CRYSTALLOGRAPHY AND KINETICS: STRUCTURE CORRELATIONS IN THE LIGHT OF MARCUS RATE-EQUILIBRIUM THEORY. Valeria Ferretti, Paola Gilli, Valerio Bertolasi and Gastone Gilli, Dipartimento di Chimica and Centro di Strutturistica Diffrattometrica, Università di Ferrara, via L. Borsari 46, I-44100 Ferrara, Italy

Systematic comparison of crystal structures containing the same molecular fragment leads to structure correlations, that is intercorrelations of fragment geometrical parameters in its configuration space. Structure correlations are supposed to map minimum-energy pathways in the fragment PES (Potential Energy Surface) (Dunitz, "X-ray Analysis and the Structure of Organic Molecules", Cornell, Ithaca, 1979; Bürgi & Dunitz, Acc. Chem. Res. 1983, 16, 153).

The exact relationship between crystal structure correlations and chemical kinetics (or chemical equilibrium) is a complex physicochemical problem which has been seldom treated (see, for instance, Bürgi in "Perspectives in Coordination Chemistry", VCH, Basel, 1992; Ferretti, Gilli, Bertolasi & Gilli, Cryst. Rev. 1996, in press). In this communication an interpretation is attempted which makes use of the Marcus rate-equilibrium theory (Marcus, Discuss. Faraday Soc. 1960, 29, 21; J. Phys. Chem. 1968, 72, 891) to relate crystal structure correlations with the kinetic concepts of activation energy barriers, reaction pathways and distances of the reactants from the transition state as well as with thermodynamic standard free energies of chemical reactions.