Strontium manganese vanadates from hydrothermal brines: Synthesis and structure of Sr2Mn2(V3O10)(VO4), Sr3Mn(V2O7)2, and Sr2Mn(VO4)2(OH)

Three new strontium manganese vanadates, Sr2Mn2(V3O10)(VO4) (I) Sr3Mn(V2O7)(2) (II), and Sr2Mn(VO4)(2)(OH) (III), were prepared using a high temperature (580 degrees C) hydrothermal method with various chloride salts as the mineralizer. Minor differences in the chloride stoichiometry led to significant differences in product. Compound I crystallizes in the monoclinic space group P2(1)/c (a = 6.8773(12) angstrom, b = 15.061(3) angstrom, c = 11.609(2) angstrom, beta = 96.745(8)degrees), and consists of edge-shared octahedral manganese(II) dimers coordinated by trimeric [V3O10] and monomeric [VO4] groups. Compound II crystallizes in the tetragonal crystal system, P4(3)2(1)2 (a = 6.9951(2) angstrom, c = 25.4390(7) angstrom), and is built from monomeric manganese(II) octahedra chelated by two pyrovanadate [V2O7] groups and linked to each other by additional pyrovanadates to form layers. Compound III is a noncentrosymmetric variation on the brackebuschite structure type, crystallizing in the monoclinic space group P2(1) (a = 7.6316(3) angstrom, b = 6.1204(3) angstrom, c = 8.6893(3) angstrom, beta = 111.3940(10)degrees). The structure is composed of octahedral manganese(III) edge-sharing chains coordinated to corner-sharing monomeric [VO4] groups, thereby forming a manganese vanadate chain. All compounds were characterized by single-crystal X-Ray diffraction, powder X-Ray diffraction, infrared spectroscopy and single-crystal Raman spectroscopy. Density functional theory calculations were employed to investigate the relative stability of compound III.