Structure, chemical bonding and 119Sn Mossbauer spectroscopy of LaRhSn and CeRhSn

The rare earth (RE) stannides LaRhSn and CeRhSn were prepared from the elements by arc-melting 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, P (6) over bar 2m, a = 748.74(5), c = 422.16(3) pm, wR2 = 0.0307, 310 F-2 values for LaRhSn and a = 745.8(1), c = 408.62(9) pm, wR2 = 0.0397, 354 F-2 values for CeRhSn with 14 variables per refinement. The structures contain two crystal lographically different rhodium sites which both have a tricapped trigonal prismatic coordination: [Rh1Sn(3)RE(6)] and [Rh2Sn(6)RE(3)]. 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 4f contribution at the Fermi level and a strong mixing of cerium 5d/4f 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. Sn-119 Mossbauer spectra of LaRhSn and CeRhSn show a single tin site at isomer shifts of delta = 1.98(2) (LaRhSn) and 1.79(1) mm/s (CeRhSn) subject to quadrupole splitting of Delta E-Q = 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.