π−π Stacking and magnetic coupling mechanism on a mononuclear Cu(II) complex

Abstract

A mononuclear copper(II) complex was synthesized and in the crystal there are three types of π−π stacking interactions among adjacent complexes. The fitting for the data of the variable-temperature magnetic susceptibilities reveals that there is a weak anti-ferromagnetic coupling among adjacent Cu(II) ions with Weiss constant θ = −2.99 K = −2.08 cm−1. Theoretical calculations reveal that two types of π−π stacking resulted in anti-ferromagnetic couplings with 2J = −12.40 cm−1 and 2J = −9.74 cm−1, respectively, and the third type of π−π stacking led to a weak ferromagnetic interaction with 2J = 4.28 cm−1. The theoretical calculations also indicate that the ferromagnetic coupling sign from the π−π stacking accords with McConnell I spin-polarization mechanism, whereas the anti-ferromagnetic coupling signs cannot be explained with McConnell I spin-polarization mechanism.