Synthesis, characterization and structure of ruthenium(II) phosphine complexes with N-heterocyclic thiolate ligands Solange O. Pinheiro a , Jackson R. de Sousa a , Marcelo O. Santiago a , Idalina M.M. Carvalho a , Ana L.R. Silva a , Alzir A. Batista b , Eduardo E. Castellano c , Javier Ellena c ,I ´ caro S. Moreira a , Izaura C.N. Dio ´ genes a, * a Departamento de Quı ´mica Orga ˆnica e Inorga ˆnica, Universidade Federal do Ceara ´ , Cx Postal 12200, 60455-760 Fortaleza, CE, Brazil b Departamento de Quı ´mica, Universidade Federal de Sa ˜o Carlos, Cx Postal 676, 13565-905 Sa ˜o Carlos, SP, Brazil c Instituto de Fı ´sica de Sa ˜o Carlos, Universidade de Sa ˜o Paulo, Cx Postal 780, 13560-250 Sa ˜o Carlos, SP, Brazil Received 21 December 2004; received in revised form 11 April 2005; accepted 5 May 2005 Available online 20 December 2005 Abstract The [Ru(dppb)(mbt) 2 ], mbt = 2-mercaptobenzothiazole, complex, isolated from the reaction of the mer-[RuCl 3 (dppb)(OH 2 )] complex with the 2,2 0 -dithiobis(benzothiazole), mbts, was characterized by spectroscopic and electrochemical techniques (E 1/2 = 0.78 V versus NHE) and its structure was determined by crystal X-ray analysis. The structural analysis suggests that the S–S bond of the mbts ligand is cleaved, thus forming two four-membered chelate rings coordinated to the ruthenium through the N,S-donor atoms of the mbt reduced ligands, with an average bite angle of 67.295(11)°. The 1 H and 13 C NMR signals observed for mbts ligand coordinated to the metal cen- ter, the changes in the vibrational spectra, and the appearance of a MLCT band in the electronic spectrum of the complex point for the reduced state of the ruthenium metal center, Ru II . These reducing processes are suggested to be due to the methanol interference, which is observed to be strongly affected by N-methylmorpholine. The cytochrome c electrochemistry was analyzed by using the SAMs formed by the mbts and the [Ru(dppb)(mbt) 2 ] complex on gold, with only the former presenting electroactivity. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Ruthenium phosphine compounds, N-Heterocyclic thiolate ligands; Chemically modified electrode; SAM; SERS; Cyt c 1. Introduction The p-back-bonding capability of the Ru(II) complexes together with the singular properties of phosphine ligands [1] constitute interesting aspects concerning the possibility of make thin inorganic films with potential coordination chemistry on surface [2]. Many studies have focused on altering the physical-chemistry properties of these materials by introducing different substituents or metal centers with different backbone capacities. This allows tuning of the electronic properties which may have applications in elect- rocatalysis or chemical sensing involving the pendant moi- eties of a given complex. Self-assembled monolayers (SAMs) formed by organ- othiol species, which are ordered and highly packed, are usually used as sensors in a general sense. For instance, the redox process of cytochrome c (cyt c) metalloprotein has been electrochemically studied [3–5] by using gold elec- trode modified by the organothiol ligand 4-mercaptopyri- dine (pyS). In a series of paper [6–8], it has been demonstrated that the p-back-bonding interaction capabil- ity of the [M II (CN) 5 ] 3 (M = Fe and Ru) metal center enhances the interaction between the gold atoms and the pyS sulfur head group portion. Another example that may be reported here is the direct electrochemistry of folic acid at a 2-mercaptobenzothiazole (mbt) SAM on gold 0020-1693/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2005.05.042 * Corresponding author. Tel.: +55 0318532889844; fax: +55 03185328 89978. E-mail address: izaura@dqoi.ufc.br (I.C.N. Dio ´ genes). www.elsevier.com/locate/ica Inorganica Chimica Acta 359 (2006) 391–400