In a remarkable example, we report a one-dimensional coordination polymer (CP) of Pb­(II) showing photosalient (PS) properties triggered by [2 + 2] cycloaddition of olefinic ligands, which is seldom observed in CPs. Macroscopic rod-shaped crystals show various photomechanical effects such as jumping, splitting, rolling, and breaking upon UV illumination. In this rare example, we could determine the solid-state structure of the 100% dimerized product and three intermediate structures, even after the shattering of crystals into small pieces. Detailed mechanistic investigation from the single-crystal data indicates that the strain generated in the unit cell due to anisotropic expansion played a bigger role for the PS effects. Nucleated growth of the photoproduct crystal created different domains inside the single crystal, which multiplied the already developed stress leading to the photomechanical movements. This example falls in the gray area of a clean single-crystal-to-single-crystal (SCSC) transformation and violent PS effect. Such photochemical behavior has never been reported before.

With emergent research on stimuli responsive materials, dynamic crystals are at the forefront of investigation.However, research on the mechanical properties of coordination polymers (CPs) is still in its infancy. Elastic deformation induced by pressure and photoactuation are rare occurrences in CPs, let alone their combination in a single CP. Here, we report a one-dimensional (1D) CP comprising PbBr2 chains with 3-fluoro-4'-styrylpyridine arms showing excellent elasticity and photomechanical properties. A slender crystal can be bent to make a circle and write different shapes with restoration of original shape upon removal of the applied force. In addition, photomechanical properties triggered by [2+2] cycloaddition of the olefinic ligand can be modulated easily by variation of the crystal sizes. Crystals with bigger width show destructive photosalient effects while the smaller ones show plastic deformation like bending, twisting, curling etc. upon UV irradiation. This example provides avenue for designing CPs for multi-stimuli responsive actuating properties. File list (12) download file view on ChemRxiv Rath et al. Manuscript.pdf (842.43 KiB) download file view on ChemRxiv Rath et al. Supp Info.pdf (1.06 MiB) download file view on ChemRxiv Video SV1_Elastic bending.mp4 (4.64 MiB) download file view on ChemRxiv Video SV2_Mechanical bending.mp4 (2.26 MiB) download file view on ChemRxiv Video SV3_Photosalient effects.mp4 (5.24 MiB) download file view on ChemRxiv Video SV4_Photoinduced bending.mp4 (3.64 MiB) download file view on ChemRxiv Video SV5_Light direction dependant bending.mp4 (4.21 MiB) download file view on ChemRxiv Video SV6_Photoinduced splitting and twisting.mp4 (2.95 MiB)

Thermally responsive crystals hold great potential for their use as actuating materials by acting as energy transducers to convert heat energy to mechanical work. Control over defined phase transition temperature with rapid reconfiguration is of great advantage for actuation. The thermosalient (TS) effect is a rarely observed phenomenon in coordination polymers (CPs), let alone the reversibility of thermosalience in CPs. Herein, we report the reversible TS effect in a one-dimensional CP due to the martensitic phase transition during both heating and cooling cycles. The TS effect was preceded by anisotropic thermal expansion showing high expansion coefficients. In addition, the nonmolecular crystals show reversible contraction and recovery during multiple heating−cooling cycles due to the self-restorative shape memory effect. The reversible actuation of the CP could be repeated for 20 heating−cooling cycles in differential scanning calorimetry experiments, suggesting its great potential as a multicyclic actuator. Such thermal responsive behavior is unique in metal−organic materials.

Sensing and monitoring toxic contaminants like Fe 3+ , CrO 4 2− , and Cr 2 O 7 2−ions in water is very important due to their harmful effects on biological and environmental systems. Enhanced hydrolytic stability, sensitivity, and selectivity, in addition to their excellent luminescence properties, are important attributes of metal−organic framework (MOF)-based sensors for sensing applications. In this work, the water stable Zn−MOF [Zn 2 (tpeb)(bpdc) 2 ] (where tpeb = 1,3,5-tri-4-pyridyl-1,2-ethenylbenzene and bpdc = biphenyl-4,4′-dicarboxylic acid) was synthesized and characterized. The framework retains its crystallinity and structural integrity in harsh acidic and basic conditions (pH 4−11). Most interestingly, the Zn−MOF demonstrates a strong blue luminescence in water that can be quenched selectively only by contaminants like Fe 3+ , CrO 4 2− , and Cr 2 O 7 2− ions. Higher K sv values and low detection limits in selective luminescence quenching confirm the superior sensing performance, which is comparable to those of contemporary materials. Furthermore, in all cases, quenching efficiency remains unaltered in the presence of interfering ions, even after the compound is used in multiple cycles, which makes this MOF an attractive, reliable, and recyclable luminescent sensor material. The luminescence quenching mechanism is based on the competitive absorption and weak interactions. It is worth noting that most of the reported MOF-based sensors used for the separate sensing of Fe(III) and chromate ions are used in organic media due to their poor hydrolytic stabilities. Reports on the dual sensing of Fe(III) and chromate ions, which are also in aqueous media, are rare. Based on these results, Zn−MOF can be considered as a suitable candidate for advanced practical applications for the efficient sensing of Fe(III) and chromate ions in water.

