Scandium–copper–indides deriving from the ZrNiAl and MnCu2Al type structures

Phase analytical studies in the Sc–Cu–In system led to samples of the solid solutions ScCu1–x–y In1+x and ScCu2–x In which were studied by X-ray powder diffraction. At room temperature the compounds ScCu1–x–y In1+x crystallize with the ZrNiAl type, space group P 6 ‾ $\overline{6}$ 2m. Exemplarily, the structure of ScCu0.76In1.17 was refined from single crystal X-ray diffractometer data, revealing strong anisotropic displacements for the scandium atoms and a mixed occupied Cu/In site. Superstructure formation is observed at low temperatures. The ScCu0.78In1.14 and ScCu0.76In1.16 structures were refined from diffraction data recorded at 90 K. Both compounds adopt the HfRhSn type, space group P 6 ‾ $\overline{6}$ 2c, a klassengleiche subgroup of index 2; doubling of the subcell c axis. The Cu/In filled trigonal Sc6 prisms are strongly distorted in the superstructure, resulting from pairwise dislocation of the Cu/In atoms from ideal positions within an equidistant chain to shorter (311.0 pm) and longer (392.8 pm) Cu/In–Cu/In distances. Single crystal data of the Heusler phases ScCu1.95In and ScCu1.94In show small degrees of copper vacancies.

RE 3Rh2Sn4 (RE = Y, Gd–Tm, Lu) – first stannides with Lu3Co2In4 type structure

The stannides RE 3Rh2Sn4 (RE = Y, Gd–Tm, Lu) were synthesized from the elements by arc-melting and subsequent annealing (1220 K for RE = Y, Gd–Tm and 1170 K for RE = Lu) in sealed silica ampoules for 11 days. X-ray powder diffraction studies confirm the hexagonal Lu3Co2In4 type structure, space group P 6 ‾ $P\overline{6}$ . The structure of Gd3Rh2Sn4 was refined from single crystal X-ray diffractometer data for a twinned crystal: a = 744.04(6), c = 409.23(4) pm, wR2 = 0.0288, 567 F 2 values and 21 variables. The RE 3Rh2Sn4 stannides derive from the well-known equiatomic stannides RERhSn (≍RE 3Rh3Sn3) by Rh/Sn ordering within the RE 6 trigonal prisms. The striking structural motif is the trigonal planar tin coordination of the Sn2 atoms with 288 pm Sn2–Sn1 distances. The Sn2 atoms carry substantially more negative charge than the Sn1 atoms. This is underlined by 119Sn isomer shifts of δ = 1.86(1) mm s−1 for Sn1 and δ = 2.26(1) mm s−1 for Sn2 detected in the Mössbauer spectrum of Lu3Rh2Sn4. From atoms in molecules (AIM) analysis of the charge density obtained with calculation based on density functional theory (DFT) for Y3Rh2Sn4, the charge transfer proceeds from yttrium towards more electronegative rhodium. Little departure from neutrality is observed for tin whose itinerant s-like states are little involved with the bonding. The site projected density of states (DOS) and the crystal orbital overlap population (COOP) plots further illustrate these observations and reveal major Y–Rh and Rh–Sn bonding, while Y–Sn bonding is weaker.