Coordination compounds with Schiff bases and d and f block ions. preparation and correlations between molecular structure and spectroscopic and magnetic properties

In the present work a total of nine complexes were studied: four of them using Cu²⁺, two mononuclear complexes, one hexa and one pentacoordinated, using the semicarbazone (hscpy) ligand, and two isomorphic binuclear compounds, one with hscpy and the other with the thiosemicarbazone (htscpy) ligand; three isomorphic mononuclear complexes using Gd³⁺, Tb³⁺ and Dy³⁺ with hscpy; and two Ru²⁺ complexes, one mononuclear using the 2,2'-pyridine and 4-amin-1,10-phenantrolin as ligands and one binuclear based on the polyfunctional ligand pyridine-2,6-bis(N-(1,10-phenantrolin-5-yl)methanamine). The structures of the mononuclear copper(II) complexes were determined by single crystal X-ray diffractometry. Quantum calculations using the atoms in molecules approach were carried out aiming the further understanding of the phenomena that lead to the differences in coordination. It was observed that the relative energies of the two species were very close and the coordination geometry was not a relevant factor, being the crystalline packing and the anion arrangement in the crystal the dominant factors in the stabilization energy of the systems. The crystal structure of the binuclear Cu(II) complex with hscpy was determined by single crystal X-ray diffraction and its magnetic properties were studied and compared to an isomorphic htscpy-based analogue complex. Through electron paramagnetic resonance and magnetic susceptibility experiments it was found that the metallic centers behave as isolated units in the complexes, which present a small antiferromagnetic behavior at low temperatures attributed to dipolar coupling. Density functional theory calculations using the broken symmetry approach showed that the magnetic orbitals of those complexes have a precarious superposition, corroborating the weak communication between the metal centers. Single crystal X-ray diffraction experiments showed that the novel lanthanide complexes with hscpy are isomorphic. The magnetic dynamic of the Tb³⁺ and Dy³⁺ compounds were evaluated through alternate current susceptometry measurements. The former only presented slow relaxation of magnetization when submitted to an external magnetic field, with an energy barrier for the inversion of magnetization of 21.9(4) cm^-1. The latter show slow relaxation of the magnetization even in the absence of an external magnetic field, having four distinct process for this relaxation, a result, as far as we know, never seen before. The characterization of the Ru²⁺ complexes where made using the ¹H and ¹³C nuclear resonance technique. Spectroscopic and electrochemical characterization were also conducted, showing that the Ru²⁺ centers are electrochemical inactive under the worked conditions, while processes were observed for the 5- amin^-1,10-phenantroline entity. Both complexes were submitted to resonance Raman experiments. The intensification of the bands in the spectra of each compound were achieved using a 457 nm laser, the wavelength which is related to a metal to ligand charge transfer band attributed to the [RuII(bipyridine)2] chromophore. (author)