Tuning spin crossover properties in Hofmann-type framework by
guest-adaptive deformation
Abstract
Three three-dimensional Hofmann-type metal-organic frameworks (MOFs)
[Fe(bpn){Ag(CN) 2} 2]·Ph
2S ( 1·Ph 2
S, bpn = 1,4-di(pyridin-4-yl)naphthalene, Ph 2S
= diphenylsulfide), [Fe(bpn){Ag(CN) 2}
2]·Ph 2SO ( 1·Ph
2 SO, Ph 2SO =
diphenylsulfoxide) and [Fe(bpn){Ag(CN) 2}
2]·Ph 2SO 2 (
1·Ph 2 SO
2, Ph 2SO 2 =
diphenylsulfone) were synthesized by employing sulfur-containing
aromatic guests varying in oxidation states. 1·Ph
2 S performed a complete four-step
spin crossover (SCO) behavior with the sequence of HS↔LS
1/3HS 2/3↔LS 1/2HS
1/2↔LS 2/3HS 1/3↔LS,
while an incomplete two-step SCO profile with the sequence of HS↔LS
1/3HS 2/3↔LS 2/3HS
1/3 and a faint SCO behavior at low temperature for
1·Ph 2 SO and 1·Ph
2 SO₂. Photomagnetic experiments
indicate the light-induced excited spin-state trapping (LIESST) effect
in 1·Ph 2 S and the
bi-directional LIESST effect for 1·Ph
2 SO and 1·Ph
2 SO₂. Variable-temperature structural
analyses reveal the evolution of host-guest synergy and highlight the
mechanism of adaptive deformation of guests mediated by phenyl rotation
amid spin transition. As the oxidation state of sulfur-containing guests
increases, the host-guest cooperation within the lattice is limited by
the steric effect, which stabilizes the high-spin state and consequently
diminishes the SCO capability in this system. These results demonstrated
herein open a new perspective on host-guest chemistry within SCO
frameworks.
, 
