A correlation involving 1H NMR spectra and exchange coupling constants of a family of phenoxo-bridged macrocyclic dicopper(II) complexes

Abstract

The ¹H NMR spectra of eleven macrocyclic tetraiminodiphenolate dicopper(II) complexes derived from 4-methyl (or tert-butyl)-2,6-diformyl/diacetyl/dibutyrylphenols and linker diamines such as 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane or 1,2-diaminobenzene have been studied in (CD₃)₂SO at 25 °C. The hyperfine-shifted ¹H NMR signals have been assigned from their measured longitudinal relaxation times (T₁) and peak areas. The two copper(II) centres in these compounds are strongly antiferromagnetically coupled with the exchange coupling constant -2J (H = -2JS₁·S₂) lying between 690 and 860 cm^-1. It is shown that a plot of the chemical shift (d) due to the phenolate ring protons of the macrocycles at 298 K s. the exchange coupling constant (-2J) of the corresponding complexes provides a smooth sigmoidal curve that can be simulated by the expression -2J = 220.6 [1 + exp{(δ - 4.12)/2.93}]^-1 + 667.