2016 New talent: crystal engineering at its biggest and strongest

This year CrystEngComm celebrates the contributions from researchers that are at the start of their independent career, or have just entered the broad field of crystal engineering. Invitations to contribute to our 2016 New talent issue turned out to be an outstanding success by all measures, with over 60 exciting papers covering topics ranging from the design of nanomaterials, organic frameworks, polymorphism of organic solids, to metal–organic frameworks (MOFs), contributed by authors across the globe, including work from Australia, Austria, Canada, China, France, Germany, India, Italy, Mexico, Singapore, South Korea, Spain, The Netherlands, United Kingdom, and USA.

Among these papers, a large fraction deals with coordination polymers and MOFs, whose use in advancing organocatalysis has been reviewed in an elaborate, detailed highlight from the Herrera and Díaz Díaz groups (DOI: 10.1039/C5CE02526E). The discovery of a new, unique (3,9)-connected topology, with abbreviation wys, is presented by the Zhang group at Sun-Yat Sen University in the form of a MOF constructed from trigonal-prismatic cobalt clusters and tripodal ligands (Fig. 1a, DOI: 10.1039/C5CE02487K). Further advancing the design of MOFs, the Kou group from Tsinghua University reports an “inverted” approach to a family of microporous materials by combining nickel-based tectons as linkers and a four-connected organic unit as a node (DOI: 10.1039/C5CE01577D). A related “metal-as-linker” design is exploited in the synthesis of one-dimensional (1-D) coordination polymers by the Wang group at Nanjing University (DOI: 10.1039/C5CE02594J). They used sterically-hindered macrocyclic ligands to design a family of building blocks containing Co^II in a pentagonal-bipyramidal environment which, in combination with suitable organic bridging units, led to topologically and magnetically diverse coordination polymers. Macrocycles, but this time with pendant carboxylate arms, were also exploited by the Maspoch group (DOI: 10.1039/C5CE02520F) in an ingenious, two-step strategy to synthesise bimetallic coordination polymers, by first coordinating the macrocycle onto a Ni^II or a Mn^II ion, and then bridging the resulting metallomacrocycles via zinc ions. Control over the structure of MOFs has been addressed also by the Gascon group, who investigated how to avoid interpenetration of MOFs electrochemically grown on a copper surface (DOI: 10.1039/C5CE02462E).

Fig. 1 (a) The assembly of tripodal building blocks leads to a new (wys) network topology, reported by the Zhang group; (b) views of the crystal structure of a copper-based MOF before (left) and after (right) evacuation, whose desolvation behaviour was studied by the Sumby group and (c) different types of (Cu₂I₂)_n (n = 1–4) clusters in the luminescent coordination polymers described by the Li group.

Several contributions deal with engineering MOF particle size or growth of thin MOF films. The former is represented by the joint report from the Serre and Horcajada (DOI: 10.1039/C5CE01864A) groups, addressing scalable synthesis and particle size control for a biocompatible framework MIL-127(Fe). The emerging area of MOF nanoparticles is the topic of a very interesting highlight by the Wuttke group, who gave an excellent, comparative overview (DOI: 10.1039/C6CE00198J) of methods for characterisation of these novel materials. Several other contributions focused on control over particle morphology through interaction of MOFs with organic molecules or surfaces: the Liang and Falcaro groups (DOI: 10.1039/C5CE02549D) described the influence of amino acids on particle properties of a popular material ZIF-8, while the Coskun group demonstrated a method to achieve MOF thin films by growing the well-known framework HKUST-1 on graphene oxide (DOI: 10.1039/C5CE02188J). In a different contribution on the same MOF, the Sun group systematically explored the effect of simple salts on crystallisation of HKUST-1, revealing a means to control size and morphology of micro- and nano-MOF particles (DOI: 10.1039/C5CE02497H). That the particle size can have a pronounced effect on the stability of MOF structures was elaborated by the Sumby group, who reported (Fig. 1b, DOI: 10.1039/C6CE00082G) how a reduction in particle size facilitates the transformation of a metastable three-dimensional (3-D) to a two-dimensional (2-D) variety of a copper(II)-based MOF, shortening the reaction time from one week to under 3 hours.

