A Multi-Technique Investigation of a New Macroacyclic Schiff Base Ligand and its Cd(II), Zn(II) and Cu(II) Complexes

A new macroacyclic Schiff base, 1,3-bis(2((Z)-(hydroxyethylimino)methyl) phenoxy)propan-2-ol, (H3L), was synthesized and characterized by infrared, ultraviolet-visible and NMR spectroscopies, and microanalysis. A series of new complexes was subsequently obtained from the reaction of the H3L ligand and Cd(II), Zn(II) and Cu(II). The prepared complexes [Cd2H2L(H2O)(NO3)2]NO3 (1), [ZnH2L]ClO4 (2), and [CuH2L]ClO4 (3), were characterized by IR spectroscopy and microanalysis, and, in the case of 1 and 2, also by NMR spectroscopy. Suitable crystals of 1 were obtained for X-ray analysis. The single crystal X-ray structural analysis of 1 showed that the complex is binuclear, with all nitrogen and oxygen atoms of the ligand (N2O5) coordinated to the two Cd(II) ions. In the crystal structure the two distorted monocapped anti-prism Cd(II) centers are bridged asymmetrically by an oxygen of a hydroxyl group of the Schiff base and a water molecule. Density functional theory calculations were performed to characterize the conformational equilibrium of the Schiff base in solution. The geometry and the 13C NMR spectrum of the Cd(II) complex were also calculated by DFT, confirming the presence of the complex in the investigated solution media. Time dependent-DFT calculations provided further insight on the interpretation of the experimental UV-Vis spectrum of the Cd(II) complex.

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