38 research outputs found
New Acentric Materials Constructed From Aminopyridines And 4-Nitrophenol
Co-crystallization of 4-nitrophenol (I) with five aminopyridines (4-aminopyridine 1, 3,4-diaminopyridine 2, 2,3-diaminopyridine 3, 3-aminopyridine 4, 2-amino-6-methylpyridine 5) and 2,4-diaminopyrimidine 6 resulted in six adducts with the ratio of components 2 : 1 in five and 1 : 1 in one final compounds. Single crystals were grown by slow evaporation technique using ethanol as a solvent. Five adducts with 1-5 crystallize in acentric P21 and Pna21 space groups, and one, 2(I)·6-in centrosymmetric P21/c space group. Compounds 2(I)·1, 2(I)·2, 2(I)·3 are isomorphous, and demonstrate similar H-bonding patterns despite the differences in aminopyridine molecules. Compound 2(I)·5 is isomorphous to two previously reported compounds. Adducts 2(I)·1, 2(I)·2, 2(I)·3, 2(I)·5, 2(I)·6 represent organic salts composed of pyridinium/pyrimidinium cation, 4-nitrophenolate anion, and 4-nitrophenol neutral molecule. The H-bonded 4-nitrophenol-4-nitrophenolate anionic dimers were found in all compounds with 2 : 1 molar ratio. In adduct I·4 both molecules are in neutral form. The IR spectral data support crystallographic conclusions on salts formation. Plane wave pseudopotential density functional theory calculations were used to predict hyperpolarizability tensor components. Our calculations suggest 2(I)·3 as the best candidate for nonlinear optical materials (14 times more active than urea). © 2013 The Royal Society of Chemistry
Pyrimidine-2,4-diamine acetone monosolvate
In the title compound, C4H6N4·C3H6O, the pyrimidine-2,4-diamine molecule is nearly planar (r.m.s. deviation = 0.005 Å), with the endocyclic angles covering the range 114.36 (10)–126.31 (10)°. In the crystal, N—H...N and N—H...O hydrogen bonds link the molecules into ribbons along [101], and weak C—H...π interactions consolidate further the crystal packing
Pyridine-2,5-diamine
In the title molecule, C5H7N3, intracyclic angles cover the range 117.15 (10)–124.03 (11)°. The N atoms of the amino groups have trigonal–pyramidal configurations deviating slightly from the pyridine plane by 0.106 (2) and −0.042 (2) Å. In the crystal, the pyridine N atom serves as an acceptor of an N—H...N hydrogen bond which links two molecules into a centrosymmetric dimer. Intermolecular N—H...N hydrogen bonds between the amino groups further consolidate the crystal packing, forming a three-dimensional network
Unusual Chemical Ratio, Z″ Values, and Polymorphism in Three New <i>N-</i>Methyl Aminopyridine–4-Nitrophenol Adducts
Cocrystallization of 4-nitrophenol
(<b>I</b>) with <i>N</i>-methyl substituted aminopyridines,
4-<i>N</i>-methylaminopyridine <b>1</b>, 2-<i>N</i>-methylaminopyridine <b>2</b>, and 2-<i><i>N,N</i></i>-dimethylaminopyridine <b>3</b>, resulted
in three novel adducts <b>1</b>·2(<b>I</b>), <b>2</b>·3(<b>I</b>), and <b>3</b>·3(<b>I</b>), one of which, <b>2</b>·3(<b>I</b>), was
found in three polymorphic forms, <b>A</b>, <b>B</b>,
and <b>C</b>. The single crystals were grown by slow
evaporation from ethanol. The proton transfer from the phenoxy to
the pyridine moieties was registered in all compounds. The adducts
comprise pyridinium cations, 4-nitrophenolate anions, and varying
in number neutral 4-nitrophenol molecules. Though the asymmetric hydrogen-bonded
network involving the −N<sup>+</sup>H groups of pyridinium
cations and the −C–O<sup>–</sup> and −C–OH
groups of 4-nitrophenol moieties is registered in the adducts, the
delicate balance of noncovalent interactions that include CH···O
hydrogen bonds and face-to-face stacking interactions between the
extended antiparallel arrays of components controls the centrosymmetric
packing. Although three polymorphs of <b>2</b>·3(<b>I</b>) share several structural common features, they reveal significant
differences in the conformation of the pyridinium cation, and the
hydrogen-bonding patterns
Pyridine-4-carbaldehyde–fumaric acid (2/1)
In the title co-crystal, 2C6H5NO·C4H4O4, two crystallographically different hydrogen-bonded trimers are formed, one in which the components occupy general positions, and one generated by an inversion centre. This results in the uncommon situation of Z = 3 for a triclinic crystal. In the formula units, molecules are linked by O—H...N hydrogen bonds
