Molecular Properties of 3d and 4f Coordination Compounds Deciphered by Raman Optical Activity Spectroscopy

Abstract

Molecular properties of coordination compounds can be efficiently studied by vibrational spectroscopy. The scope of Raman spectroscopy has been greatly enhanced by the introduction of Raman optical activity (ROA) sensitive to chirality. The present review describes some of its recent applications to study the coordination compounds. 3d and 4f metal complexes often absorb the excitation light, or exhibit luminescence. Therefore, effects caused in ROA spectra by electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) must be taken into consideration.In 3d metal complexes ECD and circularly-polarized Raman scattering compete with the resonance ROA (RROA) signal. Pure RROA spectrum can thus be obtained by subtracting the so-called ECD-Raman component. CPL is frequently encountered in 4f systems. While it can mask the ROA spectra, it is useful to study molecular structure. These electronic effects can be reduced by using near-infrared excitation although vibrational ROA signal is much weaker compared to the usual green laser excitation scenario. The ROA methodology is thus complex, but capable of providing unique information about the molecules of interests and their interaction with light.

Keywords: Raman optical activity; circular dichroism; circularly polarized luminescence; coordination compounds; molecular chirality.