11 research outputs found
Crystallization of Organic Salts and Co-crystals by Sublimation: The Effect of Experimental Conditions
The selective growth of either organic salts or co-crystals
from
the gas phase has been achieved by varying specific conditions in
a series of sublimation experiments. The effect of vacuum pressure,
sublimation time, sublimation temperature and temperature gradient,
physical separation of components, and mass scale on the sublimation
of two acid/base systems, namely succinic acid/hexamethylenetetramine
and oxalic acid/4,4′-bipyridine, was investigated. For both
systems, salt formation was favored at lower pressures and higher
temperatures, and correspondingly co-crystal was selectively formed
at lower temperatures and higher pressures
Guest Exchange in a Robust Hydrogen-Bonded Organic Framework: Single-Crystal to Single-Crystal Exchange and Kinetic Studies
The salt 3,4-lutidinium
pamoate crystallizes as its hemihydrate,
forming a hydrogen-bonded organic framework with tetrahydrofuran (THF)
as a guest in channels in the structure (<b>1·THF</b>).
Extensive investigation has shown this framework to be highly robust:
the THF in the channels can be exchanged for 20 different compounds,
with 13 of these exchanges occurring in a single-crystal to single-crystal
manner. The THF can also be exchanged for the volatile solids pyrazine
or iodine, both via single-crystal to single-crystal transformations.
Stepwise exchange of solvents is also possible, with a sequence of
five exchanges occurring before the crystals begin to deteriorate.
Investigation of the kinetics of exchange in <b>1·THF</b> revealed that exchange occurs according to a deceleratory kinetic
model for contracting volume
Selectivity Behavior of a Robust Porous Organic Salt Based on the Pamoate Ion
The
selectivity of a porous hydrogen-bonded framework, <b>1</b>,
toward various solvent mixtures has been investigated. Framework <b>1</b>, which is the hydrate of 3,4-lutidinium pamoate, crystallizes
as its THF solvate, <b>1·THF</b>. Solvent exchange can
take place either by exposing crystals of <b>1·THF</b> to
solvent vapors or by immersing the crystals in a solvent. Framework <b>1</b> shows preferential inclusion of particular solvents when
exposed to mixed solvent vapors, or to mixed solvents in the liquid
form. Analysis showed that solvents are included in the same ratios
when exposed to mixed solvents in the liquid or vapor phase, despite
the significant differences in mole ratios between the liquid and
vapor phases due to the different vapor pressures of the solvents
investigated. In some cases, when immersed in solvent mixtures containing
acetonitrile or acetone, <b>1·THF</b> recrystallizes as
an acetonitrile or acetone solvate of 3,4-lutidinium pamoate. The
crystal structures of these two new solvates are also reported
A Series of Polymorphs of Hexakis(4-fluorophenoxy)cyclotriphosphazene
A series of conformational polymorphs of hexakisÂ(4-fluorophenoxy)Âcyclotriphosphazene
have been identified and characterized. Three of the four polymorphs
are previously unreported. Thermal analysis coupled with variable
temperature powder X-ray diffraction has shown that conversion between
polymorphs occurs at well-defined temperatures. The high temperature
form is metastable at room temperature and is never obtained from
solution. Two forms are observed in solution crystallization experiments,
a monoclinic form and a triclinic form. Slurry experiments revealed
that the triclinic form is the most stable at room temperature. The
fourth polymorph is observed only at low temperatures. Interconversion
between three of the polymorphs occurs in a single-crystal to single-crystal
manner
