Crystal chemistry of defective intermetallics with empty triangular metalloid channels: The new phosphide Zr6Cr60P39

The ternary compound ZrCr60P39 has been synthesized by the tin flux method. It presents a hexagonal crystal structure [a = 21.413(2) Angstrom, c = 3.3 54(1) Angstrom], space group P6(3)/m, with one formula per unit cell. The X -ray structure has been refined from three-dimensional single-crystal inten sity data to a final R value of 0.053 (R-w = 0.056) for 451 reflections [I > 2 sigma(I)]. The resulting structure is of a new type and exhibits empty triangular phosphorus channels. This structure belongs to a new series of h exagonal defective compounds named direct series with a metal/nonmetal rati o slightly lower than 2, the first members of which are the compounds Cr12P 7 and Zr2Cr30P19. The structural relationships with the reverse series, inc luding the ternaries R2Co12P7 (R = rare earth element), Yb6Co30P19, UCo5Si3 , U6Co30Si19, and U10Co51Si33, are discussed in terms of metal vacancies an d coordination polyhedra. Finally, a general crystal chemical rule has been established that permits prediction of the different members for the two s eries and their definition structurally in terms of lattice parameters and theoretical X-ray diffraction patterns. Moreover this rule gives for each m ember the number of empty triangular metalloid channels as well as the dist ribution of the different polyhedra occupied by the metal atoms (trigonal p risms, pyramids, tetrahedra). (C) 1999Academic Press.