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Nitric oxide complexes with trans-tetraamin(trans-1,2-bis(4-pyridyl)ethylene)ruthenium and correlative species

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Author(s):
Fabio Willian Watanabe
Total Authors: 1
Document type: Master's Dissertation
Press: Ribeirão Preto.
Institution: Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC)
Defense date:
Examining board members:
Elia Tfouni; Rose Maria Carlos; Sofia Nikolaou
Advisor: Elia Tfouni
Abstract

In this work, the synthesis of the complexes [Ru(NH3)5(t-bpe)](PF6)2, [Ru(NH3)5(t-bpe)](PF6)3, trans-[Ru(SO4)(NH3)4(t-bpe)]Cl•nH2O, trans-[Ru(NH3)4(H2O)(t-bpeH)](PF6)3, trans-[Ru(NH3)4(H2O)(t-bpe)](PF6)3, trans-[Ru(SO4)(4-acpy)(NH3)4]Cl•nH2O, trans-[Ru(NH3)4(H2O)(4-acpy)](PF6)2, trans-[Ru(4-acpy)(NH3)4(t-bpe)](PF6)2, trans-[Ru(NO)(NH3)4(t-bpe)](PF6)3•H2O, [trans-Ru(4-acpy)(NH3)4(t-bpe)trans-Ru(SO4)(NH3)4](PF6)5•nH2O and [trans-Ru(4-acpy)(NH3)4(mu-t-bpe)trans-Ru(NO)(NH3)4]Cl5•2H2O are reported. The compounds were analyzed and characterized by UV-visible and IR spectroscopy, NMR, elemental analysis and electrochemical techniques. The infrared spectra of trans-[Ru(NO)(NH3)4(t-bpe)](PF6)3•H2O showed an absorption band at 1935 cm-1 and that of [trans-Ru(4-acpy)(NH3)4(mu-t-bpe)trans-Ru(NO)(NH3)4]Cl5•2H2O a band at 1925 cm-1. These bands were assigned to the stretching frequency of NO indicating its coordination to the metallic center, and a nitrosonium character. In the electronic spectra of the [Ru(NH3)5(t-bpe)](PF6)2, trans-[Ru(NH3)4(H2O)(t-bpeH)](PF6)3, trans-[Ru(NH3)4(H2O)(4-acpy)](PF6)2 and trans-[Ru(4-acpy)(NH3)4(t-bpe)](PF6)2 a metal-ligand charge transfer (MLCT) transition, in the visible region, and IL transitions in the ultraviolet region, appear. The spectra of [Ru(NH3)5(t-bpe)](PF6)3, trans-[Ru(SO4)(NH3)4(t-bpe)]Cl•nH2O, trans-[Ru(SO4)(4-acpy)(NH3)4]Cl•nH2O, trans-[Ru(NH3)4(H2O)(t-bpe)](PF6)3 and [trans-Ru(4-acpy)(NH3)4(mu-t-bpe)trans-Ru(SO4)(NH3)4](PF6)5•nH2O displayed a ligand-metal charge transfer (LMCT) transition in the region from 300 to 400 nm and, IL transitions below 300 nm. The spectra of the compounds trans-[Ru(NO)(NH3)4(t-bpe)](PF6)3•H2O and [trans-Ru(4-acpy)(NH3)4(mu-t-bpe)trans-Ru(NO)(NH3)4]Cl5•2H2O showed absorption bands in the 320 nm region with molar absorptivity around 2.8,10-4 L mol-1 cm-1, assigned to several transitions such as ligand field (LF), ligand-ligand charge transfer (LLCT), IL and metal-ligand charge transfer. The pKa values for the desprotonation of t-bpeH+ in [RuII(NH3)5(t-bpeH)]3+ (pKa 5,1), [RuIII(NH3)5(t-bpeH)]4+ (pKa 3,6), trans-[RuII(NH3)5(H2O)(t-bpeH)]3+ (pKa 4,5), trans-[RuIII(NH3)4(H2O)(t-bpeH)]4+ (pKa 2,8) and trans-[Ru(NO)(NH3)4(t-bpeH)]4+ (pKa 2,3) were determined. For the