Synthetic and structural studies of metal complexes derived from tris(3,5-bimethyl-pyrazolylmethyl)amine and pyridine derivatives

A series of metal complexes with a tripodal ligand, TMPzA, have been synthesized and characterized, and their single crystal structures have been determined by X-ray diffraction techniques. It has been found that when pyridyl derivatives as auxiliary ligands are added to the reaction mixture, the tripodal ligand TMPzA loses a pendant arm and coordinates with the metal centers to form the complexes: [Cu(DMPzA)(2,2′-bipy)]·(ClO₄)₂ (1), [(DMPzA)Cu(μ-4,4′-bipy)Cu(DMPzA)]·(ClO₄)₄ (2), [(TMPzA)Cu(μ-H₂DPC)Cu(DMPzA)]·(ClO₄)₂ (3), [(DMPzA)Co(μ-H₂DPC)Co(TMPzA)]·(ClO₄)₂ (4) [TMPzA = tris(3,5-bimethyl-pyrazolymethyl)amine; bipy = bipyridine; H₂DPC = pyridyl-2,6-bicarboxylate; DMPzA = bis(3,5-bimethyl-pyrazolmethyl)amine]. In order to investigate the effect of the pyridyl ring on the cleavage of the pendant arm in the tripodal ligand, a fifth complex, [(TMPzA)Co(μ-HZPC)Co(TMPzA)·(H₂O)₂]·(ClO₄)₃ (5), has been prepared by using pyrazole-carboxylate (HZPC) instead of pyridyl derivatives, and its crystal structure has been determined. It has been found that the pendant arm in TMPzA ligand has not been removed in complex 5. The results show that the complexes with TMPzA have a strong ability to recognize pyridine compounds in methanol solvent, and they have potential application for molecular devices in the future. The cleavage mechanism has been studied by DFT calculations and ESI-MS spectra.