Four-position disorder of cationic protonated guanylurea in a stable three-dimensional network in the structure of a triple salt decavanadate complex (HGU+)(H2Met2+)2(H3O+)(V10O28 6−)·8H2O

Abstract

A triple salt of decavanadate, V10O28 6−, containing mixed organic guanylurea (diaminomethylideneurea cation, HGU+) and metforminium(2+) (H2Met2+) cations and hydronium (H3O+) cations, has been synthesized by heating metformin hydrochloride, picolinic acid, and sodium metavanadate in aqueous solution at pH 4 and 333 K followed by maintaining the solution at 300 K overnight to give an orange crystalline product. As commonly observed, the V10O28 6− anion lies on an inversion center. Charge is balanced by two H2Met2+ dications and two monocations, one HGU+ and one H3O+, substitutionally disordered about another inversion center. The HGU+ cation is further positionally disordered by rotation of 26.3 (4)° about an axis approximately along the direction of the three essentially collinear N atoms of the cation, thereby hydrogen bonding to two adjacent rows of cluster O atoms running diagonally across the equatorial plane of the V10O28 6− anion. The highly concerted nature of the HGU+...cluster interaction in each orientation suggests a synthon that likely preexisted in solution and perhaps, along with heat, contributes to the degradation of the metformin to HGU+. The structure of the salt exhibits a complex charge-stabilized hydrogen-bonded network involving extended C 4 4(8) chains of the water molecules and the H2Met2+ cations linking the chains into two-dimensional sheets parallel to the bc plane, and V10O28 6− anions linking those sheets into a three-dimensional structure through Ow—H...O, N—H...O and C—H...O intermolecular interactions. The disordered HGU+ cation and the H3O+ cation occupy spaces with excess volume in the three-dimensional network structure.