Structural chemistry and magnetic properties of RE_2[Sn_xGe_(1-x)]_5 (RE = Nd, Sm) and RE[Sn_xGe_(1-x)]_2 (RE=Gd, Tb): Four new rare-earth metal intermetallic compounds with germanium zig-zag chains and tin square-nets

摘要

Four new rare-earth metal tin germanides with general formulae RE_2[Sn_xGe_(1-x)]_5 (RE = Nd, Sm; x approx = 0.25-0.3) and RE[Sn_xGe_(1-x)]_2 {RE = Gd, Tb; x approx = 0.2-0.25) have been synthesized from the corresponding elements by high temperature reactions using Sn flux. Their structures have been established from single-crystal and powder X-ray crystallography: orthorhombic space group Cmcm (No. 63) with cell parameters a = 4.1057(6)A, b = 35.992(5)A, c=4.2534(6)A for Nd_2[Sn_xGe_(1-x)]_5; a = 4.0707(8)A, b = 35.550(7)A, c = 4.2095(8)A for Sm_2[Sn_xGe_(1-x)]_5; a = 4.2248(ll)A, b = 30.451(8)A, c=4.0013(11)A for Gd[Sn_xGe_(1-x)]_2, and a = 4.1936(13)A, b = 30.230(9)A, c = 3.9793(12)A for Tb[Sn_xGe_(1-x)]_2, respectively. The structures of the two families can be described as being stacking variants of the ZrSi_2 and DyGe_3 types, respectively. They represent another example of site preferences between two group 14 elements, where the lighter Ge atoms preferentially form zig-zag chains while the square sheets (or double square sheets) are made up of Sn atoms, respectively. Magnetic susceptibility measurements show that all of the compounds order antiferromagnetically at low temperatures and their respective ordering temperatures are further corroborated by specific heat measurements.