Plastic crystals are solids characterized by disorder–order transitions that are often exploitable for the realization of functional materials. A major challenge in the design of such materials lies in the difficulty of both predicting and tailoring the phase stability and the relative transitions. Herein we describe a simple approach for the modulation of the plastic transition in the ferroelectric salts (R)-3-hydroxlyquinuclidinium chloride and bromide, [QH]Cl and [QH]Br, based on the formation of solid solutions. Mixed crystals of formula [QH]Cl x Br1–x could be prepared over the entire compositional range. Additionally, the iodide analogous [QH]I was synthesized showing an ordered phase not isostructural with those of [QH]Cl and [QH]Br. In spite of the structural differences, binary solid solutions [QH]I z Cl1–z and [QH]Br y I1–y could also be obtained, as well as the ternary solid solutions [QH]Cl x Br y I z . All solids were characterized by a combination of single-crystal and powder X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis techniques in order to map the composition-dependent field of stability of the phases. It was observed that the [QH]Cl x Br1–x solutions show a reversible order–disorder transition, while [QH]I z Cl1–z and [QH]Br y I1–y undergo an unusual first-order transition from the plastic phase to a glassy low-temperature phase. The ternary solid solutions, on the other hand, displayed a more complex behavior, influenced in turn by the prevailing component. Finally, the results are rationalized on the basis of the structural differences between the components, providing a simple criterion for the engineering of plastic phase transitions.
The order-disorder phase transition associated with the uprise of reorientational motion in (DABCOH2) , in the supramolecular salts of general formula [1⋅(DABCOH )]X (where 1=12-crown-4, DABCO=1,4-diazabicyclo[2.2.2]octane, and X=Cl or Br ), has been investigated by variable temperature X-ray diffraction on single crystals and powder samples, as well as by DSC and solid-state NMR spectroscopy (SSNMR). The two compounds undergo a reversible phase change at 292 and 290 K, respectively. The two crystalline materials form solid solutions [1⋅(DABCOH )]Cl Br in the whole composition range (0 < x<1), with a decrease in the temperature of transition to a minimum of ca 280 K, corresponding to x=0.5. Activation energy values for the dynamic processes, evaluated by variable-temperature C magic-angle spinning (MAS) SSNMR and line-shape analysis are ca. 50 kJ mol in all cases. Combined diffraction and spectroscopic evidence has allowed the detection of a novel dynamic process for the (DABCOH ) dications, based on a room temperature precessional motion that is frozen out below the disorder-order transition; to the best of the authors' knowledge this phenomenon has never been observed before.
Zn-to-Co transmetalation of IRMOF-9 introduces major structural changes.
The structures and solid-state dynamics of the supramolecular salts of the generalf ormula [(12-crown-4) 2 ·DABCOH 2 ](X) 2 (whereD ABCO = 1,4-diazabicyclo[2.2.2]octane, X = BF 4 ,C lO 4 )h ave been investigated as af unction of temperature (from 100 to 360 K) and pressure (up to 3.4 GPa), through the combination of variable-temperature and variable-pressure XRD techniques and variable-temperature solid-state NMR spectroscopy.T he two salts are isomorphous and crystallize in the enantiomeric space groups P3 2 2 1 and P3 1 2 1 .A ll building blocks composing the supramolecular complex display dynamic processes at ambient temperature and pressure. It has been demonstrated that the motion of the crown ethers is maintained on lowering the temperature (down to 100 K) or on increasing the pressure (up to 1.5 GPa) thankst ot he correlation between neighboring molecules, whichm esh and rotate in ac oncerted manner similar to spiralg ears. Above 1.55 GPa, ac ollapse-type transition to al ower-symmetry ordered structure, not attainable at at emperature of 100 K, takes place, proving, thus, that the pressure acts as the means to couple and decouple the gears. The relationship between temperature and pressure effects on molecular motion in the solid state has also been discussed.[a] Dr.
Herein we report that 4-pyridinylboronic acid (1) in the solid state self-assembles into tetrameric macrocycles via B–N bond formation. The tetramers are linked via O–H···O bonds resulting in a material that can be exfoliated via sonication to give thinner sheets as we demonstrate via Fourier transform infrared spectroscopy, transmission electron microscopy, selected area electron diffraction, and atomic force microscopy experiments. For comparison, the structure of the related compound 4-(pyridin-4-yl) phenylboronic acid (2) is also discussed.
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