On the nature of the high-spin ( 6A 1) ⇌ low-spin ( 2T 2) transition in [Fe(3-CH 3OSPH) 2]Y complexes

Abstract

The spin-crossover phenomenon between the low- spin ( S=1/2, 2T 2) and high-spin ( S=5/2, 6A 1) states depending on temperature is examined for two complexes of the composition [Fe(3-CH 3OSPH) 2]Y, where 3-CH 3OSPH is the monoanionic Schiff base N 2O ligand derived from the condensation of 3- methoxysalicylaldehyde and 2-pyridylhydrazine, and Y is either PF 6 − or BPh 4 −. Variable temperature magnetic susceptibility, EPR, Mössbauer, and electronic data are analysed for these two complexes. Both are seen to undergo gradual but complete spin- crossover transformation from high-spin to low-spin in the solid state. The relaxation time of the change from the high-spin to the low-spin state (and vice versa) in [Fe(3-CH 3OSPH) 2]PF 6 is slower than the 57Fe Mössbauer time scale, while [Fe(3-CH 3OSPH) 2]BPh 4 shows a single quadrupole-split doublet in the Mössbauer spectrum from 80 to 298 K. The results are interpreted in terms of a model in which the spin- interchange crossing is treated as an intramolecular mechanism, internal electron-transfer reaction. EPR spectra show that the [Fe(3-CH 3OSPH) 2] + series has one unpaired electron in a d xy orbital.