The contributions in the area of MOFs and coordination polymers reveal considerable interest in microporous solids with new or switchable optical properties, achieved either through the introduction of luminescent ligands, or through incorporation of lanthanide metals as framework nodes. The latter approach was exploited by the Wang group at the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences, who synthesised white-emitting mixed-metal MOF materials involving europium and terbium (DOI: 10.1039/C5CE02444G). The Li group at the Jilin University demonstrated four novel fluorescent MOFs, where the fluorescence is achieved by the presence of lanthanide (Gd³⁺) ions, as well as different types of oligomeric (Cu₂I₂)n clusters (n = 1–4), one of which also demonstrated mechanoresponsive behavior, i.e. fluorescence quenching upon friction and impact (Fig. 1c, DOI: 10.1039/C5CE02544C). Anion-induced control over the dimensionality and overall structure of such 3d–4f coordination materials, composed of Ni²⁺ in combination with La, Nd, Dy or Gd, is investigated in a joint contribution coming from the Kong and Long groups at Xiamen University (DOI: 10.1039/C5CE02503F).

One potential application of luminescent MOFs is for molecular sensing, as demonstrated by the joint contribution from the Liang and the Li groups at Jilin University (DOI: 10.1039/C5CE02172C). They utilised MOFs for detection of explosives based on nitrated aromatics. Fluorescence quenching, which enabled the sensing on nitrobenzene in dilute solution, was also reported by the Hong group at Korea University, in a systematic study of structures and dynamic of zinc-based mixed-ligand carboxylate MOFs with bis(imidazole) ligands (DOI: 10.1039/C6CE00155F). The Biswas group demonstrated how highly toxic H₂S gas can be detected by nitro- and azido-functionalized UiO-66 materials (DOI: 10.1039/C6CE00032K), while the Zhao group from Nankai University utilized 3-oxapentane- and glycerol-based MOFs for CrO₄²⁻ and Cr₂O₇²⁻ detection (DOI: 10.1039/C5CE02568K).

Another aspect of MOFs is their dynamic behavior. An experimental study of the water-induced interconversion between a 2-D and a 3-D copper(II) MOF based on the same pyridinecarboxylate ligand is provided by the Ghoshal group (DOI: 10.1039/C5CE01952D), while the Tan group from the University of Oxford provided a detailed study of structural dynamics in the popular framework HKUST-1 using terahertz vibrational spectroscopy, coupled with theoretical density functional theory calculations (DOI: 10.1039/C5CE02347E). The dynamic behavior in MOFs also offers opportunities for the design of switchable, photo-responsive materials, and the most recent advances in their design have been described by the Gascon group (DOI: 10.1039/C5CE02543E). An exciting example of structural dynamics in MOFs is provided in the systematic study of Co^II, Ni^II, Cd, Zn and Cu^II MOFs based on a bent dicarboxylate linker by the Neogi and Das groups (DOI: 10.1039/C6CE00151C), who noted a single-crystal-to-single-crystal (SCSC) transmetallation of a cadmium MOF with a copper salt.

A different application of MOFs, as precursors for carbon-based catalysts, comes from the Zhao group at the National University of Singapore (DOI: 10.1039/C5CE01439E). They report highly efficient carbon composite photocatalysts by controlled oxygen-free pyrolysis of heterometallic zinc–titanium MOFs. The Kuang group at Xiamen University exploited pyrolysis, but under aerobic conditions, of cobalt-doped ZIF-8 to prepare ferromagnetic samples of the semiconductor ZnO (DOI: 10.1039/C5CE02488A).

In the context of organic materials, the joint contribution of the Evans and the Doonan groups addressed the computational design of porous organic crystals (DOI: 10.1039/C6CE00064A), whereas the Xu group at the Fujian Institute of Research on the Structure of Matter focused on the synthesis of covalent organic frameworks (COFs) and improving their conductive properties (DOI: 10.1039/C6CE00168H). Another contribution on this type of materials, coming from the Bein and Medina groups, is an extensive computational and experimental study of how increased substitution on a model COF affects structure and microporosity (DOI: 10.1039/C6CE00193A). The Cuccia and Bohle groups have provided a new joint contribution on the spontaneous generation of homochirality through Viedma ripening (DOI: 10.1039/C6CE00119J), while the Perepichka group investigated the supramolecular ordering of difuryldiketopyrrolopyrrole, an important building block for organic semiconductors (Fig. 2a, DOI: 10.1039/C6CE00383D).

