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)Å, 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.