Dicopper(II,II) and dicopper(I,II) complexes of a series of dinucleating macrocycles

Abstract

The dinucleating macrocycles H₂L^m,n containing two 2,6-di(aminomethyl)-4-methylphenol entities combined through two alkane chains, (CH₂)_m and (CH₂)_n, at the amine nitrogens have been prepared for the (m,n) sets (2,3), (2,4), (2,5), (3,3) and (3,4). The dinuclear copper(II) complexes having general formula [Cu₂L^m,n][ClO₄]₂ have been prepared. Cryomagnetic investigations (80–300 K) reveal a strong antiferromagnetic spin-exchange between the copper(II) ions within each complex (J based on ℋ=–2JS₁S₂ in the range –345 to –255 cm^–1). The cyclic voltammograms show two reduction couples, Cu^IICu^II–Cu^ICu^II and Cu^ICu^II–Cu^ICu^I. The comproportionation constants K_com for the mixed-valence Cu^ICu^II complexes have been determined electrochemically. The K_com value increase in the order of the macrocycles (L^2,3)^2– < (L^2,4)^2– < (L^2,5)^2– and (L^3,3)^2– < (L^3,4)^2–. The Cu^ICu^II mixed-valence state is shown to be ‘spin-trapped’(Class I) for all the complexes based on ESR spectra.