Garfield G. Sadler

Properties of ruthenium bipyridyl dimers bridged by disubstituted anthraquinones

Abstract Ru(bpy) 2 Cl 2 reacts with 1, 4-DHAQ, 1, 5-DHAQ and 1, 4-AHAQ to form dinuclear complexes. Its reaction with 1, 8-DHAQ produces a monomer. Both 1, 4-DHAQ and 1, 4-AHAQ produce stable mixed valence complexes when oxidized, and show greater separation of ruthenium oxidation potentials than the 1, 5-DHAQ complex. K c has been calculated to be 3.7 × 10 4 for the 1, 4-DHAQ complex, 1.3 × 10 8 for the 1, 4-AHAQ complex, and 3.4 × 10 2 for the 1, 5-DHAQ complex. In all cases E 1/2 (1) for the dimers is less positive than E 1/2 (1) for the monomeric 1, 8-DHAQ complex. Spectral studies of the mixed valence states showed IT bands at approximately 2000 nm in acetonitrile for the 1, 4-DHAQ complex and at 1368 nm in acetonitrile for the 1, 4-AHAQ complex. Solvent dependence was observed for the IT band for the latter complex. The experimental evidence indicates that the three dinuclear complexes may be class II mixed valence dimers.

Properties and kinetics of dihydroxy- and diaminoanthraquinone ruthenium bipyridyl dimers

Ru(bpy)2Cl2 (bpy: 2,2′-bipyridine) reacts with 1,4-diaminoanthraquinone (1,4-DAAQ) to produce a dimeric complex which precipitates from solution in its mixed-valence form. Redox couples show that the rutheniums are easier to oxidize than those in the corresponding 1,4-DHAQ (1,4-dihydroxyanthraquinone) and 1,4-AHAQ (1-aminon-4-hydroxyanthraquinone) dimers and give a value of 2.8 × 106 for Kcom. Visible absorption bands are broad and may be combinations of transitions. The IT band in acetonitrile shows structure with λmax (log ϵ) and 845 nm (3.5), 1493 nm (4.11) and 2028 nm (4.04). Preliminary kinetic studies of the S2O82 oxidation of the 1,4-DHAQ, 1,4-AHAQ and 1,4-DAAQ dimers show a faster oxidation of the fully reduced form (|2.2|) followed by a slower oxidation of the mixed-valence form (z.sfnc;2.3z.sfnc;). No mechanism could be determined for the faster oxidation. However, the slower oxidation appeared to be first order in both dimer and S2O82−, and involved ion pairing, Kip was determined to be 13 for the 3+,2− ion pair. Values for ket were found to parallel the second ruthenium oxidation potential for the dimers, and were found to be 6 × 10 4, 8 × 10 4 and 1.1 × 10 2 M 1 s 1 for the 1,4-DHAQ, 1,4-AHAQ and 1,4-DAAQ dimers, respectively, at 25°C.

The synthesis and characterization of monomeric complexes of Ru(bpy)2 with dihydroxyanthraquinones

Abstract The monomeric complexes, Ru(bpy) 2 1,4-DHAQ + and Ru(bpy) 2 1,5-DHAQ + (bpy=2,2′-bipyridine and DHAQ=dihydroxyanthraquinone), were synthesized by the reaction of Ru(bpy) 2 Cl 2 ·2H 2 O with an excess of either 1,4-DHAQ or 1,5-DHAQ. The complexes were purified chromatographically and characterized spectroscopically and electrochemically. Comparisons between the data for these monomers and data from the corresponding free ligands and ruthenium bipyridyl dimers were made. The lowest energy spectral transition in the visible region was assigned as an MLCT transition to the DHAQ based on the red shifting from monomer to the corresponding dimer and the solvatochromism of the transition. In aqueous solution the p K a for both the 1,4- and 1,5-DHAQ monomer was determined to be 10.1±0.2 and for the 1,8-DHAQ monomer, 10.5±0.2. In all cases, p K a1 of the uncomplexed dihydroxyanthraquinones was more acidic measured under the same conditions. From the properties of the coordinated DHAQs attempts were made to evaluate whether they were σ donating or π accepting.

