Synthesis of metal-organic frameworks (MOFs): routes to various MOF topologies, morphologies, and composites.

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

The chemistry of heterocyclic carbenes has experienced a rapid development over the last years. In addition to the imidazolin-2-ylidenes, a large number of cyclic diaminocarbenes with different ring sizes have been described. Aside from diaminocarbenes, P-heterocyclic carbenes, and derivatives with only one, or even no heteroatom within the carbene ring are known. New methods for the synthesis of complexes with N-heterocyclic carbene ligands such as the oxidative addition or the metal atom template controlled cyclization of β-functionalized isocyanides have been developed recently. This review summarizes the new developments regarding the synthesis of N-heterocyclic carbenes and their metal complexes.

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

2.1.2. Low Topology/Framework Density 1003 2.1.3. Side Group Directed Superstructures 1003 2.2. Synthesis Considerations 1003 2.3. Special Properties 1004 3. Metal Imidazolate Frameworks 1004 3.1. Chains and Rings 1004 3.2. Zeolitic and Zeolite-like Frameworks 1006 3.2.1. SOD-Type Zinc(II) 2-Methylimidazolate 1007 3.3. Nonporous 4-Connected Networks 1010 3.4. Polyimidazolates 1011 4. Metal Pyrazolate Frameworks 1011 4.1. Clusters and Chains 1011 4.2. 3D Networks Based on Polypyrazolates 1012 5. Metal 1,2,4-Triazolate Frameworks 1014 5.1. Simple 3-Connected Networks 1015 5.2. Quasi-Imidazolates 1018 5.3. With Coordinative Substituents 1019 5.4. With Secondary Counterions and/or Ligands 1021 6. Metal 1,2,3-Triazolate Frameworks 1023 7. Metal Tetrazolate Frameworks 1025 7.1. Univalent Coinage-Metal Tetrazolate Frameworks 1025

Metal Azolate Frameworks: From Crystal Engineering to Functional Materials

In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping ...

Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

Comment on “On the presence of multiple molecules in the crystal asymmetric unit (Z′ > 1)” by Gautam R. Desiraju, CrystEngComm, 2007, 9, 91

Making plans for hydrogels: Calculations successfully predict the molecular structure of a robust hydrogel. Melamine and uric acid cocrystallize with water upon sonication, and using experimental data, the minimized structure (see picture) was calculated and successfully compared with powder X-ray diffraction data of the xerogel.

Structure Calculation of an Elastic Hydrogel from Sonication of Rigid Small Molecule Components

Anion binding inhibition of the formation of a helical organogel

A series of pyridyl-appended bis(urea) ligands form supramolecular gels in the presence of metal ions (metallogels), particularly copper(II) and silver(I). The gels have been characterised by rheometry and SEM, and the effect of the metal ions on gel strength and morphology examined. The metal-induced gelation is linked to the competition between urea–urea and urea–pyridyl hydrogen bonding interactions. Crystals grown from these gels reveal a wealth of structural information about these systems that can be related to gel structure using powder X-ray diffraction data of their xerogels.

Metal-induced gelation in dipyridyl ureas

A systematic study into frustration in compounds participating in more than one supramolecular synthon or simultaneously belonging to other categories such as hydrates, co-crystals or crystallizing in a chiral space groups has been undertaken using the Cambridge Structural Database (CSD). The study shows that the combination of more than one directional synthon or the combination of directional synthons with other particular categories of molecule results in markedly increased percentages of structures with Z′ > 1. The majority of combinations show percentages higher than the CSD average of 8.8% and some cases have Z′ > 1 percentages in excess of 60% such as the combination of a carboxylic acid dimer and a molecule in a chiral space group (64.7%). Individual cases have been highlighted and outliers have been discussed and resolved.

Kirsty M. Anderson

Papers

Comment on “On the presence of multiple molecules in the crystal asymmetric unit (Z′ > 1)” by Gautam R. Desiraju, CrystEngComm, 2007, 9, 91

Structure Calculation of an Elastic Hydrogel from Sonication of Rigid Small Molecule Components

Anion binding inhibition of the formation of a helical organogel

Metal-induced gelation in dipyridyl ureas

Supramolecular Synthon Frustration Leads to Crystal Structures with Z′ > 1