Theoretical Investigation of the Effect of a Spin Transition on the Second-Order Molecular Hyperpolarizability of a Bis(salicylaldiminato)Fe II Schiff Base Complex

The intermediate neglect of differential overlap-based (INDO-based) sum-over-states (SOS) perturbution theory and the density functional theory (DFT) are used to explore the effect of a spin-crossover phenomenon on the quadratic molecular NLO response ( β ) of an Fe II L complex in which the H 2 L ligand is obtained from the Schiff base condensation of 5-nitrosalicylaldehyde with 1,4,7,10-tetraazadecane. The calculations based on crystal structures recorded at different temperatures reveal that the spin transition results in a β increase of about 25% of its initial value. This effect is mainly due to geometry modifications occurring upon spin transition. In addition, a temperature dependence of β is also pointed out for the first time.