Crystal and molecular structures of some binuclear complexes of cobalt(II) and nickel(II) acetylacetonates with pyridines and piperidine and a refinement of the crystal and molecular structure of hexakis-(acetylacetonato)trinickel(II)

The crystal and molecular structures of the binuclear complexes [M₂(py)(acac)₄] [M = Ni^II, (1), M = Co^II, (2); py = pyridine, acac = acetylacetonate] and [Ni₂(pip)₂(acac)₄] (3; pip = piperidine) have been determined by single-crystal X-ray methods. Complexes (1) and (2) are isostructural in the monoclinic space group P2/c, Z = 4, with cell dimensions a = 16.859(12), b = 10.873(11) c = 17.010(15) Å, β = 112.97(7)°; and a = 17.039(12), b = 10.904(11), c = l7.106(12) Å, β = 113.55(8)° respectively. The structures have been refined to R = 0.077 for (1) and 0.062 for (2) using 1 664 and 2 791 observed diffractometer intensities respectively. Compound (3) is triclinic, space group P1, with a = 9.637(5), b = 9.052(5), c = 11.414(7) Å, α = 73.54(8), β = 113.90(9), γ 103.37(8)°, and Z = 1. R has refined to 0.077 for 1 180 observed data. The metal atoms are octahedrally co-ordinated in all three compounds. In the pyridine complexes, three oxygen atoms from chelating acetylacetonate ligands form monoatomic bridges between the two metal atoms so that the metal atom co-ordination polyhedra share a triangular face. The Ni-Ni and Co-Co separations in (1) and (2) are 2.891(3) and 2.966(5) Å whilst the Ni-O-Ni and Co-O-Co bridge angles average 87.8 and 88.2° respectively. Each M-O-M bridge is unsymmetrical and there are trigonal distortions in the metal co-ordination octahedra. Molecules of (3) are centrosymmetric and comprise two O-O edge-shared octahedra. The Ni-Ni separation is 3.240 Å. The structure of [Ni₃(acac)₆], (4), has been redetermined and refined to R = 0.0787 using 980 data and gives an average Ni-Ni separation of 2.856(7) Å and an average Ni-O-Ni bridge angle of 85.6°. There are marked trigonal distortions of the NiO₆ octahedra and the Ni-0 (bridging) distances vary considerably from 1.98(2) to 2.31(2) Å.