Spin Interactions and Magnetic Anisotropy in a Triangular Nickel(II) Complex with Triaminoguanidine Ligand Framework

The trinuclear nickel(II) complex [Ni 3 (saltag t Bu )(bpy) 3 (H 2 O) 3 ]Cl (H 5 saltag t Bu = 1,2,3‐tris[(5‐ tert ‐butylsalicylidene)amino]guanidine) was synthesized and characterized by experimental as well as theoretical methods. The complex salt crystallizes with three molecules of dimethylformamide (dmf) and water as [Ni 3 (saltag t Bu )(bpy) 3 (H 2 O) 3 ]Cl · 3dmf · 3H 2 O ( 1 ) in the trigonal space group P 3 , with the complex located on a threefold rotation axis, which is consistent with the molecular C 3 symmetry of the complex cation. Magnetic measurements reveal an antiferromagnetic coupling ( J = –35.9 cm –1 ) between the nickel(II) ions leading to a diamagnetic ground state for the trinuclear complex cation. Theoretical investigations based on broken‐symmetry DFT confirm the antiferromagnetic exchange within the complex cation of 1 . Additional single‐ion CASSCF ab initio studies reveal that magnetic anisotropy is present in the system. The experimental and theoretical results for 1 are compared with those of a structurally similar nickel(II) complex that is based on the bromo‐substituted derivative of the triaminoguanidine ligand. The differences in their magnetic properties can be attributed to the stronger elongation of the pseudo‐octahedral coordination sphere at the nickel(II) centers in case of 1 . The analysis of the magnetic properties of 1 clearly shows that for such exchange coupled systems reliable parameters for the magnetic anisotropy cannot be extracted from experimental data alone.