A novel three-dimensional metal-organic framework (MOF) that displays anisotropic thermal expansion has been prepared and characterized by single-crystal X-ray diffraction (SCD) and thermal analysis. The as-prepared MOF has one-dimensional channels containing guest molecules that can be removed and/or exchanged for other guest molecules in a single-crystal to single-crystal fashion. When the original guest molecules are replaced there is a noticeable effect on the host mechanics, altering the thermal expansion properties of the material. This study of the thermal expansion coefficients of different inclusion complexes of the host MOF involved systematic alteration of guest size, i.e., methanol, ethanol, n-propanol, and isopropanol, showing that fine control over the thermal expansion coefficients can be achieved and that the coefficients can be correlated with the size of the guest. As a proof of concept, this study demonstrates the realizable principle that a single-crystal material with an exchangeable guest component (as opposed to a composite) may be used to achieve a tunable thermal expansion coefficient. In addition, this study demonstrates that greater variance in the absolute dimensions of a crystal can be achieved when one has two variables that affect it, i.e., the host-guest interactions and temperature.

A soft porous material [Zn(L)2(OH)2]n·Guest (where L is 4-(1H-naphtho[2,3-d]imidazol-1-yl)benzoate, and Guest is water or methanol) exhibits the strongest ever observed negative area compressibility (NAC), an extremely rare property, as at hydrostatic pressure most materials shrink in all directions and few expand in one direction. This is the first NAC reported in metal-organic frameworks (MOFs), and its magnitude, clearly visible and by far the highest of all known materials, can be reversibly tuned by exchanging guests adsorbed from hydrostatic fluids. This counterintuitive strong NAC of [Zn(L)2(OH)2]n·Guest arises from the interplay of flexible [-Zn-O(H)-]n helices with layers of [-Zn-L-]4 quadrangular puckered rings comprising large channel voids. The compression of helices and flattening of puckered rings combine to give a giant piezo-mechanical response, applicable in ultrasensitive sensors and actuators. The extrinsic NAC response to different hydrostatic fluids is due to varied host-guest interactions affecting the mechanical strain within the range permitted by exceptionally high flexibility of the framework.

Astute combination of basic functionality and luminescence property can pursue multifunctional metal−organic frameworks (MOFs) with assorted applications such as selective CO 2 adsorption, specific detection of explosive nitro compounds, and toxic metal ion sensing. The bifunctional ligand 4-(4-carboxyphenyl)-1,2,4-triazole (HL) is used to build the framework [Cd(L) 2 ]•(DMF) 0.92 (1) (L = L −1 , DMF = N,N′-dimethylformamide), having a free N atom decorated porous channel. The solvothermal synthesis is extended to produce three isoskeletal frameworks in diverse solvents, where pore size maximizes in 2 by employing N,N′-diethylformamide solvent. The activated framework [Cd(L) 2 ] exhibits strong CO 2 affinity with good CO 2 /N 2 selectivity, and shows minimum CO 2 loss during five adsorption−desorption cycles. Sensing studies for nitro-aromatic compounds in DMF reveal highly specific detection of 2,4,6-trinitophenol (TNP) with remarkable quenching (K SV = 9.3 × 10 4 M −1 ) and low limit of detection (LOD: 0.3 ppm). The quenching mechanism is ascribed to the combined existence of static and dynamic quenching plus resonance energy transfer. The activated framework further shows highly selective luminescent detection of Cu 2+ ions with a quenching constant of 4.4 × 10 3 M −1 and very low LOD of 3.9 ppm. The detection of Cu 2+ ions accompanies a visible color change in solution and solid phase, which validates the present system as a potential colorimetric Cu 2+ sensor. Of note is that bifunctional sensor shows excellent reusability toward TNP and Cu 2+ detection. Overall, selective and multicycle CO 2 adsorption, together with efficient sensing of both TNP and Cu 2+ ion, manifest this pore-functionalized MOF as a versatile material for sustainability.

A peptidomimetic compound undergoes a reversible single-crystal-to-single-crystal transformation upon guest release/uptake with the transformation involving a drastic conformational change. The extensive and reversible alteration in the solid state is connected to the formation of an unprecedented "CH-π zipper" which can reversibly open and close (through the formation of CH-π interactions), thus allowing for guest sensing.

4-Bromobenzonitrile was crystallised by sublimation under vacuum. The crystals show highly flexible plastic bending along two perpendicular faces when a mechanical force is applied. The rare occurrence of bending along two perpendicular faces results in twisting or helix formation.