Syntheses of a unique molecule, nickel(II) dithiocarbamate bearing two ferrocenyl groups (3), and its oxidized product, nickel(IV) dithiocarbamate bearing three ferrocenyl groups (4+), are reported. Spectroelectrochemical investigations have shown that the complex 4+ undergoes a three-electron oxidation process, according to two quasireversible steps ([Ni(IV)(Fe(II))3]+ ⇆ [Ni(IV)(Fe(II))2Fe(III)]2++e-, [Ni(IV)(Fe(II))2- Fe(III)]2+ ⇆ [Ni(IV)(Fe(III))3]4++2e-), whose redox potentials are separated by ΔE = 250 mV. The value ΔE is related to the comproportionation equilibrium ([Ni(IV)(Fe(II))3]++[Ni(IV)(Fe(III))2Fe(II)]3+ ⇆ 2[Ni(IV)Fe(III)(Fe(II))2]2+) and results from the combination of a statistical contribution and a term which reflects the electrostatic repulsive interaction between the metal centers. In spite of the chemical equivalence of the three ferrocenyl groups, the mixed-valence state [Ni(IV)Fe(III)(Fe(II))2]2+ (42+) substantially persists in solution. Model studies with ethylenebridged bis(ferrocenylimine) (6) have revealed that the electrostatic term is much lower in the absence of the nickel(IV) center. Preliminary force-field simulations on 4+ have shown that enhanced electrostatic repulsion caused by the oxidation of the ferrocenyl subunits affects the conformation of the molecule, which results in a significant dimensional increment. Stereochemical features of the molecules are related to the electrostatic interaction and ΔG0 associated with the comproportionation process is affected by such strong deformation that a decrease in electrostatic repulsion results.
|ジャーナル||Chemistry - A European Journal|
|出版ステータス||Published - 1999 1月 1|
ASJC Scopus subject areas