Spin Crossover in a Four-Coordinate Iron(II) Complex

Abstract

The four-coordinate iron(II) phosphoraniminato complex PhB(MesIm)(3)Fe-N═PPh(3) undergoes an S = 0 to S = 2 spin transition with T(C) = 81 K, as determined by variable-temperature magnetic measurements and Mössbauer spectroscopy. Variable-temperature single-crystal X-ray diffraction revealed that the S = 0 to S = 2 transition is associated with an increase in the Fe-C and Fe-N bond distances and a decrease in the N-P bond distance. These structural changes have been interpreted in terms of electronic structure theory.

High-Temperature Wide Thermal Hysteresis of an Iron(II) Dinuclear Double Helicate

“…4 was synthesized starting from 1-phenyl-1H-1,2,3-triazole-4-carbaldehyde and 1,3-diaminopropane (Scheme 2) based on the previously reported procedure of a related ethylene-bridged compound [34]. The dinuclear 1·PF 6 and 1·AsF 6 were prepared by mixing the ligand L2 C3 , Fe II Cl 2 ·4H 2 O, and KX (X = PF 6 and AsF 6 for 1·PF 6 and 1·AsF 6 , respectively) with a 1:1:2 molar ratio in MeOH/H 2 O mixed solution, which was then recrystallized from the MeCN/MeOH mixed solution. All the synthetic procedures were performed in air and both complexes were obtained as dark-red block crystals.…”

“…In addition, characteristic bands at ca. 844 and 701 cm −1 were observed, corresponding to the counter anions, PF 6 − and AsF 6 − for 1·PF 6 and 1·AsF 6 , respectively [34,49,50].…”

“…Neighboring helicates are connected by intermolecular π-π interactions to give a chiral one-dimensional (1D) structure, and cationic 1D chains with the opposite chirality exist in the crystal lattice to give a heterochiral crystal. Magnetic and differential scanning calorimetry (DSC) studies were performed only for 1·AsF 6 , since the thermal stability in a high-temperature spin crossover (SCO) region of 1·PF 6 is poorer than that of 1·AsF 6 . 1·AsF 6 shows an unsymmetrical hysteretic SCO between the low-spin-low-spin (LS-LS) and high-spin-high-spin (HS-HS) states at above room temperature.…”

“…This phenomenon is observed in 3d 4 -3d 7 transition metal complexes with various coordination geometries (e.g., octahedral, square-pyramidal, trigonal-bipyramidal, tetrahedral, etc.) [1,[4][5][6][7], and is triggered by an external stimulus such as temperature, pressure, light irradiation, or a magnetic field [1][2][3]. While SCO originates from an individual metal center, a spin transition profile, for example, abruptness and multi-steps with or without hysteresis, is provided from the cooperative effect between SCO metal sites through intra-or intermolecular pathways [1][2][3].…”

“…Magnetic and differential scanning calorimetry (DSC) studies were performed only for 1·AsF 6 , since the thermal stability in a high-temperature spin crossover (SCO) region of 1·PF 6 is poorer than that of 1·AsF 6 . 1·AsF 6 shows an unsymmetrical hysteretic SCO between the low-spin-low-spin (LS-LS) and high-spin-high-spin (HS-HS) states at above room temperature. The critical temperatures of warming (T c ↑) and cooling (T c ↓) modes in the abrupt spin transition area are 485 and 401 K, respectively, indicating the occurrence of 84 K-wide thermal hysteresis in the first thermal cycle.…”