Cyanocalix[4]arenes: synthesis, crystal structures and reactivity studies
<p>Herein, we describe an improved method to synthesise mono-, di- and tetra-cyanocalix[4]arene and report their crystal structure determinations. We also report our attempts to further functionalise the cyanocalix[4]arenes into dithiadiazolyl-calix[4]arenes, and propose a hypothesis as to why the cyano group on a calix[4]arene is an extremely challenging group to modify.</p
A Series of Polymorphs of Hexakis(4-fluorophenoxy)cyclotriphosphazene
A series of conformational polymorphs of hexakisÂ(4-fluorophenoxy)Âcyclotriphosphazene
have been identified and characterized. Three of the four polymorphs
are previously unreported. Thermal analysis coupled with variable
temperature powder X-ray diffraction has shown that conversion between
polymorphs occurs at well-defined temperatures. The high temperature
form is metastable at room temperature and is never obtained from
solution. Two forms are observed in solution crystallization experiments,
a monoclinic form and a triclinic form. Slurry experiments revealed
that the triclinic form is the most stable at room temperature. The
fourth polymorph is observed only at low temperatures. Interconversion
between three of the polymorphs occurs in a single-crystal to single-crystal
manner
Polymorphic Behavior of Two Organic Zwitterions: Two Rare Cases of No Observable Conversion between Polymorphs
The
solid-state behavior of two organic zwitterions, (<i>Z</i>)-3-carboxy-2-(4-cyanopyridin-1-ium-1-yl)-acrylate (<b>1</b>) and (<i>Z</i>)-1-(3-carboxy-1,1-dihydroxyprop-2-en-1-ide-2-yl)-pyridin-1-ium
(<b>2</b>), has been extensively investigated. Variation of
crystallization conditions resulted in the identification of two conformational
polymorphs of <b>1</b>, a kinetic and thermodynamic form. Three
polymorphs of <b>2</b>, where the formation of a particular
polymorph depends entirely on solvent of crystallization, were also
identified. The relationship between the polymorphs of both <b>1</b> and <b>2</b> has been extensively studied, and attempts
were made to interconvert between forms to determine their relative
stability. No interconversion between polymorphs is observed in either <b>1</b> or <b>2</b>. In the case of <b>1</b>, this is
likely due to restrictions on rotation of the carboxylic group in
the solid state, which is required for conversion between polymorphs
Cobalt Porphyrin–Thiazyl Radical Coordination Polymers: Toward Metal–Organic Electronics
Herein we delineate an unusual one-dimensional
coordination polymer
(CP), <b>3</b>, prepared from <i>S</i> = 1/2 CoÂ(TPP), <b>1</b> (TPP = 5,10,15,20-tetraphenylporphyrin dianion), and <i>S</i> = 1/2 4-(4′-pyridyl)-1,2,3,5-dithiadiazolyl (py-DTDA)
radical, <b>2</b>. The atypically long S–S distance for
CP <b>3</b> (2.12 Ã…) reflects fractional electron transfer
from the formally CoÂ(II) ion into the antibonding Ï€-SOMO of
the metal-bound py-DTDA bridging ligand. The bonding in solid CP <b>3</b> involves noninteger redox states in a resonance hybrid repeat
unit best formulated as [CoÂ(TPP)]<sup>0.5+</sup> hemication (Co<sup>2.5+</sup>) bound to a dithiadiazolide hemianion (py-DTDA<sup>0.5–</sup>). DFT calculations confirm the metal to ligand charge transfer (MLCT)
character of the low-lying electronic states (641, 732, and 735 nm)
observed for CP <b>3</b> and show that oligomer chains of length
≥14 repeat units tend toward a band structure with a limiting
band gap energy of 0.669(6) eV. In dichloromethane, the reaction between
radicals <b>1</b> and <b>2</b> involves coordination of
the CoÂ(II) ion by a py-DTDA ring sulfur atom, orbitally favored spin-pairing,
and the formation of the thermodynamically favored diamagnetic five-coordinate
