Synthesis and structures of new layered ternary manganese selenides:: AMnSe2 (A = Li, Na, K, Rb, Cs) and Na2Mn2Se3

The synthesis and crystal structures of new ternary manganese selenides, AMnSe(2) (A = Li, Na, K, Rb, Cs) and Na2Mn2Se3, are reported. These compounds were synthesized by solid state reaction and cation exchange techniques. The single-crystal structures of AMnSe(2) (A = Li, Na, Rb) and Na2Mn2Se3 have been determined; LiMnSe2: a = 4.1905(3) Angstrom, c = 6.619(2) Angstrom, and P3m1 (No. 156, Z = 1); NaMnSe2: a = 4.2330(7) Angstrom, c = 6.942(3) Angstrom, and P3m1 (No. 156, Z = 1); RbMnSe2: a = 4.2660(4) Angstrom, c = 14.033(2) Angstrom, and I (4) over bar m2 (No. 119, Z = 2); Na2Mn2Se3: a = 15.689(2) Angstrom, b = 13.888(2) Angstrom, c = 7.220(1) Angstrom, beta = 115.65(2)degrees, and C2/c (No. 15, Z = 8). The fundamental building blocks of the title compounds are MnSe4 tetrahedra. AMnSe(2) (A = Li, Na) are layered compounds in which MnSe4 tetrahedra share three corners in the formation of polar (2)(infinity)[MnSe3/3Se](-) layers. AMnSe(2) (A = K, Rb, Cs) exhibit (2)(infinity)[MnSe4/2](-) layers which are built up by four-corner-shared MnSe4 tetrahedra. Na2Mn2Se3 shows four-membered zigzag chains formed by edge-shared MnSe4 tetrahedra. These chains are fused by the remaining apices to form a two-dimensional layer, (2)(infinity)[MnSe2/3Se1/3 Se-1/2](-). Magnetic susceptibility data for these compounds were fit with a modified Curie-Weiss expression, (C) 1999 Academic Press.