Modeling Spin Interactions in a Triangular Cobalt(II) Complex with Triaminoguanidine Ligand Framework: Synthesis, Structure, and Magnetic Properties

The new tritopic triaminoguanidine-based ligand 1,2,3-tris­[(pyridine-2-ylmethylidene)­amino]­guanidine (H2pytag) was synthesized. The reaction of a mixture of cobalt­(II) chloride and cobalt­(II) perchlorate with the ligand H2pytag in pyridine solution leads to the formation of the trinuclear cobalt­(II) complex [Co3(pytag)­(py)6Cl3]­ClO4. Three octahedrally coordinated high-spin cobalt­(II) ions are linked through the bridging triaminoguanidine backbone of the ligand leading to an almost equilateral triangular arrangement. The magnetic properties of the complex were investigated by magnetic measurements, variable-temperature, variable-field magnetic circular dichroism (MCD) spectroscopy, and density functional theory as well as ab initio calculations. A rather strong antiferromagnetic exchange interaction between the cobalt­(II) centers of ca. −12 cm–1 is determined together with a strong local anisotropy. The single-ion anisotropy of all three cobalt­(II) centers is found to be easy-plane, which coincides with the tritopic ligand plane. MCD measurements and theoretical investigations demonstrate the presence of rhombic distortion of the local Co surrounding.