Crystal Chemistry of Defective Intermetallics with Empty Triangular Metalloid Channels: The New Phosphide Zr6Cr60P39

Abstract

The ternary compound ZrCr60P39has been synthesized by the tin flux method. It presents a hexagonal crystal structure [a=21.413(2) Å,c=3.354(1) Å], space groupP63/m, with one formula per unit cell. The X-ray structure has been refined from three-dimensional single-crystal intensity data to a finalRvalue of 0.053 (Rw=0.056) for 451 reflections [I>2σ(I)]. The resulting structure is of a new type and exhibits empty triangular phosphorus channels. This structure belongs to a new series of hexagonal defective compounds named direct series with a metal/nonmetal ratio slightly lower than 2, the first members of which are the compounds Cr12P7and Zr2Cr30P19. The structural relationships with the reverse series, including the ternariesR2Co12P7(R=rare earth element), Yb6Co30P19, UCo5Si3, U6Co30Si19, and U10Co51Si33, are discussed in terms of metal vacancies and coordination polyhedra. Finally, a general crystal chemical rule has been established that permits prediction of the different members for the two series and their definition structurally in terms of lattice parameters and theoretical X-ray diffraction patterns. Moreover this rule gives for each member the number of empty triangular metalloid channels as well as the distribution of the different polyhedra occupied by the metal atoms (trigonal prisms, pyramids, tetrahedra).