CRYSTAL-STRUCTURE OF (PB2.8FE1.2)CU4O1.6(VO4)4(OH)2 STRUCTURAL RELATIONSHIPS WITH MINERAL GAMAGARITE

Single crystals of (Pb2.8Fe1.2)Cu4O1.6(VO4)4(OH)2 are grown by hydrothermal synthesis (180 MPa, 773K, 72 h). The symmetry is orthorhombic with a = 7.525(7) angstrom, b = 5.900(3) angstrom and c = 9.640(5) angstrom, space group Pnma, Z = 1, R = 0.025, R(w) = 0.025. The structure of this new compound is built up of infinite Cu2+ rutile type chains linked by VO4 tetrahedra. Lead and iron are randomly distributed over the same crystallographic site leading to unusual seven-fold coordinated Fe3+. Structure relationships with the mineral Gamagarite Ba4(Fe3+, Mn3+)2(VO4)4(OH)2 [1] are presented, which show that the latter mineral is a defective form of the title compound.