Polymorphic Crystal Structures Research Articles

Synthesis, Characterization, Band gap calculation, DFT study and Biological implication of Two Nitrogen-rich Proligands: Polymorphic Crystal Structures and Hirshfeld surface analyses of a Thiocarbohydrazone

A novel dihydrazone proligand 1,3-bis(pyridin-4-ylmethylideneamino)guanidine hydrochloride (H3L1) is reported along with polymorphic crystal structures of an analogous proligand 1,5-bis(4-pyridinecarboxaldehyde) thiocarbohydrazone (H2L2. H2O & H2L2. 2H2O). The crystal systems of H2L2. H2O and H2L2. 2H2O are monoclinic with P21/c and C2/c space groups. Strong hydrogen bonding interactions are found to be predominate in the H2L2. 2H2O crystal lattice. Hirshfeld surface analysis reveals that, after isotropic H···H interactions, N···H and C···H interactions are found to have the highest contribution to the overall Hirshfeld surface areas of H2L2. H2O and H2L2. 2H2O respectively. The pore volume and surface area of the thiocarbohydrazone polymorphs are also calculated. Direct band gap energies for H3L1 and H2L2 in their solid-states were estimated as 2.33 and 2.58 eV respectively using the Kubelka-Munk model. Molecular geometry of both the compounds are optimised using density functional theory and quantum chemical parameters are calculated. Frontier molecular orbital energy gaps in the gas phase for H3L1 and H2L2 are found to be 4.49 and 3.55 eV respectively, which indicates strong intermolecular interaction in the solid lattice of H3L1. Absorption, distribution, metabolism and excretion (ADME) attributes indicate both compound's potential as drug candidates. In vitro antibacterial study reveals that the thiocarbohydrazone based proligand is a more efficient inhibitor against gram-positive Staphylococcus aureus bacterial species. The anticancer activities of the compounds against MCF-7 human breast cancer cells suggested that H3L1 with an IC50 value of 172.6798 µg/mL has more potent than H2L2 (IC50 value of 279.1881 µg/mL).

Color Polymorphism and Room Temperature Phosphorescence of 4-Bromo-2,7-Di-Tert-Butyl- 9-Methoxypyrene.

Color polymorphism combined with crystal packing-dependent luminescence properties of polymorphs reflects differences in intermolecular interactions in different molecular arrangements. The title compound has two polymorphic crystal structures having strikingly different absorption and luminescence spectra that result from different packing motifs in the crystal lattice. The polymorph with brick wall-like packing of molecules is white and shows very weak violet fluorescence whereas the second polymorph, where molecules are arranged in columnar stacks, is bright yellow and displays intense green fluorescence with maximum at 487 nm (20530 cm-1). In the white polymorph, where the distance between neighboring chromophores is increased, absorption and fluorescence spectra are similar to those of monomer in solution, and intersystem crossing to triplet manifold is the dominant pathway of relaxation. In the yellow polymorph, molecules within the columnar stacks are rotated which mitigates the steric hindrance and leads to closer π-stacking of the pyrene cores. That increases the ππ overlap and strengthens intermolecular interactions decreasing energy of the excited states. This affects emission spectra and photophysical processes-fluorescence yield grows whereas triplet formation yield decreases when S1 is lowered below higher triplet states and conditions for effective vibronic spin-orbit coupling are not favorable. The effect is not observed for other similar pyrene derivatives, testifying the uniqueness of the phenomenon.

