Spin-crossover phenomenon and intermolecular interaction for the assembled Fe(II) complexes having aromatic rings

Assembled Fe(II) complex, [Fe(NCS)₂(1,5-bpna)₂·(0.6CH₂Cl₂)(C₂H₅OH)]_n (powder sample) (1,5-bpna = 1,5-bis(4-pyridyl)naphthalene), was synthesized. The powder sample showed slight decrease in magnetic susceptibility with decreasing temperature. Small amount of low-spin state was observed in Mössbauer spectrum at 78 K for the powder sample, suggesting incomplete spin-crossover phenomenon. Single crystal of [Fe(NCS)₂(1,5-bpna)₂·(toluene)]_n was obtained. Magnetic susceptibility for [Fe(NCS)₂(1,5-bpna)₂·(toluene)]_n revealed high-spin state at all temperature region. X-ray structural analysis revealed the CH-π interaction between bridging ligand and guest toluene. Such interaction forced parallel structure around iron atom, which inhibits the decrease in Fe-N distance to become low-spin state.