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AbstractDespite their apparent similarity, framework materials based on tetraphenylmethane and tetraphenylsilane building blocks often have quite different structures and topologies. Herein, we describe a new silicon tetraamidinium compound and use it to prepare crystalline hydrogen bonded frameworks with carboxylate anions in water. The silicon‐containing frameworks are compared with those prepared from the analogous carbon tetraamidinium: when biphenyldicarboxylate or tetrakis(4‐carboxyphenyl)methane anions were used similar channel‐containing networks are observed for both the silicon and carbon tetraamidinium. When terephthalate or bicarbonate anions were used, different products form. Insights into possible reasons for the different products are provided by a survey of the Cambridge Structural Database and quantum chemical calculations, both of which indicate that, contrary to expectations, tetraphenylsilane derivatives have less geometrical flexibility than tetraphenylmethane derivatives, that is, they are less able to distort away from ideal tetrahedral bond angles.

Protection of biological assemblies is critical to applications in biotechnology, increasing the durability of enzymes in biocatalysis or potentially stabilizing biotherapeutics during transport and use. Here we show that a porous hydrogen-bonded organic framework (HOF) constructed from water-soluble tetra-amidinium (1·Cl4) and tetracarboxylate (2) building blocks can encapsulate and stabilize biomolecules to elevated temperature, proteolytic and denaturing agents, and extend the operable pH range for catalase activity. The HOF, which readily retains water within its framework structure, can also protect and retain the activity of enzymes such as alcohol oxidase, that are inactive when encapsulated within zeolitic imidazolate framework (ZIF) materials. Such HOF coatings could provide valid alternative materials to ZIFs: they are metal free, possess larger pore apertures, and are stable over a wider, more biologically relevant pH range.

A series of hydrogen-bonded networks was prepared incorporating ditopic, tritopic, or tetratopic polyamidinium tectons and linear pentiptycene dicarboxylates. The ditopic amidinium forms a 1D hydro...

AbstractWhile numerous hydrogen‐bonded organic frameworks (HOFs) have been reported, typically these cannot be prepared predictably or in a modular fashion. In this work, we report a family of nine diamondoid crystalline porous frameworks assembled via hydrogen bonding between poly‐amidinium and poly‐carboxylate tectons. The frameworks are prepared at room temperature in either water or water/alcohol mixtures. Importantly, both the cationic and anionic components can be varied and additional functionality can be incorporated into the frameworks, which show good stability including to prolonged heating in DMSO or water.

AbstractDespite their ready availability, O−H groups have received relatively little attention as anion recognition motifs. Here, we report two simple hydroxy‐containing anion receptors that are prepared in two facile steps followed by anion exchange, without the need for chromatographic purification at any stage. These receptors contain a pyridinium bis(amide) motif as well as hydroxyphenyl groups, and bind mono‐ and divalent anions in 9:1 CD3CN:D2O, showing a selectivity preference for sulfate. Notably, a “model” receptor that does not contain hydroxy groups shows only very weak sulfate binding in this competitive solvent mixture. In the solid state, X‐ray crystallographic studies show that the receptors tend to form extended assemblies with anions; however, 1H and DOSY NMR studies as well as molecular dynamics simulations show that only 1:1 complexes are present in solution. Molecular dynamics simulations suggest that one of the receptors suffers from competing intramolecular hydrogen bonding, while another binds partially‐hydrated anions, with the receptor's O−H groups forming hydrogen bonds to water molecules within the anion's coordination sphere.

A crystalline 3D hydrogen bonded framework is assembled in water from tetrahedral tetraamidinium cations and antielectrostatically hydrogen bonded bicarbonate dimers. The framework forms in water, and represents a clear demonstration of the potency of these anti-Coulombic hydrogen bonds. Gentle heating of the framework (50 °C) releases CO2 and water to give the neutral tetraamidine compound.

The Cambridge Structural Database was surveyed for antielectrostatically hydrogen bonded anion complexes. The survey revealed that these complexes are relatively common, e.g. half of all structurally characterised bicarbonate anions are present as dimers. Generally, the bonding is surprisingly homogenous with O⋯O contacts close to 2.6 A for all anions. Distances are similar in length to, or slightly shorter than, those in carboxylic acid dimers, which do not have to contend with Coulombic repulsion. A heteroanion complex was identified as well as a small number of “highly antielectrostatic” dimers formed between two 2− anions.

This review covers significant advances in the use of O-H groups in anion coordination chemistry. The review focuses on the use of these groups in synthetic anion receptors, as well as more recent developments in transport, self-assembly and catalysis.