Water π-Donation in trans-Tetraammineruthenium(II):  Effect on Coordinated-Water Properties Induced by a Trans NO Ligand

• Published in: Inorganic chemistry Vol. 38; no. 25; pp. 5660 - 5667
• Main Authors: Bezerra, Cícero W. B, da Silva, Sebastião C, Gambardella, Maria T. P, Santos, Regina H. A, Plicas, Lidia M. A, Tfouni, Elia, Franco, Douglas W
• Format: Journal Article
• Language: English
• Published: American Chemical Society 13-12-1999
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic990210g

The complex trans-[Ru(NH3)4NO(H2O)]Cl3·H2O has been isolated as a decomposition product of the dimeric cation [{Ru(NH3)4NO}2(μ-S2)]6+. The elemental analysis and electronic, infrared, X-ray, and ESR spectroscopies fit well with the formulation trans-[Ru(NH3)4NO(H2O)]Cl3·H2O. The νNO (1912 cm- 1) observed and the ∠(Ru−N−O) = 178.1°(5) are consistent with the nitrosonium character of the NO ligand. Cyclic voltammetry showed only one redox process in the range −0.5 to +1.2 V, which was attributed to the reaction trans-[(H2O)(NH3)4RuII(NO+)]3+ + e- ↔ trans-[(H2O)(NH3)4RuII(NO0)]2+. The pK a values 3.1 ± 0.1 and 7.7 ± 0.1 (μ = 0.10 M, NaCl) have been measured for the reaction trans-[Ru(NH3)4L(H2O)] n + + H2O ↔ trans-[Ru(NH3)4L(OH)]( n -1)+ + H3O+, where L = NO+ and CO, respectively. The substitution of the coordinated water molecule in trans-[Ru(NH3)4(H2O)NO]3+ by chloride ions proceeds about 30-fold times slower than in [Ru(NH3)5(H2O)]3+ (k Cl _ = 8.7 × 10-5 M-1 s-1 and 3.7 × 10-6 M-1 s-1, respectively; 40 °C, μ = 2.0 NaCl, [H+] = 1.0 × 10-2 mol L-1). Quantum mechanical DFT calculations show that the mixing between the lone pair of the oxygen, π in character, and the d xz orbital of the metal is linearly related to the pK a of the water ligand and to the water lability. The calculations have also shown that the π−d mixing is strongly dependent on the trans ligand L. The electronic spectra of the trans-[Ru(NH3)4(H2O)L] n + (L = CO and NO+) species are discussed on the basis of DFT and ZINDO/S calculations.