Determination of the superstructures for the stannides ZrIrSn, HfCoSn, andHfRhSn

The title compounds are already known in the literature, however, they have only been characterized by their subcells on the basis of X-ray powder dat a. Well crystallized samples of ZrIrSn, HfCoSn, and HfRhSn were prepared fr om the elements by are-melting and subsequent annealing at 970 K. ZrIrSn, H fCoSn, and HfRhSn crystallize with a pronounced subcell of space group <P(6 )over bar>2m (ZrNiAl type). Additional very weak reflections required a dou bling of the c axis. The three structures (all space group <P(6)over bar>2c ) were refined from single-crystal X-ray data: a = 732.1(2) pm, c = 732.2(2 ) pm, wR2 = 0.0367, 539 F-2 values, 18 variables for ZrIrSn, a = 713.1(3) p m, c = 705.4(3) pm, wR2 = 0.0930, 342 F-2 values, 16 variables for HfCoSn, and a = 732.0(3) pm, c = 714.8(2) pm, wR2 = 0.0259, 528 F-2 values, 18 vari ables for HfRhSn. The three stannides crystallize with a substitution deriv ative of the Mg2Ga structure. The Zr(Hf) and tin atoms are ordered on the m agnesium positions and the Co(Rh,Ir) atoms on the gallium positions of the Mg2Ga type. The distortions in the structures of ZrIrSn, HfCoSn, and HfRhSn are most likely due to packing reasons (size of the zirconium and hafnium atoms). The structures of ZrIrSn, HfCoSn, and HfRhSn are described consider ing a group-subgroup scheme, also including the FePdP, Lu3Co2In4, Mg9Sn5, T i4Ni2Ga3, and TiFeSi type structures.