S-bound adduct, CoÂ(TPP)Â(<i>S</i>-py-DTDA), <b>3a</b>. Polymerization and crystallization of <b>3a</b> affords diamagnetic
CP <b>3</b>. Dissolution of CP <b>3</b> in DMSO favors
Co–S bond heterolysis, yielding the diamagnetic six-coordinate
purple N-bound Co<sup>III</sup>(TPP)Â(<i>N</i>-py-DTDA<sup>–</sup>)Â(Oî—»SMe<sub>2</sub>) complex (λ<sub>max</sub>, 436 nm). However, monomerization of CP <b>3</b> in dry 1,2-dichloroethane
affords bright green diamagnetic Co<sup>III</sup>(TPP)Â(<i>N</i>-py-DTDA<sup>–</sup>), <b>3b</b>, with multiple MLCT
bands in the 800–1100 nm NIR region and a red-shifted Soret
band (λ<sub>max</sub>, 443 nm). Implications for the use of
CP <b>3</b> in electronic devices are discussed based on its
density of states
Cobalt Porphyrin–Thiazyl Radical Coordination Polymers: Toward Metal–Organic Electronics
Herein we delineate an unusual one-dimensional
coordination polymer
(CP), <b>3</b>, prepared from <i>S</i> = 1/2 CoÂ(TPP), <b>1</b> (TPP = 5,10,15,20-tetraphenylporphyrin dianion), and <i>S</i> = 1/2 4-(4′-pyridyl)-1,2,3,5-dithiadiazolyl (py-DTDA)
radical, <b>2</b>. The atypically long S–S distance for
CP <b>3</b> (2.12 Ã…) reflects fractional electron transfer
from the formally CoÂ(II) ion into the antibonding Ï€-SOMO of
the metal-bound py-DTDA bridging ligand. The bonding in solid CP <b>3</b> involves noninteger redox states in a resonance hybrid repeat
unit best formulated as [CoÂ(TPP)]<sup>0.5+</sup> hemication (Co<sup>2.5+</sup>) bound to a dithiadiazolide hemianion (py-DTDA<sup>0.5–</sup>). DFT calculations confirm the metal to ligand charge transfer (MLCT)
character of the low-lying electronic states (641, 732, and 735 nm)
observed for CP <b>3</b> and show that oligomer chains of length
≥14 repeat units tend toward a band structure with a limiting
band gap energy of 0.669(6) eV. In dichloromethane, the reaction between
radicals <b>1</b> and <b>2</b> involves coordination of
the CoÂ(II) ion by a py-DTDA ring sulfur atom, orbitally favored spin-pairing,
and the formation of the thermodynamically favored diamagnetic five-coordinate
S-bound adduct, CoÂ(TPP)Â(<i>S</i>-py-DTDA), <b>3a</b>. Polymerization and crystallization of <b>3a</b> affords diamagnetic
CP <b>3</b>. Dissolution of CP <b>3</b> in DMSO favors
Co–S bond heterolysis, yielding the diamagnetic six-coordinate
purple N-bound Co<sup>III</sup>(TPP)Â(<i>N</i>-py-DTDA<sup>–</sup>)Â(Oî—»SMe<sub>2</sub>) complex (λ<sub>max</sub>, 436 nm). However, monomerization of CP <b>3</b> in dry 1,2-dichloroethane
affords bright green diamagnetic Co<sup>III</sup>(TPP)Â(<i>N</i>-py-DTDA<sup>–</sup>), <b>3b</b>, with multiple MLCT
bands in the 800–1100 nm NIR region and a red-shifted Soret
band (λ<sub>max</sub>, 443 nm). Implications for the use of
CP <b>3</b> in electronic devices are discussed based on its
density of states
Solid-State Supramolecular Chemistry of a Benzylpyridine-Functionalized Zwitterion: Polymorphism, Interconversion, and Porosity
The
reaction between acetylenedicarboxylic acid and 4-benzylpyridine
yields two products: a salt and a zwitterion. The relationship between
these two products has been investigated, revealing that the salt
is the kinetic product of the reaction and the zwitterion is the thermodynamic
product. The zwitterion has four polymorphs and three solvates. Interconversion
between these forms has been studied and was shown to be solvent-mediated
when it occurs; conversion between most polymorphic forms cannot be
achieved using thermal methods. The temperature at which the reaction
to form the zwitterion is carried out and the solvent system used
are crucial in determining which polymorphic form crystallizes from
the reaction. In addition, polymorphic Form I is shown to be porous
to dioxane