Co-ordination chemistry of pyridyl and N-methylimidazolyl ketones. Synthetic and X-ray structural studies of copper(II), nickel(II), and dimethylgold(III) complexes

Abstract

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^IIIMe₂ nitrate to form complexes that do not involve hydration of the ligand, [AuMe₂(L)]NO₃(L = pik or dik). They react similarly with copper(II) sulphate and nickel(II) nitrate, forming [Cu(pik)(SO₄)]·O.5H₂O, [Cu(dik)(SO₄)]·2H₂O [Ni(pik)₂(NO₃)₂]·0.5H₂O, and [Ni(dik)₂(NO₃)₂]·1.5MeOH; 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)Å 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 ⋯ O contact of 3.254(2)Å with a ketone oxygen. Possible reasons for different behaviour of the ligands toward hydration are discussed. Crystals of [AuMe₂(dpk·H₂O)] NO₃ are monoclinic, space group P2₁/c, a= 9.41 (1), b= 7.328(7), c= 22.17(2)Å, β= 97.85(8)°, and Z= 4. Crystals of [Cu(dik)(SO₄)]·2H₂O are monoclinic, space group P2₁/n,a= 11.982(3), b= 13.803(3), c= 8.866(2)Å, Å= 107.30(2)°, and z= 4.