Three-dimensional architectures constructed via coordination of metal ions to organic linkers (broadly termed as metal-organic frameworks, MOFs), are highly interesting for many demanding applications such as gas adsorption, molecular separation, heterogeneous catalysis, molecular sensing etc. Being constructed from heterogeneous components, such framework solids show characteristic features from both of the individual components as well as framework-specific features. One such interesting physicochemical property is thermal expansion, which arises from thermal vibration from the organic linker and metal ions. Herein, we show a very unique example of thermal responsiveness for DUT-49 framework, a MOF well-known for its distinctive negative gas adsorption (NGA) property. In the guest-free form, the framework shows another counter-intuitive phenomenon of negative thermal expansion (NTE), i.e. lattice size increase with decrease of temperature. However, in the solvated state, it shows both NTE and positive thermal expansion (i.e. lattice size decreases with lowering of temperature, PTE) based on a specific temperature range. When the solvent exists in liquid form inside the MOF pore, it retains the pristine NTE nature of the bare framework. But freezing of the solvent inside the pores induces a strain, which causes a structural transformation through in-plane bending of the linker and this squeezes the framework by ~10 % of the unit cell volume. This effect has been verified using 3 different solvents where the structural contraction occurs immediately at the freezing point of individual solvent. Furthermore, studies on a series of DUT-49(M) frameworks with varying metal confirm the general applicability of this mechanism.<br>
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Data type: Experimental spectroscopic measurements, computer simulation and analysis Files are with filename extensions: DSC, DAT, m, txt Information on origin of the data: EPR spectroscopic measurements with filename extensions DSC, DTA. EPR spectroscopic simulation and analyses with filename extension m. EPR spectra are exported as txt files in ASCII format. X-band CW-EPR spectroscopic measurements were generated by EMX spectrometer equipped with SHQ cavity produced by Bruker. If the dataset includes multiple files that relate to each other: Files in PARACAT_WP4_20201111_ULEI_21_DUT49Mn@7K folder includes X-band CW-EPR spectroscopic measurements; original data are in DTA/DSC and txt formats. Files in PARACAT_WP4_20201111_ULEI_00_DUT49Mn@simulation folder includes computer simulations/analyses of the EPR measurements; data are in m and txt formats. Information on: specialized abbreviations: DUT49Cu – DUT-49(Cu) MOF, DUT49Mn – DUT-49(Mn) MOF, DUT49CuZn – DUT-49(CuZn) MOF, DUT49MnCu – DUT-49(MnCu) MOF. @10K – measured at 10 K definitions of variables: Magnetic field, Temperature. units of measurement: Gauss (G), K, degree (°), milliTesla (mT).
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
EPR measurements at X- (9.5 GHz), Q- (34 GHz) and W-band (94 GHz) on paddlewheel (PW) type post-synthetic metal exchanged DUT-49(M,M): M- Zn, Mn, Cu MOFs are here reported (DUT–Dresden University of Technology). Temperature-dependent X-band measurements are recorded from T = 7 K to T = 170 K on monometallic DUT-49(Cu), DUT-49(Mn), and bimetallic DUT-49(Cu0.7Zn0.3), DUT-49(Cu0.5Mn0.5) MOFs. In the case of the CuII - CuII dimers in DUT-49(Cu), an isotropic exchange coupling of the metal ions (2J = −240(11) cm−1) determined from the EPR intensity of the S = 1 spin state of the CuII–CuII dimers using the Bleaney Blowers equation. The sign of the found isotropic exchange coupling constant confirms an antiferromagnetic coupling between the cupric ions. Also, the MnII ions in the paddle wheels of DUT-49(Mn) are antiferromagnetically coupled. However, at low temperatures, EPR measurements reveal the presence of CuII and MnII monomers in DUT-49(Cu) and DUT-49(Mn), respectively, either associated with extra framework sites or defective paddle wheels. Otherwise, EPR signals observed for bimetallic DUT-49(Cu0.7Zn0.3) and DUT-49(Cu0.5Mn0.5) MOFs reveal the formation of mixed ion CuII–ZnII and CuII–MnII paddle wheels with SCuZn =1/2 and SCuMn = 2 spin states, respectively.
Of all the possible methods for developing inkless and erasable printing media, the best way is to use photochromic materials where new colour can be generated by simply application of suitable light.Typically, photochromic materials have the ability to change their own colour when subjected to a suitable light source and reverts back to its initial colour when the source of the excitation is removed.Thus, by controlling the incidence of the light on the printing media, precise impression of the desired content can be achieved on the media.Again, by the virtue of the reversible nature of the photochromic materials, they can easily return to their original colour, completing the erasing cycle.Thus, a successful media for inkless and erasable printing can be generated which can be used for printing some content on the same paper for multiple cycles, and more importantly without using any ink for printing and toxic chemicals for erasing.But, traditional photochromic materials, in general, bears short lifetime for their photogenerated colour and immediately reverts back to their initial colour when the source of the excitation is removed.Therefore, an attempt to use those materials as a media for inkless and erasable printing is not much promising as the printing will be immediately vanished into the background consisting of those short lived traditional photochromic materials.To overcome this problem, we must look for such a material which can retain their photogenerated colour for a prolonged period of time.In short, we need to modify the photochromic property of the material as per our requirement via chemical modification of the photochromic chromophore.And finally, we must develop a printer which can print the contents on the obtained media precisely for a bulk scale production and application in real life.1.
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