In situ cryocrystallization of low melting chloro and bromo substituted anilines

Nonlinear optical organic-inorganic crystals: synthesis, structural analysis and verification of harmonic generation in tri-(o-chloroanilinium nitrate)

The structural and nonlinear optical properties of a new anilinium hybrid crystal of chemical formula (C₆H₇NCl⁺·NO₃^-)₃ have been investigated. The crystal structure was determined from single-crystal X-ray diffraction measurements performed at a temperature of 100 K which show that the compound crystallizes in a noncentrosymmetric space group (Pna2₁). The structural analysis was coupled with Hirshfeld surface analysis to evaluate the contribution of the different intermolecular interactions to the formation of supramolecular assemblies in the solid state that exhibit nonlinear optical features. This analysis reveals that the studied compound is characterized by a three-dimensional network of hydrogen bonds and the main contributions are provided by the O...H, C...H, H...H and Cl...H interactions, which alone represent ∼85% of the total contributions to the Hirshfeld surfaces. It is noteworthy that the halogen...H contributions are quite comparable with those of the H...H contacts. The nonlinear optical properties were investigated by nonlinear diffuse femtosecond-pulse reflectometry and the obtained results were compared with those of the reference material LiNbO₃. The hybrid crystals exhibit notable second (SHG) and third (THG) harmonic generation which confirms its polarity is generated by the different intermolecular interactions. These measurements also highlight that the THG signal of the new anilinium compound normalized to its SHG counterpart is more pronounced than for LiNbO₃.

Role of Fluorine in Weak Interactions in Co-crystals

The presence of the C–F bond (commonly referred to as organic fluorine) in a large number of pharmaceutically relevant compounds suggests that it may be used in the production of novel salts and co-crystals that have intermolecular interactions involving fluorine. There is an ongoing debate in this context as fluorine is characterized by its high electronegativity, relatively small size and very low polarizability. The propensity of hydrogen to participate in generating highly directional and energetically stable hydrogen bonds has been exploited in the design of co-crystals and salts of many pharmaceutical compounds. A direct extension of this property to fluorine, however, is not plausible and thus intermolecular interactions involving fluorine must be quantified. Recent results and new approaches designed to evaluate organic fluorine which provide useful inputs for the design of co-crystals and salts are discussed in this chapter.

Conformational preference of chlorothioformate species: molecular structure of ethyl chlorothioformate, ClC(O)SCH2CH3, in the solid phase and NBO analysis

The molecular structure of ethyl chlorothioformate, ClC(O)SCH2CH3, has been investigated in the solid phase by X-ray diffraction analysis at low temperature using a miniature zone-melting procedure and IR laser radiation. The crystalline solid consists exclusively of molecules with the synperiplanar conformation with respect to the C=O double bond and the S—C single bond, and gauche orientation of the ethyl group (syn-gauche). These results coincide with previous studies devoted to gas-phase conformational properties. The conformational preference for the ClC(O)SY (Y = Cl, CF3, CH3 and CH2CH3) series of molecules was rationalized using the natural bond orbital (NBO) scheme. It was found that both resonance (mesomeric) and anomeric (hyperconjugation) intermolecular charge-transfer interactions are important for describing the syn ↔ anti equilibrium, also illustrating the effect of electronegativity of the substituent in the conformation preference of the ClC(O)S— moiety. On the basis of the atoms in molecules (AIM) theory, intermolecular interactions have been characterized in the B3LYP/6-31G** periodic boundary electron density.