Synthesis and Structural Characterization of Two New Rare-Earth Manganese Germanates: CeMn2Ge4O12and GdMnGe2O7

Crystals of Ce+4Mn+22Ge4O12and Gd+3Mn+3Ge2O7were obtained during the exploration of the quaternary Ln-Mn-Ge-O system. Their structures have been determined by single-crystal X-ray diffraction: CeMn2Ge4O12crystallizes in the tetragonal space group P4/nbm witha= 9.816(1) ? ,c=4.888(1) ? ,Z=2, andR=0.026 while GdMnGe2O7crystallizes in the orthorhombic space group A222 witha=4.735(1) ? ,b=7.839(2) ? ,c=13.500(3) ?,Z=4, andR=0.048. Both frameworks are built up from the same polyhedra, i.e., LnO8antiprisms, MnO6octahedra, and GeO4tetrahedra. CeMn2Ge4O12is isotypic with SrNa2P4O12; the GeO4tetrahedra are linked into Ge4O12rings located between layers of CeO8and MnO6polyhedra sharing edges. On the other hand, GdMnGe2O7exhibits a novel quasi-onedimensional lattice which might be ascribed to the Jahn-Teller nature of the Mn+3ion. The structure consists of chains of MnO6octahedra alternating with parallel chains of GdO8antiprisms forming layers linked together through Ge2O7groups. A structural comparison with fluorite-related compounds as well as CeMn2Ge4O12will be discussed.