Tetrahedral and octahedral complexes of vanadium(III)

Abstract

Anhydrous vanadium trichloride and tribromide react with acetonitrile to produce non-electrolytic complexes of the type [VX₃,3CH₃CN](X = Cl or Br) both in solution and in the solid state. Addition of tetraethylammonium, methyltriphenylarsonium, or tetraphenylarsonium chlorides to acetonitrile solutions of the above result in the precipitation of complexes of the type R⁺[VX₄,2CH₃CN]^–(R = Et₄N⁺, MePh₃As⁺, or Ph₄As⁺). Mixed halogeno-species of this type may also be synthesised. Reaction of the complex Et₄N[VCl₄,2CH₃CN] with dry pyridine or with 2,2′-bipyridyl or 1,10-phenanthroline (in acetonitrile) yields complexes of the type Et₄N[VCl₄,2L], where L = py, ½ bipy, or ½ phen. Studies of the visible and infrared spectra of all the above complexes demonstrate that in each case the vanadium(III) is octahedrally co-ordinated, and estimates of the ligand-field splitting parameter (Dq) and Racah parameter (B) for these complexes are given.

Thermal decomposition of the bis-acetonitrile derivatives at 100° yield complexes of the type R⁺VX₄^–(X = Cl or Br) as well as the mixed complex Et₄N⁺ VCl₃Br^–. The electronic spectra (band positions and extinction coefficients), infrared spectra, and X-ray powder photographs of the complexes demonstrate conclusively that the VX₄^– ions are tetrahedral in the salts Ph₄AsVCl₄, Ph₃MeAsVCl₄, and Et₄NVBr₄, as might be expected for four-co-ordinate ions with the e² configuration. The parameter 10Dq is calculated to be 5400 cm.^–1 for the VCl₄^– ion. The room-temperature magnetic moments of the complexes (∼2·8 B.M.) are consistent with the presence of two unpaired electrons per vanadium atom in each case.