Abstract

Crystal packing is known to strongly influence spin crossover (SCO) behavior. The influence of the halogen substituent on the crystal structure and magnetic behavior is investigated in the series, [Fe(qsal-X)<inf>2</inf>]NTf<inf>2</inf>(qsal-X = 4-X-2-[(8-quinolylimino)methyl]phenolate; X = Cl 1, Br 2, and I 3; NTf<inf>2</inf>= CF<inf>3</inf>SO<inf>2</inf>NSO<inf>2</inf>CF<inf>3</inf>). Compounds 1 and 2 are stabilized in the low spin state (LS), whereas 3 shows an abrupt hysteretic SCO. Anion conformational change upon SCO is observed in the previously reported compound 3, whereas 1 and 2 exhibit an unchanged syn conformation supported by halogen bonds. However, the key factor is the orientation of the 1D π-πchains. For 1 and 2, the 1D chains are connected by C-H···X interactions giving rise to angled chains (ca. 15°) that lock the iron(III) centers in the LS state. For 3, the 1D chains are parallel to each other connected by C-H···πinteractions that allows SCO. Hirshfeld surface analysis supports these findings. Interestingly, this trend is applicable to a large number of qsal-X complexes with 1D π-πchains.