Structural, spectroscopic and redox studies of a new ruthenium(III) complex with an imidazole-rich tripodal ligand

Author(s)

Scarpellini, Marciela ; Toledo Júnior, José Carlos ; Neves, Ademir ; Ellena, Javier ; Castellano, Eduardo E. ; Franco, Douglas W. ^[6]

• Document type: Journal article
• Source: Inorganica Chimica Acta; v. 357, n. 3, p. 707-715, fev. 2004.
• Field of knowledge: Physical Sciences and Mathematics - Chemistry

Abstract

The present paper describes a new tripodal ligand containing imidazole and pyridine arms and its first cis-[Ru-III(L)(Cl)(2)]ClO4 complex (1). The crystal structure of 1 shows Ru-III in a distorted octahedral geometry, in which two chloride ions, cis-positioned to each other, are coordinated besides the four nitrogen atoms from the tetradentate ligand L. The cyclic voltammogram of 1 exhibits three redox processes at -67, +73 and +200 mV versus SCE, which are attributed to the Ru-III/Ru-II couple in the cis-[Ru-III(L)(Cl)(2)](+), cis-[Ru-II(L)(H2O)(Cl)](divided by) and cis-[Ru-II(L)(H2O)(2)](2+), respectively. After chemical reduction (Zn(Hg) or Eu-II) only the cis[Ru-II(L)(H2O)(2)](2divided by) species is observed in the cyclic voltammetry. Complex 1 absorbs at 470 nm (epsilon = 1.4 x 10(3) mol(-1) L cm(-1)), 335 nm (epsilon = 7.9 x 10(3) mol(-1) L cm(-1)), 301 nm (epsilon = 6.7 x 10(3) mol(-1) L cm(-1)) and 264 nm (epsilon = 9.9 x 10(3) mol(-1) L cm(-1)), in water solution (CF3COOH, 0.01 mol L-1, mu = 0.1 mol L-1 with CF3 COONa). Spectroelectrochemical experiments show a decrease of the bands at 335 and 301 nm. which are attributed to LMCT transitions from the chloride to the Ru-III center and the appearance of a broad band at 402 nm ascribed to MLCT transition from the Ru-II center to the pyridine ligand. The lability of the water ligands in the cis[Ru-II(L)(H2O)(2)](2divided by) species has been investigated using the auxiliary ligand pyrazine. Reactions in the presence of stoichiometric and excess of pyrazine yield the same species, cis-[Ru-II(L)(H2O)(pz)](2+) which exhibits a reversible redox process at 493 mV versus SCE and absorbs at 438 nm (epsilon = 5.1 X 10(3) mol(-1) L cm(-1)) and 394 nm (epsilon = 4.2 x 10(3) mol(-1) L cm(-1)). Experiments performed with a large excess of pyrazine gave a specific rate constant k(1) = (2.8 +/- 0.5) x 10(-2) M-1 s(-1), at 25degreesC, in CF3COOH, 0.01 mol L-1, mu = 0.1 mol L-1 (with CF3COONa). (AU)

• FAPESP's process: 99/07109-9 - Thermal and photochemical reactivity of ruthenium nitrosyl complexes: knowledge and control of the nitric oxide coordinated reactivity
• Grantee: Douglas Wagner Franco
• Support Opportunities: Research Projects - Thematic Grants