Factors Affecting Solution Properties of Vanadium(V) Compounds: X-ray Structure of β-cis-NH4[VO2(EDDA)]1

Abstract

The solution properties of two isomeric forms of the V-EDDA complex (the symmetric α-cis and asymmetric β-cis) have been studied using multinuclear NMR spectroscopy. The isomerization constant of the aqueous equilibrium mixture expressed as [α-cis]/[β-cis] increased on the addition of organic solvents (methanol, formamide, and DMSO) and decreased on the addition of salts (NaCl, NaClO4, and NH4Cl). The isomerization constant and corresponding thermodynamic parameters were determined under a variety of conditions. The solution studies were consistent with the interpretation that solvation is the major contributor to isomer stability. Solid state characterization of the β-cis isomer of NH4[VO2(EDDA)] confirmed this conclusion and allowed detailed examination of the role of hydrogen bonding in this complex. The structural parameters for this complex are triclinic, P1̄, a = 6.787(1) Å, b = 7.272(1) Å, c = 11.014(1) Å, α = 95.084(9)°, β= 92.805(8)°, and γ = 100.009(9)°. The dynamic processes of these complexes were examined in water and in water-DMSO mixtures resulting in observation of an unknown intramolecular dynamic process. The extent to which this complex responds to the environment is discussed, and its implications for biological studies and the mechanism of action of vanadium compounds are briefly considered.