New Talent 2018

The CrystEngComm New Talent 2018 themed issue features 28 fascinating articles from young and talented scientists all around the world on a wide variety of areas such as design and synthesis of organic, inorganic, and metal–organic crystals, as well as computational crystallography. A large fraction of these articles deals with metal–organic frameworks (MOFs, or porous coordination polymers) which are fascinating porous crystals composed of metal-based nodes and organic ligands. The articles featured in this issue demonstrate the viability of MOFs as catalysts, sensors, water purification sorbents, and gas storage and separation sorbents. Jian Zhang synthesized a homochiral zeolitic imidazolate framework using post-synthetic modification techniques and studied its enantioselective sensing and separation towards proline (DOI: 10.1039/C8CE00403J). By taking advantage of the structural versatility offered by MOFs, Jie-Peng Zhang and co-workers synthesized an aliphatic amine functionalized MOF which showed remarkable CO₂ adsorption properties (DOI: 10.1039/C8CE00574E). Katz and co-workers have investigated the crystal engineering of Zn₂(NH₂BDC)₂DABCO in order to relate the PXRD, NMR, and synthesis conditions to the overall surface area. Interestingly, they were able to illustrate that a full complement of DABCO pillars is not necessary to get high surface area (DOI: 10.1039/C8CE00848E). Further elaborating on the design of MOFs, Li has synthesized an ethynyl-based, elongated, slim ligand which resulted in a two-fold interpenetrated porous structure with enhanced gas adsorption selectivity for C₂H₂ over CO₂ and CH₄ (DOI: 10.1039/C8CE00779A). Yuan and co-workers have also designed two novel MOFs that possess open metal sites, making them attractive as heterogeneous catalysts for cyanosilylation of acetaldehydes (DOI: 10.1039/C8CE00694F). Due to the controllable textural and chemical properties offered by MOFs, they have been used as theranostic agents for bio-imaging. Gallis demonstrated that size-controlled mixed-metal MOFs can be used as efficient, biocompatible fluorescent probes for bio-imaging in the second near-infrared (NIR) window (DOI: 10.1039/C8CE00909K). Another interesting property of MOFs is their ability to achieve different arrangements of linkers and metal nodes to form supramolecular isomers (crystallizing in different topologies) using identical building blocks; this can be viewed as a challenge (for obtaining phase-pure MOFs) or an opportunity (for studying the effect of topology by eliminating the contribution from the components of the MOFs). Islamoglu and Farha demonstrated the synthesis of pure-phase mesoporous Zr-based MOFs by eliminating the formation of a secondary phase in the early stage of crystallization (DOI: 10.1039/C8CE00455B) and used large inorganic or biological molecules as probes to locate the position of the secondary phase in the crystals.

Since their discovery, stable MOFs have been explored for various environmentally conscious applications. An exciting highlight in this issue by Howarth discusses not only traditional green chemistry applications such as catalysis but also applications that fall outside the 12 principles of green chemistry such as pollution remediation (DOI: 10.1039/C8CE01002A). While the vast majority of MOFs have been constructed from transition metals, alkali metals such as Li and Na have also been explored as high energy storage materials due to their low atomic weights. Lusi and co-workers demonstrated how water uptake and hygroscopicity change in a series of lithium-based MOFs upon changing the chemical composition (DOI: 10.1039/C8CE00905H). Coordination clusters and cages are another class of hybrid crystals that offers high structural tunability. Lei Zhang reported two polyoxo-titanium clusters (PTCs) stabilized by (fluoro)salicylate ligands and tuned the photophysical properties by introducing fluorine to the coordinating ligand (DOI: 10.1039/C8CE00150B). Additionally, Lan demonstrated that the proton carrier ability of a pillar-layered polyoxometalate-based porous coordination polymer can be further modified to achieve a 28-fold enhancement in proton conductivity (DOI: 10.1039/C8CE00693H).

