The complex trans-[Ru(NH 3 ) 4 NO(H 2 O)]Cl 3 ‚H 2 O has been isolated as a decomposition product of the dimeric cation [{Ru(NH 3 ) 4 NO} 2 (µ-S 2 )] 6+ . The elemental analysis and electronic, infrared, X-ray, and ESR spectroscopies fit well with the formulation trans-[Ru(NH 3 ) 4 NO(H 2 O)]Cl 3 ‚H 2 O. The ν NO (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 reactionThe 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(NH 3 ) 4 L(H 2 O)] n+ + H 2 O T trans-[Ru-(NH 3 ) 4 L(OH)] (n-1)+ + H 3 O + , where L ) NO + and CO, respectively. The substitution of the coordinated water molecule in trans-[Ru(NH 3 ) 4 (H 2 O)NO] 3+ by chloride ions proceeds about 30-fold times slower than in [Ru-(NH 3 ) 5 (H 2 O)] 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(NH 3 ) 4 (H 2 O)L] n+ (L ) CO and NO + ) species are discussed on the basis of DFT and ZINDO/S calculations.

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In this work, we present a computational investigation on the structure and energetics of eleocarpanthraquinone, a newly isolated polyphenolic anthrone-antraquinone. Properties such as bond lengths, angles, atomic charges, bond dissociation enthalpies (BDEs), and ionization potential (IP) were determined through the use of density functional theory (DFT). The B3LYP and M06-2X exchange-correlation functionals were employed along with the 6-31+G(d,p), 6-31++G(d,p), and 6-311+G(d,p) basis sets for performing computations in the gas-phase, water, methanol, and ethanol. The conformation presenting all the hydroxyl groups undergoing hydrogen-bond interactions with neighboring oxygen atoms (conformation 5) was assigned as the most stable structure while its counterpart presenting no hydrogen-bond interaction was found to be 36.45 kcal/mol less stable than conformation 5 in the potential energy surface probed at the B3LYP/6-311+G(d,p) level of theory in the gas-phase, for instance. More importantly, the lowest O-H bond dissociation enthalpy was determined to be 93.80 kcal/mol at the B3LYP/6-311+G(d,p) level of theory in water against the 146.58 kcal/mol regarding the IP computed at the same approach, suggesting the hydrogen atom transfer mechanism as being preferred over the single electron transfer mechanism in regards to the antioxidant potential for the case of eleocarpanthraquinone; the same conclusion was drawn from the outcomes of all the other approaches used.