Charge‐Transfer Isomers and Mixed‐Valence Properties

Crutchley, Robert J.

doi:10.1002/anie.200501598

Cited by 31 publications

(10 citation statements)

References 10 publications

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“…It is currently accepted that in class II-III systems solvent dynamics are averaged with respect to their contribution to ET. This is not what is observed in the systems described here (1-3), which are generally accepted as being on the class II-III borderline (Crutchley 2005). Were the solvent dynamics averaged when the solvent is in the fluid state, we would not expect to observe such dramatic changes in the ET rate upon freezing.…”

Section: Discussioncontrasting

confidence: 90%

Electron transfer at the class II/III borderline of mixed valency: dependence of rates on solvent dynamics and observation of a localized-to-delocalized transition in freezing solvents

Glover

Lear

Salsman

et al. 2007

Phil. Trans. R. Soc. A.

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The dependence of the rates of intramolecular electron transfer (ET) of mixed-valence complexes of the type {[Ru 3 O(OAc) 6 (CO)(L)] 2 -BL} K1 , where L is the pyridyl ligand and BL is the pyrazine on solvent type and temperature is described. Complexes were reduced chemically to obtain the mixed-valence anions in acetonitrile (CH 3 CN) and methylene chloride (CH 2 Cl 2 ). Rate constants for intramolecular ET were estimated by simulating the observed degree of n(CO) infrared (IR) bandshape coalescence in the mixed-valence state. In the strongly coupled mixed-valence states of these complexes, the electronic coupling, H AB , approaches l/2, where l is the total reorganization energy. The activation energy is thus nearly zero, and rate constants are in the 'ultrafast' regime where they depend on the pre-exponential terms within the frequency factor, n N . The frequency factor contains both external (solvent dynamics) and internal (molecular vibrations) contributions. In general, external solvent motions are slower than internal vibrations, and therefore control ET rates in fluid solution. A profound increase in the degree of n(CO) IR bandshape coalescence is observed as the temperature approaches the freezing points of the solvents methylene chloride (f.p. K928C) and acetonitrile (f.p. K448C). Decoupling the slower solvent motions involved in the frequency factor n N for ET by freezing the solvent causes a transition from solvent dynamics to internal vibration-limited rates. The solvent phase transition causes a localized-to-delocalized transition in the mixed-valence ions that accelerates the rate of ET.

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Section: Discussioncontrasting

confidence: 90%

Electron transfer at the class II/III borderline of mixed valency: dependence of rates on solvent dynamics and observation of a localized-to-delocalized transition in freezing solvents

Glover

Lear

Salsman

et al. 2007

Phil. Trans. R. Soc. A.

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“…In a more sophisticated fashion, Kubiak and co-workers have established experimentally [29,33] the existence of dynamic equilibrium mixtures containing "charge-transfer isomers" of mixed-valent ruthenium complexes within the molecular frameworks of [{Ru 3 (m-O)(m-CH 3 COO) 6 ( 12 C 16 O)(L')}(m-BL)-{Ru 3 (m-O)(m-CH 3 COO) 6 ( 13 C 18 O)(L'')}] (in which m-BL = pyrazine derivatives) by monitoring the n(CO) vibrations in the infrared spectra. The mixed-valent charge transfer isomers differ in the location of the odd electron, and the slightly asymmetric ligand environment around the metal centers facilitates their experimental identification.…”

Section: Access To Ultrafast Electron-transfer Dynamics Through the Smentioning

confidence: 99%

“…[29,33] The experimental evidence for the existence of bistable mixed-valent isomers 22 A and 22 B and their switching times of about 10 À12 s as inferred from temperature-dependent coalescence of carbonyl stretching bands may be eventually employed to provide a solid basis for the fabrication of molecular electronic devices. Figure 11.…”

Section: Access To Ultrafast Electron-transfer Dynamics Through the Smentioning

confidence: 99%

“…The conventional type [33] of ligand-bridged diruthenium mixed-valent complexes as dealt with in typical review articles [10][11][12][13][14][15][16][17][18] can be summarized as follows: It is a usually dinuclear M II /M III complex with simple, apparently redoxinnocent ancillary ligands (L) and bridging ligands (BL). Its straightforward classification following the Robin and Day scheme [2] (see Section 2.11) is based on mostly parallel electrochemical and optical-spectroscopic manifestations of metal-metal interaction and on the metal-metal distance.…”

Section: New Developments: An Overviewmentioning

confidence: 99%

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Unconventional Mixed‐Valent Complexes of Ruthenium and Osmium

2007

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Recent developments have helped to extend the repertoire of mixed-valent ruthenium and osmium complexes beyond conventional systems. This extension has been achieved by using sophisticated ligands and by creating more variegated coordination patterns. The strategies employed include the use of multidentate ligands (which give rise to multinuclear and chelate complexes) and the use several redox active components (non-innocent ligands and oxidation-state ambivalence). The results offer enhanced chemical insight into metal-ligand electron-transfer situations and suggest that mixed-valent materials may eventually be exploited in molecular electronics and molecular computing.

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“…Molecular vibrations and solvent modes are coupled which have different time scales and coupling mechanisms. Different measurements can appear to give different results (Brown 1980;Prassides 1991;Demadis et al 2001;Brunschwig et al 2002;Crutchley 2005;D'Alessandro & Keene 2006a,b).…”

Section: Introductionmentioning

confidence: 99%

Probing the localized-to-delocalized transition

Concepcion

Dattelbaum

Meyer

et al. 2007

Phil. Trans. R. Soc. A.

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Detailed understanding of the transition between localized and delocalized behaviour in mixed valence compounds has been elusive as evidenced by many interpretations of the Creutz-Taube ion, [(NH 3 ) 5 Ru(pz)Ru(NH 3 ) 5 ] 5C . In a review in 2001, experimental protocols and a systematic model to probe this region were proposed and applied to examples in the literature. The model included: (i) multiple orbital interactions in ligand-bridged transition metal complexes, (ii) inclusion of spin-orbit coupling which, for dp 5 -dp 6 complexes, leads to five low-energy bands, two from interconfigurational (dp/dp) transitions at the dp 5 site and three from intervalence transfer transitions, (iii) differences in time scale between coupled vibrations and solvent modes which can result in solvent averaging with continued electronic asymmetry defining 'class II-III', an addition to the Robin-Day classification scheme, and (iv) delineation of coupled vibrations into barrier vibrations and 'spectator' vibrations. The latter provide direct insight into localization or delocalization and time scales for electron transfer. In this paper, the earlier model is applied to a series of mixed-valence molecules.

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Charge‐Transfer Isomers and Mixed‐Valence Properties

Cited by 31 publications

References 10 publications

Electron transfer at the class II/III borderline of mixed valency: dependence of rates on solvent dynamics and observation of a localized-to-delocalized transition in freezing solvents

Electron transfer at the class II/III borderline of mixed valency: dependence of rates on solvent dynamics and observation of a localized-to-delocalized transition in freezing solvents

Unconventional Mixed‐Valent Complexes of Ruthenium and Osmium

Probing the localized-to-delocalized transition

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