Lattice solvent-directed crystal packing : switching between mer–fac isomerism and spin crossover in Fe(II) complexes Based on 1,3,4-thiadiazole

Abstract

A direct correlation between solvent effects and coordination isomerism in iron(II) spin crossover complexes is reported using the novel ligand 1-(5-(naphthalen-2-yl)-1,3,4-thiadiazol-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine (LNaph-TDA). Crystallization from acetonitrile yields the facial isomer [Fe(LNaph-TDA)(NCBH3)2]·2 MeCN (C1), whereas a dichloromethane solution results in the meridional isomer [Fe(LNaph-TDA)(NCBH3)2]·0.9 DCM (C2). The two distinct coordination geometries were characterized by variable-temperature single-crystal X-ray diffraction, revealing solvent-dependent packing arrangements that modulate the SCO behavior. SQUID magnetometry shows that both solvatomorphs undergo spin transitions, and the differences in the dielectric properties of the lattice solvents likely contribute to the stabilization of the distinct isomers and the changes in observed cooperativity of the spin transition.