From molecules to crystal engineering: supramolecular isomerism and polymorphism in network solids.

Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

This critical review highlights supermolecular building blocks (SBBs) in the context of their impact upon the design, synthesis, and structure of metal–organic materials (MOMs). MOMs, also known as coordination polymers, hybrid inorganic–organic materials, and metal–organic frameworks, represent an emerging class of materials that have attracted the imagination of solid-state chemists because MOMs combine unprecedented levels of porosity with a range of other functional properties that occur through the metal moiety and/or the organic ligand. First generation MOMs exploited the geometry of metal ions or secondary building units (SBUs), small metal clusters that mimic polygons, for the generation of MOMs. In this critical review we examine the recent (<5 years) adoption of much larger scale metal–organic polyhedra (MOPs) as SBBs for the construction of MOMs by highlighting how the large size and high symmetry of such SBBs can afford improved control over the topology of the resulting MOM and a new level of scale to the resulting framework (204 references).

Design and synthesis of metal-organic frameworks using metal-organic polyhedra as supermolecular building blocks.

Recently sulfate radical-based advanced oxidation processes (SR-AOPs) attract increasing attention due to their capability and adaptability in decontamination. The couple of cobalt and peroxymonosulfate (PMS) is an efficient way to produce reactive sulfate radicals. This article reviews the state-of-the-art progress on various heterogeneous cobalt-based catalysts for PMS activation, including cobalt oxides, cobalt-ferrite and supported cobalt by diverse substrates. We summarize the intrinsic properties of these catalysts and their fundamental behaviors in PMS activation, as well as synthetic approaches. In addition, influencing factors and synergistic techniques of Co/PMS systems in organic degradation and possible environmental applications are also discussed. Finally, we propose perspectives on challenges related to cobalt-based catalysts, heterogeneous Co/PMS systems and their potential applications in practical environmental cleanup.

Cobalt-catalyzed sulfate radical-based advanced oxidation: A review on heterogeneous catalysts and applications

How do molecules aggregate in solution, and how do these aggregates consolidate themselves in crystals? What is the relationship between the structure of a molecule and the structure of the crystal it forms? Why do some molecules adopt more than one crystal structure? Why do some crystal structures contain solvent? How does one design a crystal structure with a specified topology of molecules, or a specified coordination of molecules and/or ions, or with a specified property? What are the relationships between crystal structures and properties for molecular crystals? These are some of the questions that are being addressed today by the crystal engineering community, a group that draws from the larger communities of organic, inorganic, and physical chemists, crystallographers, and solid state scientists. This Perspective provides a brief historical introduction to crystal engineering itself and an assessment of the importance and utility of the supramolecular synthon, which is one of the most important concepts in the practical use and implementation of crystal design. It also provides a look to the future from the viewpoint of the author, and indicates some directions in which this field might be moving.

Crystal engineering: from molecule to crystal.

2,7,12,17‐Tetrapropylporphycene—Counterpart of Octaethylporphyrin in the Porphycene Series

Hydroxy and amino groups are complementary as regards hydrogen-bond donors and acceptors. This is expected to lead to molecular recognition among alcohols and primary amines, i.e., to a propensity towards formation of 1 : 1 alcohol–amine complexes, driven by a 50% increase of the number of hydrogen bonds as compared with the uncomplexed constituents. Possible hydrogen-bonded architectures of such complexes are suggested, and the concept is successfully exploited for crystal engineering purposes by drawing upon linear diphenols, aromatic diamines, and aminophenols as supramolecular partners. Specifically, the crystal-structural chemistry is reported of the 1 : 1 molecular complexes between hydroquinone and p-phenylenediamine, hydroquinone and benzidine, 4,4′-dihydroxybiphenyl and p-phenylenediamine, 4,4′-dihydroxybiphenyl and benzidine, as well as of p-aminophenol, and of 4,4′-hydroxyaminobiphenyl. The diphenol–diamine complexes form hyderogen-bonded super-diamond lattices with 1.5 O(H) N bonds per oxygen and nitrogen atoms, respectively. Again exclusively via O(H)N bonds, the aminophenol structures are also supertetrahedral but after the manner of the polar wurtzite variant. Some similar reported structures are analysed in the light of the present concepts and results, and implications are discussed of the finding that molecular recognition is possible among molecules as standard as simple alcohols and amines.

Molecular recognition among alcohols and amines: super-tetrahedral crystal architectures of linear diphenol–diamine complexes and aminophenols

15N-CPMAS-NMR Study of the Problem of NH Tautomerism in Crystalline Porphine and Porphycene

The preparation of a 3:1 complex of hydroquinone (HQ) and C60, (HQ)3C60, is reported and its X-ray crystal structure described. The HQ host builds up a single H-bonded super-polonium network with super-cubes as building blocks, which accommodate the large C60 guest molecules. The enclathration of C60 is rather tight (high density of the complex) owing, in part, to favorable charge-transfer host-guest interactions (π-donor-acceptor complex). Nonetheless, the C60 molecules arc orientationally disordered, and no individual bond lengths could be measured. In contrast, the HQ host network is essentially ordered and well-defined with normal intramolecular geometry. No appreciable (powder) conductivity could be observed for (HQ)3C60, yet ESR spectra of single crystals showed interesting narrow signals.

Otto Ermer

Papers

2,7,12,17‐Tetrapropylporphycene—Counterpart of Octaethylporphyrin in the Porphycene Series

Molecular recognition among alcohols and amines: super-tetrahedral crystal architectures of linear diphenol–diamine complexes and aminophenols

15N-CPMAS-NMR Study of the Problem of NH Tautomerism in Crystalline Porphine and Porphycene

3:1 Molecular Complex of Hydroquinone and C60

Distorted Triple‐Diamond Structure of 3,3‐Bis(carboxymethyl)glutaric Acid (“Methanetetraacetic Acid”)