Synthesis, Crystal Structure, and Luminescent Properties of Novel Zinc Metal–Organic Frameworks Based on 1,3-Bis(1,2,4-triazol-1-yl)propane

Three new zinc three-dimensional coordination polymers with flexible 1,3-bis­(1,2,4-triazol-1-yl)­propane ligand were synthesized. The crystal structures of synthesized compounds were determined, and structural peculiarities are discussed. Coordination compounds with composition [Zn­(btrp)­(bdc)]·<i>n</i>DMF are interpenetrated frameworks, while metal–organic framework (MOF) [Zn₃(btrp)­(bdc)₃]·<i>n</i>DMF is not. Thermal stability and luminescent properties of synthesized compounds have been investigated. The possibility of usage of such compounds as sensitive materials for some aromatic compounds are explored, and it was shown that luminescence of coordination polymers is completely quenched in the presence of nitrobenzene. Sorption properties of synthesized MOFs toward nitrogen, carbon dioxide, and hydrogen were evaluated

Multifunctional Metal–Organic Frameworks Based on Redox-Active Rhenium Octahedral Clusters

The redox-active rhenium octahedral cluster unit [Re₆Se₈(CN)₆]^4– was combined with Gd³⁺ ions and dicarboxylate linkers in novel types of metal–organic frameworks (MOFs) that display a set of functional properties. The hydrolytically stable complexes [{Gd­(H₂O)₃}₂(L)­Re₆Se₈(CN)₆]·<i>n</i>H₂O (<b>1</b>, L = furan-2,5-dicarboxylate, fdc; <b>2</b>, L = thiophene-2,5-dicarboxylate, tdc) exhibit a 3D framework of trigonal symmetry where 1D chains of [{Gd­(H₂O)₃}₂(L)]⁴⁺ are connected by [Re₆Se₈(CN)₆]^4– clusters. Frameworks contain spacious channels filled with H₂O. Solvent molecules can be easily removed under vacuum to produce permanently porous solids with high volumetric CO₂ uptake and remarkable CO₂/N₂ selectivity at room temperature. The frameworks demonstrate an ability for reversible redox transformations of the cluster fragment. The orange powders of compounds <b>1</b> and <b>2</b> react with Br₂, yielding dark-green powders of [{Gd­(H₂O)₃}₂(L)­Re₆Se₈(CN)₆]­Br·<i>n</i>H₂O (<b>3</b>, L = fdc; <b>4</b>, L = tdc). Compounds <b>3</b> and <b>4</b> are isostructural with <b>1</b> and <b>2</b> and also have permanently porous frameworks but display different optical, magnetic, and sorption properties. In particular, oxidation of the cluster fragment “switches off” its luminescence in the red region, and the incorporation of Br^– leads to a decrease of the solvent-accessible volume in the channels of <b>3</b> and <b>4</b>. Finally, the green powders of <b>3</b> and <b>4</b> can be reduced back to the orange powders of <b>1</b> and <b>2</b> by reaction with hydrazine, thus displaying a rare ability for fully reversible chemical redox transitions. Compounds <b>1</b>–<b>4</b> are mentioned as a new class of redox-active cluster-based MOFs with potential usage as multifunctional materials for gas separation and chemical contamination sensors

High Proton Conductivity and Spectroscopic Investigations of Metal–Organic Framework Materials Impregnated by Strong Acids

Strong toluenesulfonic and triflic acids were incorporated into a MIL-101 chromium­(III) terephthalate coordination framework, producing hybrid proton-conducting solid electrolytes. These acid@MIL hybrid materials possess stable crystalline structures that do not deteriorate during multiple measurements or prolonged heating. Particularly, the triflic-containing compound demonstrates the highest 0.08 S cm^–1 proton conductivity at 15% relative humidity and a temperature of 60 °C, exceeding any of today’s commercial materials for proton-exchange membranes. The structure of the proton-conducting media, as well as the long-range proton-transfer mechanics, was unveiled, in a certain respect, by Fourier transform infrared and ¹H NMR spectroscopy investigations. The acidic media presumably constitutes large separated droplets, coexisting in the MIL nanocages. One component of proton transfer appears to be related to the facile relay (Grotthuss) mechanism through extensive hydrogen-bonding interactions within such droplets. The second component occurs during continuous reorganization of the droplets, thus ensuring long-range proton transfer along the porous structure of the material

Enhancement of CO₂ Uptake and Selectivity in a Metal–Organic Framework by the Incorporation of Thiophene Functionality

The complex [Zn₂(tdc)₂dabco] (H₂tdc = thiophene-2,5-dicarboxylic acid; dabco = 1,4-diazabicyclooctane) shows a remarkable increase in carbon dioxide (CO₂) uptake and CO₂/dinitrogen (N₂) selectivity compared to the nonthiophene analogue [Zn₂(bdc)₂dabco] (H₂bdc = benzene-1,4-dicarboxylic acid; terephthalic acid). CO₂ adsorption at 1 bar for [Zn₂(tdc)₂dabco] is 67.4 cm³·g^–1 (13.2 wt %) at 298 K and 153 cm³·g^–1 (30.0 wt %) at 273 K. For [Zn₂(bdc)₂dabco], the equivalent values are 46 cm³·g^–1 (9.0 wt %) and 122 cm³·g^–1 (23.9 wt %), respectively. The isosteric heat of adsorption for CO₂ in [Zn₂(tdc)₂dabco] at zero coverage is low (23.65 kJ·mol^–1), ensuring facile regeneration of the porous material. Enhancement by the thiophene group on the separation of CO₂/N₂ gas mixtures has been confirmed by both ideal adsorbate solution theory calculations and dynamic breakthrough experiments. The preferred binding sites of adsorbed CO₂ in [Zn₂(tdc)₂dabco] have been unambiguously determined by in situ single-crystal diffraction studies on CO₂-loaded [Zn₂(tdc)₂dabco], coupled with quantum-chemical calculations. These studies unveil the role of the thiophene moieties in the specific CO₂ binding via an induced dipole interaction between CO₂ and the sulfur center, confirming that an enhanced CO₂ capacity in [Zn₂(tdc)₂dabco] is achieved without the presence of open metal sites. The experimental data and theoretical insight suggest a viable strategy for improvement of the adsorption properties of already known materials through the incorporation of sulfur-based heterocycles within their porous structures