Spectroscopic and magnetic properties of [FeL2(salacen)]PF6(L = imidazole or N-methylimidazole): new examples of intermediate electronic relaxation between S=½ and S=52 states. X-Ray crystal structure of [Fe(Him)2(salacen)]PF6

Abstract

The iron(III) complexes [FeL₂(salacen)]PF₆[L = imidazole (Him) or N-methylimidazole (mim), salacen = ethylene(N-acetylacetonylideneiminate)(N′-α-methylsalicylideneiminate)] were synthesized, and the phenomenon of the spin transition between high-spin (S=5//₂ ) and low-spin (S=½) states depending on temperature was confirmed by temperature-dependent magnetism and Mössbauer spectra. The time-averaged Mössbauer spectra between the high-spin and low-spin states were observed for [Fe(mim)₂(salacen)]PF₆. A stochastic model was proposed to estimate a spin-interconversion rate from the Mössbauer spectra of spin-crossover complexes. The spin-interconversion rates of 6.7 × 10⁶ s^–1 at 298 K and 3.1 × 10⁶ s^–1 at 221 K were estimated using the model. Crystals of [Fe(Him)₂(salacen)]PF₆ are triclinic, space group P, with a= 10.642(2), b= 12.771(3), c= 9.430(1)Å, α= 89.69(1), β= 104.03(1), γ= 96.97(2)°, and Z= 2. The average bond distances Fe–N 1.970 and Fe–O 1.895 Å are in good agreement with the corresponding values reported for low-spin isomers of other spin-crossover iron(III) complexes.