Donor-acceptor intermolecular hardness on charge transfer reactions of substituted cobalt phthalocyanines

We present a theoretical study of the donor-acceptor intermolecular hardnes s (eta (DA)) associated with the interaction between substituted cobalt pht halocyanines (CoPc(X)(n)) and donors such as molecular oxygen (O-2) or acce ptor species such as 2-mercaptoethanol (OHCH2CH2SH), hydrazine (NH2NH2) and hydroxylamine (NH2OH). Semiempirical (PM3) and ab initio (ROHF/ CEP-31G an d ROHF/6-31G) theoretical methods were used to determine lit,, for the four charge transfer interactions. Theoretical results of eta (DA) correlate we ll with rate constants for electro-oxidation of 2-mercaptoethanol, hydrazin e and hydroxylamine and for electro-reduction of O-2 for processes occurrin g on phthalocyanines confined on a graphite electrode. The lower eta (DA) t he higher is the reactivity. We also determined the molecular hardness (eta ), as defined in density functional theory, of CoPc(X)(n). Linear correlati ons obtained between eta (DA) and of CoPc(X)(n) for each of the charge tran sfer reactions studied indicate that the donor-acceptor intermolecular hard ness is a reactivity index and possesses a predictive value in determining the catalytic activity of macrocyclic complexes confined on electrode surfa ces. (C) 2001 Elsevier Science B.V. All rights reserved.