Cobalt Metal–Organic Frameworks Incorporating Redox-Active Tetrathiafulvalene Ligand: Structures and Effect of LLCT within the MOF on Photoelectrochemical Properties

Abstract

Understanding the effect of charge transfer on the physical properties of metal–organic frameworks (MOFs) is essential for designing multifunctional MOF materials. In this work, three redox-active tetrathiafulvalene (TTF)-based MOFs, formulated as [Co6L6(bpe)6(EtOH)2(MeOH)2(H2O)] n ·5nH2O (1), [Co5(μ3–OH)2L4(bpe)2] n (2), and [CoL­(bpa)­(H2O)] n ·2nH2O (3) (L = dimethylthio-tetrathiafulvalene-bicarboxylate, bpe = 1,2-bis­(4-pyridyl)­ethene, bpa = 1,2-bis­(4-pyridyl)­ethane), are crystallographically characterized. Complexes 1 and 3 are two-dimensional (2D) coordination polymers, and 2 features an unusual three-dimensional (3D) MOF. The structure of 2 contains a cluster chain constructed from μ2-O bridged pentanuclear cluster subunits, which is first found for 3D MOFs. Complexes 1 and 2 are comprised of the same ligands L and bpe but with different multidimensional configuration, and complexes 1 and 3 have the same 2D layered structures with the same ligand L but with different conjugation ligand bpe/bpa, which provide a good comparison for the structure–property relationship. The charge-transfer (CT) interactions within MOF 1 are stronger than those of 2 due to the closer packing of electron donor (D) L and electron acceptor (A) bpe in 1, and no CT occurs within MOF 3 because of the unconjugated bpa. The order of photocurrent density is 1 > 2 ≫ 3, which is in accordance with that of CT interactions. Further analysis reveals that the CT interactions within the MOF are not beneficial for the supercapacitance which is verified by the highest supercapacitance performance of 3. This work is the first study of the structures and CT effects on the supercapacitance performance.

Redox-active benzoquinones as challenging “non-innocent” linkers to construct 2D frameworks and nanostructures with tunable physical properties

“…34 One of the most extensively used redox-active metal ions in 2D networks is the Fe II /Fe III couple, 25 since the report of mixed-valence Prussian blue, [Fe III 4 {Fe II (CN) 6 } 3 ]· x H 2 O, 35 which has been commonly used as a dye. The commonly used redox-active linkers in CPs and MOFs are the derivatives of tetrathiafulvalene, 36 viologen, 37 quinone, 38 triphenylamine, 39 porphyrin, 40 ferrocene, 41 pyrazine, 42 hexaaminobenzene 43 and tetrazine 44,45 (Chart 1). Among these ligands, quinone and its derivatives have been widely studied for their impressive redox properties.…”

A Tetrathiafulvalene/Naphthalene Diimide-Containing Metal–Organic Framework with fsc Topology for Highly Efficient Near-Infrared Photothermal Conversion

“…Tetrathiafulvalene (TTF), a sulfur-rich conjugated molecule, has been extensively used as an important electron donor to construct novel charge transfer (CT) multifunctional materials. − Naphthalene diimide (NDI), which is electron-deficient, is used as an electron acceptor in various fields. Both of them have reversible multistep redox activity. − In 2021, we reported one two-dimensional (2D) MOF, Co-MOF , constructed from organic ligands TTF and NDI, which showed good near-infrared photothermal conversion performance.…”

Redox-Active Metal-Organic Frameworks with Three-Dimensional Lattice Containing the m-Tetrathiafulvalene-Tetrabenzoate

“…In various organic building blocks, the electron-rich tetrathiafulvalene (TTF) unit, owing to its two stable oxidized states, has become a famous redox-active building block in the construction of functional MOFs [1,10]. Among the TTF-carboxylate ligands, dimethylthio-tetrathiafulvalene-bicarboxylate (H 2 TTFBC), tetrathiafulvalene-tetracarboxylate (H 4 TTFTC), and tetrathiafulvalene-tetrabenzoate (H 4 TTFTB) are well-researched in the previous works [10][11][12][13][14][15][16][17]. For H 4 TTFTB, Dincă et al first reported its synthesis and assembly of Zn 2+ in a semiconductive MOF [18].…”