SrCo_2Sn_8 and BaCo_2Sn_8: Tin-rich Stannides with Distorted SnSn6 Octahedra within Three-dimensional [Co_2Sn_8] Networks

摘要

The tin-rich stannides SrCo_2Sn_8 and BaCo_2Sn_8 were synthesized from the elements in sealed tantalum tubes. They crystallize with a new structure type, space group Cccm with a=1006.0(3), b=1514.4(6), c=1385.0(6) pm for SrCo_2Sn_8 and a=1032.8(2), b=1516.8(3), c=1405.1(3) pm for BaCo_2Sn_8. The structure of the barium compound was refined on the basis of single-crystal X-ray diffractometer data: wR2=0.0450, 1715 F~2 values, 57 variables. The cobalt atoms have seven nearest tin neighbors with Co–Sn distances ranging from 257 to 273?pm. These CoSn_7 units are condensed via common rectangular faces to [Co_2Sn_(10)] double units which build up a covalently bonded three-dimensional network through Sn–Co–Sn bridges. Larger voids left by this network are filled by the barium and the Sn2 atoms. The latter have distorted octahedral tin coordination with Sn2–Sn distances of 311–315pm. The barium atoms have 13 nearest tin neighbors (352–399pm Ba–Sn). Temperature-dependent magnetic susceptibility data of BaCo_2Sn_8 show Pauli paramagnetism.