- Heterobi-, tri- and tetra-metallic cyanide-bridged complexes based on pentacarbonylcyanochromate(0) and penta-, cis-tetra- and fac-tri-ammineruthenium(III) groups: Optical metal-metal charge transfer and electrochemical characteristics
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The heterobi-, tri- and tetra-metallic Robin-Day Class II mixed-valence complexes, [(OC)5Cr(μ-CN)Ru(NH3)5]2+ (CrRu), cis-[{(OC)5Cr(μ-CN)}2Ru(NH3) 4]+ (Cr2Ru) and fac-[{(OC)5Cr(μCN)}3Ru(NH3)3] (Cr3Ru) have been synthesised directly by coupling [Cr(CO)5CN]- with an appropriate penta-, tetra-or tri-ammineruthenium precursor and characterised by electrochemical, analytical and spectroscopic methods. The complexes exhibit solvent-ammine hydrogen-bonding induced solvatochromism in the MMCT energy which linearly varies with the Gutmann solvent donor number (DN) at 219, 158 and 116(±7) cm-1/DN respectively which corresponds to a linear variation of 51(± 6) cm-1/DN/NH3 group. Electrochemical and spectrosopic evidence points to the ligating equivalence of [Cr(CO)5CN]- and NH3 groups in this series. Cyclic and square-wave voltammograms, CV and SWV, show reversible couples at + 0.45 and -0.36 V (versus ferrocene) for the chromium(0/I) and ruthenium(III/II) potentials in the complex set. Dispersion in CV and peak broadening in SWV, for CrxRu (x = 2,3), indicate weak Cr-Cr coupling through the ammineruthenium centre corresponding to a separation of ~ 65 mV. We report electrochemical data for [(OC)5Cr(μ-CN)Os(NH3)5]2+ (CrOs) and its visibly spectacular solvatochromism (188 cm-1/DN) from blue to purple, red, orange and yellow colourations.
- Laidlaw,Denning
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- The unusually fast reactions between ruthenium(III)-ammine complexes and NO revisited
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The kinetics of the unusually fast reactions between [RuIII(NH3)5X](3-n)+ (Xn- = Cl-, NH3, H2O) and NO were reinvestigated in acidic aqueous solution in order to clarify the underlying reaction mechanism. The measured second-order rate constants (kNH3 = 0.30 ± 0.01 M-1 s-1, kH2O = 55.6 ± 3.2 M-1 s-1 at 26°C) are in good agreement with literature data for X = ammonia and halide. The activation parameters determined for the reactions are: ΔH≠ = 41 ± 2 kJ mol-1, ΔS≠ = -114 ± 7 J K-1 mol-1 and ΔV≠ = -13.6 ± 0.3 cm3 mol-1 for [Ru(NH3)6]3+; ΔH≠ = 34.4 ± 1.0 kJ mol-1, ΔS≠ = -132 ± 3 J K-1 and ΔV≠ = -18.0 ± 0.5 cm3 mol-1 for [Ru(NH3)5Cl]2+; and ΔH≠ = 31.0 ± 0.7 kJ mol-1 and ΔS≠ = -108 ± 2 J K-1 mol-1 for [Ru(NH3)5(H2O)]3+. Bond formation with the entering nucleophile appears to be substantial in the transition state for the reaction. An associative substitution mechanism coupled to a concerted electron transfer process to produce [RuII(NH3)5- (NO+)]3+ is proposed for all three reactions. Possible reasons for the significantly faster reaction observed in case of the aqua complex are discussed.
- Czap, Almut,Van Eldik, Rudi
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- Kinetics of reduction of aqueous hexaammineruthenium(III) ion at Pt and Au microelectrodes: Electrolyte, temperature, and pressure effects
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Rate constants kel obtained by impedance spectroscopy for the reduction of Ru(NH3)63+ at polycrystalline Pt and Au ultramicroelectrodes depend strongly on the identity and concentration of the anion present in t
- Vijaikanth, Vijendran,Li, Guangchun,Swaddle, Thomas W.
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p. 2757 - 2768
(2013/04/10)
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