Structure, Chemical Bonding and 119Sn Mössbauer Spectroscopy of LaRhSn and CeRhSn

The rare earth (RE) stannides LaRhSn and CeRhSn were prepared from the elements by arcmelting or by reactions in sealed tantalum tubes in a high-frequency furnace. The structures have been refined from X-ray single crystal diffractometer data: ZrNiAl type, P6̅2̅m, a = 748.74(5), c = 422.16(3) pm, wR2 = 0.0307, 310 F2 values for LaRhSn and a = 745.8(1), c = 408.62(9) pm, wR2 = 0.0397, 354 F2 values for CeRhSn with 14 variables per refinement. The structures contain two crystallographically different rhodium sites which both have a tricapped trigonal prismatic coordination: [Rh1Sn3RE6] and [Rh2Sn6RE3]. Together the rhodium and tin atoms (280 - 288 pm Rh-Sn distances in LaRhSn and 277 - 285 pm in CeRhSn) build up three-dimensional [RhSn] networks in which the rare earth atoms fill distorted hexagonal channels. DFT band structure calculations reveal a large cerium 4 f contribution at the Fermi level and a strong mixing of cerium 5d/4 f with rhodium 4d orbitals. These results are in agreement with the short Ce-Rh bonds (304 and 309 pm) and also with the electronic and magnetic properties. 119Sn Mössbauer spectra of LaRhSn and CeRhSn show a single tin site at isomer shifts of δ = 1.98(2) (LaRhSn) and 1.79(1) mm/s (CeRhSn) subject to quadrupole splitting of Δ EQ = 0.79(4) (LaRhSn) and 1.12(3) mm/s (CeRhSn). The 1.8 K data show no transferred hyperfine field at the tin site for CeRhSn.