Electronic and Steric Control of the Spin-Crossover Behavior in [(Cp^R)₂Mn] Manganocenes

A computational study of the spin-crossover behavior in the family [(Cp^R)₂Mn] (R = Me, ⁱPr, ^tBu) is presented. Using the OPBE functional, the different electronic and steric effects over the metal's ligand field are studied, and trends in the spin-crossover-temperature (T_1/2) behavior are presented in terms of the cyclopentadienyl (Cp) ligand functionalization. Our calculations outlined a delicate balance between both electronic and steric effects. While an increase in the number of electron-donating groups increases the spin-crossover temperature (T_1/2) to the point that the transition is suppressed and only the low-spin state is observed, steric effects play an opposite role, increasing the distance between the Cp rings, which in turns shifts T_1/2 to lower values, eventually stabilizing the high-spin state. Both effects can be rationalized by exploring the electronic structure of such systems in terms of the relevant d-based molecular orbitals.