Mono- and bi-nuclear copper(II) complexes of azaparacyclophanes with a single aromatic spacer. Crystal structure of [Cu2L2Cl4]·1.5H2O (L2= 2,5,8, 11-tetraaza[12]paracyclophane)

Abstract

The protonation behaviour of the azaparacyclophanes 2, 6, 9, 13-tetraaza[14]paracyclophane (L1), 2, 5, 8, 11-tetraaza[12]paracyclophane (L2) and 2, 5, 8, 11, 14-pentaaza[15]paracyclophane (L3) has been studied at 298.1 K in 0.1 5 mol dm–3 NaClO4 by potentiometry, direct microcalorimetry, and 1H and 13C NMR spectroscopy. The data obtained by the different techniques suggest that first protonation of L1 and L2 occurs mainly on the benzylic nitrogens. All three ligands form mononuclear copper(II) complexes in aqueous solution characterized by an incomplete participation of the nitrogen donors in the co-ordination to the metal ion. The ligands L2 and L3 also form the binuclear species [Cu2L2(OH)2]2+ and [Cu2L3]4+, [Cu2L3(OH)]3+ and [Cu2L3(OH)2]2+ in solution. The crystal structure of the complex [Cu2L2Cl4]·1.5H2O has been solved by X-ray crystal diffraction analysis [space group P21/n, a= 10.625 (3), b= 14.014(3), c= 14.952(7)A, β= 109.55(3)°β= 109.55(3)°, Z = 4, R = 0.066 and R′= 0.06]. Both metal ions show a distorted square-pyramidal co-ordination geometry. The basal plane is defined for each metal centre by a benzylic nitrogen atom, the adjacent nitrogen atom in the chain and two chloride ions. The apical position is occupied by another chloride from a symmetry-related molecule with a much weaker bond than those in the plane. The presence of the para-phenylene subunit imposes enough strain to divide the macrocyclic cavity of L2 into two separate ethylenediamine subunits.