Structural design of coordination polymers

CrystEngComm is a specialist journal for crystal engineering research, aiming at the design and understanding of solid-state and crystalline materials. As a central branch of crystal engineering, coordination polymers have been continually developed in their diversity, complexity, and scope for two decades. A pioneering work of Hoskins and Robson aroused worldwide attention in the simple assembly of organic linkers with metallic nodes to achieve a facile strategy for the structural design of coordination polymers. The idea was then extended to the use of metal clusters as secondary tectons and further evolved into constructing porous coordination solids. The creation of new molecules is a major theme of chemistry, and the design of new structures is the major theme of crystal engineering. Furthermore, the potential applications of coordination polymers are developing at an extraordinary pace, underpinned by targeted structural design.

“Design” usually means a high-level synthetic strategy via planning, and sometimes seems inconsistent with self-assembly processes. Nevertheless, molecular crystal engineers and supramolecular chemists are seeking and finding the keys to open the “black box”, allowing the design of desired structures. Design is enabled by the ordered nature of crystalline structures, allowing X-ray diffraction analysis to determine structure–property correlations. Design forms an iterative cycle with an ever expanding library of synthetic tools and methods. The field has developed to a stage where we have great confidence in preparing a crystalline material with specific features in metrics, physicochemical properties, and finally function. Consequently, it is timely to publish this themed issue of CrystEngComm, which focuses on contributions to the latest advances in this dynamic realm. Topics discussed here include: effective synthetic strategies for coordination networks; the influence of different interactions on fabricating supramolecular systems; crystallization and computational design of targeted crystalline materials; adsorption or separation, catalysis, drug delivery, and photoluminescent behaviors of hybrid materials; structural transformations of flexible coordination networks.

For structural prediction, in the highlight contribution by Goesten and Gascon et al. (DOI: 10.1039/C3CE41241E), they discussed the chemistry around pre-existing clusters and correspondingly assembled novel materials using a priori information about the connectivity of an investigated metal cluster, where various ligands can be maturely applied to construct coordination polymers. Using rigid tetrahedral ligands with interesting symmetric elements, Zhou et al. (DOI: 10.1039/C3CE41105B) prepared a family of porous coordination polymers, some of which are promising materials for industrial applications in gas storage. He et al. (DOI: 10.1039/C3CE40445E) successfully realized the control of interpenetrating structures in coordination polymers by tuning the conformations of flexible bis(triazole) ligands. Ferrando-Soria and Pardo et al. (DOI: 10.1039/C3CE41022F) reported the first 3D chiral coordination polymer based on mixed oxalate–oxamato tectons through an in situ reaction. The design of a V-shaped polycarboxylate-based chiral coordination polymer controlled by host–guest key–lock interactions was addressed by Wu, Lai, and Lu et al. (DOI: 10.1039/C3CE41047A). A co-ligand synthetic strategy was highlighted by Maji et al. (DOI: 10.1039/C3CE41438H) and used by Lang et al. (DOI: 10.1039/C3CE41059E) to construct a series of entangling coordination polymers. Thaimattam and Arunachalam et al. (DOI: 10.1039/C3CE41067F) extended the concept of supramolecular synthons into flexible polyaminocarboxylate-based coordination polymers. Several novel dipyridylazacrown ether-based coordination polymers were synthesized by Batten et al. (DOI: 10.1039/C3CE41202D). Heterometallic coordination polymers, specifically with W/Cu/S-based secondary building units, were highlighted by Zheng et al. (DOI: 10.1039/C3CE40992A). Chen and Du et al. (DOI: 10.1039/C3CE41108G) successfully introduced different alkali metal ions as structure-directing agents to afford distinct crystalline materials with high water solubility. The formation of Co–Na, Co–Mn, and Fe–Ni mixed-metal coordination polymers was explored by Bu et al. (DOI: 10.1039/C3CE41117F), Walton et al. (DOI: 10.1039/C3CE41268G), and Do et al. (DOI: 10.1039/C3CE41453A), respectively. Of further interest, many less studied alkali- or alkali earth-based and molybdenum coordination polymers were presented by Ray et al. (DOI: 10.1039/C3CE41070F), Sumby and Doonan et al. (DOI: 10.1039/C3CE41253A), Zhou et al. (DOI: 10.1039/C3CE41106K), and Burrows et al. (DOI: 10.1039/C3CE40484F), respectively. Subtle influences of synthetic factors on the resultant crystalline structures were studied, including anions by Jiang and Su et al. (DOI: 10.1039/C3CE41071D), and Verma et al. (DOI: 10.1039/C3CE41164H), solvent by Du et al. (DOI: 10.1039/C3CE41116H), and pH by Sun et al. (DOI: 10.1039/C3CE41056K) and Senkovska et al. (DOI: 10.1039/C3CE41121D). Polyoxometalates as templates were explored by Zhang, Doonan, and Li et al. (DOI: 10.1039/C3CE41136B). Lloyd et al. (DOI: 10.1039/C3CE41332B) reported the first use of a mild amide synthesis method for the post-synthetic modification of Ti–MIL125–NH₂. The post-synthetic strategy employed by Wright et al. (DOI: 10.1039/C3CE41228H) to incorporate Ni^II into CPO-27(Mg) will result in new materials with enhanced permanent porosity. Notably, molecular simulation combined with experiments was shown to be effective for the structural design of coordination polymers by Yang and Liu et al. (DOI: 10.1039/C3CE41081A), and Mellot-Draznieks et al. (DOI: 10.1039/C3CE41103F).

