Compartmental ligands. Part 11. Copper(II) complexes of ‘half-unit’ Schiff bases: crystal and molecular structure of one monomeric and of one dimeric complex

Abstract

The syntheses of ‘half-unit’ Schiff bases derived from 1-(2′-hydroxyphenyl)butane-1,3-dione (Hhpbdo) and αω-alkanediamines are reported, together with that of the related compound derived from Hhpbdo and 2-(2′-aminoethyl)pyridine. The copper(II) complexes of these ligands are reported and three-dimensional X-ray crystal structure analyses were carried out for acetato[1-(2′-hydroxyphenyl)-3-methyl-6-(2′-pyridyl)-4-azahex-2-en-1-onato-O,N,N′]copper(II), [Cu(HL⁵)(O₂CMe)], and acetato[6-amino-1-(2′-hydroxyphenyl)-3-methyl-4-azahept-2-en-1-onato-O,N,N′]copper(II), [Cu(HL¹)(O₂CMe)]. The crystal structure of [Cu(HL₅)(O₂CMe)] is triclinic, R= 0.0332, for 2 529 reflections. The copper(II) atom is five-co-ordinate, with the nitrogen atoms, ketonic oxygen of the ligand, and one acetate oxygen providing a tetrahedrally distorted (15°) square plane, with a further acetate oxygen at 2.55 Å. The structure of [Cu(HL¹)(O₂CMe)](R= 0.0476,1 550 reflections) shows an acetate-bridged, dinuclear dimer in which there is a copper–copper distance of 3.51 Å. The co-ordinating atoms comprise four short interactions (ketonic oxygen, imino-nitrogen, primary amine nitrogen, and acetate oxygen) with two longer interactions, one towards the bridging acetate oxygen, and the other to the second oxygen of the acetate anion which is the more strongly bound to the copper(II). The application of the ‘half-units’ to the synthesis of unsymmetrical Schiff bases and the metal complexation properties of these bases are discussed briefly.