Exploring anticancer and antibacterial activities of two self-assembling units: Band gap calculations, DFT studies, and polymorphism of a carbohydrazone ligand

The synthesis and physicochemical characterization of a novel self-assembling unit 1,3-bis(4-hydroxyphenylmethylideneamino)guanidine hydrochloride (H5L1) and polymorphic crystal structures of an analogous proligand 1,5-bis(4-hydroxybenzaldehyde) carbohydrazone (H4L2. DMF & H4L2. H2O) are reported. The crystal systems of H4L2. DMF and H4L2. H2O are monoclinic with C2/c and P21/c space groups. The intermolecular contacts are calculated by Hirshfeld surface analyses, which reveal that H···H interactions have a maximum contribution in the total Hirshfeld surfaces in both the crystal structures. The study also signifies that hydrogen bonding interactions are dominant in the crystal lattice of H4L2. H2O, while the C–H∙∙∙π interactions are also significant in H4L2. DMF lattice. Density functional theory is used for optimizing geometry and calculating quantum chemical parameters. Theoretical frontier molecular energy gaps in the gas phase for H5L1 and H4L2 are found to be 3.49 and 4.09 eV respectively. The solid-state band gaps of H5L1 and H4L2 are determined experimentally using the Kubelka-Munk model and are found to be 2.72 and 2.43 eV respectively, which is indicative of strong intermolecular association in the solid lattice of H4L2. ADME properties are estimated to predict the drug-likeness of the compounds. In vitro antibacterial activity study reveals that the diaminoguanidine based proligand is a more efficient inhibitor against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacterial species. Also, in vitro study of the compounds against human breast cancer MCF-7 cells shows that with the increase in the concentrations of the compounds the percentage of cell viability decreases, which indicates the anticancer potentials of both compounds. The IC50 values of H5L1 and H4L2 against MCF-7 cell lines (205.62 and 247.31 µg/mL) are also found to be better compared to the same (274.59 and 375.45 µg/mL) against the non-cancerous Mouse Fibroblast (L929) cell lines.

A comprehensive study on the intermolecular interactions and energy frameworks exist in crystal structures of Form-I, Form-II and Form-III polymorphs of Ethyl maltol

The present study serves as a comprehensive investigation into the molecular crystal structures of three polymorphic forms of ethyl maltol. Crystal structures of the polymorphs grown via slow evaporation and quench cooling crystallization processes were determined through single crystal X-ray diffraction (SCXRD) analysis. Through the utilization of SCXRD data CIF file as an input, we explored the nature and strength of intermolecular interactions, atom pair close contacts, interaction types, 2D fingerprint plots, surface characteristics and percentage of voids present within each polymorph of ethyl maltol. The comparative analysis involves the application of advanced methods, such as Hirshfeld surface analysis and 3D-energy frameworks using Crystal Explorer 17.5. In a supramolecular organization, intermolecular interaction between the carbonyl and hydroxyl groups is a collective structural motif employed among the three polymorphs. However the three polymorphs share common structural features, but the conformations within the crystal packing of each form are different from each other. Shape Index and Curvedness surfaces reveal π stacking interactions with varying properties on differing sides of the molecular moieties between the polymorph. Fingerprint analysis emphasizes that (H…H) is the predominant interaction whereas (O…H) and (H…O) interactions contribute more towards the generation of H-bond interactions in the structure of ethyl maltol polymorphs. The crystal structures of all the three ethyl maltol polymorphs stabilized by various intermolecular contacts within the Hirshfeld surface area was comparable. The interaction energy and the 3D-energy frameworks offer a visualization of the crystal packing topology, enhancing our understanding of the three-dimensional arrangement of molecules and their structural stability. The resulting overall average total energy values for Form-I, Form-II and Form-III polymorphs of ethyl maltol are -56.3 kJ /mol, -74 kJ /mol and -80.45 kJ /mol respectively which reveals that all the three polymorphs show a significant difference in their total energies and reveals further that Form-III polymorph of ethyl maltol is the most stable one while Form-I is the least stable and Form-II is metastable relatively. Moreover, the dispersion energy framework is predominant over the electrostatic energy framework. The void analysis reveals the percentage of volume occupied by the voids present in the unit cell of Form-I, Form-II, and Form-III polymorphs of ethyl maltol are found to be 7.20%, 6.55 %, and 9.43% respectively.

High Thermoelectric Power Factors in Plastic/Ductile Bulk SnSe2 -Based Crystals.

