Halogen bond-enhanced spin dynamics: investigating co-crystallization effects on spin crossover in mononuclear Mn(iii) Schiff-base complexes

Abstract

We present co-crystallization with 1,3,5-trifluoro-2,4,6-triiodobenzene (TFTIB) as an approach to tuning the spin crossover (SCO) properties of mononuclear Mn(III) Schiff-base complexes. The isostructural complexes [Mn(naphth-sal-N-1,5,8,12)]Y (Y = Br (1) and Y = I (2)) and (naphth-sal-N-1,5,8,12)²⁻, which is a big conjugated hexadentate Schiff-base ligand, share similar magnetic behavior and between them complex 2 shows gradual SCO with transition temperature T_1/2 ∼ 380 K. These complexes [Mn(naphth-sal-N-1,5,8,12)]·TFTIB·Y (Y = Br (3) and Y = I (4)) are synthesized by the co-crystallization of their parent complexes 1 and 2 with TFTIB and they both exhibit more gradual SCO with T_1/2 rising to over 400 K. For comparison, complex [Mn(5-F-sal-N-1,5,8,12)]·2TFTIB·Br·CH₃CN (5) was also synthesized, which maintains a high spin (HS) state over the measured temperature range. An anion–TFTIB network connected by halogen–halogen bonds has a significant influence on cation–anion crystal packing and finally on the cooperative effects of the SCO complexes.