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

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