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Dessapt, R., Collet, M., Coue, V., Bujoli-Doeuff, M., Jobic, S., Lee, C. & Whangbo, M.-H. (2009) Kinetics of Coloration in Photochromic Organoammonium Polyoxomolybdates. Inorg. Chem. 48 574–580.
Added by: Laurent Cournède (2016-03-10 21:41:25) |
| Type de référence: Article DOI: 10.1021/ic8013865 Numéro d'identification (ISBN etc.): 0020-1669 Clé BibTeX: Dessapt2009 Voir tous les détails bibliographiques  |
Catégories: MIOPS Mots-clés: approximation, crystal-structure, octamolybdate Créateurs: Bujoli-Doeuff, Collet, Coue, Dessapt, Jobic, Lee, Whangbo Collection: Inorg. Chem. |
Consultations : 13/604
Indice de consultation : 1% Indice de popularité : 0.25% |
| Résumé |
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The excellent photochromic properties of (H(2)DABCO)(2)(HDMA)(0.5)Na-0.75(H3O)(0.75)[Mo8O27]center dot 3H(2)O (4), a new member of the (H(2)DABCO)(2)(A)(x)[Mo8O27]center dot nH(2)O series, are compared with those of (H(2)DABCO)(2)(NH4)(2)[Mo8O27]center dot 4H(2)O (1), (H(2)DABCO)(2)(H(2)pipz)[Mo8O27] (2), and (H(2)pipz)(3)[Mo8O27] (3). All these powdered materials turn from white to purple under illumination at 365 nm, which is associated with photoreduction of Mo6+ cations into Mo5+ cations. We show that the rates of coloration, which increase in the order 1 {<} 3, 2 {<} 4, are related to the decrease in the concentration of reducible Mo6+ centers with irradiation time and follow a second-order reaction law because the event of light absorption at a reducible Mos+ site does not necessarily coincide with that of the N+-H bond breaking in the N+-H center dot center dot center dot O hydrogen bond associated with the Mo6+ site. First-principles density functional electronic structure calculations were carried out to find that this trend correlates with the homolytic dissociation energies of the N+-H bonds in the organic cations HDMA(+), H(2)pipz(2+), H(2)DABCO(2+), and NH4+. This observation is consistent with a photochromic mechanism based on the homolytic cleavage of N+-H bonds rather than on the heterolytic cleavage of N+-H bonds.
Added by: Laurent Cournède |