A Redox Non-Innocent Ligand Controls the Life Time of a Reactive Quartet Excited State - An MCSCF Study of [Ni(H)(OH)](+)

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The electronic structures of the low and high-spin states of the cationic complex [Ni(H)(OH)](+) that was previously found to be highly reactive toward CH4 and O-2 were examined. Earlier computational work suggested that the low-spin doublet state D-0 of the Ni-III-d(7) system is significantly lower in energy than its high-spin quartet analogue Q(1). Recent DFT-studies indicated, however, that Q(1) is the reactive species requiring Q(1) to have a sufficiently long lifetime for undergoing thermal reactions with the small molecule reactants under single collision conditions in the gas phase. These observations raise the question as to why Q(1) does not spontaneously undergo intersystem crossing. Our work based on DFT, coupled-cluster and MCSCF calculations suggests that the hydroxyl ligand behaves as a redox noninnocent ligand and becomes oxidized to formally afford an electronic structure that is consistent with a Ni-II-(OH)center dot species. As a result, the doublet and quartet ground states are not related by a single electron spin flip and the intersystem crossing becomes inhibited, as indicated by unexpectedly small spin-orbit coupling constants. After extensive sampling of the potential energy surfaces, we concluded that there is no direct way of converting Q(1) to the ground state doublet D-0 Alternative multistep pathways for the Q(1) -> D-0 decay involving doublet excited states were also evaluated and found to be energetically not accessible under the experimental conditions.
Publisher
AMER CHEMICAL SOC
Issue Date
2009-09
Language
English
Article Type
Article
Keywords

TRANSITION-METAL-COMPLEXES; NONADIABATIC UNIMOLECULAR DISSOCIATION; EFFECTIVE CORE POTENTIALS; MOLECULAR CALCULATIONS; ELECTRONIC-STRUCTURE; RADIATIONLESS DECAY; WATER OXIDATION; POLYATOMIC-MOLECULES; CORRELATION ENERGIES; DENSITY FUNCTIONALS

Citation

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, v.131, no.35, pp.12634 - 12642

ISSN
0002-7863
DOI
10.1021/ja902093f
URI
http://hdl.handle.net/10203/203318
Appears in Collection
CH-Journal Papers(저널논문)
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