A PARTIAL SUBSTITUTION OF PHOSPHORUS WITH THE METAL ATOM CO - THE CRYSTAL-STRUCTURE OF HF5CO1-X(XP3)

The new phosphide Hf5Co1+xP3-x has been prepared by are melting of HfP , Hf and Co, and subsequent annealing at 1500 degrees C in an inductio n furnace. It crystallizes in a new structure type, space group Pnma ( No. 62), lattice constants a = 16.980(3) Angstrom, b = 3.6101(7) Angst rom, c = 10.175(1) Angstrom, V = 623.8(2) Angstrom(3). This structure consists of six-membered Hf-channels, condensed to a double channel. E ach channel contains one Co and one P atom, which form an infinite -Co -P- zigzag chain. The channels are connected via short Hf-Hf contacts to a three-dimensional network with two further P positions located in trigonal prismatic voids of the Hf sublattice. Unusually, one P site - that with the higher bond order - is partially occupied with Co, ind icating that phosphorus is able to take part in delocalized metallic b onds, as well as cobalt. The partial Co/P exchange is related to the s imilar atomic radii and the expected negative charge for Co and P in t his Hf-rich phosphide. A significant phase range is observed.