SYNTHESIS, CRYSTAL-STRUCTURE, AND OPTICAL-PROPERTIES OF A NEW BISMUTH MAGNESIUM VANADATE - BIMG2VO6

A new bismuth magnesium vanadate, BiMg2VO6, has been synthesized and structurally characterized from single crystal X-ray diffraction data. It crystallizes in orthorhombic symmetry with a = 7.9136(6) Å, b = 12.246(2) Å, c = 5.444(2) Å, V = 527.6(2)Å3, z = 4, and a space group of Cmcm (No. 63). An unusual fivefold coordination is found for Mg. The five O atoms bound to Mg form a square pyramidal coordination polyhedron with MgO bond lengths ranging from 1.973(7) to 2.066(3) Å. The Bi atom is coordinated by four O atoms with BiO bond lengths 2.213(2) Å forming a square pyramid. The V atom bonds to four O atoms with VO distances from 1.672(6) to 1.725(5) Å; all the OVO angles are very close to the value of an ideal VO4 tetrahedron. The BiMg2VO6 structure may be viewed as connected chains of edge-shared BiO4 units and corner-shared MgO5 units extending along the c axis. These chains are then connected to each other through the VO4 tetrahedra and edge sharing of the MgO5 units. The absorption edge (about 450 nm) determined from the photothermal deflection technique is consistent with results from the excitation-emission spectrum. An emission band around 650 nm was observed. The IR spectrum of this compound is also reported. © 1992.