Synthesis, Structures, and Spectroscopic Characterization of a Series of N,N‘-Dimethyl-2,11-diaza[3.3](2,6)pyridinophane Vanadium(III), -(IV), and -(V) Complexes

Abstract

Three vanadium-containing complexes, [(L-N4Me2)VCl2](BPh4) (1), [(L-N4Me2)VClO](ClO4) (2), and [(L-N4Me2)VO2](BPh4) (3) where L-N4Me2 is the tetradentate ligand N,N‘-dimethyl-2,11-diaza[3.3](2,6)pyridinophane, have been prepared and characterized by X-ray diffraction and electrochemical methods as well as by IR, 1H-NMR, EPR, and electronic absorption spectroscopy. Complex 1 crystallizes in monoclinic space group P21/n (No. 14) with a = 16.940(4) Å, b = 9.902(3) Å, c = 21.936(8) Å, β = 108.21(2)°, V = 3495(2) Å3, and Z = 4, complex 2 in orthorhombic space group P212121 (No. 19) with a = 10.163(2) Å, b = 13.351(3) Å, c = 14.762(3) Å, V = 2003(1) Å3 and Z = 4, and complex 3 in monoclinic space group P21/c (No. 14) with a = 14.349(3) Å, b =14.040(5) Å, c = 18.131(10) Å, β = 110.62(3)°, V = 3419(2) Å3, and Z = 4. In all these complexes a distorted cis-octahedral coordination geometry is found with the cis coordination sites occupied either by terminal chloro and/or oxo ligands. Thus, a rather unique series of mononuclear complexes has been established where, for example, in reaction with air consecutive replacements of both chloride ions by oxo donors increases the oxidation state of the six-coordinate vanadium ion from III over IV to V while the residual coordination environment remains preserved. Interestingly, in each complex the electronic properties of the cis donor atom set stabilize only one specific oxidation state of the vanadium ion in order to warrant the isolation of the complex.