Crystallographic, spectroscopic and thermal studies of 1-(4-bromophenyl)-5-(2,5-dimethyl-1H-pyrrol-1-yl)-3-methyl-1H-pyrazole.

The new title pyrrole-pyrazole derivative, C16H16BrN3, was synthesized through a citric acid-catalyzed Paal-Knorr reaction between acetonylacetone and 1-(4-bromophenyl)-3-methyl-1H-pyrazol-5-amine under mild reaction conditions. This synthetic protocol is noteworthy for its utilization of stoichiometric amounts of the reactants, an ecofriendly solvent and a cost-effective, non-toxic and biodegradable organocatalyst. A comprehensive understanding of the molecular structure was gained through spectroscopic, thermal and X-ray crystallographic analyses. The crystal structure is characterized by weak interactions, where only C-H...π connections contribute to the hydrogen-bond contacts. The supramolecular assembly is controlled by dispersion forces. However, the energy frameworks demonstrate that these forces act in three dimensions, providing enough stability, as observed in TGA-DSC (thermogravimetric analysis-differential scanning calorimetry) studies.

A Theoretical Analysis of Interaction Energies and Intermolecular Interactions between Amphotericin B and Potential Bioconjugates Used in the Modification of Nanocarriers for Drug Delivery.

Amphotericin B (AmB) is an antibiotic with a wide spectrum of action and low multidrug resistance, although it exhibits self-aggregation, low specificity, and solubility in aqueous media. An alternative for its oral administration is its encapsulation in polymers modified with bioconjugates. The aim of the present computational research is to determine the affinity between AmB and six bioconjugates to define which one could be more suitable. The CAM-B3LYP-D3/6-31+G(d,p) method was used for all computational calculations. The dimerization enthalpy of the most stable and abundant systems at pH = 7 allows obtaining this affinity order: AmB_1,2-distearoyl-sn-glycerol-3-phosphorylethanolamine (DSPE) > AmB_γ-cyclodextrin > AmB_DSPEc > AmB_retinol > AmB_cholesterol > AmB_dodecanol, where DSPEc is a DSPE analog. Quantum theory of atoms in molecules, the non-covalent interactions index, and natural bond orbital analysis revealed the highest abundance of noncovalent interactions for AmB-DSPE (51), about twice the number of interactions of the other dimers. Depending on the interactions' strength and abundance of the AmB-DSPE dimer, these are classified as strong: O-H---O (2), N-H---O (3) and weak: C-H---O (25), H---H (18), C-H---C (3). Although the C-H---O hydrogen bond is weak, the number of interactions involved in all dimers cannot be underestimated. Thus, non-covalent interactions drive the stabilization of copolymers, and from our analysis, the most promising candidates for encapsulating are DSPE and γ-cyclodextrin.

Infrared Spectroscopy Evidence of Weak Interactions in Frustrated Lewis Pairs Formed by Tris(pentafluorophenyl)borane.

Frustrated Lewis pairs (FLPs) have been widely investigated as promising catalysts due to their metal-free feature and ability to activate small molecules. Since their discovery, many works have been investigating how these Lewis pairs (intermolecular pairs) are held together in an encounter complex. This prompted several studies based on theoretical investigations, but experimental ones are limited yet. In this communication we show evidence of weak intermolecular interactions between Lewis acids and Lewis bases, distinguishing the Lewis adduct from FLPs, by probing fluorine-carbon vibrational modes using infrared spectroscopy. The main evidence is based on the band shifts occurring in FLPs due to weak hydrogen bonds between the hydrogen atoms of the Lewis base and the fluorine atoms of Lewis acid.

Two rhodamine 6G derivative compounds: a structural and fluorescence single-crystal study.

The synthesis, characterization, structural analysis and fluorescence properties of two rhodamine 6G derivatives are described, namely a propargylamine derivative, 3',6'-bis(ethylamino)-2',7'-dimethyl-2-(methylcyanide)spiro[isoindole-1,9'-xanthen]-3(2H)-one (I), and a γ-aminobutyric acid (GABA) derivative, 3',6'-bis(ethylamino)-2',7'-dimethyl-3-oxospiro[isoindole-1,9'-xanthen]-2(3H)-yl)butyricacid (II). Both structures are compared with four similar ones from the Cambridge Structural Database (CSD), and the interactions involved in the stabilization are analyzed using the atoms in molecules (AIM) theory. Finally, a single-crystal in-situ reaction study is presented, carried out by fluorescence methods, which enabled the `opening' of the spirolactam ring in the solid phase.

