Effects of the Encapsulation of Alkali Ions into Iron(III) Complexes with a Macrocyclic Ring on Magnetic Properties

Abstract

Abstract New spin-crossover iron(III) complexes [FeM(salten)L]X with an alkali ion in a macrocycle have been prepared, and the magnetic properties of the complexes in the solid and in acetonitrile solution have been examined, where M is Li+, Na+, K+, or Rb+, H2salten is 4-aza-heptamethylene-1,7-bis(salicylideneiminate) and L is N-(4-picolyl)-aza-15-crown-5-ether. The spin-crossover behaviors of the iron(III) complexes dependent on temperature in the solid are observed on the Mössbauer spectra and magnetic susceptibilities, and those in acetonitrile on the electronic spectra. The magnetic properties of the complexes in the solid are changed with the species of alkali metal ions included in a macrocycle. Li-complexes show the magnetic moment of 4.00 B.M. at 300 K and 2.19 B.M. at 80 K, and Na-complexes 5.03 B.M. at 300 K and 4.21 B.M. at 80 K. The Mössbauer spectra of Li-complexes show that the interexchange rates of the spin-state transition between high-spin and low-spin states are as fast as the reciprocal of the lifetime of the excited state of 57Fe(10−7s) above 110 K. The magnetic behaviors of all of the complexes in acetonitrile are similar.