Eliminating restraints: a trigonal-bipyramidal structure has been found to be the energetically f... more Eliminating restraints: a trigonal-bipyramidal structure has been found to be the energetically favored geometry of the hypervalent AX(5) molecule Sb(C(6)F(5))(5) in the solid state and also in fluid solution, where molecules move freely and no crystal packing effects operate.
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 11, 2015
A star-shaped tris(triazolyl)triazine is shown to establish hydrogen-bond interactions with polyc... more A star-shaped tris(triazolyl)triazine is shown to establish hydrogen-bond interactions with polycatenar benzoic acids. The formation of hydrogen-bonded triazine/acid complexes has been demonstrated both in solution and in bulk by different techniques. The complexes, mainly formed by nonmesogenic components, all show enantiotropic hexagonal columnar mesomorphism, which relies on the formation of hydrogen-bond complexes in a triazine/acid ratio of 1:3. This approach combines the straightforward synthesis of a nonmesomorphic triazine core by click chemistry, and the preparation of a supramolecular complex, providing a much more convenient route than covalent synthesis to modify the periphery of triazine discotics and thus to modulate their functionality.
ABSTRACT Chiral ordered mesoporous silica (COMS) was synthesized in basic media by combining tetr... more ABSTRACT Chiral ordered mesoporous silica (COMS) was synthesized in basic media by combining tetraethyl orthosilicate and quaternized aminosilane (with a templating role) silica sources together with four different standard amino acids (arginine, histidine, isoleucine, and proline). Besides the hexagonal MCM-41-type structure, narrow pore size distribution, and high specific surface area, it was found that these solids have potential for enantiomeric separation because of the transference of chirality from the amino acid to the silica. This is illustrated by the resolution of several racemic mixtures (those of proline, isoleucine, trans-4-hydroxyproline, pipecolic acid, valine, leucine, and phenylglycine) with the calcined COMS prepared with l-proline. The opposite behavior observed in induced circular dichroism experiments with calcined COMS, obtained using both enantiomers of proline, confirmed their chiral nature. The high number and variety of existing amino acids, and chiral organic compounds in general, makes these ordered silicas attractive for the production of enantiopure substances.
The self-assembly of polycatenar molecules derived from 1,6-diphenyl-3,4-dipropyl-3-hexen-1,5-diy... more The self-assembly of polycatenar molecules derived from 1,6-diphenyl-3,4-dipropyl-3-hexen-1,5-diyne has been studied in detail by solution NMR spectroscopy. The analysis of the concentration- and temperature-dependent evolution of the chemical shifts and the diffusion coefficients in [D12]cyclohexane agrees well with an isodesmic model of association in this solvent. The association constants for the stacking and entropy and enthalpy of the process have been obtained. The driving force for the aggregation process is provided by a negative enthalpy (ΔH), which is partially compensated by a negative entropy (ΔS). A structural study of the self-assembly in solution has been carried out with the help of NOESY NMR spectroscopic experiments.
Polyenic nonlinear optic (NLO)-phores with a proaromatic 1,4-dithiafulvene electron donor and the... more Polyenic nonlinear optic (NLO)-phores with a proaromatic 1,4-dithiafulvene electron donor and the little explored 1,1,3-tricyano-2-phenylpropene acceptor have been synthesized. Their configurational and conformational features, ground state polarization, and linear and nonlinear optical properties have been determined experimentally and theoretically, and the results are compared to those of tetrathiafulvalene-related derivatives. The newly prepared compounds show close to optimal bond length alternation values for maximizing the first molecular hyperpolarizability, and one of them displays the highest mu beta0 value ever reported for a dithiafulvene-based NLO-phore. The first example of a dithiafulvenylmethylene transfer reaction is also reported.
Eliminating restraints: a trigonal-bipyramidal structure has been found to be the energetically f... more Eliminating restraints: a trigonal-bipyramidal structure has been found to be the energetically favored geometry of the hypervalent AX(5) molecule Sb(C(6)F(5))(5) in the solid state and also in fluid solution, where molecules move freely and no crystal packing effects operate.
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 11, 2015
A star-shaped tris(triazolyl)triazine is shown to establish hydrogen-bond interactions with polyc... more A star-shaped tris(triazolyl)triazine is shown to establish hydrogen-bond interactions with polycatenar benzoic acids. The formation of hydrogen-bonded triazine/acid complexes has been demonstrated both in solution and in bulk by different techniques. The complexes, mainly formed by nonmesogenic components, all show enantiotropic hexagonal columnar mesomorphism, which relies on the formation of hydrogen-bond complexes in a triazine/acid ratio of 1:3. This approach combines the straightforward synthesis of a nonmesomorphic triazine core by click chemistry, and the preparation of a supramolecular complex, providing a much more convenient route than covalent synthesis to modify the periphery of triazine discotics and thus to modulate their functionality.
ABSTRACT Chiral ordered mesoporous silica (COMS) was synthesized in basic media by combining tetr... more ABSTRACT Chiral ordered mesoporous silica (COMS) was synthesized in basic media by combining tetraethyl orthosilicate and quaternized aminosilane (with a templating role) silica sources together with four different standard amino acids (arginine, histidine, isoleucine, and proline). Besides the hexagonal MCM-41-type structure, narrow pore size distribution, and high specific surface area, it was found that these solids have potential for enantiomeric separation because of the transference of chirality from the amino acid to the silica. This is illustrated by the resolution of several racemic mixtures (those of proline, isoleucine, trans-4-hydroxyproline, pipecolic acid, valine, leucine, and phenylglycine) with the calcined COMS prepared with l-proline. The opposite behavior observed in induced circular dichroism experiments with calcined COMS, obtained using both enantiomers of proline, confirmed their chiral nature. The high number and variety of existing amino acids, and chiral organic compounds in general, makes these ordered silicas attractive for the production of enantiopure substances.
The self-assembly of polycatenar molecules derived from 1,6-diphenyl-3,4-dipropyl-3-hexen-1,5-diy... more The self-assembly of polycatenar molecules derived from 1,6-diphenyl-3,4-dipropyl-3-hexen-1,5-diyne has been studied in detail by solution NMR spectroscopy. The analysis of the concentration- and temperature-dependent evolution of the chemical shifts and the diffusion coefficients in [D12]cyclohexane agrees well with an isodesmic model of association in this solvent. The association constants for the stacking and entropy and enthalpy of the process have been obtained. The driving force for the aggregation process is provided by a negative enthalpy (ΔH), which is partially compensated by a negative entropy (ΔS). A structural study of the self-assembly in solution has been carried out with the help of NOESY NMR spectroscopic experiments.
Polyenic nonlinear optic (NLO)-phores with a proaromatic 1,4-dithiafulvene electron donor and the... more Polyenic nonlinear optic (NLO)-phores with a proaromatic 1,4-dithiafulvene electron donor and the little explored 1,1,3-tricyano-2-phenylpropene acceptor have been synthesized. Their configurational and conformational features, ground state polarization, and linear and nonlinear optical properties have been determined experimentally and theoretically, and the results are compared to those of tetrathiafulvalene-related derivatives. The newly prepared compounds show close to optimal bond length alternation values for maximizing the first molecular hyperpolarizability, and one of them displays the highest mu beta0 value ever reported for a dithiafulvene-based NLO-phore. The first example of a dithiafulvenylmethylene transfer reaction is also reported.
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