Electron spin resonance study of dimer formation in some bis(N-alkylsalicylideneiminato)copper(II) complexes in inert solvents

Abstract

The complexes [Cu(N-R-sal)₂](R = Et, Prⁿ, Prⁱ, Buⁿ, n-hexyl, cyclohexyl, and n-octyl) show well defined triplet-state e.s.r. spectra in methylcyclohexene for both ΔM= 1 and 2 transitions with the zero-field splitting due to dipolar interaction between the copper(II) pairs. Computer analysis of the spectra has revealed that these complexes adopt various dimeric structures according to R which do not require apical co-ordination of the phenolic oxygen atoms, and that the structures in methylcyclohexane are different from those in toluene. Intradimer spin-exchange interactions for these dimers are weakly antiferromagnetic (1.1–4.5 cm^–1 from the temperature dependence of intensity for ΔM= 2 transitions in the range 1.57–4.2 K). Thermodynamic constants for dimer formation in methylcyclohexane have been estimated as ΔH≈–3 kcal mol^–1 and ΔS≈–9 cal K^–1 mol^–1 and are discussed.