Inclusion of spin-orbit and low-symmetry effects in a vibronic coupling (PKS) model for mixed-valence dimers: application to the Creutz-Taube ion

Neuenschwander, K.; Piepho, S. B.; Schatz, P. N.

doi:10.1021/ja00312a010

Cited by 28 publications

(7 citation statements)

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“…There have been other attempts in the literature to incorporate more than one orbital on each subunit of a mixed-valent dimer in a vibronic interaction model to fit the observed IVCT transition band shape. Specifically, Piepho and co-workers and Ondrechen et al − included more than one t 2g orbital on each of the two Ru centers in the Creutz−Taube ion in order to theoretically simulate the observed IVCT band shape. On the basis of the resulting electronic structure, Borshch and Kotov calculated the adiabatic potentials of the complex. , In all of the mentioned treatments of the Creutz−Taube ion, mixing of the subunit d orbitals was assumed to be mediated by spin−orbit coupling.…”

Section: Discussionmentioning

confidence: 99%

Low-Energy Bands of Ferrocene−Ferrocenium Dimers: Bandshape Analysis with a Four-Level Two-Mode Vibronic Coupling Configuration Interaction (VCCI) Model Including Asymmetry

Warratz

Tuczek

2009

Inorg. Chem.

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Ferrocene-ferrocenium dimers exhibit a double-peak intervalence charge-transfer (IVCT) band in the NIR/MIR region, which is analyzed in terms of a four-level, two-mode vibronic coupling configuration interaction (VCCI) scheme. Besides providing satisfactory fits of the measured spectra, the model also gives electronic and vibronic coupling parameters as well as CI mixing coefficients. A temperature-dependent asymmetry of the potential is introduced in order to describe the temperature dependence of the solid-state spectra and account for complementary Mossbauer data, which indicate a temperature-driven electron localization-delocalization transition in the singly bridged radical cations. The VCCI model is also successfully applied to the doubly bridged Fe(II)-Fe(III) bisfulvalenide dimer, which exhibits a double-peak IVCT transition as well. The VCCI analysis reveals that all dimers have a one-minimum potential in the ground state, leading in the absence of asymmetry to class III behavior (electron delocalization). If electron localization corresponding to class II characteristics occurs, it is due to an asymmetric (but still one-minimum) potential and not, as usual, to a double-minimum potential, explaining the class II-III borderline behavior observed for these systems.

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Section: Discussionmentioning

confidence: 99%

Low-Energy Bands of Ferrocene−Ferrocenium Dimers: Bandshape Analysis with a Four-Level Two-Mode Vibronic Coupling Configuration Interaction (VCCI) Model Including Asymmetry

Warratz

Tuczek

2009

Inorg. Chem.

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“…The energycoordinate curves that result are functions of H ab , the quantum spacing for the coupled vibration and the reorganization energy (Piepho et al 1978;Neuenschwander et al 1985;Piepho 1990;Reimers & Hush 1996).…”

Section: Background (A ) Theorymentioning

confidence: 99%

“…In the quantum PKS treatment, the Schrödinger equation is solved with the nuclear kinetic energy operator included giving expressions for energies and wave functions that depend on both electron and nuclear coordinates. The energycoordinate curves that result are functions of H ab , the quantum spacing for the coupled vibration and the reorganization energy (Piepho et al 1978;Neuenschwander et al 1985;Piepho 1990;Reimers & Hush 1996).…”

Section: (A ) Theorymentioning

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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“…The “two-state” model (i.e., the description of a mixed-valence compound in terms of interactions between the two localized states {L x M n }(μ-bridge){M n +1 L x } and {L x M n +1 }(μ-bridge){M n L x }) provides a backdrop against which a host of different and more complex electronic situations can be contrasted. For example, the coupling of vibrational and electronic processes has long been recognized, and various models have been proposed to account for the effect of vibrational modes associated with the bridging ligand on the intramolecular electron exchange reaction. − Mixed-valence complexes that are “almost delocalized” have been coined as class II−III and provide fascinating opportunities to distinguish and compare the contributions from inner- and outer-sphere reorganization in the electron-transfer event. ,, Mixed-valence complexes derived from heavy-metal atoms with pronounced spin−orbit coupling constants give rise to multiple IVCT processes as, for example, the degeneracy of the metal orbitals in a pseudo-octahedral field is lifted, ,, and there is an increasing body of evidence that suggests that similar effects can be observed in mixed-valence complexes of the lighter metals with low local symmetry at the metal centers. , The mixing of electronic character from the bridging and ancillary ligands with the metal in the redox sites leads to more complex multiple-well potential energy surfaces, which not only changes the shape of the IVCT band but also introduces new transitions with important MLCT character into the optical spectrum. − Within systems where the bridge orbitals of the appropriate symmetry are close in energy to the metal-based orbitals, the role of the bridge in mediating the electron-exchange event, through either superexchange or hopping mechanisms, also becomes important. This mixing of metal and ligand based states should be distinguished from situations in which the metal- and ligand-based orbitals mix significantly, the latter situation being especially common in organometallic complexes .…”

Section: Introductionmentioning

confidence: 99%

Molybdenum Complexes of C,C-Bis(ethynyl)carboranes: Design, Synthesis, and Study of a Weakly Coupled Mixed-Valence Compound

et al. 2010

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The design and study of organometallic mixed-valence complexes is complicated by the mixing of metal d and bridging ligand π orbitals, which often makes the assignment of metal oxidation states ambiguous. However, in the case of complexes based on the cycloheptatrienyl-ligated molybdenum fragment, Mo(dppe)(η-C 7 H 7 ), the strong ring to metal π bonding and metal to ring δ back-bonding interactions stabilize four of the metal d orbitals, while the d z 2 orbital is destabilized by filled-filled interactions with the a-type MO of the C 7 H 7 ring. When the Mo(dppe)(η-C 7 H 7 ) auxiliary is used in conjunction with a 1,12-bis(ethynyl)-1,12-carbaborane-based bridging ligand, a weakly coupled (Robin and Day class II) mixed-valence system, [{Mo(dppe, with well-defined molybdenum oxidation states can be prepared. The near-IR region of [2] þ exhibits three intervalence charge transfer (IVCT) transitions and two lower intensity interconfigurational (or dd) transitions, which have been resolved through spectral deconvolution. The band shape of the lowest energy IVCT transition associated with [2] þ , which arises from electron exchange between the d z 2-type orbitals at the two Mo centers, is in excellent agreement with the predictions of the Hush two-state model for weakly coupled mixed-valence complexes. The halfheight bandwidths of the higher energy IVCT transitions, which arise from transitions between lower lying metal orbitals that have symmetry properties that permit more significant mixing with the bridging ligand, are in less good agreement with the Hush model, due to the breakdown of the two-state approximation through the greater involvement of the bridge-based orbitals in those transitions.

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Inclusion of spin-orbit and low-symmetry effects in a vibronic coupling (PKS) model for mixed-valence dimers: application to the Creutz-Taube ion

Cited by 28 publications

References 2 publications

Low-Energy Bands of Ferrocene−Ferrocenium Dimers: Bandshape Analysis with a Four-Level Two-Mode Vibronic Coupling Configuration Interaction (VCCI) Model Including Asymmetry

Low-Energy Bands of Ferrocene−Ferrocenium Dimers: Bandshape Analysis with a Four-Level Two-Mode Vibronic Coupling Configuration Interaction (VCCI) Model Including Asymmetry

Probing the localized-to-delocalized transition

Molybdenum Complexes of C,C-Bis(ethynyl)carboranes: Design, Synthesis, and Study of a Weakly Coupled Mixed-Valence Compound

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