Dinuclear Iron(II) Triple Helicates Exhibiting Room Temperature Spin‐Transition Behaviour in Solid and Solution Phase

Abstract

AbstractHerein, three dinuclear iron(II) helicates bearing the molecular formula [Fe2(L1)3](ClO4)4 ⋅ 2CH3OH ⋅ 3H2O (complex 1), [Fe2(L2)3](ClO4)4 ⋅ 6CH3CN (complex 2), and [Fe2(L3)3](ClO4)4 ⋅ 0.5H2O (complex 3) have been synthesized using imidazole and pyridine‐imine‐based ligands having fluorene moiety in the backbone. A change in the ligand field strength by terminal modulation led to a change in the spin‐transition behaviour from incomplete, multi‐step to complete, around room temperature in the solid state. Spin transition behaviour has also been observed in the solution phase characterized using variable temperature 1H nuclear magnetic resonance spectroscopy (Evans method) and correlated using UV‐visible spectroscopy. Fitting the NMR data using the ideal solution model yielded the transition temperature in the order T1/2 (1)<T1/2 (2)<T1/2 (3), which indicates an increase in the ligand field strength from complexes 1 to 3. This study accentuates the interplay between the ligand field strength, crystal packing, and supramolecular interactions in fine‐tuning the spin transition behaviour effectively.