TI2NI2IN, ZR2CO2IN, AND ZR2PD2IN - INTERMETALLIC COMPOUNDS WITH ORDERED U3SI2 AND ZR3AL2 TYPE-STRUCTURE

Ti2Ni2In, Zr2Co2In, and Zr2Pd2In were synthesized by reacting the elem ents in an arc-melting furnace and subsequent annealing at 1070 K. The compounds were investigated by ?C-ray diffraction on both powders as well as single crystals. Zr2Co2In adopts the ordered U3Si2 type struct ure: P4/mbm, a = 720.54(7), c = 331.59(4) pm. The structure consists o f planar [Co2In] layers with Co-2 dumb-bells which are separated by th e zirconium atoms. Ti2Ni2In and Zr2Pd2In crystallize with the ordered Zr3Al2 type structure (space group P4(2)/mnm), a superstructure of U3S i2: a = 694.3(2), c = 623.2(2) pm for Ti2Ni2In and a = 746.0(1), c = 6 86.1(1) pm for Zr2Pd2In. The Ni-2 and Pd-2 dumb-balls in the Ni2In and Pd2In layers of Ti2Ni2In and Zr2Pd2In are shifted from the mirror pla nes of the subcell resulting in puckered layers with weak interlayer N i-Ni and Pd-Pd contacts, respectively. The indium atoms in these compo unds occupy [Ti-8] and [Zr-8] square prisms while the transition metal atoms are surrounded by [Ti-6] and [Zr-6] trigonal prisms. These stru ctural fragments are derived from the CsCl and AlB2 type structures. C hemical bonding in these intermetallic compounds is briefly discussed. Magnetic susceptibility measurements of compact polycrystalline sampl es indicate Pauli paramagnetism.