The Crystal and Molecular Structure of a Nickel Complex of the Schiff Base, Bis(trifluroacetylacetone)triethylenetetraamine

Abstract

The Schiff base, bis(trifluoroacetylacetone)triethylenetetraamine (H2L), forms a nickel complex with the composition NiC16F6H22N4O2 (NiL). Crystals of NiL belong to the monoclinic space group P21/c with a = 10.040(2), b = 15.077(7), c = 13.943(7) Å, β = 111.88(5)°, Dc = 1.610 g/cc, Do = 1.61(2) g/cc, Z = 4. A total of 1686 independent reflections with F2 ≥ 2σ(F2), 2θ ≤ 42° were measured on a Picker 4-circle diffractometer by the θ–2θ scan technique with MoKα radiation. A full matrix least squares refinement of the structure yielded an unweighted R factor of 0.057. The structure confirms that condensation of triethylenetetraamine with trifluoroacetylacetone occurs through the acetyl group, not through the trifluoroacetyl group. The nickel atom is octahedrally coordinated by the four nitrogen and two oxygen atoms of the L2− ligand. The triethylenetetraamine moiety has the α-configuration, so that the oxygen atoms occupy cis positions on the octahedron. Distortions in the octahedral geometry are due to the three contiguous five-membered rings in the complex; the average N—Ni—N angle is 81.1°. The trifluoroacetylacetone fragments are essentially planar, with an average O—Ni—N angle of 90.6°. These rings are folded about the O—N lines, the folding angles being 17.1 and 8.0° for the two rings. The average Ni—O, Ni—N (trigonal), and Ni—N (tetrahedral) distances are 2.037, 2.044, and 2.128 Å, respectively.