Crystal Growth of New Hexahydroxometallates Using a Hydroflux

A series of seven compounds, Sr2Mn(OH)(6), Ba2Mn(OH)(6), Sr2Co(OH)(6), Ba2Co(OH)(6), Sr2Ni(OH)(6), Ba2Ni(OH)(6), and Ba2Cu(OH)(6), were synthesized using a low-melting hydroflux, a hybrid approach between aqueous hydrothermal and molten hydroxide flux techniques. Crystals of the hexahydroxometallates were obtained by dissolving appropriate amounts of alkaline-earth nitrates or hydroxides and transition-metal oxides, acetates, or chlorides in the hydroflux and reacting at 180-230 degrees C. The isostructural compounds all crystallize in the monoclinic space group P2(1)/n. The monoclinic structure consists of isolated transition-metal octahedra within a three-dimensional framework of corner- and edge-shared eight-coordinate, alkaline-earth polyhedra. Magnetic susceptibility data show that all compounds are simple paramagnets. Thermogravimetric analysis indicates that these hydroxides lose water between 215 and 350 degrees C and transform into oxide products, the identity of which depends on the metal cations present in the parent hexahydroxometallates.