The role of OH O and CH O hydrogen bonds and H H interactions in ethanol/methanol-water heterohexamers.

Bioethanol is one of the world's most extensively produced biofuels. However, it is difficult to purify due to the formation of the ethanol-water azeotrope. Knowledge of the azeotrope structure at the molecular level can help to improve existing purification methods. In order to achieve a better understanding of this azeotrope structure, the characterization of (ethanol)5-water heterohexamers was carried out by analyzing the results of electronic structure calculations performed at the B3LYP/6-31+G(d) level. Hexamerization energies were found to range between -36.8 and -25.8 kcal/mol. Topological analysis of the electron density confirmed the existence of primary (OH…O) hydrogen bonds (HBs), secondary (CH…O) HBs, and H…H interactions in these clusters. Comparison with three different solvated alcohol systems featuring the same types of atom-atom interactions permitted the following order of stability to be determined: (methanol)5-water > (methanol)6 > (ethanol)5-water > (ethanol)6. These findings, together with accompanying geometric and spectroscopic analyses, show that similar cooperative effects exist among the primary HBs for structures with the same arrangement of primary HBs, regardless of the nature of the molecules involved. This result provides an indication that the molecular ratio can be considered to determine the unusual behavior of the ethanol-water system. The investigation also highlights the presence of several types of weak interaction in addition to primary HBs. Graphical Abstract Water-ethanol clusters exhibit a variety of interaction types between their atoms, such as primary OH...O (blue), secondary CH...O (green) and H...H (yellow) interactions as revealed by Quantum Chemical Topology.

A comparative study of the packing of two polymorphs of the nickel(II) pincer complex [2,6-bis(di-tert-butylphosphinoyl)-4-(3,5-dinitrobenzoyloxy)phenyl-κ(3)P,C(1),P']chloridonickel(II).

Pincer complexes can act as catalysts in organic transformations and have potential applications in materials, medicine and biology. They exhibit robust structures and high thermal stability attributed to the tridentate coordination of the pincer ligands and the strong σ metal-carbon bond. Nickel derivatives of these ligands have shown high catalytic activities in cross-coupling reactions and other industrially relevant transformations. This work reports the crystal structures of two polymorphs of the title Ni(II) POCOP pincer complex, [Ni(C29H41N2O8P2)Cl] or [NiCl{C6H2-4-[OCOC6H4-3,5-(NO2)2]-2,6-(OP(t)Bu2)2}]. Both pincer structures exhibit the Ni(II) atom in a distorted square-planar coordination geometry with the POCOP pincer ligand coordinated in a typical tridentate manner via the two P atoms and one arene C atom via a C-Ni σ bond, giving rise to two five-membered chelate rings. The coordination sphere of the Ni(II) centre is completed by a chloride ligand. The asymmetric units of both polymorphs consist of one molecule of the pincer complex. In the first polymorph, the arene rings are nearly coplanar, with a dihedral angle between the mean planes of 27.9 (1)°, while in the second polymorph, this angle is 82.64 (1)°, which shows that the arene rings are almost perpendicular to one another. The supramolecular structure is directed by the presence of weak C-H...O=X (X = C or N) interactions, forming two- and three-dimensional chain arrangements.

A temperature-induced order-disorder phase transition in a 4-substituted 4,2':6',4''-terpyridine.

Crystals of 4'-(isoquinolin-4-yl)-4,2':6',4''-terpyridine (iqtp), C24H16N4, grown from an ethanol solution, undergo a reversible first-order single-crystal to single-crystal phase transition at Tc in the range 273-275 K, from a disordered higher-temperature phase [form (I)] in the space group P21/c, with one single molecule in the asymmetric unit, to an ordered lower-temperature one [form (II)] in the space group P21/n, with two independent molecules in the asymmetric unit. There is a group-subgroup relationship linking (I)-(II), due to cell doubling and the disappearance of a number of symmetry operations. In addition to X-ray diffraction, the transition has been monitored by Raman spectroscopy and differential scanning calorimetry, the latter disclosing an enthalpy change of 0.72 (6) kJ mol(-1). Variations of the unit-cell parameters with temperature between 170 and 293 K are presented. The evolution of diffraction spots in the vicinity of the transition temperature shows the coexistence of both phases, confirming the first-order character of the transition. Structural details of both phases are analyzed and intermolecular interactions compared in order to investigate the mechanism of the phase transition. A three-dimensional Hirshfeld surface analysis was performed to corroborate the significant changes in the intermolecular features.