Structure, chemical bonding, and properties of ZrIn2, IrIn2, and Ti3Rh2In3

摘要

ZrIn2, IrIn2, and Ti3Rh2In3 were prepared from the elements by reactions in sealed tantalum tubes. ZrIn2 and IrIn2 have previously been characterized only on the basis of X-ray powder data. Their structures were now refined from single-crystal X-ray diffractometer data: I4(1)/amd, a = 338.70(8) pm, c = 2723.8(7) pm, wR2 = 0.0308, 561 F-2 values, 14 variables for ZrIn2 (HfGa2-type); Fddd, a = 980.1(1) pm, b = 533.67(8) pm, 1801.9(2) pm, wR2 = 0.0462, 522 F-2 values, 17 variables for IrIn2 (Mg2Cu-type); and P (6) over bar 2m, a = 728.7(3)pm, c = 306.7(1)pm, wR = 0.0192, 261 F-2 values, 12 variables for Ti3Rh2In3 (ordered Th3Pd5-type). ZrIn2 crystallizes with a superstructure of the cubic close-packing. Six different ordered fee cells are stacked one upon each other. A group-subgroup scheme for various fee superstructures is presented. Due to the distortions in the superstructure, the two crystallographically different indium atoms form separate networks: zig-zag chains by In1 and a square network by In2. The iridium atoms in IrIn2 form infinite chains with an Ir-Ir distance of 280 pm. Each iridium atom has a square antiprismatic indium coordination. Also in IrIn2 we observe two independent indium networks: the In1 atoms form a spiral-like three-dimensional network which is penetrated by planar two-dimensionally infinite layers of condensed enlongated In-6 hexagons. LMTO electronic structure calculations revealed that the In-in interactions within the In networks of ZrIn, and IrIn2 are slightly stronger than those between these networks. ZrIn2 and IrIn2 are Pauli paramagnetic and good metallic conductors. Ti,Rh,In, is the first compound which adopts an ordered Th3Pd5-type structure. The rhodium and indium atoms form a two-dimensional [Rh2In3] network, The distorted pentagonal prismatic channels of the [Rh2In3] network are threaded by linear chains of titanium atoms with a Ti-Ti distance of 307 pm. According to LMTO electronic structure calculations, the strongest bonding interactions occur for the Ti-Rh contacts. Ti-Ti bonding in Ti3Rh3In3 is compared with Ti-Ti and Hf-Hf bonding in Ti2In5 and Hf2In5, respectively, and the hexagonal close-packed structures of titanium and hafnium. (C) 2000 Academic Press [References: 54]