Water pi-donation in trans-tetraammineruthenium(II): Effect on coordinated-water properties induced by a trans NO ligand

The complex trans-[Ru(NH3)(4)NO(H2O)]Cl-3. H2O has been isolated as a decom position product of the dimeric cation [{Ru(NH3)(4)NO}(2) (mu-S-2)](6+). Th e elemental analysis and electronic, infrared, X-ray, and ESR spectroscopie s fit well with the formulation trans-[Ru(NH3)(4)NO(H2O)]Cl-3. H2O. The v(N O) (1912 cm(-1)) observed and the <(Ru-N-O) = 178.1 degrees(5) are consiste nt with the nitrosonium character of the NO ligand. cyclic voltammetry show ed only one redox process in the range -0.5 to +1.2 V, which was attributed to the reaction trans-[(H2O)(NH3)(4)Ru-II(NO+)](3+) + e(-) <----> trans-[( H2O)(NH3)(4)RuII(NO0)](2+). The pK(a) values 3.1 +/- 0.1 and 7.7 +/- 0.1 (m u = 0.10 M, NaCl) have been measured for the reaction trans-[Ru(NH3)(4)L(H2 O)](n+) + H2O <----> trans-[Ru-(NH3)(4)L(OH)]((n-1)) + H3O+ where L = NO+ a nd 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 x 10(-5) M-1 s(-1) and 3.7 x 10(-6) M-1 s(-1), respectively; 40 degrees C, mu = 2.0 NaCl, [H+] = 1 .0 x 10(-2) mol L-1). Quantum mechanical DFT calculations how that the mixi ng between the lone pair of the oxygen, pi in character, and the d(xz) orbi tal of the metal is linearly related to the pK(a) of the water ligand and t o the water lability. The calculations have also shown that the pi-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 th e basis of DFT and ZINZDO/S calculations.