Systematic synthesis, structural characetrization, and reactivity studies of vanadium(V)-citrate anions [VO_2(C_6H_6O_7)]_(2~2-), isolated from aqueous solutions in the presence of different cations

摘要

The aqueous chemisty of vanadium with physiologically relevant ligands constitutes a subject of burgeoning rsearch, extending from bacterial metalloenzymic functions to human-health physiology. Vanadium, in the form of VCl_3 and V_2O_5 reacted expediently with citric acid, in a 1:2 molar ratio in water at pH approx 4, and, in the presence of various cations, afforded crystalline materials bearing the general formula (Cat)_2[V_2O_4(C_6O_6O_7)_2]-nH_2O (A) (Cat~+ - Na~+, n = 2; Me_4N~+, K~+, n = 4). Exploration of the reaction of the reactivity of A toward H_2O_2 yielded the peroxo-containing complexes (Cat)_2[V_2O_2(O_2)_2(C_6H_6O_7)_2] centre dot 2H_2O (B) (Cat~+ = K~+, NH_4~+). Both classes of compounds were characterized analytically and spectroscopically. The X-ray structures of complexes A and B emphasize the exceptional stability of the dimeric rhombic unit V_(2~V)O_2, which is retained upon H_2O_2 reaction, and the preserved mode of coordination of the citrate ligand as a doubly deprotonated moiety. In these complexes, typical six and eight coordination numbers were obwerved for the Na~+ and K~+ counter-ions, respectively. The variety of synthetic approaches leading to A, along with the stepwise and direct assembly and isolation of peroxo-compounds (B), denotes the significance of reaction pathways and intermediates in vanadium(III-V)-citrate synthetic chemistry. Hence, a systematic investigation of reactivity modes in aqueous vanadium-citrate systems emerges as a crucial tool for the establishment of chemical interconnectiv-ity among low MW complex species, potentially participating in intricate biodistribution of that metal ion in biological fluies.