Síntese, caracterização, estudos químicos e fotoquímicos de sistemas supramoleculares

Abstract

The synthesis and some properties of monomers of ruthenium of the type trans— [Ru(NH3)4L(bpa)]2+, where L = pyridine or isonicotinamide and bpa = 1,2-bis(4-pyridyl)ethane monomers of chromium cis-[Cr(dcbH2)2Cl2] Cl, where dcz = 4,4'—dicarboxy - 2,2'-bipyridine and polinucleares systems of the type cis-{trans-[Ru(NH3)4L(bpa)}2[Cr(dcbH2)2](BF4)Cl3, are reported. These compounds presented in electronic spectra UV-Visible, bands in both regions. The bands of absorption of the monomers in the ultraviolet region, are similar in intensity and observed position in the spectra corresponding individual ligands, being attributed the internal transitions π- π * (IL) of the ligands. In the region of the visible, the electronic spectra of the ruthenium monomers present one or two denominated bands of MLCT (metal-ligands charge transfer), quite intense (and varying of 1 x 104 mol-1 L cmd). The most intense band and of smaller energy it is denominated of MLCT-1, and the more energetics, even so of smaller intensity it is denominated of MLCT-2. Usually, similar compositions obtained with bidentates ligands, without groups substitutes, it has been presenting a series of 3 bands in the absorption spectrum, even so the composed of chromium here reported, presented a series of two bands. The observed bands was attribute a co—excitement vibracional involving a joining inside between the transition d-d and the transitions vibracionais of the ligands. The polinuclear system formed starting from the chromium monomers and ruthenium, presented the same spectra characteristics of the monomers that gave it origin, with bands MLCT (characteristics of the ruthenium monomers), d-d (characteristic of the chromium monomer) and IL (characteristics of the internal transitions of the ligands). The formal potentials of reduction Ef, for the ruthenium monomers and polinucleares systems was obtained by ciclic voltammetry in aqueous solution. The values of E, amplify the increase of the capacity aceptor and the capacity donors of the ligantes pyridinics decrease, evidenced by the groups substitutes. The voltammograms obtained through the monomers suggests that just exists a type of present ruthenium. The results voltammetrycs obtained for the system polinucleares, also points for an increase of Ef, with the increase of the capacity aceptor of the ligande pyridinics. The study of the compositions in several solvents showed for the monomers, a variation in the position of the absorption bands (MLCT). An increase was observed in the position of the bands with the increase of the number of Gutmann’s donor (DN). As larger the increase of the donicidade of the larger solvent the increase of the electronic density of the group amínico and consequently adult is the transfer of that ligand for the metal center. The study accomplished for the systems polinucleares was harmed by the difficult solubilization of the compositions in the solvent, even so solvents in that the composition was soluble, it was observed increase it in the position of the band with the increase of DN. The infrared spectra, showed the differences among the monômeros obtained with the ligand pyridine and isonicotinamide; The monomers of isonicotinamide presented picks, in the characteristic of the group substituinte -CONH2 region of 1600 cm-1. The spectra obtained starting from the tríades, showed a differentiation in the area of 3300 cm-1, due to presence of the group -COOH, belonging to the chromium monomer. Other possible differentiations that could exist, they were masked by the groups carboxi (-COOH), that generate in the spectrum very wide bands. Photochemistry was studied the photoaquation reactions for the synthesized triads. The compositions were photolized in several wave lengths being the products of the photolysis analyzed potentiometry (NH3) and for ionic change (ligands pyridinics). According to the classification adopted by Malouf and Ford, the compositions were denominated as non reactions, due to the low obtained quantum revenue and the dependent reaction of the wave length.