Here, 600 mg of trans-[Ru(NH₃)₄SO₂Cl]Cl (synthesized as previously described in the literature [6] - [8] [19] ) was suspended in 11 ml of water, followed by the slow addition of 347 mg of sodium bicarbonate. Then, the ligand (L = 4-acpy, py, ISN, 4-pic) was added in excess. The final solution was filtered and about 5 mL of concentrated HCl was added to the filtrate. The mixture was placed in an ice bath to precipitate and the solid obtained was filtered, rinsed with ethanol and ether and air dried (brown solid in all ligands). The brown solid obtained was dissolved in approximately 50 ml of a solution of 0.1 mol・L⁻¹ HCl, followed by the addition of a few drops of H₂O₂, until the color changed (pale yellow to brown). Then, 500 ml of acetone was added, resulting in the precipitation of a light yellow solid. After cooling, the solid was collected by filtration, washed with ethanol and ether and air dried. The medium yield was 60%.

Here, 180 mg trans-[Ru(NH₃)₄SO₄L]Cl (L = isn, 4-pic, 4-acpy and py) was dissolved in 2.0 ml of previously distilled and deaerated water. Argon was bubbled for 15 minutes in this yellow solution and then zinc amalgam was added. This solution remained under an inert atmosphere for about 20 minutes. During the reaction, the solution turned to an orange-red color. In parallel, 440 mg of the ligand 1,2-bis (4-pyridyl) ethane (BPA) was dissolved in the lowest portion of distilled and deaerated water possible, by addition to the initial solution. The resulting mixture was left under constant argon bubbling for 2 hours, protected from light. After this period, the resulting solution was filtered over a freshly prepared saturated solution of NaBF₄ and filtered on a 1:1 basis (NaBF₄ 1 g/1 ml of water), and then taken to a refrigerator to crystallize. The resulting mixture was filtered and the crystals washed with ethanol, ether and dried in a vacuum. The medium yield was 50%.

Elemental analysis of carbon, nitrogen and hydrogen was performed at the Chemistry Institute of the University of São Paulo. Trans-[Ru(NH₃)₄(py)(bpa)](BF₄)₂・NaBF₄・5H₂O: calcd.: C, 25.29; N, 12.15; H, 4.83. found.: C, 24.96; N, 13.21; H, 4.17. Trans-[Ru(NH₃)₄(isn)(bpa)](BF₄)₂・NaBF₄・3H₂O: calcd.: C, 26.56; N, 13.77; H, 4.42. found.: C, 26.73; N, 13.40; H, 4.14. Trans-[Ru(NH₃)₄(4-pic)(bpa)](BF₄)₂・2NaBF₄. H₂O: calcd.: C, 25.20; N, 11.43; H, 3.88. found.: C, 25.12; N, 12.00; H, 4.12. Trans-[Ru(NH₃)₄(4-acpy)(bpa)](BF₄)₂・NaBF₄.: calcd.: C, 30.11; N, 12.94; H, 4.12. found.: C, 30.80; N, 13.92; H, 4.50.

The spectroscopic monitoring for the compounds obtained is shown in Figures 1-4. We observed the formation of charge-transfer bands (MLCT-1) as well as the appearance of a second charge transfer band for the compounds trans-[Ru(NH₃)₄(isn)(bpa)]²⁺ and trans-[Ru(NH₃)₄(4-acpy)(bpa)]²⁺. Due to the structural similarity of py and 4-pic binders, it is possible to observe the initial existence of 4 well-defined peaks, where the first band observed between 200 and 300 nm is attributed to internal transitions of the ligand (IL) π − π* in analogy to other ruthenium amines [6] [19] [20] . The energies and intensity observed are similar to those of the free ligands, but shifted to higher energies. With the development of the reaction (Figure 1), the decrease in intensity of this band is observed (IL) indicating the greater interaction of ligands with the metal [6] [19] [20] . It can be observed that the bands at 319 nm, 424 nm and 520 nm are characteristic of the compound trans-[Ru(NH₃)₄SO₂L’]²⁺, where L = py

