A new 1 --> infinity [Ni7] cluster in LaNi7In6 and distorted bcc indium cubes in LaNiIn4.

Abstract

LaNiIn4 and LaNi7In, were prepared by reaction of the elements in an arc melting furnace and subsequent annealing at 870 K for five weeks. Both compounds were investigated by X-ray diffraction on powders and single crystals and the structures were refined from single-crystal data: Cmcm, a = 448.2(1), b = 1689.5(4). c = 722.1(1) pm, wR2 = 0.0340, 472 F2 values, 24 variables for LaNiIn4, and Ibam, a = 806.6(2). b = 924.8(2). c = 1246.5(2) pm. wR2 = 0.0681. 726 F2 values and 40 variables for LaNi7In,. LaNiIn4 adopts the YNiAl4-type structure. The nickel and indium atoms form a three-dimensional infinite [NiIn4] polyanion in which the lanthanum atoms fill distorted hexagonal channels. No Ni-Ni contacts occur. The indium substructure consists of distorted bcc-like indium cubes. LaNi7In6 crystallizes with a peculiar new structure type. The nickel atoms build a 1 --> infinity [Ni7] cluster unit with Ni-Ni distances ranging from 249 to 269 pm. The cluster units are enveloped by indium atoms. These larger units show an orthorhombic rod packing with the lanthanum atoms filling the space between the rods. Several nickel clusters in ternary rare earth metal nickel indides and the structural relations of the LaNi7In6 structure with the cubic NaZn13 type are discussed.