Nickel(II) Complexes of Chiral Tripodal N,O,S‐Ligands: Square‐Planar vs. pseudo‐Octahedral Coordination in the Solid State and in Solution, Metal‐Induced Racemization of the Ligand

The complexation behavior of three chiral, tripodal N,O,S‐ligands with nickel(II) salts was examined. It was found that the coordination mode of the ligands (bidentate N,O and N,S; tridentate N,O,S) and of the central nickel ion (square‐planar vs. pseudo‐octahedral) is not simply an intrinsic property of the ligand‐metal combination, but also a function of the counter ions and of the solvent of crystallization. In the case of one ligand, a diamagnetic square‐planar and a paramagnetic pseudo‐octahedral form could be switched back and forth, by just changing the solvent of crystallization from methanol to ethanol. By using an enantiomerically pure tripodal N,O,S‐ligand, a metal induced racemization was unveiled which would have otherwise remained undetected.