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Photochemistry of the dinuclear cobalt(III) complexes (CN)/sub 5/Co(. mu. -CN)Co(NH/sub 3/)/sub 5/ and (CN)/sub 5/Co(. mu. -NC)Co(NH/sub 3/)/sub 5/. Intramolecular energy transfer between metal centers

Journal Article · · Inorg. Chem.; (United States)
DOI:https://doi.org/10.1021/ic50221a017· OSTI ID:6427784
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Irradiation of aqueous (NC)/sub 5/Co(..mu..-NC)Co(NH/sub 3/)/sub 5/ in the wavelength region 254 to 365 nm leads to photoaquation of the pentacyanocobaltate(III) center, giving Co(CN)/sub 5/H/sub 2/O/sup 2 -/ and Co(NH/sub 3/)/sub 5/CN/sup 2 +/ as products with large quantum yields (0.2 to 0.3 mol/einstein). These wavelengths represent ligand field (LF) excitation of the pentacyanocobaltate(III) chromophore; hence, efficient photoreaction of that center indicates that in this case energy transfer to the lower LF states of the pentaamminecobalt(III) chromophore is at best competitive with ligand labilization. In contrast, LF excitation of the former chromophore in the linkage isomer dinuclear complex (NC)/sub 5/Co(..mu..-CN)Co(NH/sub 3/)/sub 5/ leads to very little reaction at that site. Since Co(CN)/sub 6//sup 3 -/ is quite photoactive under these conditions, this result implies that coordination of the Co(NH/sub 3/)/sub 5//sup 2 +/ moiety to one CN provides a new pathway for rapid deactivation of the Co(CN)/sub 6//sup 3 -/ LF states. The differences between the two dinuclear complexes' photochemical behaviors are rationalized in terms of symmetry restrictions and larger Franck-Condon terms inhibiting energy transfer between the two cobalt(III) centers of (NC)/sub 5/Co(..mu..-NC)Co(NH/sub 3/)/sub 5/ relative to the linkage isomer. For comparison the complex ion Co(CN)/sub 5/(CH/sub 3/CN)/sup 2 -/ has been synthesized. Ligand field excitation of this species leads to highly efficient photoaquation of CH/sub 3/CN exclusively (phi approx. 0.4).

Research Organization:
Univ. of California, Santa Barbara
OSTI ID:
6427784
Journal Information:
Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 20:7; ISSN INOCA
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
AMMONIA
AQUEOUS SOLUTIONS
CHEMICAL REACTIONS
COBALT COMPLEXES
COMPLEXES
CYANIDES
DECOMPOSITION
DISPERSIONS
ENERGY TRANSFER
HYDRIDES
HYDROGEN COMPOUNDS
INORGANIC ACIDS
LIGANDS
MEDIUM TEMPERATURE
MIXTURES
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
PERCHLORIC ACID
PH VALUE
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
SOLUTIONS
TRANSITION ELEMENT COMPLEXES