Environmentally induced multiple intervalence transitions in a symmetrically substituted analog of the Creutz-Taube ion

Roberts, Jody A.; Hupp, Joseph T.

doi:10.1021/ic00028a004

Cited by 25 publications

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“…This is a small effect for the high-frequency ν(CN) mode in cis -[Ru(bpy) 2 (py)(CN)] + since the solvent shifts are <1% of the quantum spacing, Figure and Table . It may be more important for low-frequency skeletal modes 30a…”

Section: Discussionmentioning

confidence: 99%

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Influence of Solvent on the Spectroscopic Properties of Cyano Complexes of Ruthenium(II)

et al. 1996

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UV−visible spectra, emission spectra, and RuIII/II reduction potentials have been measured for cis-[Ru(bpy)2(py)(CN)]+ (bpy is 2,2‘-bipyridine; py is pyridine), cis-Ru(bpy)2(CN)2, [Ru(tpy)(CN)3]- (tpy is 2,2‘:6‘,2‘‘-terpyridine), [Ru(bpy)(CN)4]2-, and [Ru(MQ+)(CN)5]2- (MQ+ is N-methyl-4,4‘-bipyridinium cation) in twelve solvents. The shifts in the metal-to-ligand charge transfer (MLCT) absorption (E abs) or emission (E em) band energies with solvent increase linearly with the number of cyano ligands and correlate well with the Gutmann “acceptor number” of the solvent. Intraligand π → π* band energies also correlate with acceptor number, but with only ∼30% of the shifts for the MLCT bands. The solvent dependence arises through mixing of the π → π* transitions with lower energy MLCT transitions. MLCT absorption and emission spectra are convolutions of overlapping vibronic components, and a Franck−Condon analysis of emission spectral profiles for cis-Ru(bpy)2(CN)2* has been used to evaluate the energy gap, E 0, and χ‘0,gs, where χ‘0,gs is the sum of the solvent reorganizational energy for the ground state below the excited state and the inner-sphere reorganizational energy of the low-frequency modes, χi,L, is treated classically. Both E 0 and χ‘0,gs correlate well with acceptor number with ΔE 0/ΔAN = 44 ± 2 cm-1/AN unit and Δχ0,gs/ΔAN = 21 ± 3 cm-1/AN unit if it is assumed that χi,L is solvent independent. From electrochemical measurements and the difference in E 1/2 values for metal oxidation and bpy reduction, ΔΔG°es/ΔAN ≃ 70 ± 7 cm-1/AN unit with ΔG°es the free energy of the excited state above the ground state. These correlations show that the energy gap is far more sensitive to solvent than χ0,gs. Δχ0,gs/ΔAN can also be estimated from the relation ΔΔG°es/ΔAN = ΔE 0/ΔAN + Δχ‘0,gs/ΔAN, which gives Δχ0,gs/ΔAN = 26 ± 7 cm-1/AN unit. The solvent reorganizational energy of the excited state above the ground state is χ0,es. Its variation with acceptor number can be estimated from the relation ΔE abs/ΔAN − ΔG°es/ΔAN = Δχ0,es (=13 ± 8 cm-1/AN) or from ΔE abs/ΔAN − ΔE em/ΔAN − Δχ0,gs/ΔAN (=14 ± 8 cm-1/AN), if χi,L is solvent independent. These results suggest that χ0,gs is more sensitive to solvent than χ0,es by as much as a factor of 2. ΔE em/ΔAN = 45 ± 3 cm-1/AN unit ≃ ΔE 0/ΔAN = 44 ± 2 cm-1/AN unit, showing that the emission maximum gives accurate information about the solvent dependence of the energy gap. A model is invoked to explain the acceptor number dependence. It is based on electron pair donation from the lone pair on cyanide to individual solvent molecules through donor-acceptor interactions. The model is consistent with variations in ν(CN) with acceptor number in cis-[Ru(bpy)2(py)(CN)]+ and in E 1/2(RuIII/II) for the series of complexes. In this model it is assumed that donor−acceptor interactions are more important in the ground state than in the excited state, consistent with pK a measurements, and that they are additive in the number of cyanide ligands. These and H-bonding interactions in related ammine c...

