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Proton in a Confined Space: Structural Studies of H+⊂Crypt-111 Iodide and Some Halogen-Bonded Derivatives
No full textInvited for the cover of this issue is the group of Giuseppe Resnati at the Politecnico di Milano. The image depicts proton cryptation by crypt-111, the smallest cryptand and an effective proton sponge. Read the full text of the article at 10.1002/chem.201701699
Making crystals from crystals: three solvent-free routes to the hydrogen bonded co-crystal between 1,1'-di-pyridyl-ferrocene and anthranilic acid
No full textPolymorphism in Crystalline Cinchomeronic Acid
No full textThe structural relationship between the two crystal forms of cinchomeronic acid (CA 3,4-dicarboxypyridine) has been investigated by single crystal X-ray diffraction, IR and Raman spectroscopy and solid state NMR spectroscopy, showing that the two polymorphs form a monotropic system, with the orthorhombic form I being the thermodynamically stable form, while the monoclinic form II is unstable. In both forms CA crystallizes as a zwitterion and decomposes before melting. The crystal structure and spectroscopic analysis indicate that the difference in stability can be ascribed to the strength of the hydrogen-bonding patterns established by the protonated N-atom and the carboxylic/carboxylate O-atoms
Hydrogen bonding and dynamic behaviour in crystals and polymorphs of dicarboxylic-diamine adducts: A comparison between NMR parameters and X-ray diffraction studies
No full textFumaric, malonic, maleic, and hydromuconic (HOOCCH2(CH)(2)CH2COOH) acids were used to prepare a series of hydrogen-bonded adducts or salts, depending on whether acid-base proton transfer takes place, with the dibase [N-(mu CH2CH2)(3)N] in various stoichiometric ratios. The resulting compounds have been investigated by using the H-1 MAS, N-15, and C-13 cross polarisation magic-angle spinning (CPMAS) methods and discussed in relation to X-ray diffraction studies to ascertain the nature of the O-(HO)-O-..., (NH)-H-...-O, and N+-(HO)-O-...-hydrogen bonds between the various species. In addition, two polymorphic forms of the nialonic compound and a hydrate in the maleic case were examined. We also present the correlations between the chemical shifts of the hydrogen-bonded protons and those from the proton transfer reaction (acid-to-base) with the heavy atom distances. The dynamic behaviour in the solid-state of the [N-( mu CH2C2)(3)N adducts with fumaric 2:1, maleic 1:1 hydrate, and hydromuconic acids, and a malonate 2:1 polymorph adduct have been investigated by using variable-temperature H-1 spinlattice relaxation times. A substantial agreement between the activation energies obtained from fitting the T-1 data and the results of potential energy barrier calculations demonstrates that the facile reorientation of the [N-(mu CH2CH2)(3)N] molecule occurs in several of the adducts
Solid-State Dynamics and High-Pressure Studies of a Supramolecular Spiral Gear
Full text linkThe structures and solid-state dynamics of the supramolecular salts of the general formula [(12-crown-4)2⋅DABCOH2](X)2 (where DABCO=1,4-diazabicyclo[2.2.2]octane, X=BF4, ClO4) have been investigated as a function 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. The two salts are isomorphous and crystallize in the enantiomeric space groups P3221 and P3121. All 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) thanks to the correlation between neighboring molecules, which mesh and rotate in a concerted manner similar to spiral gears. Above 1.55 GPa, a collapse-type transition to a lower-symmetry ordered structure, not attainable at a temperature 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
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