Solvent Effects on the Spin Crossover Properties of Manganese (III) (sal-N-1,5,8,12) Complexes

The interplay of host-guest interactions and controlled modulation of spin-crossover (SCO) behavior is one of the most exploited topics regarding data storage, molecular sensing, and optical technologies. This study examines the effect of solvents on the spin-crossover (SCO) behavior of manganese(III) complexes [Mn(sal-N-1,5,8,12)]I•S (S=CH₃OH, C₂H₅OH, CH₃CN) (1) and [Mn(sal-N-1,5,8,12)]I₃ (2), where (sal-N-1,5,8,12)²⁻ is 2,2′-((1E,13E)-2,6,9,13-tetraazatetradeca-1,13-diene-1,14-diyl)diphenol synthesized by salicylaldehyde and 1,2-bis(3-aminopropylamino)ethane. The complexes, crystallizing in orthorhombic or monoclinic systems, exhibit similar supramolecular arrangements with one-dimensional cationic chains at low temperatures. Magnetic studies reveal that solvent inclusion sharpens the SCO transition and lowers the transition temperature. Specifically, 1⋅CH₃OH shows a 13 K thermal hysteresis due to methanol‘s mobility through the channels in the cationic framework. Although the solvent-free compound was not obtained, compound 2 with a linear I₃⁻ anion was synthesized, displaying extensive cation-anion contacts and a distinct 13 K thermal hysteresis upon heating due to altered intermolecular cooperativity. This emphasizes the significant role of solvent introduction and variation in crystal packing and their impact on the SCO properties.