Two new mononuclear cobalt(II) complexes of pyrazole-based ligands: synthesis, structures and magnetic studies

We have synthesized two mononuclear cobalt(II) complexes (1 and 2) of pyrazole-based bidentate (NN) and tridentate (NNN) tripodal ligands. X-ray crystal structure determination reveals that complex 1 has a tetrahedral geometry, while complex 2 has a trigonal-bipyramidal geometry. Both the complexes have been characterized by variable-temperature magnetic measurements between 2 and 300 K. A weak ferromagnetic exchange interaction (J = +1.5 cm(-1)) is observed for complex 2. Due to the presence of supramolecular CH center dot center dot center dot Cl and pi center dot center dot center dot pi interactions, a good magnetostructural correlation was found between the D parameter and angular distortion (delta) for complex 1 and related complexes reported in the literature.