A theoretical study of the spin-forbidden reaction Fe(CO)₄+CO → Fe(CO)₅

Abstract

The spin-forbidden reaction of Fe(CO)₄ + CO → Fe(CO)₅ has been investigated with multiconfigurational quantum chemical methods (CASSCF/CASPT2). The structure of the minimum energy crossing point (MECP) between the singlet and triplet energy surfaces as well as the equilibrium structures of Fe(CO)₅ (a singlet state) and Fe(CO)₄ (a triplet state) has been determined. The partition rational function (RF) method has been used for the geometry optimization together with approximate numerical gradient vectors and Hessian matrices. The Fe–CO bond angles of the MECP are between those of the equilibrium structures of the ground states of Fe(CO)₅ and Fe(CO)₄, while a considerable extension of the Fe–CO bonds have been shown to occur at the MECP when transferring from the triplet (reactant) PES to the singlet (product) PES. It has also been shown that the MECP prefers to have a C _s symmetry structure with the incoming CO tilted rather than a C _2v structure with Fe and the incoming CO on a straight line.

Acknowledgements

It is a pleasure to dedicate this paper to Mike Robb on his 60th birthday, a longstanding and good friend of one of us (BOR). Let me take this opportunity to thank you for many years of friendship and scientific contacts and in particular for your highly appreciated contributions to the European Summerschool in Quantum Chemistry. The work was supported by the Swedish Research Council and the Swedish Foundation for Strategic Research.