Computational Determination of Electrochemical Stability

The last two remarks deserve a more quantitative explanation. The influence of the anions and several substituents such as electron-withdrawing groups on the oxidation potential can be calculated. 

Horowitz et al. [265] have shown that useful correlations are obtained between the oxidation voltages of the anion and the averaged Hammett cr-function or Ingold and Taft s a -function of the substituents around a boron atom. Both empirical functions reflect the electron-withdrawing ability of the substituent group. Hammett s averaged n-values are obtained from the dissociation constants of meta-substituted benzoic acids, (T -values are obtained from comparative rates of acid and alkaline ester hydrolysis (for details see Ref. [265]). 

A more recent but closely related explanation of the shift of oxidation potentials by electron-withdrawing substituents is based on results of semi-empirical quantum-mechanical calculations [219, 266-268]. Methods such as MNDO, AMI, PM3, HF/3-21G, or B3LYP/6-31G are used to yield the energy of the highest occupied molecular orbital homo of the anion. Gorrelations of Eqx with Phomo are linear for a given set of compounds of similar structure. 

There is a difference in the behavior of benzenediolatoborate and naphthalenediolatoborate solutions on the one hand and hthium bis[2,2 -biphenyldioIato(2-)-0,0 ]borate (5), Uthium bis[sahcylato(2-)]borate (6) or benzenediolatoborate/phenolate mixed solutions on the other hand. This can be tentatively explained by the assumption of different decomposition mechanisms due to different structures which entail the formation of soluble colored quinones from benzenediolatoborate anions and Uthium-ion conducting films from solutions of compounds (5) and (6) [107]. The assumption of a different mechanism and the formation of a hthium-ion conducting electronically insulating film are supported by  

Theoretical calculations of oxidation potentials ox are based on a linear correlation of the first ionization potential Ip to the electrochemical oxidation potential Eox [274]. From a theoretical point of view, the linear correlation of the ionization potentials to oxidation potentials qx is based on Koopmans theorem [275], which states that the negative orbital energy Iihomo of the highest occupied molecular orbital (HOMO) equals the first ionization potential Ip. But this is only valid at H F 

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