Fig. 2 (a) Surface assembly of an organic semiconductor building block reported by the Perepichka group: (left) scanning tunnelling microscopy image and (right) proposed molecular model; (b) the environment of a chloride ion in a hydrogen-bonded network with hexahydroxytriphenylene reported by the White group and (c) transmission electron microscopy image of trimetallic nanoparticles reported by the Wang group.

Further among the contributions dedicated to organic or hybrid materials relevant for energy applications or electronic, the Wang group at the Beijing Institute of Technology provided a highlight of the inorganic and organic electrolytes for lithium ion batteries (DOI: 10.1039/C6CE00171H), the Yuan group at the Wuhan University prepared an extensive overview of the cutting edge carbon-based materials for use as “smart” supercapacitors (DOI: 10.1039/C5CE02510A), and the Ma and Zhai groups at Huazhong University of Science and Technology (HUST) summarised the recent developments in layered metal chalcogenides as field-effect transistors and photodetectors (DOI: 10.1039/C5CE01986A). As an actual example of the latter, the contribution from the Yan group at the Tsinghua University presents an improved design for using the metal–organic perovskite methylammonium lead iodide in a self-powered photodetector (DOI: 10.1039/C5CE02531A).

Polymorphism of organic molecules remains a topic of high interest within academia as well as in the pharmaceutical industry, and the Braun group approached the control over polymorphic behavior of a two-component crystal, 4-aminoquinaldine monohydrate, via a combination of experimental studies and crystal structure prediction (DOI: 10.1039/C5CE01758K). The Cuppen group conducted an elaborate theoretical study on the potential mechanisms behind the polymorphic transformation of β- to α-DL-norleucine (DOI: 10.1039/C5CE02550H). Inorganic polymorphism is the topic of theoretical work by the Demichelis group, who investigated the effect of the length and curling on the stability of single-walled chrysotile nanotubes (DOI: 10.1039/C6CE00190D).

Focusing more strongly on the interplay of supramolecular interactions in the solid state, the White group addressed the architecture and synthesis of hydrogen-bonded networks made by anion-templated assembly of hexahydroxytriphenylene (Fig. 2b, DOI: 10.1039/C6CE00297H), the Halder group revealed the formation of a biologically important motif, the tryptophane zipper, in the crystalline assembly of a synthetic tripeptide (DOI: 10.1039/C5CE02005K), and the Mehrotra group described the existence and interplay of n⋯π⋯n (n = lone pair) and S⋯F⋯S interactions in solid tris-arylthiotriazines (DOI: 10.1039/C6CE00496B). An entry focusing on the design of non-crystalline organic materials was provided by the Srivastava group (DOI: 10.1039/C5CE02545A), who looked at the formation of aqueous gels with building blocks based on L-phenylalanine. Two contributions discussed new solid materials based on hydrogen-bonded assembly of polyoxometallates: the Pradeep group reports photocatalytically active materials based on self-assembly of sodium phosphotungstate with metal–organic ytterbium(III) complexes (DOI: 10.1039/C5CE02546J), while the Wei group at Tsinghua University and Peking University described a strategy for the synthesis of amino-substituted polyoxovanadates (DOI: 10.1039/C5CE02534F).

Several groups have focused on single-molecule properties in organic and metal–organic solids. Such is the joint contribution coming from the Zhou and Yao groups from the Changchun Institute of Applied Chemistry, who undertook the synthesis and extensive characterization of two new boron oxadiazole complexes, acting as deep blue emitters and electron transport materials (DOI: 10.1039/C6CE00066E). In search for new organic light-emitting diode materials (OLEDs), the Liu and Bian groups at Peking University reported the structures and highly emissive properties of thermally stable copper(I) binuclear complexes involving Cu₂I₂ luminophores (DOI: 10.1039/C5CE02533H). At the interface of organic chemistry and materials engineering, the Patra group at the Indian Institute of Science Education and Research Bhopal compared a Suzuki coupling to a Schiff base condensation in generating a fluorescent organic material from a biologically relevant pyridoindole (DOI: 10.1039/C5CE02489G). The Wang and Gao groups from Peking University described two new evaporable single molecule magnets based on non-symmetrical β-diketonate complexes of dysprosium(III) (DOI: 10.1039/C5CE02571K), while Hatcher describes a switchable materials based on a new palladium complex that undergoes nitro–nitrito photoinduced switching near room temperature (DOI: 10.1039/C5CE02434J). The Patra group at the Indian Institute of Technology Kanpur provided the structural characterisation of four biologically active mononuclear complexes of samarium(III) and erbium(III), which can bind to DNA (as well as bovine serum albumin), thus permitting photo-induced cleavage of supercoiled into nicked circular DNA (DOI: 10.1039/C5CE02387D).