The recently discovered plastic/ductile inorganic thermoelectric (TE) materials open a new avenue for the fabrication of high-efficiently flexible TE devices, which can utilize the small temperature difference between human body and environment to generate electricity. However, the maximum power factor (PF) of current plastic/ductile TE materials is usually around or less than 10 µW cm-1 K-2 , much lower than the classic brittle TE materials. In this work, a record-high PF of 18.0 µW cm-1 K-2 at 375 K in plastic/ductile bulk SnSe2 -based crystals is reported, superior to all the plastic inorganic TE materials and flexible organic TE materials reported before. The origin of such high PF is from the modulation of material's stacking forms and polymorph crystal structures via simultaneously doping Cl/Br at Se-site and intercalating Cu inside the van der Waals gap, leading to the significantly enhanced carrier concentrations and mobilities. An in-plane fully flexible TE device made of the plastic/ductile SnSe2 -based crystals is successfully developed to show a record-high normalized maximum power density to 0.18W m-1 under a temperature difference of 30 K. This work indicates that the plastic/ductile material can realize high TE power factor to achieve large output electric power density in flexible TE technology.

Optothermal crystallization of hard spheres in an effective bidimensional geometry.

Using colloids effectively confined in two dimensions by a cell with a thickness comparable to the particle size, we investigate the nucleation and growth of crystallites induced by locally heating the solvent with a near-infrared laser beam. The particles, which are "thermophilic," move towards the laser spot solely because of thermophoresis with no convection effects, forming dense clusters whose structure is monitored using two order parameters that gauge the local density and the orientational ordering. We find that ordering takes place when the cluster reaches an average surface density that is still below the upper equilibrium limit for the fluid phase of hard disks, meaning that we do not detect any signof a proper "two-stage" nucleation from a glass or a polymorphic crystal structure. The crystal obtained at late growth stage displays a remarkable uniformity with a negligible amount of defects, arguably because the incoming particles diffuse, bounce, and displace other particles before settling at the crystal interface. This "fluidization" of the outer crystal edge may resemble the surface enhanced mobility giving rise to ultra-stable glasses by physical vapor deposition.

Polymorphic amyloid nanostructures of hormone peptides involved in glucose homeostasis display reversible amyloid formation

A large group of hormones are stored as amyloid fibrils in acidic secretion vesicles before they are released into the bloodstream and readopt their functional state. Here, we identify an evolutionarily conserved hexapeptide sequence as the major aggregation-prone region (APR) of gastrointestinal peptides of the glucagon family: xFxxWL. We determine nine polymorphic crystal structures of the APR segments of glucagon-like peptides 1 and 2, and exendin and its derivatives. We follow amyloid formation by CD, FTIR, ThT assays, and AFM. We propose that the pH-dependent changes of the protonation states of glutamate/aspartate residues of APRs initiate switching between the amyloid and the folded, monomeric forms of the hormones. We find that pH sensitivity diminishes in the absence of acidic gatekeepers and amyloid formation progresses over a broad pH range. Our results highlight the dual role of short aggregation core motifs in reversible amyloid formation and receptor binding.

Polymorphism in carboxamide compounds with high-Z′ crystal structures

Repetitivity of 21-axis symmetry element in three polymorphic crystal structures of carboxamide compound with highZ′ packing problem.

Polymorphic ternary metal chalcogenide solid solution nanopowder as electrocatalyst for hydrogen and oxygen evolution reaction

