pH-specific synthesis, isolation, spectroscopic and structural characterization of a new dimeric assembly of dinuclear vanadium(V)–citrate–peroxo species from aqueous solutions

Outstanding among the plethora of roles of vanadium in biological systems is its ability to act as an insulin mimetic agent, counteracting hyperglycemia. Poised to comprehend the interactions of V(V) with physiological substrates of low molecular mass, research efforts were launched to investigate the aqueous synthetic chemistry of the ternary V(V)–citric acid–H2O2 system. In a pH-specific fashion, reaction of VCl3 with citric acid and H2O2 in aqueous ammonia led to the isolation of a unique assembly of ternary dinuclear complexes in (NH4)6[V2O2(O2)2(C6H5O7)2] · [V2O2(O2)2(C6H6O7)2] · 6H2O (1). This unique assembly of dinuclear species was characterized by elemental analysis, FT-IR spectroscopy and X-ray crystallography. The structure of 1 reveals two dinuclear V2O2 core complexes, bearing peroxo moieties and bound citrates of variable deprotonation state and coordination mode. The physicochemical data: (a) present an unusual “instant picture” of the pH-specific aqueous speciation of the investigated system, attest to the presence of known species and clearly suggest the existence of a new discrete species in the aqueous structural speciation of the ternary system, (b) exemplify the usefulness of the synthetic strategy in the discovery of new discrete V(V)–citrate–peroxo species, and (c) offer insight into the ternary interactions of V(V) toward O-containing substrates relevant to insulin mimetic activity.