Syntheses, Characterization, and Properties of Vanadium(III) Complexes Containing Tripodal Tetradentate Ligands with Single Pyridyl Groups

The syntheses, characterization, and properties of [V(pda)(OH)(H2O)] (1a), [V2(μ-O)(pda)2(H2O)2] (1b), [V2(μ-O)(bpg)2Br2] (2), and [V2(μ-O)Br2(tpa)2]Br2 (3) are described, where pda (N-(2-pyridylmethyl)iminodiacetate), bpg (N,N-bis(2-pyridylmethyl)glycinate), and tpa (tris(2-pyridylmethyl)amine) are tripodal tetradentate ligands with single pyridyl groups. Complexes 1a, 1b, and 2 were characterized on the basis of their electronic and Raman spectra. The structure of 3 was determined by X-ray crystallography. Complex 3 crystallizes in the space group with the following unit cell dimensions: a = 11.505(5), b = 11.509(5), c = 16.348(7) Å, α = 103.73(2)°, β = 103.71(2)°, γ = 93.26(3)°, and Z = 2. The V–O–V angle is 175.3(2)° and the V–μ-O distances are 1.783(2) and 1.784(2) Å. In complex 3, the four unpaired electrons are ferromagnetically coupled. It was found that there is a positive correlation between 2 × νas(V–O–V) and the energy of the oxo-to-V(III) charge-transfer transition for single oxo-bridged dinuclear vanadium(III) complexes including the present complexes. This correlation is discussed in terms of the π character of the V(III)–μ-O bond that is affected by the remaining donor groups.