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

A Spin-Frustrated Trinuclear Copper Complex Based on Triaminoguanidine with an Energetically Well-Separated Degenerate Ground State

We present the synthesis and crystal structure of the trinuclear copper complex [Cu₃(saltag)­(bpy)₃]­ClO₄·3DMF [H₅saltag = tris­(2-hydroxybenzylidene)­triaminoguanidine; bpy = 2,2′-bipyridine]. The complex crystallizes in the trigonal space group <i>R</i>3̅, with all copper ions being crystallographically equivalent. Analysis of the temperature dependence of the magnetic susceptibility shows that the triaminoguanidine ligand mediates very strong antiferromagnetic interactions (<i>J</i>_CuCu = −324 cm^–1). Detailed analysis of the magnetic susceptibility and magnetization data as well as X-band electron spin resonance spectra, all recorded on both powdered samples and single crystals, show indications of neither antisymmetric exchange nor symmetry lowering, thus indicating only a very small splitting of the degenerate <i>S</i> = ¹/₂ ground state. These findings are corroborated by density functional theory calculations, which explain both the strong isotropic and negligible antisymmetric exchange interactions