Investigation of the two-step spin crossover complex Fe[5-NO ₂-sal-(1,4,7,10)] using density functional theory

A quantum chemical study of the Fe[5-NO₂-sal-(1,4,7,10)] ((1,10-bis(5-nitrosalicylaldehyde)-1,4,7,10-tetra-ezdecane-O,O′,N, N′,N″,N‴)iron(II)) molecule was performed using density functional theory (DFT). Starting from the different X-ray crystallographic structures, geometry optimizations have been performed. These calculations confirmed the conformational isomerism of this complex in each spin states of the molecule (¹A_1g and ⁵T_2g). Each employed DFT method (B3LYP, B3LYP*, BP86, HCTH407) reproduced correctly the structural differences between the two calculated conformers when compared to the experimental structures. Furthermore, electronic polarizabilities have been calculated in each spin state and for each conformer. These calculations revealed a higher polarizability in the singlet state in agreement with the measured higher dielectric constant in this state.