Reiko Hirota

Preparation and characterisation of bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)copper(II) complexes with diazaaromatic compounds. Part 1. Crystal structures and characterisation of several adducts with diazines

The reactions of [Cu(hfac)2](Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) with diazines (tmpyz = 2,3,5-trimethylpyrazine, mpym = 5-methylpyrimidine and mpydz = 3-methylpyridazine) in light petroleum have been studied and the following complexes obtained: [{Cu(hfac)2}3(µ-tmpyz)2]1b, [Cu(hfac)2(tmpyz)]1e, [{Cu(hfac)2(µ-mpym)n}]2a, [{Cu(hfac)2}3(µ-mpym)2]2b, [{Cu(hfac)2}2(µ-mpym)]2c, [Cu(hfac)2(mpym)2]2d, and [Cu(hfac)2(mpydz)2]3d. The crystal structures of 1b, 2b and 3d have been determined. Although 1b and 2b are both trinuclear complexes with bridging diazole molecules, the geometry around atom Cu(2) is trigonal bipyramidal for 1b and tetragonal pyramidal for 2b. The geometry around atom Cu(1) is tetragonal bipyramidal in both complexes. The distance Cu(1)–N(1) is longer in 1b than in 2b, while the Cu(2)–N(2) is somewhat shorter in the former. The steric effects of the ligands on the structural differences between these complexes are discussed. On the basis of the relation between the geometry of the co-ordinated hfac ligands and ν(C–O) values, structures of some of the other complexes are suggested.

Existence and distribution of geometrical isomers of bis(VIC-dioximato)nickel(II) complexes in solution

The existence of geometrical isomers of several bis (vic-dioximato)nickel complexes with non-symmetrical ligands has been clarified by 1H NMR. The general formula of the ligands is CH3C(NOH)C(NOH)R, here R = Et, Prn, Bun, Ph, p-MeC6H4, p-MeOC6H4 and p-ClC6H4. The trans isomer of each complex is predominant in pyridine-d5 solution. The cis-trans equilibrium constants of these complex in pyridine-d5 have been estimated.

An electron spin resonance study on the interactions between bis-(pentane-2,4-dionato)copper(II) and some heterocycles. Part 2. The 1 : 1 adducts with aza-aromatic compounds and azacyclohexanes

E.s.r. spectra of a series of Cu(acac)2 adducts of aza-aromatic compounds and azacyclohexanes (L) were measured. The 1 : 1 adduct Cu(acac)2L is formed almost exclusively in chloroform solution, L occupying an apical site. Their g∥ and |A∥| values were determined in order to investigate the steric and electronic effects on co-ordination. When the frontal steric hindrance of the base is not large, the |A∥| values of Cu(acac)2L are linearly related to the pKa values of L. Since the nitrogen atoms in 2,6-dimethylpyridine, 2- and 8-methylquinoline, acridine, and N-methylazacyclohexanes have considerable frontal steric hindrance, remarkable deviations from the straight line are observed for these compounds. The presence of two 1 : 1 adducts is shown for N-methylmorpholine, the O-adduct being more favourable than the N-adduct because of steric hindrance.