Synthesis and structural characterization of Keggin polyoxometalate compounds with argininium(2+) cations

New organic–inorganic hybrid compounds, with formula (H2Arg)3[PM12O40]2·4H2O and (H2Arg)4[SiM12O40]·nH2O (n = 0–1), where Arg = L-arginine and M = Mo, W, were prepared and characterized by analytical, spectroscopic, and X-ray diffraction techniques. Thermal analysis was performed to study their thermal stability. The crystal structure of (H2Arg)3[PMo12O40]2·15H2O·EtOH (triclinic, space group P1, Z = 1) was determined by X-ray diffraction. The chiral H2Arg2+ cations and the Keggin anions are involved in hydrogen bonding interactions which lead to the formation of an infinite three-dimensional network. This study adds new members to the important family of argininium/inorganic anions hybrid salts. To our best knowledge these are the first compounds of diprotonated arginine and Keggin-type polyoxoanions and also the first crystal structure determination of an argininium(2+) compound with an inorganic anion of the polyoxometalate family.