Role of the alkali metal ion and hydrogen bonds in M[VO(O2)2bpy] · nH2O (M = Li+, Na+, K+ and Rb+) and Cs[VO(O2)2bpy] · H2O2 complexes: The X-ray crystal structures and spectroscopic properties

Both V2O5 and MVO3, were used for the synthesis of the M[VO(O2)2bpy] · nH2O · mH2O2 complexes (M = alkali metal ion, bpy = 2,2′-bipyridine). The method with MVO3 was found to be more convenient. The complexes were characterized in the solid state by X-ray crystal structure analyses, IR and electronic spectroscopy. The number of water (n) and hydrogen peroxide molecules (m) depends on the type of alkali metal ion as follows: m = 0, n = 5 (Li+), 8 (Na+), 4 (K+), 4 (Rb+); and n = 0, m = 1 (Cs+). Analysis of the crystal structures shows extensive hydrogen bonding networks (except for the caesium complex) involving water molecules and peroxo groups. The complex anions possess a distorted pentagonal bipyramidal geometry with the vanadyl oxygen ion and one of bipyridyl’s nitrogen atom at the apices and the peroxo groups and the second bpy nitrogen atom in the equatorial plane. The frequency of the ν(VO) and ν(O–O) bands in the IR spectra depends on the alkali metal ion; for ν(VO), a red-shift is observed in the sequence Na > Li > K ≈ Rb > Cs.

The type of alkali metal ion (M) in the M[VO(O2)2bpy] · nH2O · mH2O2 complexes influences the degree of hydration, the network of hydrogen bonds involving water molecules and peroxo groups as well the interaction of the M with the oxidovanadium(V) oxygen and/or peroxo ligand.Figure optionsDownload as PowerPoint slide