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)A, 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 A. 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.