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The effect of concentration, organic co-solvent, and salt modulators on the crystallisation of a hydrogen bonded framework was studied. The framework contains ∼1.4 nm wide channels and contains a diazobenzene based dicarboxylate anion. Light-induced

Benzamidinium compounds have found widespread use in both medicinal and supramolecular chemistry. In this work, we show that benzamidiniums hydrolyse at room temperature in aqueous base to give the corresponding primary amide. This reaction has a half-life of 300 days for unsubstituted benzamidinium at pH 9, but is relatively rapid at higher pHs (e.g. t1/2 = 6 days at pH 11 and 15 hours at pH 13). Quantum chemistry combined with first principles kinetic modelling can reproduce these trends and explain them in terms of the dominant pathway being initiated by attack of HO– on benzamidine. Incorporation of the amidinium motif into a hydrogen bonded framework offers a substantial protective effect against hydrolysis.

Hydroxypyridinium and hydroxyquinolinium compounds containing acidic O–H groups attached to a cationic aromatic scaffold were synthesized, i.e. N-methyl-3-hydroxypyridinium (1+) and N-methyl-8-hydroxyquinolinium (2+). These very simple compounds are capable of binding to chloride very strongly in CD3CN and with moderate strength in 9:1 CD3CN:D2O. Comparison with known association constants reveal that 1+ and 2+ bind chloride in CD3CN or CD3CN:D2O with comparable affinities to receptors containing significantly more hydrogen bond donors and/or higher positive charges. Crystal structures of both compounds with coordinating anions were obtained, and feature short O–H∙∙∙anion hydrogen bonds. A receptor containing two hydroxyquinolinium groups was also prepared. While the low solubility of this compound caused difficulties, we were able demonstrate chloride binding in a competitive 1:1 CD3CN:CD3OD solvent mixture. Addition of sulfate to this compound results in the formation of a crystallographically-characterised solid state anion coordination polymer.

Despite 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.

Based on Coulomb's Law alone, electrostatic repulsion between two anions is expected to prevent their dimerization. Contrary to that idea, this Tutorial Review will present evidence showing that anion-anion dimers of protic hydroxyanions can form readily, and describe conditions that facilitate their formation. From X-ray crystal structures, we learn that hydroxyanions dimerize and oligomerize by overcoming long-range electrostatic opposition. Common examples are hydroxyanions of phosphate, sulfate, and carbonate, often in partnership with charged and neutral receptors. Short-range hydrogen bonds between anionic donors and acceptors are defined as anti-electrostatic hydrogen bonds (AEHBs) with insight from theoretical studies. While anion dimers are difficult to identify unequivocally in solution, these solution dimers have recently been definitively identified. The development of the supramolecular chemistry of anion-anion dimers has led to applications in hierarchical assemblies, such as supramolecular polymers and hydrogen bonded organic frameworks.

In this work four new tripodal tris(halopyridinium) receptors containing potentially halogen bonding groups were prepared. The ability of the receptors to bind anions in competitive CD3CN/d6-DMSO was studied using 1H NMR titration experiments, which revealed that the receptors bind chloride anions more strongly than more basic acetate or other halide ions. The solid state self-assembly of the tripodal receptors with halide anions was investigated by X-ray crystallography. The nature of the structures was dependent on the choice of halide anion, as well as the crystallisation solvent. Halogen bond lengths as short as 80% of the sum of the van der Waals radii were observed, which is shorter than any halogen bonds involving halopyridinium receptors in the Cambridge Structural Database.

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.

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...

While 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.