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

Herein, three dinuclear iron(II) helicates bearing the molecular formula [Fe-2(L1)(3)](ClO4)(4) center dot 2CH(3)OH center dot 3H(2)O (complex 1), [Fe-2(L2)(3)](ClO4)(4) center dot 6CH(3)CN (complex 2), and [Fe-2(L3)(3)](ClO4)(4) center dot 0.5H(2)O (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 H-1 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 T-1/2 (1)

Automated summary

In this study, three dinuclear iron(II) helicates with imidazole and pyridine-imine-based ligands were synthesized. The spin-transition behavior of these complexes in the solid state was changed from incomplete, multi-step to complete transition around room temperature by modulating the ligand field strength. The spin transition behavior was also observed in solution phase and correlated using spectroscopy.