Intermolecular interaction and magnetic coupling mechanism on a mononuclear CoII complex

Anti-ferromagnetic interaction was observed in a new crystal that consists of mononuclear Co^II complexes, namely [Co(PMP)(N₃)] (PMP?=?2,9-bis(pyridin-2-methoxyl)-1,10-phenanthroline); in the mononuclear complex Co^II has a distorted trigonal-bipyramidal geometry. Analysis for the crystal structure indicates six magnetic coupling pathways among adjacent complexes, in which three involve π–π stacking and the other three deal with intermolecular interactions. The fitting for the variable-temperature magnetic susceptibilities with the Curie–Weiss formula shows an anti-ferromagnetic interaction between adjacent Co^II ions with θ?=??5.49 K?=??3.82?cm^?1. Theoretical calculations on the spin section reveal that the three π–π stacking systems result in magnetic coupling constants 2J?=??0.10?cm^?1, ?0.10?cm^?1, and 1.24?cm^?1, respectively, and the three intermolecular interactions lead to weak anti-ferromagnetic interactions with 2J?=??0.36?cm^?1, ?0.26?cm^?1, and ?0.32?cm^?1, respectively. The theoretical calculations and the experimental magnetic data imply that the anti-ferromagnetic interaction involves the orbital contribution of the relevant Co^II ions.