Flexible metal–organic frameworks (MOFs) are dynamic materials that combine long-range structural order with reversible stimulus-responsive phase transitions. In this study, we report the synthesis and characterization of two isoreticular flexible MOFs, TPPM-CPW(Me) and TPPM-CPW(Ph), constructed by combining the ligand tetra-4-(4-pyridyl)phenylmethane (TPPM) with specific Cu(II) paddle-wheel (CPW) secondary building units (SBUs). These MOFs exhibit reversible transitions between open- and closed-pore forms triggered by external stimuli, such as temperature- and pressure-induced guest removal and uptake. The stability of these frameworks is influenced by the residual equatorial groups on the Cu(II) SBUs, with phenyl-functionalized TPPM-CPW(Ph) displaying dynamic behavior characteristic of third-generation soft porous crystals. Notably, TPPM-CPW(Ph) exhibited high adsorption affinity toward fluorinated guests, including SF₆ and volatile anesthetics (VAs) such as desflurane and sevoflurane. This material, when used in solid-phase microextraction (SPME) as fiber coating for the preconcentration of these VAs in air, outperformed commercial CAR/PDMS fibers, underscoring the potential of these versatile flexible MOFs in addressing environmental challenges associated with the use of volatile fluorinated compounds.

Carmine is a red pigment made from dried cochineal, a scale insect that has been a source of brilliant scarlet reds in clothing and art for more than two millennia, with records dating back to 700 BC. Since the 16th century, it has been intensely traded all over the world and was one of the most important trade goods for the Spanish empire at its economic peak. Despite still being used on an industrial scale, with hundreds of metric tonnes produced annually, the exact molecular and crystal structures of the dyestuff remains undetermined. Notably, both modern-day commercial carmine and pigments prepared following historical recipes show strikingly similar diffraction patterns, indicating a common crystalline structure. Here we show that the crystal structure of carmine can, at last, be determined using three-dimensional electron diffraction measurements, revealing a tetranuclear complex that assembles into a nanoporous supramolecular structure with pore diameters of approximately 1.8 nm, held together by intermolecular hydrogen bonding. Our results establish a definite structure of carmine, unveiling a surprisingly complicated arrangement in a long-used commodity with economic and cultural impact, while also highlighting the serendipitous creation of a man-made supramolecular material that dates back hundreds if not thousands of years.

Understanding the structure of Ru(V)-oxo species is crucial for designing novel catalysts for sustainable energy applications, such as water splitting for green hydrogen production. This study reports the EPR detection of a Ru(V)-oxo intermediate stabilized by terpyridine and phenanthroline carboxylate ligands. The interaction between the carboxylate group and the ruthenium center, along with PCET-dependent hemilability under oxidative conditions, plays a critical role in achieving the high-valent state. Subtle changes in the coordination environment around the central metal also proved to be essential. Low-temperature NMR, high-resolution mass spectrometry, UV–Vis spectroscopy, and density functional theory calculations support these findings.

The V-shaped linker molecule 2,5-furandicarboxylic acid (H₂FDC), which can be derived from lignocellulosic biomass, was used in a systematic screening with various iron salts and led to the discovery of a new iron-based metal–organic framework (Fe-MOF) with the composition [Fe₃(μ₃-O)(FDC)₃(OH)(H₂O)₂]·5H₂O·H₂FDC, designated as CAU-52 (CAU = Christian-Albrechts-Universität zu Kiel). The crystal structure of CAU-52 was determined using 3D electron diffraction (3D ED) and further refined by Rietveld refinement against powder X-ray diffraction (PXRD) data. CAU-52 contains the well-known trinuclear [Fe₃(μ₃-O)]⁷⁺ cluster as the inorganic building unit (IBU) that is six-connected by FDC^2– ions to form the pcu net. The connectivity leads to two types of cubic cages, similar to the ones observed in soc-MOFs. Comprehensive characterization of the title compound, including N₂ and water vapor sorption measurements, confirmed its chemical composition. CAU-52 exhibits microporosity toward nitrogen with a type-I isotherm (77 K), yielding a specific surface area of a_s,BET = 1077 m²/g. The H₂O sorption measurement at 298 K leads to an isotherm that exhibits three steps. The water sorption capacity was determined to be 390 mg/g, and it decreases slightly in subsequent sorption cycles. The MOF is stable up to 250 °C in air and chemically resistant in various solvents.

