3], where R = Me, Et, Pr[n] and Bu[i], were fortuitously obtained. Investigations of these and of dithiocarbamates of manganese(II) and cobalt(II), are described in the second part of the thesis. New compounds of manganese(II) containing dithio- carbamate or dicyclohexylxanthate ions as ligands have been isolated and their properties investigated. Interest in the manganese(II) dithiocarbamates was stimulated by a claim that Mn(S[2]CNEt[2])[2] was planar with manganese(II) in an unusual spin-quartet (S = 3/2) ground state. Magnetic, X-ray powder and other studies reported in this thesis show the claim to be erroneous ; this compound is high-spin (S = -5/2), but with its magnetic moment reduced below the spin-only value through antiferromagnetic interaction in an octahedral polymeric structure. Similarly, it has been found that the complexes Mn(S[2]CNR[2])[2], where R = Me, Bu[i] and 1\2 C[4]H[8], have octahedral polymeric structures, but Mn(S[2]CNPr[2][n])[2] appears to be binuclear. In contrast, the dicyclohexylxanthate complexes Mn(Chxn)[2]L[2], where L = pyridine, isoquinoline, 3,5-lutidine and ?-picoline, consist of high-spin manganese(II) ions in a monomeric octahedral environment. In an effort to synthesize cobalt(II) dithiocarbamates of the type Co(S[2]CNR[2])[2], where R = Me, Et, Pr[n], Bu[i] and 1/2 C[4]H[8], the cobalt (III) tris-chelates were obtained, apparently admixed with some paramagnetic cobalt oxide except where R = Me and 1/2 C[4]H[8]. Magnetic studies show that Co(S[2]CNMe[2])[2] exhibits spin-isomerism over the temperature range 295-90°K, whereas Co(S[2]CNC[4]H[8])[2] appears to be a high-spin cobalt(II) complex in which there is some antiferromagnetic interaction. The analogous cobalt(III) complexes Co(S[2]CNR[2])[3] were also synthesized for comparative purposes.