The new quasi-binary Zr 2.7 Hf 11.3 P 9 was synthesized by arcmelting of Zr, Hf, Co, and HfP in a ratio corresponding to the initial composition ''Zr 2.25 Hf 6.75 Co 2 P 4 ''. Zr 2.7 Hf 11.3 P 9 crystallizes in the Zr 14 P 9 structure type, which is unknown in the binary Hf/P system. The ideal orthorhombic lattice dimensions (space group Pnnm (No. 58), Z โซุโฌ 4) were refined to a โซุโฌ 16.640(7) A s s , b โซุโฌ 27.40(2) A s s , c โซุโฌ 3.619(1) A s s , V โซุโฌ 1650(2) A s s 3 . The structure consists of three-dimensional condensed one-, two-, and threecapped trigonal (Zr, Hf ) 6 P prisms, occurring with numerous short M-M bonds (M โซุโฌ Zr, Hf ). Each of the 15 metal sites is statistically occupied by a mixture of Zr and Hf, which varies significantly from site to site. The Hf/Zr ratio in a given site depends on the M-M and M-P interactions. The systematic increase of this ratio with increasing total bond order, as evaluated via Mulliken overlap populations and Pauling bond orders, can be understood based on the trend that Hf forms stronger M-M and M-P bonds than Zr. As expected for a metal-rich phosphide, band structure calculations for the hypothetical ''Hf 14 P 9 '' carried out with the extended Huยจckel approximation result in a significant density of states at the Fermi level. 1998 Academic Press