Here, in this work, a novel synthesis route of polymorphic FexNi1-xSe2 nanopowders consisting of nanoparticles and nanorods for x = 0.2–0.8 has been investigated by a simple hydrothermal process. Coral shaped NiSe2 (x = 0) and nanorod structured FeSe2 (x = 1) are in pure cubic and orthorhombic phase, respectively whereas FexNi1-xSe2 solid solution nanopowder is a combination of both. After important basic characterizations, electrochemical hydrogen evolution reaction (HER) and oxygen evolution reactions (OER) are carried out using FexNi1-xSe2 as cathode and anode, respectively. Among all the variations, x = 0.4 has exhibited the highest HER activity with low overpotential of −106 mV for 10 mA/cm2 in acidic medium and x = 0.2 is the most efficient as anode in OER in alkaline medium with overpotential of 280 mV to drive the current density of 10 mA/cm2 with a small amount of oxidation. Long term stability is achieved without any degradation for both HER and OER in extreme pH for FexNi1-xSe2. The insertion of Fe in the lattice of NiSe2 has improved the conductivity thereby increasing the charge transfer phenomenon. The coexistence of two different morphologies for the optimum ratio of Fe/Ni has generated more active sites participating in the electrochemical reactions. The easy oxidation of catalysts during OER can be restricted by the polymorphic crystal structure of FexNi1-xSe2.

Control of optical properties of luminescent BiVO4:Tm3+ by adjusting the synthesis parameters of microwave-assisted hydrothermal method

Microwave-assisted hydrothermal method was used to synthesise single phase sub-microcrystalline BiVO4:Tm3+ powders with two polymorphic crystal structures – tetragonal zircon-type phase (I41/amd) or monoclinic fergusonite-type phase (I2/b). A single tetragonal phase of BiVO4:Tm3+ was obtained at alkaline pH and it was maintained after annealing up to 400°C, while a single monoclinic phase at acidic pH and in the annealing temperature range of 600-900°C. The structural properties of both phases were correlated with their optical properties, such as the energy gap and luminescent properties. It was observed that the crystal structure and the decreasing the crystallites size changes the bandgap value for BiVO4:Tm3+. The NIR luminescence of Tm3+ ions analysed for both structural phases of the samples with the smallest crystallites sizes showed that the emission intensity is higher for the monoclinic phase than for the tetragonal phase.

Revision of the Crystal Structure of the Orthorhombic Polymorph of Oxyma: On the Importance of π–Hole Interactions and Their Interplay with H–Bonds

In this work the crystal structure of the previously described orthorhombic polymorph of the coupling reagent Oxyma has been revised, corrected now as centrosymmetric and analyzed by means of DFT calculations. In the solid state the structure forms a network of H-bonds and self–assembled dimers that are held together by the formation of N···C π–hole interactions involving the C-atom of the imino group. The H-bonding and π–hole interactions observed in the solid state were rationalized using molecular electrostatic potential (MEP) surfaces, focusing on the H-bond donor-acceptor groups and the π-hole observed above and below the molecular plane. The interactions and their interplay have been characterized by using two methodologies based on the topology of the electron density, which are the quantum theory of “atom-in-molecules” (QTAIM) and the noncovalent interaction plot (NCIplot).

Behavior of counterpoise correction in many-body molecular clusters of organic compounds: Hartree-Fock interaction energy perspective.

The counterpoise (CP) correction by Boys and Bernardi has been well accepted as a reliable strategy to account for basis set superposition error (BSSE) in intermolecular complexes. The behavior of the CP correction was thoroughly studied in individual molecules of molecular complexes. This work studies the performance of the CP correction in many‐body clusters including three‐body clusters of organic compounds in the 3B‐69 dataset. Additionally, we used crystal structures of polymorphs of benzene, aspirin, and oxalyl dihydrazide (ODH) to construct a many‐body cluster dataset, abbreviated as the MBC‐36 dataset, consisting of two, four and eight molecules, and 16 molecules in the case of benzene. A series of Dunning's basis sets—cc‐pXZ and aug‐cc‐pXZ (X = D and T)—were used to predict CP‐corrected Hartree–Fock (HF) interaction energies of the 3B‐69 and MBC‐36 datasets. The CP‐corrected interaction energies were found to be basis‐set independent, whereas the non‐CP corrected interaction energies were found not to a follow a smooth exponential fitting as previously found for electronic energies of individual molecules. This observation was attributed to the presence of non‐additive induction forces in some clusters. Two 2 × 2 × 2 supercells of benzene polymorphs were constructed to explore the local nature of BSSE effects. A cut‐off radius of 10 Å was demonstrated to be sufficient to fully recover these effects. Although the behavior of CP correction was found to be non‐conventional in many‐body clusters of organic compounds, the use of a small basis set such as cc‐pVDZ showed excellent performance in the prediction of HF interaction energies.

