ESR studies of some iron(II) spin crossover complexes.

X-band ESR powder studies have been done on the spin transition in Mn 2- doped [Fe(bpp)2][CF3SO3] 2·H2O, [Fe(bpp)2][BF4] 2 and [Fe(5NO2-sal N(1,4,7,10))] complexes. The use of Mn 2+ as an ESR probe in the studies is based on the knowledge that the ion is very sensitive to changes in its surrounding environment, enabling the changes within the system during HS ↔ LS crossover to be observed. The computer simulations of the powder ESR spectra of Mn2+ ion in these complexes using the SimFonia simulation program, obtained from Broker, gave numerical values of D and E for Mn2+ in the [Fe(bpp)2][CF3SO 3]2·H2O and [Fe(bpp)2][BF 4]2 systems. The magnitudes of D for Mn2+ ion are very different in the HS and LS phases of both the [Fe(bPP)2 ][CF3SO3]2·H2O and [Fe(bpp)2][BF4]2 systems, indicating that the spin transition in these systems is accompanied by a phase transformation. The spears show that during the transition there are separate domains for each spin state. Attempts to simulate the powder ESR spew of Mn2+ in [Fe(5-NO2-sal-N(1,4,7,10))] complex were unsuccessful owing to their poor quality, and further ESR study of this system was not pursued. In summary, ESR studies of [Fe(bpp)2][CF3SO 3]2·H2O show that the phase transformation is coupled to the thermally-induced spin crossover, whereas in [Fe(bpp) 2][BF4]2 the phase transformation takes place first. The rate of HS → LS phase transformation in the [Fe(bpp) 2][CF3SO3]2·H2O system, when the HS state is formed by rapidly cooling the HS state, is the same as the HS → LS conversion reported in the literature using magnetic susceptibility measurements. The rate of HS → LS phase transformation in the [Fe(bpp) 2][BF4]2 system, when the HS state is formed by rapidly cooling the HS state, is twice the rate of the spin-state transition reported in the literature using Mossbauer spectroscopy. There is also no evidence of a phase change seen in the ESR spectra of the [Fe(5-NO2-sal-N(1,4,7,10))] complex. (Abstract shortened by UMI.) Source: Dissertation Abstracts International, Volume: 61-09, Section: B, page: 4745. Adviser: Bruce R. McGarvey. Thesis (Ph.D.)--University of Windsor (Canada), 1998