DEDICATED TO PROFESSOR H. D. LUTZ ON THE OCCASION OF HIS 65TH BIRTHDAY
The crystal structures of the title compounds were reinvestigated. The previously reported KHg 2 (CeCu 2 ) type structure with statistical distribution of the platinum and germanium atoms corresponds only to the subcell of the ordered orthorhombic YPdSi type structure (Pmmn, Z ؍ 8) of these compounds, which was refined from single-crystal X-ray diffractometer data of CePtGe: a ؍ 445.0( 1) pm, b ؍ 1464.8(3) pm, c ؍ 761.8(2) pm; PrPtGe: a ؍ 444.01(3) pm, b ؍ 1456.57(9) pm, c ؍ 761.71(5) pm; and the low-temperature ( ) modification of SmPtGe: a ؍ 440.0(1) pm, b ؍ 1428.1(2) pm, c ؍ 756.6( 1) pm. Nevertheless, some evidence for disorder was obtained from the refinement of the occupancy parameters of these compounds. The results suggest the substitution of germanium by platinum atoms and/or vice versa in the order of a few at%. The high-temperature ( ) modification of SmPtGe with TiNiSi type structure was confirmed by a refinement from single crystal diffractometer data. The magnetic properties of these compounds were investigated with a SQUID magnetometer. CePtGe, PrPtGe, and NdPtGe follow the Curie-Weiss law with magnetic moments close to those of the trivalent rare earth elements. The magnetic properties of -and -SmPtGe are dominated by the Van Vleck paramagnetism of the samarium atoms. Antiferromagnetic ordering was detected for CePtGe, NdPtGe, and both modifications of SmPtGe with Ne´el temperatures between 4 and 6 K, while PrPtGe remains paramagnetic down to 2 K. The crystal structures of these compounds are briefly discussed together with those of the LaPtSi and LaIrSi type structures, which occur for LaPtGe and Eu-PtGe, respectively.