In the field of metal-organic frameworks, the use of yttrium(iii) cations and the formation of 3D inorganic building units are rather rare. Here we report an yttrium(iii) metal-organic framework based on the V-shaped ditopic linker 4,4′-oxydibenzoate, oba2−: [Y16(μ-OH2)(μ3-OH)8(oba)20(dmf)4]·7H2O·7dmf, 1, which was solvothermally prepared, with single crystal X-ray diffraction revealing an unusual 3D metal secondary building unit. When activated at 200 °C, 1 desolvated to form compound 2, [Y16(μ-OH2)(μ3-OH)8(oba)20]·6H2O, retaining the same structure with a 3% shrinkage in unit cell volume.

A family of responsive enaminitrile molecular switches showing tunable turn-on fluorescence upon switching and aggregation is reported. When activated by the addition of acid/base, isomerization around the C═C bond could be effectuated, resulting in complete and reversible switching to the E- or Z-isomers. Typical aggregation-induced emission (AIE) could be recorded for one specific state of the different switches. By subtle tailoring of the parent structure, a series of compounds with emissions covering almost the full visible color range were obtained. The switchable AIE features of the enaminitrile structures enabled their demonstration as solid-state chemosensors to detect acidic and basic vapors, where the emission displayed an “off-on-off” effect. Furthermore, switching to the Z-configuration could be driven out-of-equilibrium through transient changes in acidity while giving rise to fluorescence. Single-crystal X-ray diffraction measurements suggested a luminescence mechanism based on restriction of intramolecular rotation and an intramolecular charge transfer effect in the AIE luminogens.

Aluminum acetates have been in use for more than a century, but despite their widespread commercial applications, essential scientific knowledge of their synthesis-structure-property relationships is lacking. High-throughput screening, followed by fine tuning and extensive optimization of reaction conditions using Al3+, OH− and CH3COO− ions, has unraveled their complex synthetic chemistry, yielding for the first time the four phase pure products Al(OH)(O2CCH3)2 ⋅ x H2O (x=0, 2) (1A and CAU-65, 1B), Al3O(HO2CCH3)(O2CCH3)7 (2), and the porous aluminum salt [Al24(OH)56(CH3COO)12](OH)4 (CAU-55-OH, 3). Structure determination by electron and X-ray diffraction was carried out and the data suggested porosity for 1B and 3, which was confirmed by physisorption experiments. Even the scale-up to the 10 L scale was accomplished for 1A, 1B and 3 with yields of up to 1.1 kg (99 %). This study of a seemingly simple chemical system provides important information on both fundamental inorganic chemistry and porous materials.

The catalytic alkylation of amines with alcohols is a highly atom-economical approach that produces water as the sole by-product. Existing catalytic systems lack generality and are primarily applicable to electron-poor amines or to non-oxidizable amines, such as anilines. The outstanding effectiveness of an Ir-NHC catalyst in forming C−N bonds from alcohols and amines, both aliphatic and aromatic, is presented here. The catalyst performs remarkably under mild conditions, even at room temperature, attaining complete selectivity in all tested cases toward monoalkylation, even for challenging aliphatic amines, and under base-free conditions. Thorough mechanistic investigation to understand the outstanding activity and selectivity, combining experimental, theoretical, and both in situ and ex situ X-ray absorption spectroscopy (XAS) studies, are presented.

A direct catalytic stereoselective synthesis of C4’ functionalized furanoside and nucleoside derivatives with a tetrasubstituted stereocenter is disclosed. The amine-catalyzed stereoselective α-aminomethylation reactions on furanoside-derived aldehyde derivatives gave the corresponding C4’ functionalized D- or L-ribose derivatives in good to excellent yields (67⁻94%) with up to >20:1 dr.

A. Ken Inge pores over the history and applications of bismuth subsalicylate, from dispelling digestive distress to breaching bacterial biodefences.