Self-seeded crystallization and optical changes of polymorphism poly (vinylidene fluoride) films

Poly (vinylidene fluoride) (PVDF) films with polymorphic crystal structure, α, γ, and γ′, were prepared at 155 °C. The melting points of the three crystals increase progressively in the order of α, γ, and γ′, and the partially melting and recrystallization of the polymorphic PVDF was revealed. During the crystallization process, the α-to-γ′ transition takes place in solid state, result in a great deal of γ tiny crystals or seeds which can survive above melting temperature of α crystals. when heat-treated at 178 °C and cooled, the density of γ self-seeds is so high that no γ spherulites can grow, but only bundles of tube-like γ lamellae, distribute irregularly in the film, without birefringence. With increasing heat-treated temperature (Th), the amount of γ self-seeds decreases. The lamellae after annealing can organize into γ-PVDF spherulites with negative birefringence, and the sizes increase gradually with Th. The second melting one is γ spherulite, which can recrystallize into γ one again at low Th, for example, 180 °C. The γ′-PVDF crystal melt finally, owing to its highest melting point. At low Th, it just loses the birefringence, but can reappear and induce γ crystals to grow from the surrounding melt. At higher Th, 186 °C, it can recrystallize into γ crystals, keeping its original outline, also induce γ crystals, but the nucleation density decreases. At 188 °C, the crystal history of the film is removed completely, the kinetically favored α crystallization reoccurs after cooling. These results can provide a useful way to induce the formation of polar PVDF phases.

Correction to “The Effect of High Pressure on the Crystal Structures of Polymorphs of l-Histidine”

Correction to “The Effect of High Pressure on the Crystal Structures of Polymorphs of <scp>l</scp>-Histidine”

Crystal Structure of Polymorph II and the Pressure–Temperature Phase Diagram of the Dimorphic Anesthetic Butamben

The crystal structure of the low-temperature form II of butamben has been solved in a P21/c space group very similar to that of form I. Form II possesses virtually the same packing as that of the h...

The Impact of Chiral Citronellyl‐Functionalization on Indolenine and Anilino Squaraine Thin Films

AbstractThe impact on chiral aggregation in solution processed and thermally annealed thin films of two indolenine and one anilino squaraines with chiral (S)‐citronellyl functionalization at the nitrogen of the squaraine backbone is investigated. A pseudo polymorphic crystal structure is obtained for one of the indolenine squaraines, but thin films of both compounds are basically non‐aggregated and truly isotropic as evidenced by spectroscopic ellipsometry. The anilino squaraine coalesces and readily aggregates to circular dichroic but discontinuous thin films. The extent of circular dichroism correlates with the morphology of the samples, which is quantified by Mueller matrix polarimetry in combination with atomic force microscopy. The shape of the CD spectra reinforces the hybrid Frenkel and charge‐transfer excitonic nature of the characteristic double hump signatures within unpolarized absorbance spectra of previously investigated non‐chiral anilino squaraines with linear alkyl chain functionalization. Such excitonic CD offers an additional design parameter for next‐generation opto‐electronic devices.

Crystal Structure Prediction for Benzene Using Basin-Hopping Global Optimization.

Organic molecules can be stable in distinct crystalline forms, known as polymorphs, which have significant consequences for industrial applications. Here, we predict the polymorphs of crystalline benzene computationally for an accurate anisotropic model parametrized to reproduce electronic structure calculations. We adapt the basin-hopping global optimization procedure to the case of crystalline unit cells, simultaneously optimizing the molecular coordinates and unit cell parameters to locate multiple low-energy structures from a variety of crystal space groups. We rapidly locate all the well-established experimental polymorphs of benzene, each of which corresponds to a single local energy minimum of the model. Our results show that basin-hopping can be both an efficient and effective tool for polymorphic crystal structure prediction, requiring no a priori experimental knowledge of cell parameters or symmetry.

