Synthesis and structural characterization of two new rare-earth manganese germanates: CeMn2Ge4O12 and GdMnGe2O7

Crystals of Ce+4Mn2+2Ge4O12 and Gd+3Mn+3Ge2O7 were obtained during the expl oration of the quaternary Ln-Mn-Ge-O system, Their structures have been det ermined by single-crystal X-ray diffraction: CeMn2Ge4O12 crystallizes in th e tetragonal space group P4/nbm with a = 9.816(1) Angstrom, c = 4.888(1) An gstrom, Z = 2, and R = 0.026 while GdMnCe2O7 crystallizes in the orthorhomb ic space group A222 with a = 4.735(1) Angstrom, b = 7.839(2) Angstrom, c = 13.500(3) Angstrom, Z = 4, and R = 0.048, Both frameworks are built up from the same polyhedra, i.e., LnO(8) antiprisms, NnO(6) octahedra, and GeO4 te trahedra. CeMn2Ge4O12 is isotypic with SrNa2 P4O12; the GeO4 tetrahedra are linked into Ge4O12 rings located between layers of CeO8 and MnO6 polyhedra sharing edges, On the other hand, GdMnGe2O7 exhibits a novel quasi-one-dim ensional lattice which might be ascribed to the Jahn-Teller nature of the M n+3 ion. The structure consists of chains of MnO6 octahedra alternating wit h parallel chains of GdO8 antiprisms forming layers linked together through Ge2O7 groups. A structural comparison with fluorite-related compounds as w ell as CeMn2Ge4O12 will be discussed. (C) 1999 Academic Press.