Effect of intermolecular anionic interactions on spin crossover of two triple-stranded dinuclear Fe(II) complexes showing above room temperature spin transition.

Two new Fe(II)-based dinuclear triple helicates having the formula {[Fe(L)]·(CFSO)·6.5HO·CHOH} (complex 1) and {[Fe(L)]·(ClO)·7HO·1.35CHOH} (complex 2), displaying near room temperature spin transition have been synthesized and the effect of intermolecular interactions and co-operativity between metal centers on the spin crossover (SCO) has been studied. Picolinimidamide-based ligand system is chosen to provide maximum intermolecular interactions. Variable-temperature single crystal X-ray diffraction (SCXRD), magnetic study, and Hirshfeld analysis reveal that complex 1 shows a multistep spin transition, whereas, complex 2 shows an abrupt spin transition from [LS-LS] ↔ [HS-HS]. In complex 2 the presence of perchlorate anion induces high intermolecular O-H interaction that enhances the cooperativity resulting in high of 330 K. This study accentuates the interplay between anion effect, crystal packing, and supramolecular interactions in tuning the magnetic properties of SCO compounds.