Increasing the [pi]-[pi] Interactions in Trinuclear NiII3 Triplesalophen Complexes

The new triplesalophen ligand H6kruseBr was synthesized as a variation of the triplesalophen ligands H6baronR by replacing a phenyl by a methyl group at the terminal ketimine in order to allow closer contacts of trinuclear complexes due to less steric hindrance by the smaller methyl group. The ligand H6kruseBr was used to synthesize the trinuclear complex [(kruseBr)NiII3], which is insoluble in organic solvents despite the coordinating solvent pyridine. Recrystallization from pyridine results in the complex [(kruseBr){Ni2(Ni(py)2)}], which was characterized by single-crystal X-ray diffraction. Two NiII ions are four-coordinate by the salophen-like subunits while the third NiII ion is six-coordinate by two additional pyridine donors. The analysis of the molecular and crystal structure in comparison to that of NiII3 complexes of (baronR)6- reveals that the methyl group in [(kruseBr){Ni2(Ni(py)2)}] results in less ligand folding and in closer contact distance of two NiII3 complexes by π-π interactions of 3.2 Å. This indicates that trinuclear complexes of H6kruseBr are more suitable than complexes of H6baronR as molecular building blocks for the anticipated synthesis of nonanuclear single-molecule magnets.