Magnetic Circular Dichroism of IrCl62− in Crystalline (CH3NH3)2SnCl6

The magnetic circular dichroism (MCD) of IrCl₆²⁻ doped into crystalline (CH₃NH₃)₂ SnCl₆ has been studied from liquid helium to room temperature over the spectral region 6000–3000 Å. The results confirm the new assignment (based on solution MCD data) wihch places the ${}^2{T}_{\text{1u}}$ charge‐transfer state at lower energy than the corresponding ${}^2{T}_{\text{2u}}$ state. The spin–orbit splitting of the ${}^2{T}_{\text{2u}}$ state which is not apparent in the absorption spectrum or solution MCD shows up strikingly in the crystal MCD illustrating the potentialities of such studies, particularly at low temperatures. The approximate $\text{1\hspace{0.17em}/\hspace{0.17em}T}$ variation in the MCD from room temperature to 6°K shows conclusively that the allowed charge‐transfer bands in MCD arise primarily from $C$ terms and is the first experimental demonstration over a very wide range of temperature of this theoretically expected temperature dependence. There is no indication of antiferromagnetic coupling, at least down to 6°K.