Polymorphism and structure formation in copper phthalocyanine thin films.

Many polymorphic crystal structures of copper phthalocyanine (CuPc) have been reported over the past few decades, but despite its manifold applicability, the structure of the frequently mentioned α polymorph remained unclear. The base-centered unit cell (space group C2/c) suggested in 1966 was ruled out in 2003 and was replaced by a primitive triclinic unit cell (space group P 1). This study proves unequivocally that both α structures coexist in vacuum-deposited CuPc thin films on native silicon oxide by reciprocal space mapping using synchrotron radiation in grazing incidence. The unit-cell parameters and the space group were determined by kinematic scattering theory and provide possible molecular arrangements within the unit cell of the C2/c structure by excluded-volume considerations. In situ X-ray diffraction experiments and ex situ atomic force microscopy complement the experimental data further and provide insight into the formation of a smooth thin film by a temperature-driven downward diffusion of CuPc molecules during growth.

Polymorphs of 2-[2-[(2,6-dichlorophenyl)amino]phenyl]acetic acid (Diclofenac): Differences from crystallography, Hirshfeld surface, QTAIM and NCIPlots

Differences from crystallography, Hirshfeld surface, QTAIM, and NCIPlots in two monoclinic polymorphs from Diclofenac were studied, in space groups, P 21/ c and C 2/ c , and we make a new refinement of the C 2/ c form. • A new refinement is reported for Diclofenac. • The non-covalent interactions are analyzed using a variety of computational methods. • This work provides a better understanding of the nature of non-covalent interactions on two Diclofenac polymorphs. • The strength of the intermolecular hydrogen bond is the main difference between Diclofenac polymorphs. In this work, an experimental and theoretical comparison of the crystal structure of both polymorphs of the title compound was achieved. Hirshfeld surface analysis ( d norm surface and two-dimensional fingerprint plots) which reveal the nature of intermolecular interactions for the title compounds were performed and discussed. The H∙∙∙H contacts were the major contributors to the Hirschfeld surface with 32.5% and 32.8% for Diclofenac (I) and Diclofenac (II), respectively. The contributions of the O∙∙∙H/H∙∙∙O (15.2%) and O∙∙∙H/H∙∙∙O (13.9%) interactions are smaller, but significant for the crystal architecture of Diclofenac (I) and Diclofenac (II), respectively. The quantum theory of atoms in molecules, reduced density gradient and natural bonds orbital studies was performed. The analysis showed the Cl∙∙∙π, H∙∙∙π, arene-CH∙∙∙Cl, and Cl∙∙∙Cl interactions as the main stabilizing forces of the crystal structure of polymorphs. The strength of the intermolecular hydrogen bond in Diclofenac (I) is greater than Diclofenac (II). The orbital origin of the hydrogen bond is attributed to the electron density transfer from the lone-pair of carbonyl oxygen in the carboxylic group to both, the intermolecular σ*(OH) from the carboxylic group and the intramolecular σ*(NH).

A Toroidal Zr70 Oxysulfate Cluster and Its Diverse Packing Structures

AbstractHerein, we report the discovery of a toroidal inorganic cluster of zirconium(IV) oxysulfate of unprecedented size with the formula Zr70(SO4)58(O/OH)146⋅x(H2O) (Zr70), which displays different packing of ring units and thus several polymorphic crystal structures. The ring measures over 3 nm across, has an inner cavity of 1 nm and displays a pseudo‐10‐fold rotational symmetry of Zr6 octahedra bridged by an additional Zr in the outer rim of the ring. Depending on the co‐crystallizing species, the rings form various crystalline phases in which the torus units are connected in extended chain and network structures. One phase, in which the ring units are arranged in layers and form one‐dimensional channels, displays high permanent porosity (BET surface area: 241 m2 g−1), and thus demonstrates a functional property for potential use in, for example, adsorption or heterogeneous catalysis.