N,O VERSUS O,O' COORDINATION IN BETA-IMINODIKETONATO COMPLEXES - A REINVESTIGATION

The solid-state structures of the iminodiketonato complexes obtained in the reaction of cyanogen with [M(acac)2] (M = Ni or Cu, acac = acetylacetonate) and [Cu(bzacen)] (bzacen = Schiff base anion formed between ethane-1,2-diamine and benzoylacetone) have been reinvestigated. The X-ray data have been recollected, under improved conditions, for one form of [Ni(acac.C2N2)2] (labelled beta) and the structure determined according to an N,O co-ordination mode. This model gives a better crystallographic R factor compared with the previous one based on an O,O' atom ligating set (0.029 vs. 0.047) and, in addition, clearly indicates the presence of the imino hydrogen. The structures of the analogous copper derivative and of [Cu(bzacen.2C2N2)] have been recalculated from the reported data and, also in these cases, the hypothesis of N,O co-ordination improves the refinement of the data (R = 0.055 vs. 0.062 and 0.060 vs. 0.081, respectively). An accurate Fourier-transform IR study, including C-13 labelling, of the two forms (alpha and beta) in which [Ni(acac.C,N2)2] can be isolated indicates that this co-ordination mode is also adopted by the alpha form, which is thus a ligand conformation isomer of the beta form.