MOLECULAR AND CRYSTAL-STRUCTURE OF 1-1 GUEST-HOST BIS(HEXAFLUOROACETYLACETONATO)CALCIUM COMPLEX WITH 18-CROWN-6

We have carried out an X-ray structural study of the title complex (a CAD-4F diffractometer, lambdaMoK(alpha), graphite monochromator, omega/2theta scan mode, theta(max) = 30-degrees direct methods, 1465 reflections, R = 0.036). Crystals are monoclinic with a = 17.971(13), b = 13.475(3), c = 13.379(8) angstrom, beta = 106.67(5)degrees, Z = 4CaO10C22H26F12, space group C2/c, d(calc) = 1.537 g/cm3. The complex (C2 symmetry) has a molecular structure and belongs to the guest-host type. The Ca atom is located in the center of the 18-crown-6 cavity; bidentate hexafluoroacetylacetonate guest ligands occupy the trans-positions relative to the plane of a maxidentate macrocycle. The Ca-O distances in a ten-vertex Ca polyhedron are 2.474-2.666 angstrom. The macrocycle conformation is characterized by six gauche C-C bonds and two gauche and ten trans C-O bonds. The dihedral COCC angle differs significantly (by 38.1-degrees) from the angle of 60-degrees, which is common to a gauche conformation. The six-membered cycle formed by oxygen atoms has a twist form with the annular O-O distances of 5.132-5.329 angstrom. Structural features explaining an easy sublimation of the compound are discussed.