STERIC EFFECTS IN THE STRUCTURE OF MIXED-LIGAND NICKEL(II) CHELATES - CRYSTAL-STRUCTURE AND MOLECULAR-STRUCTURE OF [N,N'-DIPHENYL-1,2-DIAMINOETHANE)-BIS(1,1,1,5,5,5,-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 controlled 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 full-matrix least-squares to a conventional R = 0.076 for all observed reflections with I > 2 sigma(I). The nickel(II) ion is six-coordinated and is positioned at the centre of an almost regular octahedron. The best (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 imperceptibly longer than the Ni - O ones. In the five-membered chelate ring the 1,2-diamine adopts the gauche conformation with the phenyl groups.