Magnetic Circular Dichroism of [Fe(CN)6]3−

Magnetic circular dichroism (MGD) of [Fe(CN)6]3− was measured in aqueous solution and in a polyvinylalcohol film. The use of the polyvinylalcohol (PVA) film made it possible to measure the MCD and the absorption spectrum of an electrolyte such as K3[Fe(CN)6] at dry ice - methanol and liquid nitrogen temperatures, since the film was still optically transparent at lower temperatures. From a comparison between the observations at 300°K, 195°K and 77°K, the magnitude of an angular momentum due to the orbital motion of a hole in the ground state 2T2g (t2g5) was calculated to be 0.04–0.07 Bohr magneton (β). The observed reduction of the angular momentum was interpreted to be due to partial quenching of the orbital motion by the Jahn-Teller distortion, and also to the delocalization effect between the iron dπ orbital and the antibonding π molecular orbitals of the coordinating CN− ions. The B term in [Fe(CN)6]3−, which had been ignored, was predicted to be non-zero and was estimated as −2.4×10−3 β/cm−1 at the band I and 0.97×10−3 β/cm−1 at the band II.