Nickel Complexes of Tetradentate Asymmetric Ligands.

The crystal structures of asymmetric tetraaza and Schiff base ligands and of their nickel complexes have been determined by X-ray structural analysis: all molecules exhibit a saddle-shaped conformation which minimises the steric repulsion. The compound 5,14-dihydro-6,17-dimethyl-8,15-diphenyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine (H(2)TAA) (monoclinic, P2(1)/a, a = 14.968(2), b = 20.812(2), c = 17.745(2) Angstrom, beta = 113.60(10)degrees, Z = 8) crystallises with two different molecules in the asymmetric unit: the two amino hydrogens in the tetraaza ring are bonded to the opposite nitrogens with an appreciable bond interaction with the nitrogen atom of the same propanediiminato fragment. The related complex NiTAA (triclinic, P (1) over bar, a = 11.556(2), b = 14.043(2), c = 9.656(2) Angstrom, alpha = 106.90(10), beta = 105.10(10), gamma = 67.20(10)degrees, Z = 2) shows a more extended bond delocalisation as the result of coordination to the metal centre. The Schiff base bis(benzoylacetone)-o-phenylenediamine (H(2)DAO) (monoclinic, P2(1)/a, a = 9.564(2), b = 22.727(2), c = 10.981(2) Angstrom beta = 115.20(10)degrees, Z = 4) is characterised by a very marked single-double bond alternation and the NNOO set of atoms largely deviate from planarity. Its nickel complex NiDAO (monoclinic, P2(1)/a, a = 18.151(2), b = 12.188(2), c = 19.362(2) Angstrom, beta = 96.80(10)degrees, Z = 8) has two different molecules with very similar structural parameters in the asymmetric unit: the Ni-O and Ni-N bonds have very similar lengths and form an almost regular square plane structure.