Photo‐ and Electronically Switchable Spin‐Crossover Iron(II) Metal–Organic Frameworks Based on a Tetrathiafulvalene Ligand

Abstract

A major challenge is the development of multifunctional metal-organic frameworks (MOFs), wherein magnetic and electronic functionality can be controlled simultaneously. Herein, we rationally construct two 3D MOFs by introducing the redox active ligand tetra(4-pyridyl)tetrathiafulvalene (TTF(py) ) and spin-crossover Fe centers. The materials exhibit redox activity, in addition to thermally and photo-induced spin crossover (SCO). A crystal-to-crystal transformation induced by I doping has also been observed and the resulting intercalated structure determined. The conductivity could be significantly enhanced (up to 3 orders of magnitude) by modulating the electronic state of the framework via oxidative doping; SCO behavior was also modified and the photo-magnetic behavior was switched off. This work provides a new strategy to tune the spin state and conductivity of framework materials through guest-induced redox-state switching.

A Two‐Dimensional Iron(II) Coordination Polymer with Synergetic Spin‐Crossover and Luminescent Properties

“…The design and synthesis of multifunctional materials, especially those featuring an interplay or synergy between two or more properties,have attracted considerable attention in recent years. [1] Theintrinsic properties of the building units commonly used include luminescence, [2] magnetism, [3] electrical conductivity, [4] and chirality. [5] Among them, ahighlight area is the combination of spin crossover (SCO) and luminescence,w hich may expand the horizon of SCO-based applications,e specially in magneto-optical switches.T he optical properties of the Fe II core have been well-documented, where the SCO transition is accompanied by ar eversible change from ah ighly colored high-spin (HS) state to the pale to colorless low-spin (LS) state.…”

“…1·3CH 3 OH adopts the monoclinic space group C2/c and the asymmetric unit contains one crystallographically independent [FeL] subunit, half of TPPE ligand, and three CH 3 OH molecules.C rystallographic data and structure refinements of 1·3CH 3 OH at 263 and 123 Ka re summarized in the Supporting Information, Table S1. Thecoordination of the Fe II is as lightly distorted [FeN 4 O 2 ]o ctahedron with four nitrogen and two oxygen atoms that are in cis positions ( Figure 1a). As expected for SCO complexes,the octahedron contracts on going from the high-spin state at 263 Kt ot he low-spin state at 123 K. TheF e À Nb ond lengths vary from 2.025 to 2.201 and the FeÀOare 2.070 at 263 Kand they decrease to the range 1.924 to 2.008 for FeÀNwhile the FeÀ Ob ecome non-equivalent, 1.924 and 1.956 at 123 K (Supporting Information, Table S2).…”

Direct Visualization of Pyrrole Reactivity upon Confinement within a Cyclodextrin Metal–Organic Framework

“…The average bond length within each crystallographically distinct I 3 À anion, 2.85 ,a grees well with the value reported. [21] Thei mpregnation and oxidative polymerization of pyrrole or thiophene is an effective strategy to endow insulating MOFs with extrinsic electrical conductivity,s imply by backfilling the pores with the conducting polymers generated in situ. [11,12,19,20,22] Oxidation generally leads to morphological damage that results in polycrystalline samples that are often amorphous.A saresult, previous works on extrinsically conductive MOFs make use of pressed pellets to collect electrical measurements.However,Rb-CD-MOF crystals are hundreds of micrometers wide and robust enough to withstand SCSC transformation and can be directly contacted to minimize the influence of grain boundaries in the conductivity measurements.T oi nvestigate the effect of short-range polymerization over the conductivity of the inclusion compound, we measured the electrical conductivity of Rb-CD-MOF, &Py,a nd &TPy single crystals by using at wo-probe contacts method (Figure 5a).…”

Photo‐ and Electronically Switchable Spin‐Crossover Iron(II) Metal–Organic Frameworks Based on a Tetrathiafulvalene Ligand

“…Thep reparation, structural analyses,magnetic,conducting and solid-state electrochemical and spectroelectrochemical properties of the frameworks are studied. [33] All the Fe II ions are in ad istorted [FeN 6 ]o ctahedral coordination environment. [6] Thec rystal structure of 1 adopts the monoclinic space group P2 1 /c and 2 adopts the orthorhombic space group Pbam (Table S1 in the Supporting Information).…”

“…[6] Thec rystal structure of 1 adopts the monoclinic space group P2 1 /c and 2 adopts the orthorhombic space group Pbam (Table S1 in the Supporting Information). [33] All the Fe II ions are in ad istorted [FeN 6 ]o ctahedral coordination environment. In 1,the Fe II ions are linked by four dca ligands into 2D [Fe(dca) 2 ] n layers which are pillared by the TTF(py) 4 ligand, thus generating at wofold interpenetrated 3D framework which can be regarded as a( 4,6)-connected binodal sqc173type topological network (Figure 1, Figure S1, and Table S4).…”