In the area of inorganic materials, the engineering of crystalline micron-sized structures for catalytic applications was addressed by the Kleitz group, who demonstrated core-shell SiO₂@zeolite structures made up of a crystalline silica core, surrounded by a porous silicalite-1 shell doped with catalytically active transition metals, such as cobalt, manganese or titanium (DOI: 10.1039/C6CE00286B).

The rising importance of nanoparticle design and synthesis in crystal engineering is reflected by almost a dozen contributions dedicated to properties and synthesis of nanoparticles or materials based on nanoparticles of metals or metal oxides. For example, in the context of nano-sized inorganic materials for energy applications, the Louvain group has demonstrated the unexpected discovery of submicron, mesoporous anatase (TiO₂) as a sodium-ion battery (NaB) electrolyte with high stability and excellent cyclability (DOI: 10.1039/C5CE02598B). The Wang and Wang groups at Beihang University and Beijing Institute of Technology described a route to the synthesis of ZnO nanorods with controllable aspect ratio, for use in composite materials with controllable microwave absorption properties (DOI: 10.1039/C5CE02498F). The composite nanoparticles of CeO₂ and MoS₂ with core–shell architecture have been devised by the Du group at Xi'an Jiaotong University for use as high capacitance, energy and power density supercapacitors (DOI: 10.1039/C5CE02466H). The Jiang, Luo and Deng groups from Fudan University and Donghua University demonstrated the controlled assembly of siliceous vesicles using self-assembled organoammonium templates (DOI: 10.1039/C5CE02592C), while the Li and Zhou groups at Jilin University described a template-free synthesis of vanadia nanoparticles and hollow nanospheres with potential applications as cathode materials in lithium-ion batteries, by controlled thermolysis of metal–organic vanadyl glycerolate precursors (DOI: 10.1039/C5CE01398D). They found that lower temperatures preferred the formation of double- and single-walled hollow architectures, while increased temperatures led to the assembly of solid nanoparticles. The Song group at the Korea Advanced Institute of Science and Technology developed intricate hybrid metal–metal oxide nanostructures by the assembly of silver nanoparticles onto octapodal MnO nanoparticle (DOI: 10.1039/C5CE02486B). Remarkably, the association between the two types of nanostructures is sufficiently stable to allow for partial etching of the silver nanostructure and replacement with gold. The synthesis of branched and chemically complex nanostructures has been addressed by the Wang group from Tsinghua University who present a one-pot process for the production of trimetallic nanoparticles via simultaneous reduction of Pt^IV, Pd^II and Ni^II (or Co^II) species in solution (Fig. 2c, DOI: 10.1039/C5CE02478A). Three-component nanowires based on Pd, Pt and Te have been synthesised by the Yu and the Liu groups, using tellurium nanowires as templates (DOI: 10.1039/C5CE02551F). A complex nanoscale architecture, composed of light upconversion nanoparticles functionalized with Pb²⁺-sensitive DNA fragments, and either carbon nanohorns or graphene oxide, was designed by the Sun group at Shanghai University as a fluorescence emission sensor for lead (DOI: 10.1039/C5CE02537K). A persistent challenge in nanochemistry is the reliable synthesis of ultrasmall metal nanoparticles, with diameters below 2 nm. For this special issue, the advances in this area, in the context of silver-based nanoparticles, have been summarized by the Xing group at the Northeast Normal University (DOI: 10.1039/C5CE02494C).

Overall, the topic diversity and the large number of interesting, high-quality contributions received in response to the call for the 2016 New talent issue does well to demonstrate the strength and diversity of modern Crystal Engineering across the globe. It also made a problem for us – because the number of articles greatly exceeded the number of contributions in a typical issue! So, we decided to publish the contributions in two consecutive issues, based on the manuscript publication date. It is, therefore, our pleasure to present not one, but two, CrystEngComm New talent issues demonstrating the interests, ingenuity, broadness of scope and productivity of new talents in Crystal Engineering.

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