An oxo-bridged binuclear vanadium(III) 2,2'-bipyridine complex and its vanadium(IV) and vanadium(V) oxidation products

Abstract

Vanadium(III) in water reacts with 2,2′-bipyridine to form an oxo-bridged binuclear complex that crystallizes as [{VCl-(bpy)]O],Cl·3HO in the orthorhombic space group Pbcn with unit cell dimensions a = 18.820 (8) A, b = 9.507 (2) A, c = 25.792 (6) A, V = 4614.8 A, and Z = 8. The complex in its crystalline form has a magnetic moment per vanadium of 3.176 ± 0.002 µ, an unusually high value, considering all available evidence supports the III oxidation state. Aerial oxidation yields an oxovanadium(IV) complex that crystallizes from an aqueous acetone perchlorate solution as [VOCl(bpy)]ClOin the monoclinic space group P2/c with a = 12.960 (3) A, b = 12.310 (4) A, c = 13.642 (3) A, β = 105.78 (2)°, V = 2094.4 A, and Z = 4. Further oxidation in aqueous tetrahydrofuran produces crystals of [VO(bpy)]Cl·4HO with the triclinic space group Pl with a = 1 1.527 (5) A, b = 15.102 (5) A, c = 6.738 (3) A, ± = 97.33 (4)A, ² = 97.26 (4)°, γ = 101.31 (3)°, V= 1126.9 A, and Z = 2. The structures of the first and third complexes were refined by a full-matrix least-squares procedure, and a blocked-matrix procedure was employed for the refinement of the vanadyl complex. Refinement on 2364 statistically significant reflections yielded final R = 0.063 and R= 0.071 for the oxo-bridged complex; on 2402 reflections, R = 0.065 and R= 0.071 for the vanadyl complex; and on 2212 reflections, R = 0.076 and R= 0.084 for the dioxovanadium(V) complex. The coordination geometries show similar distortions from a regular octahedral structure dictated by repulsions between the two anionic ligands, the small bite angle of the chelates, and the effects of trans ligands on the coordinate bond lengths. The binuclear complex has a Caxis relating the two units, which are twisted 61.6° relative to each other. The V-O-V group is close to linear with a bond angle of 173.5 (4)°.