Porous CoFe O /C NRAs supported on nickel foam@NC (denoted as NF@NC-CoFe O /C NRAs) are directly fabricated by the carbonization of bimetal-organic framework NRAs grown on NF@poly-aniline(PANI), and they exhibit high electrocatalytic activity, low overpotential, and high stability for the oxygen evolution reaction in alkaline media.

Postsynthetic ion exchange of [Co2(μ-Cl)2(btta)] (MAF-X27-Cl, H2bbta =1H,5H-benzo(1,2-d:4,5-d')bistriazole) possessing open metal sites on its pore surface yields a material [Co2(μ-OH)2(bbta)] (MAF-X27-OH) functionalized by both open metal sites and hydroxide ligands, giving drastically improved electrocatalytic activities for the oxygen evolution reaction (an overpotential of 292 mV at 10.0 mA cm(-2) in 1.0 M KOH solution). Isotope tracing experiments further confirm that the hydroxide ligands are involved in the OER process to provide a low-energy intraframework coupling pathway.

X-Ray single-crystal diffraction has been the most straightforward and important technique in structural determination of crystalline materials for understanding their structure-property relationships. This powerful tool can be used to directly visualize the precise and detailed structural information of porous coordination polymers or metal-organic frameworks at different states, which are unique for their flexible host frameworks compared with conventional adsorbents. With a series of selected recent examples, this review gives a brief overview of single-crystal X-ray diffraction studies and single-crystal to single-crystal transformations of porous coordination polymers under various chemical and physical stimuli such as solvent and gas sorption/desorption/exchange, chemical reaction and temperature change.

Separating ethene (C2H4) from ethane (C2H6) is of paramount importance and difficulty. Here we show that C2H4 can be efficiently purified by trapping the inert C2H6 in a judiciously designed metal-organic framework. Under ambient conditions, passing a typical cracked gas mixture (15:1 C2H4/C2H6) through 1 litre of this C2H6 selective adsorbent directly produces 56 litres of C2H4 with 99.95%+ purity (required by the C2H4 polymerization reactor) at the outlet, with a single breakthrough operation, while other C2H6 selective materials can only produce ca. ⩽ litre, and conventional C2H4 selective adsorbents require at least four adsorption–desorption cycles to achieve the same C2H4 purity. Single-crystal X-ray diffraction and computational simulation studies showed that the exceptional C2H6 selectivity arises from the proper positioning of multiple electronegative and electropositive functional groups on the ultramicroporous pore surface, which form multiple C–H···N hydrogen bonds with C2H6 instead of the more polar competitor C2H4.

Conventional adsorbents preferentially adsorb the small, high-polarity, and unsaturated 1,3-butadiene molecule over the other C hydrocarbons from which it must be separated. We show from single-crystal x-ray diffraction and computational simulation that a hydrophilic metal-organic framework, [Zn(btm)], where Hbtm is bis(5-methyl-1-1,2,4-triazol-3-yl)methane, has quasi-discrete pores that can induce conformational changes in the flexible guest molecules, weakening 1,3-butadiene adsorption through a large bending energy penalty. In a breakthrough operation at ambient temperature and pressure, this guest conformation-controlling adsorbent eluted 1,3-butadiene first, then butane, butene, and isobutene. Thus, 1,3-butadiene can be efficiently purified (≥99.5%) while avoiding high-temperature conditions that can lead to its undesirable polymerization.

The paddle-wheel type cluster Co(RCOO)(L) (R = substituent group, L = terminal ligand), possessing unusual metal coordination geometry compared with other cobalt compounds, may display high catalytic activity but is highly unstable especially in water. Here, we show that with judicious considerations of the host/guest geometries and modular synthetic strategies, the labile dicobalt clusters can be immobilized and stabilized in a metal-organic framework (MOF) as coordinative guests. The Fe(na)(L) fragment in the MOF [{Fe(μ-O)(bdc)}{Fe(na)(L)}] (Hbdc = 1,4-benzenedicaboxylic acid, Hna = nicotinic acid) can be removed to give [{Fe(μ-O)(bdc)}] with a unique framework connectivity possessing suitable distribution of open metal sites for binding the dicobalt cluster in the form of Co(na)(L). After two-step, single-crystal to single-crystal, postsynthetic modifications, a thermal-, water-, and alkaline-stable MOF [{Fe(μ-O)(bdc)}{Co(na)(L)}] containing the desired dicobalt cluster was obtained, giving extraordinarily high electrocatalytic oxygen evolution activity in water at pH = 13 with overpotential as low as 225 mV at 10.0 mA cm.

Porous materials combining high hydrophobicity, large surface area, as well as large and uniform pore size are very useful but rare. The nanoporous zeolitic metal azolate framework, RHO-[Zn(eim)2] (MAF-6, Heim = 2-ethylimidazole), is an attractive candidate but thought to be unobtainable/unstable. In this work, the supramolecular isomerism of [Zn(eim)2] is thoroughly studied using a rapid solution mixing reaction of [Zn(NH3)4](OH)2 and Heim, which enables MAF-6 with high crystallinity, purity, and thermal/chemical stabilities to be synthesized in large quantity. Gas and vapor adsorption isotherms, gas chromatography, and water contact angle measurements, as well as transient breakthrough and molecular dynamics simulations show that MAF-6 exhibits large surface area (langmuir surface area 1695 m(2) g(-1)), pore volume (0.61 cm(3) g(-1)), pore size (d = 18.4 Å), and aperture size (d = 7.6 Å) with high hydrophobicity on both the internal pore and external crystal surfaces. It can barely adsorb water or be wetted by water (contact angle 143°) but readily adsorb large amounts of organic molecules including methanol, ethanol, mesitylene, adamantane, C6-C10 hydrocarbons, xylene isomers, and saturated/unsaturated analogues such as benzene/cyclohexene/cyclohexane or styrene/ethylbenzene. It can also separate these organic molecules from each other as well as from water by preferential adsorption/retention of those having higher hydrophobicity, lipophilicity, or oil/water partition coefficient. These properties are very different with other porous materials such as SOD-[Zn(mim)2] (Hmim = 2-methylimidazole, MAF-4/ZIF-8) with a hydrophobic pore surface but a hydrophilic crystal surface and small aperture size.

Converting CO into fuels via photochemical reactions relies on highly efficient and selective catalysts. We demonstrate that the catalytic active metal center can cooperate with neighboring hydroxide ligands to boost the photocatalytic CO reduction. Six cobalt-based metal-organic frameworks (MOFs) with different coordination environments are studied at the same reaction condition (photosensitizer, electron donor, water/organic mixed solvent, and visible light). In pure CO at 1.0 atm, the MOFs bearing μ-OH ligands neighboring the open Co centers showed CO selectivities and turnover frequencies (TOFs) up to 98.2% and 0.059 s, respectively. More importantly, their TOFs reduced only ca. 20% when the CO partial pressure was reduced to 0.1 atm, while other MOFs reduced by at least 90%. Periodic density functional theory calculations and isotope tracing experiments showed that the μ-OH ligands serve not only as strong hydrogen-bonding donors to stabilize the initial Co-CO adduct but also local proton sources to facilitate the C-O bond breaking.