Spin-Crossover Behaviors of Iron(III) Compounds with Strong Intermolecular Interactions

Iron(III) spin-crossover compounds with H3-OMe-salRen ligands [Fe(3-OMe-salRen)2]ClO4 (1–5) were prepared and characterized by single-crystal X-ray diffraction, Mössbauer spectra, magnetic susceptibilities, and electronic spectra, where 3-OMe-salRen is a tridentate ligand derived from 3-methoxysalicylaldehyde and N-R-ethylenediamine (R = H, Me, Et, Pr, and Bu for 1, 2, 3, 4, and 5). The structures of compounds 1, 2, 3, and 5 at 90 and 298 K, and that of compound 4 at 298 K were determined. Compounds 1, 2, 3, and 5 exhibited a spin transition depending on temperature; the transition temperatures for 1, 2, 3, and 5 were >400, 360, 196, and 223 K, respectively. Compound 4 was in the high-spin state in the temperature range of 5 to 400 K. σ–π or π–π interactions exist in compounds 1–5, and the structures of the compounds were made clear in both the high-spin and low-spin states. Compound 3 exhibited a spin transition with thermal hysteresis.