Guanylurea metformium double salt of decavanadate, (HGU+)4(HMet+)2(V10O286−)·2H2O

Metformin and vanadate were combined to form a double salt of decavanadate (V10O286−) with two cations, namely metformium and a hydrolysis product of metformin, protonated guanylurea (HGU+). The material was prepared by heating metformin and decavanadate in aqueous solution at pH 6.5 at 60 °C for 25 h. The title compound crystallizes in the triclinic space group P 1 ¯ , Z = 1. The structures of both cations and the decavanadate anion correspond to those reported previously. The V10O286− lies on an inversion center and charge is balanced by four HGU+ cations around the central axis and two HMet+ cations capping the ends of the V10O286− cylinder. These ions and two waters of solvation engage in an extensive multiple H-bonded network with the HGU+ bound at the strongest H-bond acceptor sites of the V10O286− and the HMet+ at lesser sites. The hydrolysis of metformin in the presence of a vanadium(V) (i.e. decavanadate, VO2+ or H2VO4−) catalyst was confirmed in solution studies using 1H, 13C, and 51V NMR spectroscopy.