An ab initio MO/SD-CI study of model complexes of intermediates in electrochemical reduction of CO{sub 2} catalyzed by NiCl{sub 2}(cyclam)
- Kumamoto Univ. (Japan)
Ab initio MO/SD-CI calculations of several Ni{sup I} and Ni{sup II}CO{sub 2} complexes indicate that CO{sub 2} can coordinate to Ni{sup I}F(NH{sub 3}){sub 4}, yielding a stable {eta}{sup 1}-CO{sub 2} complex, but cannot to [Ni{sup II}F(NH{sub 3}){sub 4}]{sup +}, [Ni{sup I}(NH{sub 3}){sub 4}]{sup +}, and [Ni{sup I}(NH{sub 3}){sub 5}]{sup +}. The HOMO of Ni{sup I}F(NH{sub 3}){sub 4}({eta}{sup 1}-CO{sub 2}) is largely contributed from the O p{sub {pi}} orbital and lies higher in energy than the HOMO (nonbonding {pi} orbital) of the uncomplexed CO{sub 2}. At the same time, the electron density increases around the O atom upon CO{sub 2} coordination. As a result, the coordinated CO{sub 2} in Ni{sup I}F(NH{sub 3}){sub 4}({eta}{sup 1}-CO{sub 2}) is activated to electrophilic attack and is expected to undergo facile protonation. MO calculations show that the second one-electron recuction can easily occur in the protonated species [NiF-(NH{sub 3}){sub 4}(CO{sub 2}H)]{sup +}, yielding the triplet state of [NiF(NH{sub 3}){sub 4}(CO{sub 2}H)], but cannot in the unprotonated species NiF(NH{sub 3}){sub 4}(CO{sub 2}). The second reduction significantly weakens the C-OH bond, which suggests that OH{sup -} easily dissociates from [NiF(NH{sub 3}){sub 4}(CO{sub 2}H)], yielding the triplet state of [Ni{sup II}F(NH{sub 3}){sub 4}(CO)]{sup +}. The CO coordinate bond to Ni{sup II} is calculated to be weak, which suggests that CO easily dissociates from Ni{sup II}. All these results support Sauvage`s reaction mechanism of electrocatalytic reduction of CO{sub 2} by NiCl{sub 2}(cyclam). 41 refs., 8 figs., 5 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 237273
- Journal Information:
- Journal of the American Chemical Society, Vol. 114, Issue 6; Other Information: PBD: 11 Mar 1992
- Country of Publication:
- United States
- Language:
- English
Similar Records
Kinetics and mechanisms of the reactions of aliphatic free radicals with organocobaloximes and fluoropentaamminecobalt(III) ion, and of iron(III) with methylrhodoxime. [C(CH/sub 3/)/sub 2/OH and C(CH/sub 3/)OC/sub 2/H/sub 5/ radicals]
Electrocatalytic reduction of CO/sub 2/ by Ni cyclam/sup 2 +/ in water: study of the factors affecting the efficiency and the selectivity of the process