Studies On The Coordination Chemistry Of Novel Functionalized Diazamesocyclic Ligands

In order to systematically investigate the coordination chemistry of the diazamesocyclic ligands, the typical 1,4-diazacycloheptane (DACH) was selected as the backbone to further our study, based on the results of our previous work. Firstly, the structures and spectra of a series of N~III and Cu~II complexes of DACH have been studied. The coordination geometry of the N~III center in all complexes is square planar, coordinated to two DACH ligands in trans-position. However, the ligands in the Cu~II complexes are in cis-position, and the Cu~II centers are either four-or five-coordinated. The four coordinated Cu~II complexes can be obtained only in the presence of anions and solvents with very weak coordinating ability and one additional strong ligand such as halogen anion or water can be easily coordinated to the Cu~II ion to form the five-coordinated complex. Secondly, a phenolic derivative of DACH, 1,4-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-1,4-diazacycloheptane (H2L1), together with its Cu~II, Co~II, and N~III complexes, has been synthesized and characterized. In the crystal structure of the ligand H2L1, the two phenolic pendant donors and the nitrogen atoms of the DACH backbone are in trans-position, which convert into the cis-form in the Cu~II complex. The DACH ring in the ligand takes the unusual chair-configuration, which transfers into the boat-form when coordinated to the metal ions. Thirdly, a series of bis-and mono-substituted derivatives of DACH fictionalized by the heterocyclic pendant groups have been synthesized. The Cu~II complex of the mono-substituted ligand L5 is obtained as a di-μ-Cl binuclear complex, similar to that of DACO. The bis-substituted imidazole (L4) and pyridine (L3) derivatives of DACH give the very rare mono-μ-Cl binuclear Cu~II complexes, although the transitional metal complexes of N-methyl imidazole derivative (L2) are obtained as mononuclear complexes. The magnetic properties of the mono-μ-Cl binuclear Cu~II complexes have been firstly investigated, and the maganeto-structural relationship has been further developed. The N~III complexes of the pyridine derivate L3 can be obtained in different colors, green and red. The N~III center in the former is five-coordinated, and it is unstable and can transform into the latter when exposed to the air. Two different coordination cations have been found in the red case: one has the square pyramidal coordination geometry of N~III and the other is in the square planar geometry. The UV-vis spectra of both complexes are identical, both being the typical spectra of the N~III complex with square pyramidal geometry.