Dinuclear complexes of transition metals containing carbonate ligands. VIII. Kinetics and mechanism of carbon dioxide uptake by the tri-μ-hydroxo-bis (1,5-diamino-3-aza-pentane)cobalt(III) ion in weakly basic aqueous carbonate solution

Abstract The kinetics of formation of the complex ion, μ-carbonato-di-μ-hydroxo-bis((1,5-diamino-3-aza-pentane) cobalt(III), from the tri-μ-hydroxo-bis((1,5-diamino-3-aza-pentane(III)cobalt(III)) ion in aqueous buffered carbonate solution have been studied spectrophotometrically at 295 nm over the ranges 20.0⩽θ°C⩽34.8, 8.03⩽pH⩽9.44, 5 mM⩽ [CO32−⩽35 mM and at an ionic strength of 0.1 M (LiClO4). On the basis of the kinetic results a mechanism, involving rapid cleavage of an hydroxo bridge followed by carbon dioxide uptake with subsequent bridge formation, has been proposed. At 25 °C, the rate of the carbon dioxide uptake is 0.58 M−1 s−1 with ΔH≠ = (13.2±0.7) kcal mol−1 and ΔS≠ = (−15.1 ± 0.7) cal deg−1 mol−1. The results are composed with those obtained for several mononuclear cobalt(III) and one dinuclear cobalt(III) complexes.

Dinuclear complexes of transition metals containing carbonate ligands. IV: Synthesis and characterization of some novel dinuclear complexes derived from the complex, μ-amido-μ-hydroxotetraamminebis(carbonato)cobalt(III))

Abstract Five novel dinuclear cobalt(III) complexes of the type [(NH 3 ) 4 Co(μ-NH 2 )(μ-OH)CoL 4 ], where L = H 2 O, CN, NO 2 , 1 2 NTA and N 3 , were prepared from the recently isolated complex [(NH 3 ) 4 Co(μ-NH 2 )(μ-OH)Co(CO 3 ) 2 ]. The complexes were characterized by UV-visible and infra-red spectroscopy. The acid dissociation constants of the terminal water molecules in the complex [(NH 3 ) 4 Co(μ-NH 2 )(μ-OH)Co(H 2 O) 4 ] 4+ were determined by pH-metric titration.

Kinetics and mechanism of the decomposition of μ-amido-μ-hydroxo(tetraamminecobalt(III)(tetraaquacobalt(III) ion in acidic aqueous solution

The title complex undergoes decomposition in acidic aqueous solution resulting in equimolar concentration of aquapentaamminecobalt(III) and hexa- aquacobalt(II). The kinetic studies over the ranges of 0.048 M ⩽ [H+] ⩽ 0.385 M, 25 ⩽ θc ⩽ 41.5°C and at I = 0.5 M reveals that the intricate mechanism involves protonation equilibrium of the title complex, followed by a rate determining bridge cleavage. The further follow-up reaction is a fast electron transfer process to form products. The rate expression derived from the mechanism is kobs = k1K1[H+]/(1 + K1[H+]) where the values of k, and K, are found to be 8.9 × 10−4 s−1 and 3.5 M−1 respectively at 25 °C. The results are compared with that obtained for the decomposition reactions of mononuclear aquaammine complexes of cobalt(III).

Dinuclear complexes of transition metals containing carbonate ligands Part IX. Kinetics and mechanism of decarboxylation and formation of the μ-amido-μ-carbonato-bis(bis(ethylenediamine)cobalt(III)) ion in aqueous solution

Abstract The title compound has been prepared and characterized for the first time. The kinetics of acid hydrolysis of this compound leading to the μ-amido-μ- hydroxo-bis(bis(ethylenediamine)cobalt(III)) ion have been studied spectrophotometrically in the range 0.9 M ⩾ [H + ] ⩾ 0.01 M and 49.1 °C ⩾ θ ⩾ 40.3 °C at an ionic strength ( I ) of 1.0 M. The k obs values have been found to be completely independent of [H + ] and this has been explained by a suitable mechanistic scheme. The kinetics of base hydrolysis have been studied over the range 0.7 M ⩾ [OH − ] ⩾ 0.025 M at 40 °C and I = 1.0 M. The results are consistent with the mechanistic scheme where there is a rapid preequilibrium followed by a rate determining step resulting in a μ-amido-dihydroxo complex species. The kinetics of formation of the title complex cation from the μ-amido-μ-hydroxobis(bis(ethylenediamine)cobalt(III)) ion in aqueous buffered carbonate solution have also been studied spectrophotometrically over the ranges 0.05 M ⩾ [CO 3 ] T ⩾ 0.02 M and 9.11 ⩾ pH ⩾ 8.54 at 40 °C and I = 0.1 M. On the basis of kinetic evidence, a mechanism is proposed in which the μ-amido-μ-hydroxo species undergoes bridge cleavage followed by an attack by aqueous CO 2 to form the μ-carbonato species. The results are compared to those of other dinuclear cobalt(III) complexes previously studied.