Novel Quaternary Metal-Rich Phosphides: Stabilization by Differential Fractional Site Occupancies and Polar Intermetallic Bonding

Abstract

The new phosphide Hf5Nb5Ni3P5 has been prepared by arc-melting of a pressed stoichiometric mixture of HfP, Nb, and Ni. Single crystals suitable for the structure determination were obtained after annealing in an induction furnace at 1350 °C. Hf5Nb5Ni3P5 crystallizes in the hexagonal space group P62m (No. 189). The early transition metal atoms Hf and Nb are found on three crystallographically different sites, with refined occupancies of 100% Hf for the M1, 59.5(4)% Hf and 40.5(4)% Nb for the M2, and 13.1(6)% Hf and 86.9(6)% Nb for the M3 site. Small variations of the Hf to Nb ratio are possible, occurring with significantly different lattice parameters. The early transition elements form a three-dimensional framework with numerous M−M (M = Hf, Nb) interactions, including Ni and P in its trigonal prismatic voids. The differential fractional site occupancies can be understood on the basis of the different preferences of Hf and Nb to form M−M, M−Ni, and M−P bonds. The metallic character is confirmed by the P...