Another fascinating class of porous crystals are hydrogen-bonded organic frameworks (HOFs) which are constructed from multitopic linkers held together with intermolecular hydrogen bonds. Zhong's highlight discusses the key progress in HOF-based materials, including their design, structures, and potential applications (DOI: 10.1039/C8CE00655E). While the strong hydrogen bonding interactions mentioned in this highlight result in porous crystals which are relatively stable towards activation, Lo Presti demonstrated the significance of weak hydrogen bonds in crystal packing in his computational study; he concluded that weak hydrogen bonds might control the molecular recognition modes at the very initial stages of the nucleation event, but the crystal structure is generally determined by the interactions among larger supramolecular assemblies (DOI: 10.1039/C8CE00674A). In a different computational study by Mohamed on predicting crystal hydration, it was found that the commonly used structural descriptor of solvent accessible volume is a poor predictor of crystal hydration, but the use of packing efficiencies coupled with a careful analysis of the lattice positions of the crystal voids can provide a good assessment of the risk of crystal hydration (DOI: 10.1039/C8CE00758F). Similar to the hydrogen-bonded frameworks discussed above, halogen-bonding can also be utilized to obtain extended structures. Cinčić and co-workers demonstrated a simple strategy for the synthesis of halogen-bonded metal–organic cocrystals by utilizing the M–Cl⋯I motif (DOI: 10.1039/C8CE00754C).

In situ photocrystallography has been instrumental for distinguishing between many structurally similar potential intermediates, which is challenging using solution spectroscopy. Hatcher revealed single-crystal-to-single-crystal linkage isomerism in a photoswitchable Re-nitrite crystal, shedding new light on the photoactive properties of potential Re(I) photocatalysts (DOI: 10.1039/C8CE00774H). Another single-crystal-to-single-crystal transformation of photoswitchable units was reported by Sekine on a spiropyran derivative where the crystal structure was modified by visible light and the life-time of the colored species in the photochromic reaction of the spiropyran was controlled (DOI: 10.1039/C8CE00982A). Controlling the structures of photoactive materials is essential for achieving the desired properties, since the electronic properties of these materials are strongly related to their structural components and the specific interactions of those components with each other. McQueen and co-workers reported that catalytic amounts of lead iodide can be used to engender the formation of novel, lead free, mixed metal organic–inorganic hybrid materials, and they also elucidated the origin of this remarkable effect (DOI: 10.1039/C8CE00702K).

While condensed phase matter is typically perceived as a rigid material, amphidynamic crystals, which have components that experience motion in a structurally designed manner, are an emerging class of crystalline materials. Catalano has highlighted the recent research efforts that have been directed towards the engineering of amphidynamic crystals to achieve specific functions such as sensing, gas separation and switchable dielectrics (DOI: 10.1039/C8CE00420J). Designing solid state sensors remains a topic of high interest in crystal engineering, and therefore attention to the development of stimuli-responsive smart materials has been ever growing. Gassensmith and co-workers have discovered a family of compounds that are thermochromic and thermo-salient single crystals (DOI: 10.1039/C8CE00798E). Importantly, the thermo-responsive properties of these crystals have been maintained, even in 3D printed composite materials. Deák introduced a stimuli-responsive gold(I) complex that exhibits guest-dependent optical properties and demonstrated its colorimetric properties upon exposure to acid/base vapors (DOI: 10.1039/C8CE00652K).

In the area of engineering of cyclophosphazene frameworks, Garcia reported the synthesis of a selenium oxidised cyclodiphosph(V/V)azane species and its use as a supramolecular building block. He also demonstrated the versatility and robustness of this species as a prospective building block for creating reproducible supramolecular synthons for main group crystal engineering purposes (DOI: 10.1039/C8CE00395E). In the context of the role of mechanical processes in the kinetics and self-ordering of solid products, Chizhik reported on the mechanisms of solid state heterogeneous reactions and factors controlling the structures of their reaction interfaces (DOI: 10.1039/C8CE00683K).

Overall, the CrystEngComm New Talent 2018 special issue has received high-quality and interesting contributions from new talents from all over the world to demonstrate the strength and diversity of modern Crystal Engineering.

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