ruthenium(III) complexes, [RuIII(NH3)5(t-bpeH)]4+ and trans-[RuIII(NH3)5(H2O)(t-bpeH)]4+, the pKa values were smaller than in the ruthenium(II) complexes, [RuII(NH3)5(t-bpeH)]3+ and trans-[RuII(NH3)5(H2O)(t-bpeH)]3+. The pKa for trans-[Ru(NO)(NH3)4(t-bpeH)]4+ was the smallest one indicating a Ru(III) character for ruthenium. The 1H NMR spectrum of [Ru(NH3)5(t-bpe)](PF6)2 showed 3 signals from 8,6 to 7,6 ppm, with 4:4:2 integration, assigned to aromatic and ethylenic protons of the t-bpe ligand. For trans-[Ru(NO)(NH3)4(t-bpe)](PF6)3•H2O there are 5 signals with chemical shifts from 8,7 to 7,6 ppm due to the NO influence. One of them is a doubled doublet assigned to ethylenic protons. The spectrum of [trans-Ru(4-acpy)(NH3)4(mu-t-bpe)trans-Ru(NO)(NH3)4]Cl5•2H2O, has 6 signal located from 8,8 to 7,2 ppm, with 2:2:4:2:2:2 integration. These are assigned to aromatic and ethylenic protons of the t-bpe and aromatic of the 4-acpy. Only Ru2+/3+ processes were observed in the cyclic voltammograms of [Ru(NH3)5(t-bpe)](PF6)2 (E1/2’ = +116 mV vs Ag/AgCl), trans-[Ru(NH3)4(H2O)(t-bpeH)](PF6)3 (E1/2’ = +165 mV vs Ag/AgCl), trans-[Ru(4-acpy)(NH3)4(H2O)](PF6)2 (E1/2’ = +247 mV vs Ag/AgCl) and trans-[Ru(4-acpy)(NH3)4(t-bpe)](PF6)2 (E1/2’ = +405 mV vs Ag/AgCl). The cyclic voltammograms trans-[Ru(NO)(NH3)4(t-bpe)](PF6)3•H2O and [trans-Ru(4-acpy)(NH3)4(-t-bpe)trans-Ru(NO)(NH3)4]Cl5•2H2O displayed {RuNO}3+/{RuNO}2+ processes (Ec = -170 mV vs Ag/AgCl and Ec = -188 mV vs Ag/AgCl, respectively) and cathodic peaks indicating {RuNO}2+/{RuNO}+ processes (Ec = -640 mV vs Ag/AgCl and Ec = -650 mV vs Ag/AgCl, respectively). The compound trans-[Ru(NO)(NH3)4(t-bpe)](PF6)3•H2O was irradiated at 313 and 366 nm, at pHs 1,2 and 7,0. Uv-vis and infrared spectrophotometries were used to analyze the product of the photochemical reaction. The decrease of the absorption band, NO, indicated the NO released. The quantum yields were determined for irradiations in 313 nm at pH 1,2 and 7,0 (0,10 and 0,12, respectively) and irradiations in 366nm at pH 1,2 and 7,0 (0,04 and 0,04, respectively) and are in agreement with those of other trans-[Ru(NO)(NH3)4(L)]3+ (L = py-X) complexes. Very promising preliminary photochemical results showed that irradiation of [trans-Ru(4-acpy)(NH3)4(mu-t-bpe)trans-Ru(NO)(NH3)4]Cl5•2H2O with ultraviolet or visible light result in NO release. The data set showed a weak electronic communication between the extremities of t-bpe and that the NO release from [trans-Ru(4-acpy)(NH3)4(mu-t-bpe)trans-Ru(NO)(NH3)4]Cl5•2H2O with visible light is a result of that weak communication which causes visible light absorption by the binuclear complex. Thus, this class of complexes is very promising for the development of NO donors directed for biological applications, such as photochemical therapy. (AU)