CRYSTAL-STRUCTURES OF ISOTYPICAL DIPHOSPHATES PBCO3(P2O7)(2) AND PBFE3(P2O7)(2)

Single crystals of the mixed metal diphosphates PbCo3(P2O7)(2) (I) and PbFe3(P2O7)(2) (II) have been prepared by direct fusion and character ized by single-crystal X-ray diffraction, for Pb Co-3(P2O7)(2) (I), a = 7.275(5), b = 7.725(11), c = 9.511(4) Angstrom, beta = 111.89(4)degr ees, monoclinic space group P2(1)/c, V = 509.3(5) Angstrom 3, d(calc) = 4.768 g cm(-3), Z = 2, R/R(w) = 3.9/5.1% for 1192 observed reflectio ns. For PbFe3(P2O7)(2) (II), a = 7.487(1), b = 7.739(1), c = 9.516(2) Angstrom, beta = 111.95(1)degrees, monoclinic space group P2(1)/c, V = 511.4(2) Angstrom(3), d(calc), = 4.693 g cm(-3), Z = 2, R/R(w) = 4.13 /4.87% for 1153 observed reflections. (I) and (II) are isotypical with PbNi3(P2O7)(2) and SrNi3(P2O7)(2). The solid lattice is characterized by layers of P2PO74- groups, parallel to the crystallographic plane ( 001) and joined by Pb2+ and Co2+ ions in (I) and Pb2+ and Fe2+ ions in (II). Lead is seen surrounded by eight oxygen atoms whereas the trans ition elements are found in chains of linked trimers extending in the [010] direction [Co-Co 3.182(3) and 3.256(3) Angstrom; Fe-Fe, 3.186(3) and 3.264 (3) Angstrom] with distorted octahedral geometry at each me tal atom. (C) 1995 Academic Press, Inc.