Synthesis and Electrical Properties of Covalent Organic Frameworks with Heavy Chalcogens

Synthesis and Electrical Properties of Covalent Organic Frameworks with Heavy Chalcogen

Controlled Gas Uptake in Metal–Organic Frameworks with Record Ammonia Sorption

Ammonia is a vital commodity in our food supply chain, but its toxicity and corrosiveness require advanced protection and mitigation. These needs are not met efficiently by current materials, which suffer from either low capacity or low affinity for NH₃. Here, we report that a series of microporous triazolate metal–organic frameworks containing open metal sites exhibit record static and dynamic ammonia capacities. Under equilibrium conditions at 1 bar, the materials adsorb up to 19.79 mmol NH₃ g^–1, more than twice the capacity of activated carbon, the industry standard. Under conditions relevant to personal protection equipment, capacities reach 8.56 mmol g^–1, 27% greater than the previous best material. Structure–function relationships and kinetic analyses of NH₃ uptake in isostructural micro- and mesoporous materials made from Co, Ni, and Cu reveal stability trends that are in line with the water substitution rates in simple metal–aquo complexes. Altogether, these results provide clear, intuitive descriptors that govern the static and dynamic uptake, kinetics, and stability of MOF sorbents for strongly interacting gases

Pt Electrodes Enable the Formation of μ₄‑O Centers in MOF‑5 from Multiple Oxygen Sources

The μ₄-O^2– ions in the Zn₄O­(O₂C−)₆ secondary building units of Zn₄O­(1,4-benzenedicarboxylate)₃ (MOF-5) electrodeposited under cathodic bias can be sourced from nitrate, water, and molecular oxygen when using platinum gauze as working electrodes. The use of Zn­(ClO₄)₂·6H₂O, anhydrous Zn­(NO₃)₂, or anhydrous Zn­(CF₃SO₃)₂ as Zn²⁺ sources under rigorous control of other sources of oxygen, including water and O₂, confirm that the source of the μ₄-O^2– ions can be promiscuous. Although this finding reveals a relatively complicated manifold of electrochemical processes responsible for the crystallization of MOF-5 under cathodic bias, it further highlights the importance of hydroxide intermediates in the formation of the Zn₄O­(O₂C–R) secondary building units in this iconic material and is illustrative of the complicated crystallization mechanisms of metal–organic frameworks in general

Single-Ion Li⁺, Na⁺, and Mg²⁺ Solid Electrolytes Supported by a Mesoporous Anionic Cu–Azolate Metal–Organic Framework

A novel Cu­(II)–azolate metal–organic framework (MOF) with tubular pores undergoes a reversible single crystal to single crystal transition between neutral and anionic phases upon reaction with stoichiometric amounts of halide or pseudohalide salts. The stoichiometric transformation between the two phases allows loading of record amounts of charge-balancing Li⁺, Na⁺, and Mg²⁺ ions for MOFs. Whereas the halide/pseudohalide anions are bound to the metal centers and thus stationary, the cations move freely within the one-dimensional pores, giving rise to single-ion solid electrolytes. The respective Li⁺-, Na⁺-, and Mg²⁺-loaded materials exhibit high ionic conductivity values of 4.4 × 10^–5, 1.8 × 10^–5, and 8.8 × 10^–7 S/cm. With addition of LiBF₄, the Li⁺ conductivity improves to 4.8 × 10^–4 S/cm. These are the highest values yet observed for MOF solid electrolytes

High and Reversible Ammonia Uptake in Mesoporous Azolate Metal–Organic Frameworks with Open Mn, Co, and Ni Sites

A series of new mesoporous metal–organic frameworks (MOFs) made from extended bisbenzenetriazolate linkers exhibit coordinatively unsaturated metal sites that are responsible for high and reversible uptake of ammonia. Isostructural Mn, Co, and Ni materials adsorb 15.47, 12.00, and 12.02 mmol of NH₃/g, respectively, at STP. Importantly, these near-record capacities are reversible for at least three cycles. These results demonstrate that azolate MOFs are sufficiently thermally and chemically stable to find uses in recyclable sorption, storage, and potentially separation of chemically challenging and/or corrosive gases, especially when designed to exhibit a high density of open metal sites

High and Reversible Ammonia Uptake in Mesoporous Azolate Metal–Organic Frameworks with Open Mn, Co, and Ni Sites

A series of new mesoporous metal–organic frameworks (MOFs) made from extended bisbenzenetriazolate linkers exhibit coordinatively unsaturated metal sites that are responsible for high and reversible uptake of ammonia. Isostructural Mn, Co, and Ni materials adsorb 15.47, 12.00, and 12.02 mmol of NH₃/g, respectively, at STP. Importantly, these near-record capacities are reversible for at least three cycles. These results demonstrate that azolate MOFs are sufficiently thermally and chemically stable to find uses in recyclable sorption, storage, and potentially separation of chemically challenging and/or corrosive gases, especially when designed to exhibit a high density of open metal sites

Conformational Locking by Design: Relating Strain Energy with Luminescence and Stability in Rigid Metal–Organic Frameworks

Minimization of the torsional barrier for phenyl ring flipping in a metal–organic framework (MOF) based on the new ethynyl-extended octacarboxylate ligand H₈TDPEPE leads to a fluorescent material with a near-dark state. Immobilization of the ligand in the rigid structure also unexpectedly causes significant strain. We used DFT calculations to estimate the ligand strain energies in our and all other topologically related materials and correlated these with empirical structural descriptors to derive general rules for trapping molecules in high-energy conformations within MOFs. These studies portend possible applications of MOFs for studying fundamental concepts related to conformational locking and its effects on molecular reactivity and chromophore photophysics

High Charge Mobility in a Tetrathiafulvalene-Based Microporous Metal–Organic Framework

The tetratopic ligand tetrathiafulvalene-tetrabenzoate (H₄TTFTB) is used to synthesize Zn₂(TTFTB), a new metal–organic framework that contains columnar stacks of tetrathiafulvalene and benzoate-lined infinite one-dimensional channels. The new MOF remains porous upon desolvation and exhibits charge mobility commensurate with some of the best organic semiconductors, confirmed by flash-photolysis-time-resolved microwave conductivity measurements. Zn₂(TTFTB) represents the first example of a permanently porous MOF with high charge mobility and may inspire further exploration of the electronic properties of these materials

Mn₂(2,5-disulfhydrylbenzene-1,4-dicarboxylate): A Microporous Metal–Organic Framework with Infinite (−Mn–S−)_∞ Chains and High Intrinsic Charge Mobility

The reaction of MnCl₂ with 2,5-disulfhydrylbenzene-1,4-dicarboxylic acid (H₄DSBDC), in which the phenol groups in 2,5-dihydroxybenzene-1,4-dicarboxylic acid (H₄DOBDC) have been replaced by thiophenol units, led to the isolation of Mn₂(DSBDC), a thiolated analogue of the M₂(DOBDC) series of metal–organic frameworks (MOFs). The sulfur atoms participate in infinite one-dimensional Mn–S chains, and Mn₂(DSBDC) shows a high surface area and high charge mobility similar to that found in some of the most common organic semiconductors. The synthetic approach to Mn₂(DSBDC) and its excellent electronic properties provide a blueprint for a potentially rich area of exploration in microporous conductive MOFs with low-dimensional charge transport pathways