Solid state and solution structures of two structurally related dicopper complexes with markedly different redox properties

Abstract

The dinuclear dicopper(I) complex of a 26-membered macrocycle, L¹, obtained from the 2 + 2 condensation of terephthalaldehyde and 3-azapentane-1,5-diamine, has been isolated as an air stable red-orange complex in good yield. The crystal structure of [Cu₂(NCMe)₂L¹][ClO₄]₂[triclinic, space group P, a= 10.5773(9), b= 10.8385(8), c= 7.9715(4)Å, α= 99.572(6), β= 91.698(7), γ= 108.952(6)°] showed two distorted tetrahedrally co-ordinated copper(I) centres with a Cu–Cu separation of 7.04 Å. The air stability of [Cu₂(NCMe)₂L¹]²⁺ contrasts with the oxygen sensitivity of the dicopper(I) complex of the 24-membered macrocycle L³(2 + 2 condensation of isophthalaldehyde and 3-azapentane-1,5-diamine) which leads to oxygenation of one of the aromatic rings. The marked difference in reactivity is discussed on the basis of the structural differences between the two isomeric compounds, analysed with molecular mechanics calculations. The dinuclear dicopper(II) complexes of the 24- and 26-membered macrocyclic hexaamines L² and L⁴, derived by reduction of L¹ and L³, respectively, exhibit dipole–dipole coupling in their EPR spectra. The solution structures of the two dicopper(II) complexes have been determined by a combination of molecular mechanics calculations and the simulation of their EPR spectra.