Metrics & More Article Recommendations CONSPECTUS: Conducting a reaction in the solid state eliminates the usage of solvents. If such reactions are conducted in a single-crystal to singlecrystal (SCSC) fashion, then structural characterization by single-crystal Xray crystallography (SCXRD) techniques provides unequivocal structural details. Although topochemical principles govern, getting single crystals at the end of a SCSC reaction purely depends on the experimental skills of the researchers. SCSC reactions are common among solid-state [2 + 2] cycloaddition reactions (hereafter "photoreaction") after the classical work of Schmidt and co-workers in 1960s. Synthons and tectons in the crystal engineering box can be exploited to bring the functional groups into the required alignment and packing to achieve the desired chemical reactivities and physical properties, respectively. Bringing a pair of alkenes closer together in the organic molecules provides an effective starting point to achieve the goal of crystal engineering.Further, understanding and controlling photoreactivity in the solid state provide a gateway to designing new advanced materials, for example, making cycloreversible optical storage materials, photosalient and photomechanical materials, highly crystalline or even single-crystalline organic polymers, covalent organic framework structures, and organic polymers incorporated inside metal−organic frameworks (MOFs). Photoreactions often proceed in a SCSC manner due to the limited movements of the closely disposed reactive functional groups in the crystals. Thus, these photoreactions yield not only quantitative photoproducts but also regio-and stereospecificity, which are otherwise inaccessible by solution syntheses.The traditional definition of crystals being hard, rigid, and brittle is no longer valid ever since the mechanically responsive crystals were discovered. These dynamic crystals undergo various movements like curling, jumping, hopping, popping, splitting, and wiggling, when exposed to light (called "photosalient effect") or heat (called "thermosalient" effect). These crystals generate new methods of transforming light and heat energy into mechanical work. Recently, photosalient behavior during the [2 + 2] cycloaddition reaction under UV light has been frequently observed. With the emergence of the field of "crystal adaptronics", dynamic photoreactive crystals have emerged as smart actuating materials. This Account aims to provide an overview of the development in this area, since it has garnered much attention among solid state chemists. While presenting selected examples of important strategies, we try to illustrate the intentions and concepts behind the methods developed, which will help in a rational approach for the fabrication of advanced solid state materials. Apart from topochemical transformations, the important roles played by weak interactions, guest solvents, and mechanical grinding have been highlighted in several classes of compounds to show structural transformations that defy th...

The development of multistimuli receptive actuators demands rational combination of suitable functionalities. Achieving such actuating properties in a single crystalline material is a challenge. In spite of several investigation on photo-, thermo-and mechano-responsive crystals, single crystalline material displaying all these effects is unknown. By a judicious combination of photoreactive 2-fluoro-4'-styrylpyridine units and flexible Pb(SCN)2 units, multistimuli responsive 1D CP showing all these dynamic effects has been fabricated. Single crystals of the CP display rapid ballistic events upon UV irradiation triggered by [2+2] cycloaddition of the photoreactive ligands. In addition, macroscopic jumping, bending, splitting of the crystals were observed during both heating and cooling cycles, because of the reversible phase transition. In addition, slander crystals of the CP exhibt elastic deformation upon the application of mechanical force. With handful examples CPs showing macroscopic dynamic effects, this CP paves the way for designing multistimuli responsive multi-salient actuating materials.

A supramolecular crystallization-based approach has been developed for the shape-dependent separation of geometrical isomers under near-ambient conditions. Difficulties to separate such isomers arise because of their very similar physical properties. The present approach relies on the ability of C60 to preferentially form solvate crystals with molecules of a specific geometry. Subsequently, these molecules are released upon mild heating to regenerate pure C60 . By taking isomers of xylene and trimethylbenzene (TMB) as examples, we show that one of the isomers can be extracted from the rest with very high purity. To separate TMB isomers, a new C60 -1,3,5-TMB solvate was developed, which led to the isolation of isomer purities greater than 99.6 %. Versatility, a low operating temperature of approximately 100 °C, a separation efficiency of more than 10 weight % of C60 per cycle, and reagent recyclability makes this a promising molecular shape-sorting approach.

This highlight presents the recent scientific developments in the mechanical properties of crystalline coordination polymers (CPs). CPs have emerged as relatively new crystalline materials in the field of mechanically responsive...