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Reaction of dichlorotris(triphenylphosphine) ruthenium(II) [RuCl(2)(PPh(3))(3)] with 1,8-bis(2-pyridyl)-3,6-dithiaoctane (pdto), a (N(2)S(2)) tetradentate donor, yields a new compound [Ru(pdto)(PPh(3))Cl]Cl (1), which has been fully characterized. (1)H and (31)P NMR studies of 1 in acetonitrile at several temperatures show the substitution of both coordinated chloride and triphenylphosphine with two molecules of acetonitrile, as confirmed by the isolation of the complex [Ru(pdto)(CH(3)CN)(2)]Cl(2) (2). Cyclic voltammetric and spectroelectrochemical techniques allowed us to determine the electrochemical behavior of compound 1. The substitution of the chloride and triphenylphosphine by acetonitrile molecules in the Ru(II) coordination sphere of compound 1 was also established by electrochemical studies. The easy substitution of this complex led us to use it as starting material to synthesize the substituted phenanthroline coordination compounds with (pdto) and ruthenium(II), [Ru(pdto)(4,7-diphenyl-1,10-phenanthroline)]Cl(2).4H(2)O (3), [Ru(pdto)(1,10-phenanthroline)]Cl(2).5H(2)O (4), [Ru(pdto)(5,6-dimethyl-1,10-phenanthroline)]Cl(2).5H(2)O (5), [Ru(pdto)(4,7-dimethyl-1,10-phenanthroline)]Cl(2).3H(2)O (6), and [Ru(pdto)(3,4,7,8-tetramethyl-1,10-phenanthroline)]Cl(2).4H(2)O (7). These compounds were fully characterized, and the crystal structure of 4 was obtained. Cyclic voltammetric and spectroelectrochemical techniques allowed us to determine their electrochemical behavior. The electrochemical oxidation processes in these compounds are related to the oxidation of ionic chlorides, and to the reversible transformation from Ru(II) to Ru(III). On the other hand, a single reduction process is associated to the reduction of the substituted phenanthroline in the coordination compound. The E(1/2) (phen/phen(-)) and E(1/2) (Ru(II)/Ru(III)) for the compounds (3-7) were evaluated, and, as expected, the modification of the substituted 1,10-phenanthrolines in the complexes also modifies the redox potentials. Correlations of both electrochemical potentials with pK(a) of the free 1,10-phenathrolines, lambda(max) MLCT transition band, and chemical shifts of phenanthrolines in these complexes were found, possibly as a consequence of the change in the electron density of the Ru(II) and the coordinated phenanthroline.

The structural and solution characterization of novel Fe(II) compounds of the general formula [Fe(bztpen)X]PF6 and [Fe(bztpen)CH3CN](PF6)2 is presented, where bztpen is the pentadentate ligand N-benzyl-N,N',N'-tris(2-methylpyridyl)ethylenediamine and X- is a monodentate ligand. All complexes were characterized in solution and in the solid state, employing the usual techniques and single-crystal X-ray diffraction. The results obtained are discussed in terms of the existing information for some previously reported analogous compounds to arrive at a rationalization regarding the influence of a variation in the coordination environment of all compounds and to evaluate their relative stability. The observed magnetic response in the solid state is paramagnetic in the entire temperature range for the Cl-, Br-, I-, OCN-, and SCN- derivatives, while the N(CN)2-, CH3CN, and CN- derivatives are diamagnetic. The diamagnetic character of these last two compounds is confirmed in acetonitrile solution, while a spin transition step is observed for the N(CN)2- derivative. Diffraction data for all compounds as hexafluorophosphates shows that the I-, Br-, and OCN- derivatives crystallize in the orthorhombic space group Pbca, while the CN-, SCN-, and CH3CN compounds crystallize in the triclinic space group P. Average bond lengths and the trigonal distortion parameter can be correlated to the observed magnetic susceptibility depending on the coordinated monodentate ligand. Solution measurements of electronic properties for the compounds follow the trend established by the spectrochemical series. The relative stability of the Fe(II) complexes can be established in terms of the percentage of dissociation from the voltammetry and conductivity results, which are consistent with those obtained spectrophotometrically, mainly, the larger stability for the CN- derivative and the lower for the I- derivative. The redox potential and percentage of dissociation values allow for the estimation of the relative stability constants for the Fe(II) and Fe(III) complexes.