Flux Synthesis, Crystal Structures, and Magnetism of the Series La2n+2MnSen+2O2n+2 (n = 0-2)

Three members of the homologous series of manganese oxyselenides with the general formula La2n+2MnSen+2O2n+2 (n = 0-2) have been synthesized in a NaI/KI flux and characterized by single-crystal X-ray diffraction, powder X-ray diffraction and magnetic measurements. The structures consist of chains of edge-sharing MnSe4O2-octahedra along the b-axis which are linked together along the a-axis by edge-sharing OLa4- and/or OLa3Mn-tetrahedra forming infinite ribbons of increasing width. -La2MnSe2O2 (Pb2HgCl2O2-type,, a = 11.6621(5) angstrom, b = 3.9719(1) angstrom, c = 7.2049(3) angstrom, = 121.655(2) represents a new polymorph of this compound. La4MnSe3O4 (P2/m), a = 9.0055(4) angstrom, b = 4.0186(1) angstrom, c = 7.1946(3) angstrom, = 109.715(2)) and La6MnSe4O6 (C2/m , a = 24.760(2) angstrom, b = 4.0359(3) angstrom, c = 7.1850(6) angstrom, = 104.162(3)degrees) exhibit new structure types. Magnetic measurements suggest antiferromagnetic order of the moments below about 15 K with effective magnetic moments of 5.53(1), 5.99(1) and 6.01(1) B per formula unit for n = 1, 2 and 3, respectively.