Bis(N-methylethylenediminesalicylaldiminato)iron(III) complexes. Magnetic, Moessbauer, and intersystem crossing rate studies in the solid and solution states for a new (S = /sup 1///sub 2/) in equilibrium (S = /sup 5///sub 2/) spin-equilibrium case

TLDR: In this paper, an upper bound of approximately 10/sup 7/s/sup -1/ has been established for the rate of intersystem crossing in the solid state, as verified by variable-temperature magnetic susceptibility (10 to 300 K) and Moessbauer spectroscopy.

Abstract: Bis(N-methylethylenediaminesalicylaldiminato)iron(III) complexes, (Fe(X-Salmeen)/sub 2/)(PF/sub 6/), with their FeN/sub 4/O/sub 2/ cores have been shown by variable-temperature magnetic susceptibility (10 to 300 K) and Moessbauer spectroscopy to be new (low-spin, S = /sup 1///sub 2/) reversible (high-spin, S = /sup 5///sub 2/), spin-squilibrium compounds in the solid state. From the Moessbauer spectra, an upper limit of approximately 10/sup 7/s/sup -1/ has been established for the rate of intersystem crossing in the solid state. The spin equilibria are also supported in the solution state, as verified by variable-temperature (200 to 300 K) magnetic susceptibility and electronic spectroscopy measurements. In solution, laser Raman temperature-jump kinetics has been employed to directly measure the forward (k/sub 1/) and reverse (k/sub -1/) rate constants for the intersystem crossings with 2 x 10/sup 7/s/sup -1/ < or approximately k < or approximately 2 x 10/sup 8/s/sup -1/. Intersystem crossing rate constant data for these bis-tridentate (Fe/sup III/(X-Salmeen)/sub 2/)/sup +/ complexes are discussed and compared to data already available for the electronically similar (same FeN/sub 4/O/sub 2/ core) but structurally different (hexadentate ligand) spin-equilibrium species, (Fe/sup III/(Sal)/sub 2/trien)/sup +/. 4 tables, 6 figures, 40 references.