STERIC EFFECTS IN THE STRUCTURE OF MIXED-LIGAND NICKEL(II) CHELATES -CRYSTAL-STRUCTURE AND MOLECULAR-STRUCTURE OF 1,5,5,5,-HEXAFLUORO-2,4-PENTANEDIONATO)NICKEL(II)]

The monoclinic structure of the dark green title compound, [Ni(hfac)(2 ) Phi en Phi], was elucidated employing a PHILIPS PW1100 PC-computer c ontrolled automatic diffractometer using MoKalpha radiation. The space group is A2/n, Z = 4, and cell dimensions a = 13.932 Angstrom, b = 10 .222 Angstrom, c = 19.958 Angstrom, and beta = 93.34 degrees. A total of 2105 reflections were measured and the structure was refined by ful l-matrix least-squares to a conventional R = 0.076 for all observed re flections with I > 2 sigma(I). The nickel(II) ion is six-coordinated a nd is positioned at the centre of an almost regular octahedron. The be st (equatorial) plane encompasses the nitrogens of the diamine ligand and one carbonyl oxygen atom of each beta-dionato metallocyclic ring. The other oxygen donor atoms occupy the remaining apical positions and are equidistant from the metal centre. The Ni-N distances are imperce ptibly longer than the Ni - O ones. In the five-membered chelate ring the 1,2-diamine adopts the gauche conformation with the phenyl groups.