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Section: Discussionmentioning

confidence: 99%

“…It has been shown (see ref a) for [Ru(bpy)(NH 3 ) 4 ] 2+ that selected vibrations that contribute to the internal reorganizational energy are modulated significantly by specific ammine−solvent hydrogen bonding interactions. Similar effects may exist for the cyano complexes.…”

Section: Referencesmentioning

confidence: 99%

Influence of Solvent on the Spectroscopic Properties of Cyano Complexes of Ruthenium(II)

et al. 1996

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“…The investigations of optical CT in mixtures of acetonitrile and DMSO carried out by the groups of Hupp ,, and Curtis provide some of strongest evidence for these “specific” solvent effects in the condensed phase. They found that E op exhibited a more pronounced dependence on solution composition for DMSO mole fractions below 0.1 than the dielectric properties of the bulk solvent mixture in studies involving metal-to-metal CT in mixed-valence Ru II −Ru III dimers and MLCT in Ru II complexes having ammine ligands.…”

Section: Discussionmentioning

confidence: 99%

Metal-to-Ligand Charge Transfer in the Gas-Phase Cluster Limit

et al. 1998

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The solvent dependence of metal-to-ligand charge transfer (MLCT) in the bis(2,2‘,2‘‘-terpyridyl)iron(II) complex, [Fe(terpy)2]2+, isolated in small gas-phase clusters with one or four molecules of the polar, organic solvents acetone, acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, methanol, and pyridazine is reported. The shift in the maximum of the MLCT band, E op, for [Fe(terpy)2·(solvent)1]2+ clusters, measured using laser photofragmentation mass spectrometry, relative to the corresponding values in bulk solution ranges from +601 cm-1 for acetone to +764 cm-1 for pyridazine. The solvent dependence of the outer-sphere reorganization energy predicted by a dielectric continuum model provides a context for comparing E op values determined for MLCT in [Fe(terpy)2·(solvent) n ]2+ clusters (n = 1, 4) with those measured in solution. A model derived from Kirkwood's equation for the mutual electrostatic interaction energy of an ion and a polar medium predicts that the solvent reorganization energy associated with MLCT in [Fe(terpy)2]2+ is a linear function of (1 − D op)/(2D op + 1), where D op is the optical dielectric constant of the bulk solvent. A linear relationship between E op and (1 − D op)/(2D op + 1) is observed not only in the bulk solvents, as anticipated, but also in clusters containing as few as four solvent molecules.

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“…Systems of this genre have provided important experimental insights into the roles of solvent dynamics [2][3][4][5][6][7][8][9][10][11][12][13][14][15], ion-pairing [16][17][18][19][20][21], encapsulation [22,23], temperature [24][25][26][27][28], and redox asymmetry [29,30], and they have been used as model systems to verify the salient predictions of several important theoretical models that describe the activation barrier to electron transfer [31][32][33][34][35].…”

Section: Introductionmentioning

confidence: 99%

Diastereoisomers as probes for solvent reorganizational effects on IVCT in dinuclear ruthenium complexes

D’Alessandro

Keene

2006

Chemical Physics

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Environmentally induced multiple intervalence transitions in a symmetrically substituted analog of the Creutz-Taube ion

Cited by 25 publications

References 0 publications

Influence of Solvent on the Spectroscopic Properties of Cyano Complexes of Ruthenium(II)

Influence of Solvent on the Spectroscopic Properties of Cyano Complexes of Ruthenium(II)

Metal-to-Ligand Charge Transfer in the Gas-Phase Cluster Limit

Diastereoisomers as probes for solvent reorganizational effects on IVCT in dinuclear ruthenium complexes

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