Synthesis, structure and properties of the high-pressure modifications of the ternary compounds REPtSn (RE = La, Pr, Sm)

The hexagonal high-pressure (HP) modifications of the ternary compounds REPtSn (RE = La, Pr, Sm) were prepared under multianvil high-pressure (9 - 14 GPa) high-temperature (1050 - 1400 degrees C) conditions from the orthorhombic normal-pressure (NP) modifications. The HP-REPtSn stannides were investigated by X-ray diffraction on powders and single crystals: ZrNiAl type, space group P (6) over bar 2m, a = 762.6(2), c = 418.55(7) pm, wR2 = 0.1147, 256 F-2 values and 14 variables for HP-LaPtSn, a = 754.97(7), c = 412.64(3) pm, wR2 = 0.0782, 252 F-2 values and 14 variables for HP-PrPtSn, and a = 750.1(2), c = 407.6(1) pm, wR2 = 0.1060, 229 F-2 values and 14 variables for HP-SmPtSn. The high-pressure modifications have two crystallographically independent platinum positions in trigonal prismatic coordination, Pt1Sn(6)RE(3) and Pt2Sn(3)RE(6). The shortest interatomic distances occur between the platinum and tin atoms within the three-dimensional [PtSn] networks. The rare earth atoms fill distorted hexagonal channels within these networks and they are bound through short RE-Pt contacts. Susceptibility measurements of HP-PrPtSn reveal paramagnetic behaviour with an experimental magnetic moment of 3.31(2) mu(B)/Pr atom. Low-temperature susceptibility and specific heat data point to inhomogeneous magnetism in HP-PrPtSn.