Synthesis, characterization and crystal structures of mono and dinuclear macrocyclic cobalt(ii) complexes with a new tetraaza m-xylyl-based macrocyclic ligand

Abstract

A new tetraaza macrocycle bearing two xylyl spacers was synthesized as a potential binucleating ligand (L) and the crystal structure of its tetrachloride salt was determined by single crystal X-ray diffraction analysis. Corresponding Co(II) complexes were isolated as both mono- and dinuclear complexes of [Co(H₂L)Cl₂]Cl₂, [Co₂LBr₂OH]Br and [Co₂LI₂OH]I, and characterized using different physico-chemical techniques. The single crystal X-ray diffraction technique for [Co(H₂L)Cl₂]Cl₂ and [Co₂LI₂OH]I indicates that the Co ions adopt the geometry of a distorted tetrahedron in a tetracoordinated environment. The two metal centers in the [Co₂LI₂OH]I complex are bridged by a hydroxyl group with Co⋯Co distance of 3.501(1) Å. The bromo- and iodo-complexes show antiferromagnetic behavior which can be described by spin only Hamiltonian while spin–orbital coupling for tetrahedral coordinating cobalt ions is very small.