π–π Stacking, hydrogen bonding and anti-ferromagnetic coupling mechanism on a mononuclear Cu(II) complex

Abstract

Weak anti-ferromagnetic coupling is observed in a mononuclear copper(II) complex, [Cu(Pid)(OSO₃)(H₂O)] · (H₂O) (Pid = 2,2′-(1,10-phenanthrolin-2-ylimino)diethanol). The Cu(II) complex is a distorted square pyramid. Analysis of the crystal structure indicates that there are two types of magnetic coupling pathways, where one pathway involves π–π stacking between adjacent complexes and the second one involves the O–H ··· O hydrogen bonds between adjacent complexes. The variable-temperature magnetic susceptibilities show that there is a weak anti-ferromagnetic coupling between adjacent Cu(II) ions with Curie–Weiss constant θ = −13.71 K = −9.93 cm⁻¹. Theoretical calculations reveal that the π–π stacking resulted in anti-ferromagnetic coupling with 2J = −6.30 cm⁻¹, and the O–H ··· O hydrogen-bonding pathway led to a weaker anti-ferromagnetic interaction with 2J = −3.38 cm⁻¹. The theoretical calculations also indicate that anti-ferromagnetic coupling sign from the π–π stacking accords with the McConnell I spin-polarization mechanism.

Keywords:

• Crystal structure
• Magnetic coupling
• π–π Stacking
• Hydrogen bond
• Copper complex

Acknowledgments

This study was supported by the Natural Science Foundation of China (Grant no. 20971080) and the Natural Science Foundation of Shandong Province (Grant no. ZR2009BM026 and ZR2009BL002).