A water-tuned reversible spin transition with the largest hysteresis loop in 3D Hofmann frameworks pillared by flexible ligands

Abstract

Using rigid linear ligands as pillars for constructing 3D Hofmann-type frameworks is an important strategy to synthesize spin-crossover (SCO) materials with a large hysteresis loop. However, application of the flexible...

Modulation of the spin transition in 2D Hofmann frameworks via π⋯π stacking between the axial 2,5-dipyridyl-1,3,4-oxadiazoles

“…At 300 K, the χ M T values of 1 and 3 are 3.56 and 3.57 cm 3 K mol −1 , respectively, which is consistent with an octahedral Fe 2+ ion in the HS state. 11 Upon further cooling, an incomplete and gradual one-step HS to LS spin transition occurs between 230 and 25 K for both 1 and 3 . The χ M T value is 2.11 cm 3 K mol −1 for 1 and 2.28 cm 3 K mol −1 for 3 at 25 K, which indicates that the 41% HS Fe 2+ ion in 1 and 36% in 3 undergoes spin transition.…”

“…The characteristic peak at 2164, 2164 and 2152 cm À1 can be assigned to the vibrations of the -CRN group in 1-3, respectively. 11 The bands at 1618 and 1544 in 1, 1618 and 1545 in 2, and 1619 and 1546 cm À1 in 3 may be ascribed to the coordinated 4pyridyl and uncoordinated 2-pyridyl ring, respectively. 7 In addition, The experimental and simulated PXRD curves of 1-3 are depicted in Fig.…”

“…1–4 Up to now, most of the reported SCO systems focus on Fe 2+ complexes with an octahedral [FeN 6 ] configuration. 5–11 Among them, Fe 2+ Hofmann-type SCO frameworks are one of the most notable systems. 6,10–35 These frameworks generally contain neutral bimetallic layers consisting of Fe 2+ ions and [M(CN) 4 ] 2− anions (M = Pt 2+ , Pd 2+ , Ni 2+ ) in the equatorial plane, which allow a large number of linear N-donor ligands to coordinate axially to the Fe 2+ centers in order to produce 2D/3D Hofmann SCO materials.…”

“…5–11 Among them, Fe 2+ Hofmann-type SCO frameworks are one of the most notable systems. 6,10–35 These frameworks generally contain neutral bimetallic layers consisting of Fe 2+ ions and [M(CN) 4 ] 2− anions (M = Pt 2+ , Pd 2+ , Ni 2+ ) in the equatorial plane, which allow a large number of linear N-donor ligands to coordinate axially to the Fe 2+ centers in order to produce 2D/3D Hofmann SCO materials. 10 If the linear exo -bidentate ligands are used as pillars, 3D porous Hofmann SCO frameworks can be constructed, 11 while 2D Hofmann SCO networks will be built if the axial ligands are merely monodentate.…”

“…6,10–35 These frameworks generally contain neutral bimetallic layers consisting of Fe 2+ ions and [M(CN) 4 ] 2− anions (M = Pt 2+ , Pd 2+ , Ni 2+ ) in the equatorial plane, which allow a large number of linear N-donor ligands to coordinate axially to the Fe 2+ centers in order to produce 2D/3D Hofmann SCO materials. 10 If the linear exo -bidentate ligands are used as pillars, 3D porous Hofmann SCO frameworks can be constructed, 11 while 2D Hofmann SCO networks will be built if the axial ligands are merely monodentate. 12 Since the monodentate ligand is always more readily available than the bidentate one, the 2D Hofmann SCO networks can be more easily constructed, which will provide a good opportunity for exploring the influence of intermolecular interactions (hydrogen bonding, π⋯π stacking and interdigitated effect) on the SCO behavior.…”