The magnetic study of a binuclear Cu(ii) complex with π–π stacking interactions

Abstract

An anomalous magnetic interaction is observed in a very common and unpublished binuclear copper(II) complex, [Cu₂(μ₂-OOCCH₃)₂(bpydiol-H)₂(H₂O)₂] (bpydiol-H = mono deprotonated 2,2′-bypyridine-3,3′-diol). In the complex, the two Cu(II) ions are bridged by two acetate anions and there is a π–π stacking interaction between the adjacent pyridine rings. Theoretical calculations reveal that the acetate bridge ligand leads to an antiferromagnetic coupling with 2J = −166.72 cm⁻¹, whereas the π–π stacking developed a ferromagnetic interaction with 2J = 21.0 cm⁻¹. The offset from the antiferromagnetic interaction and the ferromagnetic interaction may be one of main factors that resulted in the weaker magnetic coupling with experimental fitting 2J = −59.61 cm⁻¹. This is the first example using theoretical calculations that evaluate the magnetic coupling intensity for a π–π stacking system.