A Family of Cobalt(II) Complexes Exhibiting Record Dissymmetry Factors in Vibrational Circular Dichroism

Abstract

Abstract A family of novel chiral cobalt(II) complexes with two diketonate and one bis(oxazoline) ligand, [Co(dkt) 2 (BOX)], is reported. These complexes exhibit octahedral coordination geometry and feature a chiroptical superspectrum extending from UV to mid‐IR regions. Vibrational circular dichroism (VCD) enhancement occurs thanks to the coupling between ligand vibrations and low‐lying electronic transitions allied to the distorted octahedral high‐spin Co II d 7 core, generating VCD bands of unprecedented intensity in the mid‐IR region with dissymmetry factors up to 3.6 × 10 −2 for a VCD peak at 1453 cm −1 and > 5 × 10 −2 for its shoulder at 1430 cm −1 . These values correspond to a ≈ 100‐fold enhancement with respect to the diamagnetic Zn II analog and set a record among non‐aggregated species in solution. The extraordinarily enhanced intensity allows recording a VCD spectrum with a signal‐to‐noise (S/N) ratio of ≈ 30 in a single acquisition.