ER3PD7P4 - CRYSTAL-STRUCTURE DETERMINATIO N AND EXTENDED HUCKEL CALCULATIONS

Er3Pd7P4 was prepared by heating the elements (1050-degrees-C) and inv estigated by means of single-crystal X-ray methods. The compound cryst allizes in a new structure (C2/m; a = 15.180(3) angstrom, b = 3.955(1) angstrom, c = 9.320(1) angstrom, beta = 125,65(1)degrees; Z = 2) with a three-dimensional framework of Pd and P atoms and with Er atoms in the holes. The Pd atoms are surrounded tetrahedrally, trigonally or li nearly by P atoms, which are coordinated by nine metal atoms in the fo rm of a tricapped trigonal prism. Therefore the atomic arrangement of Er3Pd7P4 is related to the structures of ternary transition metal phos phides with a metal: phosphorus ratio of 2:1. Band calculations using the Extended Huckel method show strong covalent Pd-P bonds and weak bo nding interactions between Pd atoms with Pd-Pd distances shorter than 2.9 angstrom.