Structural Diversity in the Complexes of Trimeric Perfluoro‑<i>o</i>‑phenylene Mercury with Tetrathia- and Tetramethyltetraselenafulvalene
Five
potential charge transfer complexes of trimeric perfluoro-<i>o</i>-phenylene mercury (<b>I</b>) with tetrathiafulvalene
(TTF) and tetramethyltetraselenefulvalene (TMTSF) were grown from
different solvent mixtures. The adducts (<b>I</b>)<sub>2</sub>·TTF (<b>1</b>) and <b>I</b>·TTF (<b>2</b>) were grown by slow evaporation from the 1:1 mixture of dichloromethane
(CH<sub>2</sub>Cl<sub>2</sub>, DCM) and carbon disulfide (CS<sub>2</sub>). Use of the different 1:1 solvent mixtures of dichloromethane (CH<sub>2</sub>Cl<sub>2</sub>, DCM) and dichloroethane (C<sub>2</sub>H<sub>4</sub>Cl<sub>2</sub>, DCE) has led to the crystalline adducts <b>I</b>·TTF (<b>3</b>) and <b>I</b>·TTF·DCE
(<b>4</b>). Adduct <b>I</b>.TMTSF (<b>5</b>) was
grown by the interface crystallization on the border of two immiscible
layers, ethyl acetate, and carbon disulfide. The cocrystals differ
by the donor–acceptor ratio, molecular packing, and the solvent
inclusion. The components in <b>1</b>–<b>5</b> form
mixed donor–acceptor stacks. The stacks are stabilized by Hg···S
and Hg···C short contacts, while the lateral interactions
between stacks include F···F, CH···F,
and S/Se···F short contacts
Spatially Non-uniform Trap State Densities in Solution-Processed Hybrid Perovskite Thin Films
The
facile solution-processability of methylammonium lead halide
(CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>) perovskites has catalyzed
the development of inexpensive, hybrid perovskite-based optoelectronics.
It is apparent, though, that solution-processed CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films possess local emission heterogeneities,
stemming from electronic disorder in the material. Herein we investigate
the spatially resolved emission properties of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> thin films through detailed emission intensity
versus excitation intensity measurements. These studies enable us
to establish the existence of nonuniform trap density variations wherein
regions of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films exhibit
effective free carrier recombination while others exhibit emission
dynamics strongly influenced by the presence of trap states. Such
trap density variations lead to spatially varying emission quantum
yields and correspondingly impact the performance of both methylammonium
lead halide perovskite solar cells and other hybrid perovskite-based
devices. Of additional note is that the observed spatial extent of
the optical disorder extends over length scales greater than that
of underlying crystalline domains, suggesting the existence of other
factors, beyond grain boundary-related nonradiative recombination
channels, which lead to significant intrafilm optical heterogeneities
Structural Diversity in the Complexes of Trimeric Perfluoro‑<i>o</i>‑phenylene Mercury with Tetrathia- and Tetramethyltetraselenafulvalene
Five
potential charge transfer complexes of trimeric perfluoro-<i>o</i>-phenylene mercury (<b>I</b>) with tetrathiafulvalene
(TTF) and tetramethyltetraselenefulvalene (TMTSF) were grown from
different solvent mixtures. The adducts (<b>I</b>)<sub>2</sub>·TTF (<b>1</b>) and <b>I</b>·TTF (<b>2</b>) were grown by slow evaporation from the 1:1 mixture of dichloromethane
(CH<sub>2</sub>Cl<sub>2</sub>, DCM) and carbon disulfide (CS<sub>2</sub>). Use of the different 1:1 solvent mixtures of dichloromethane (CH<sub>2</sub>Cl<sub>2</sub>, DCM) and dichloroethane (C<sub>2</sub>H<sub>4</sub>Cl<sub>2</sub>, DCE) has led to the crystalline adducts <b>I</b>·TTF (<b>3</b>) and <b>I</b>·TTF·DCE
(<b>4</b>). Adduct <b>I</b>.TMTSF (<b>5</b>) was
grown by the interface crystallization on the border of two immiscible
layers, ethyl acetate, and carbon disulfide. The cocrystals differ
by the donor–acceptor ratio, molecular packing, and the solvent
inclusion. The components in <b>1</b>–<b>5</b> form
mixed donor–acceptor stacks. The stacks are stabilized by Hg···S
and Hg···C short contacts, while the lateral interactions
between stacks include F···F, CH···F,
and S/Se···F short contacts