LaPt2Ge2 and EuPt2Ge2 -: Revision of the crystal structures

LaPt2Ge2 was rechecked by single crystal X-ray methods resulting in space group P2(1)/c (in place of P2(1)) and the lattice constants a = 9.953(3) b = 4.439(1), c = 8.879 angstrom, beta = 90.62(4)degrees, and Z = 4. In contrast to previous reports the cell Volume had to be doubled. The same is true for EuPt2Ge2 (a = 9.731(1), b = 4.446(1), c = 8.823(1) angstrom, beta = 91.26(1)degrees). The crystal structures correspond to a monoclinic variant of the tetragonal CaBe2Ge2 type, whereas the distortion can be described as different rotations of the coordination polyhedra around the La and Eu atoms, respectively It is most likely that the Compounds APt(2)Ge(2) with A = Ca, Y, La-Dy undergo phase transitions at higher temperatures forming then the undistorted CaBe2Ge2 type, space group P4/nmm. This was confirmed for SMPt2Ge2 (a = 4.292(1), c = 9.980(1) angstrom; Z = 2) and might also be the case for APt(2)Ge(2), with A Ca, Nd, Sin, Eu, and Gd.