Intervalence energy effects accompanying double crown encapsulation of the Creutz-Taube ion: An interpretation based on three-site mixing

Journal Article · Wed Sep 14 04:00:00 EDT 1994 · Inorganic Chemistry

DOI:https://doi.org/10.1021/ic00097a038· OSTI ID:457871

Hupp, J T; Dong, Yuhua ^[1]

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1. Northwestern Univ., Evanston, IL (United States)

Recently, the authors reported the profound effects of second-sphere crown either binding upon the redox energetics and intervalence spectroscopy of selected mixed-valence species. (Crown/metal complex association is driven primarily by ether oxygen/ammine hydrogen interactions, where the H-bond-donating capability of NH{sub 3} is greatly enhanced by coordination to a transition-metal cation.) For delocalized species such as the Creutz-Taube ion and its derivatives, asymmetric binding of a single crown can significantly perturb the basic electronic structure of the system, resulting in striking shifts in intervalence absorption energies, substantial changes in intervalence line shapes, and drastic redistributions of intervalence related Franck-Codon activity. Collectively these effects have been attributed to the possible onset of asymmetry-induced valence localization or partial localization. Consistent with that interpretation, binding of a second crown ether largely restores the original spectra (and, of course, the overall supramolecular symmetry). Nevertheless, closer examination of the available data for doubly bound or encapsulated complexes shows the modest spectral changes (in comparison to the case of free species) do accompany the binding. Most notably, intervalence spectra become somewhat narrower and are shifted detectably in energy. These effects, while small, are difficult to understand within the context of standard two-site models for valence delocalization. The authors show here that related effects occur in the visible portion of the electronic spectrum, that the effects in both spectral regions increase with increasing macrocycle size, and that the effects can be correlated with previously observed, crown-induced electrochemical effects. The authors additionally show that the multiplicity of spectral effects can be explained - at least qualitatively - on the basis of a three-site description of electronic delocalization.

• Sponsoring Organization: USDOE
• OSTI ID: 457871
• Journal Information: Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 19 Vol. 33; ISSN 0020-1669; ISSN INOCAJ
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ABSORPTION SPECTROSCOPY
CROWN ETHERS
ELECTRONIC STRUCTURE
RUTHENIUM COMPLEXES
VALENCE