Co-ordination Chemistry of Pyridyl and N-Methyl imidazolyl Ketones. Synthetic and X-Ray Structural t Studies of Copper(II), Nickel(II), and Dimethylgold(III) Complexes

Di-2-pyridyl ketone (dpk) reacts with dimethylgold(III) nitrate in water to form the complex [AuMe2(dpk.H2O)]NO3 in which the ligand has been hydrated to form a geminal diol. The closely related ketones 2-pyridyl-N-methyl-2-imidazolyl ketone (pik) and di(N-methyl-2-imidazolyl) ketone (dik) react with Au(III)Me3 nitrate to form complexes that do not involve hydration of the ligand, [AuMe3(L)]NO3 (L = pik or dik). They react similarly with copper(II) sulphate and nickel(II) nitrate, forming [Cu(pik)(SO4)].0.5H2O, [Cu(dik)(SO4)].2H2O, [Ni(pik)(N03)2].0.5H2O and [Ni(dik)2(NO3)2].l.5Me0H; dpk forms [Ni(dpk.H2O)2(NO3)2].0.5H2O on reaction with nickel(II) nitrate. The crystal structures of [AuMe2(dpk.H2O)]NO3 and [Cu(dik)(SO4)].2H2O have been determined by single-crystal X-ray diffraction at 295 K and refined by least-squares methods to R = 0.045 and 0.032 for 2 031 and 4 754 independent 'observed' reflections, respectively. The cation [AuMe2(dpk.H2O)]+ has the ligand N,N-chelated with cis-square-planar co-ordination for gold(III), with an intramolecular hydroxy group positioned 2.850(8) A from the gold atom. The complex [Cu(dik)(SO4)].2H2O has square-pyramidal co-ordination for copper(II), with the N,N-chelated ligand in the basal plane together with a water molecule and unidentate sulphate ion, and a water molecule co-ordinated axially. There is an intermolecular Cu...0 contact of 3.254(2) A with a ketone oxygen. Possible reasons for different behaviour of the ligands toward hydration are discussed.