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

Abstract Metformin and vanadate were combined to form a double salt of decavanadate (V 10 O 28 6 − ) 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 V 10 O 28 6− 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 V 10 O 28 6− 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 V 10 O 28 6− and the HMet + at lesser sites. The hydrolysis of metformin in the presence of a vanadium(V) ( i.e. decavanadate, VO 2 + or H 2 VO 4 − ) catalyst was confirmed in solution studies using 1 H, 13 C, and 51 V NMR spectroscopy.