High magnetic fields in chemistry

Abstract

Recent applications of large (∼ 1 T ∼ 30 T) magnetic fields in modern chemical research are reviewed. Magnetic field effects of chemical relevance appear on the levels of quantum mechanics, thermodynamics, and macroscopic forces. Quantum mechanical magnetic field effects are governed by the Zeeman interaction and are borne out as static and dynamic effects in spectroscopy and in chemical kinetics. Magnetic circular dichroism (MCD) spectroscopy and magnetic fluorescence quenching in the gas phase serve to illustrate the former, while radical pair spin chemistry is representative of the latter. The principles of the radical pair mechanism are outlined and highfield applications are illustrated in some detail for photo-induced electron transfer reactions of some transition metal complexes. Thermodynamic effects concern the magnetization of chemical samples, which is the focus of magnetochemistry or more modern molecular magnetism, and the equilibrium of chemical reactions. Representative examples of both aspects are described. Finally, the exploitation of orientational forces caused by the magnetic anisotropy of larger particles (from macromolecules to micro-crystals) is exemplified. Crystal growth in a magnetic field may hold a potential for achieving better control of the quality of protein crystals for structural analysis.