Extensive investigations on structure–property correlations of coordination polymers have been emphasized in this collection. On the one hand, coordination frameworks with diverse pores will give good performances for adsorption or separation. Jiang and Zhang et al. (DOI: 10.1039/C3CE40548F) reported a 10-connected bct net with high CO₂ and H₂ uptake and good selectivity for CO₂ over N₂. A microporous coordination polymer with an unprecedented topology (chs-1) was prepared by Fröba et al. (DOI: 10.1039/C3CE40594J), which shows good gas storage capacities for H₂, CH₄, and CO₂. The gas sorption behavior of a coordination polymer reported by Lah et al. (DOI: 10.1039/C3CE40929E) well matches its 3D porous network. He and Chen et al. (DOI: 10.1039/C3CE41062E) reported a mesoporous lanthanide–organic framework with cages of 2.4 nm in diameter and a hey topology. Two rare indium–metalloporphyrin porous networks with pts topology were presented by Ma et al. (DOI: 10.1039/C3CE41090K), showing interesting CO₂ adsorption properties. Using an unsymmetrical tricarboxylate ligand, Bai et al. (DOI: 10.1039/C3CE41119B) afforded a highly porous material with agw topology and good capacity for CO₂ and H₂ adsorption. Of great interest, some MOF-5 analogs were reported to possess higher gas adsorption amounts by Sanchiz and Janiak et al. (DOI: 10.1039/C3CE41426D), and Procopio and Navarro et al. (DOI: 10.1039/C3CE41339J). Remarkably, a subtle modification on the substituent group of the organic ligand was shown to be a facile approach to optimize the adsorption properties of coordination polymers by Farha, Snurr, and Hupp et al. (DOI: 10.1039/C3CE40198G), Ghosh et al. (DOI: 10.1039/C3CE40795K), Cohen et al. (DOI: 10.1039/C3CE41124A), Canivet et al. (DOI: 10.1039/C3CE41260A), and Banerjee et al. (DOI: 10.1039/C3CE41083h).

As highlighted by Bharadwaj et al. (DOI: 10.1039/C3CE41257A), dynamic structural changes, especially single-crystal to single-crystal transformations of coordination polymers, can be exploited to interestingly enhance their functionality, which can be induced by solvent mediation (Bourne et al. DOI: 10.1039/C3CE41064A; Yuan et al. DOI: 10.1039/C3CE41095A; Vittal et al. DOI: 10.1039/C3CE41176A) or heat treatment (Zhang and Chen et al. DOI: 10.1039/C3CE41111G). Film processing and patterning techniques are significant to fully explore the potential of coordination polymers in integrated applications. Related to this, Vos and Ameloot et al. (DOI: 10.1039/C3CE41025K), Müller-Buschbaum et al. (DOI: 10.1039/C3CE41087K), Coronas et al. (DOI: 10.1039/C3CE40847G), Attfield et al. (DOI: 10.1039/C3CE40943K), and Lotsch et al. (DOI: 10.1039/C3CE41152D) are pursuing an optical synthetic approach. In addition, coordination polymers are also topical in other diverse fields of applications, such as catalysis (Lee et al. DOI: 10.1039/C3CE41072B; Monge et al. DOI: 10.1039/C3CE41123K), lithium batteries (Xu and Lou et al. DOI: 10.1039/C3CE40996A; Tominaka and Cheetham et al. DOI: 10.1039/C3CE41150H), drug delivery (Morris and Barea et al. DOI: 10.1039/C3CE41289J), treatment of waste water (Biradha et al. DOI: 10.1039/C3CE41501E), and explosives detection (Li et al. DOI: 10.1039/C3CE41680A).

As guest editors, we would like to thank all the worldwide authors who contributed 78 papers in this themed issue on “Structural Design of Coordination Polymers”, who are from nearly 20 countries and regions. To the best of our knowledge, this reveals the second largest themed collection in CrystEngComm since its launch in 1999. These contributions definitely illustrate the scope of both intellectual and practical foundations to be stimulating and fascinating. Certainly, this issue showcases only a small fraction of the current achievements, yet provides a variety of appealing developments in this field.

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