converged to only one band at 422 nm with the addition of bpa ligand; this may be attributed to the replacement process of bpa to the SO₂ ligand. Similar remarks can be made for the compound obtained for ligand L’ = 4-pic (Figure 2). The final intense bands observed at 422 (L = py) and 424 (L = 4-pic), where e is in the order of 10⁴ mol⁻¹・cm⁻¹ ml in the visible region, have been attributed to electronic transitions between molecular orbital centered on metal (orbital t_2g) and a molecular orbital centered ligand (p^* of ligand) [19] [21] (Figure 5(a)). Already for the compounds trans-[Ru(NH₃)₄(isn)(bpa)]²⁺ and trans-[Ru(NH₃)₄(4-acpy)(bpa)]²⁺, bands were obtained at 275, 325 and 400 nm (isn) and 285 and 340 nm (4-acpy). The spectral behavior reveals that for compound trans-[Ru(NH₃)₄(isn)(bpa)]²⁺, a displacement of the bands observed at 325 and 400 nm occurs as a result of substitution of the SO₂ by bpa ligand with maintenance of the band (IL) in the region of 275 nm, which is characteristic of the ligand (isn) (Figure 3); also, there is displacement of the bands 325 nm to 366 nm and 400 nm to 474 nm, which is attributed to electronic transitions between molecular orbitals centered on metal (orbital t_2g) and molecular orbital centered ligands (p^* ligand). The spectral behavior of the compound trans- [Ru(NH₃)₄ (4-acpy)(bpa)]²⁺ (Figure 4) exhibits a shift of the band at 285 nm (IL) to 275 nm and 340 nm to 382 nm, resulting from replacement of the ligand SO₂ by bpa. It also shows the appearance of an intense band at 510 nm attributed to electronic transitions between the molecular orbital centered on the metal (t_2g orbital) and the ligand (p^* ligand). The literature shows [6] [9] [19] that the trans-tetra ammine of ruthenium (II) may present more than one absorption band in the visible region when L ≠ L’, and second band MLCT is weak [20] . Comparing the ligands involved in this series of compounds, it can be observed that the pyridinic ligands, (isn and/or 4-acpy) show the pyridine ring substituent groups that change the charge density on the metal; this change is evidenced by the presence of MLCT bands with low energy (366 and 382 nm) (Figure 5(b)).

Table 1 summarizes the spectroscopic properties of the complex trans-[Ru(NH₃)₄L(L’)]⁺² reported here.

Electronic spectroscopy in the medium infrared region: The absorption spectrum in the infrared region was used to characterize the ligands coordinated to the metal according to the energy of their vibrations Figure 6. Table 2 shows the values identified are highlighted to vibrational groups and their respective wave numbers of complex trans-[Ru(NH₃)(bpa)(L)]⁺² where L = py, isn 4-acpy and 4-pic in comparison to the experimental vibrational spectra of free ligands. The displacement observed in the symmetric stretch of the ν_s(CCN) group of the complex compared to ν_s(CCN) group in the free ligand is indicative of coordination of the pyridine group to the Ru²⁺ metallic centre [22] . It was also noted that there is no significant displacements at asymmetric and symmetric stretching mode of the carbonyl group of free ligand (4-acpy and isn) compared to complex. Meanwhile, the rise of a second stretching is observed in the complexes assigned to ν_s(C = C) group of bpa ligand. It was not observed asymmetric and symmetric stretching displacement of ν_s(C = C) group of the pyridine ring between free ligand and the complex for the obtained compounds with pyridine (py), and 4-picoline (4-pic) which shows that there was no interaction at this site. The intense band observed around 1070 cm⁻¹, and attributed to the asymmetric stretching of (bpa) group, present in all of the compounds as well as the band seen in 3400 cm⁻¹ range.

From the cyclic voltammograms obtained, the parameters are: i_pa, i_pc, E_pa, E_pc, E_1/2a, and E_1/2c; these are listed in

^*This work.

Table 3. The results obtained for the potential has an uncertainty of the order of 10 mV, and for all compounds studied here, generally fit the criteria of reversibility [25] - [29] . The potential anodic and cathodic peaks for compounds are within the experimental error and are independent of the potential sweep speed. Comparing the spectral data with voltammetry, as shown in Table 4, there is a decrease in the formal potential (E_f), similar to the decreased energy observed in the electronic spectra of the monomers. This decrease can be attributed to an increase in the electron captor capacity of the substituent groups on the aromatic rings of ligands that occurs in

^arefer [23] ; ^bfree gas-phase [24] .

solvents (Donor Number), leading to an increase in the formal potential. Already in dimethylsulfoxide solvent, systems have shown evidence of electrochemical reactions, which can be attributed to the basicity of the solvent employed (high Gutmann donor number [30] ), making it possible to replace the pyridinic ligands.