Terminal Substituent Induced Differential Anion Coordination and Self-Assembly: Case Study of Flexible Linear Bis-Urea Receptors

Abstract

For a comprehensive analysis of host–guest binding propensity in their neutral form, three linear flexible bis-urea receptors (L 1 –L 3 ) with different terminal substituents have been synthesized. It has been established that, with the existence of electron-withdrawing or π-acidic phenyl substituents, they act as a possible system that can proficiently coordinate with anions of diverse dimensions constantly initiated by the size of the countercations. The 3,5-bis­(trifluoromethyl)­phenyl-derived isomer (L 1 ) can readily form cooperative neutral self-assemblies irrespective of the size the monovalent halides (viz. chloride, bromide, and iodide anions) and noncooperative neutral self-assemblies with planar divalent carbonate anion. The meta isomer L 2 captures spherical halides, i.e. chloride and bromide, in an isostructural way, forming a 1:2 host–guest assembly, whereas the isomeric para receptor L 3 shows cooperative binding with chloride anions, having coordination number 3. However, due to the greater flexibility and lesser hydrophobicity of receptor L 2 and L 3 in comparison to receptor L 1 , successful crystallization of any oxyanion complexes through the meta and para isomers was not successful.

Self-Assemblies of Solvates, Ionic Cocrystals, and a Salt Based on 4-{[(4-Nitrophenyl)carbamoyl]amino}-N-(pyrimidin-2-yl)benzene-1-sulfonamide: Study in the Solid and Solution States

“…These obvious distinctions in the bond parameters occurred as a consequence of the differences in the ionic radii of the three halides. For the ionic cocrystals of the tetrabutylammonium halides with urea, ,− oximes suggest the requirement of hydrophobic space to accommodate the cation. , In the present case, the hydrophobic arms of the TBA are positioned in the hydrophobic concave part by the geometrically adjustable angular-shaped host in the assembly held by the C29–H···O interactions.…”

“…The nitrification ability of urea derivatives has been enhanced by sulfa drugs . Some alkaline-earth-metal salts have been used to degrade urea derivatives, , and ionic cocrystals of urea have importance in the study of fertilizer actions. , Generally, charge-assisted hydrogen bonds have energy in the range between 12 and 25 kcal/mol, which provides stability to a halide-assisted assembly. − Due to their electrostatic nature, the charge-assisted hydrogen bonds have higher strengths and such hydrogen bonds are possible in an self-assembly of a urea derivative. , Various urea and related compounds have been used as anion receptors of organic ammonium halides. − Urea derivatives are commonly used to selectively detect fluoride ions over the other halide ions present in a solution. In these processes two issues get priority: one is the solvent, and the other is proton transfer from a chromogenic probe molecule.…”

“…Accordingly, the semirigid urea derivative of a sulfadiazine drug, namely 4-{[(4-nitrophenyl)­carbamoyl]­amino}- N -(pyrimidin-2-yl)­benzene-1-sulfonamide (abbreviated as H3Sulfaurea ; Figure ), has been studied. It has an adjustable tether and also has the potential to form dimeric synthons by utilizing hydrogen bond donor–acceptor properties of the NC–NH group. , On the basis of our earlier studies − on the preparation of a tetrabutylammonium cation barricaded in adjustable spaces formed between self-assembled host molecules, a hydrogen-bonded dimer of H3Sulfaurea would have also the possibility of binding to a halide and accommodating the cation on its folds even when the size of the halide ion varies. With such a design thought, the angular-shaped H3Sulfaurea (Figure ) has been chosen as a host; it has an intervening −SO 2 – group controlling the geometry of the molecule.…”

Study on Typical Diarylurea Drugs or Derivatives in Cocrystallizing with Strong H-Bond Acceptor DMSO

“…Diarylureas are frequently used in self-assembly, anion recognition, and cocrystallization as they can act as both H-bond donors through their double NH units and acceptors by the urea CO group. − Etter has summarized complexing rules for diphenylureas taking 1,3-bis­( m -nitrophenyl)­urea as the model substrate in the early 1990s. , The major conclusion is that diarylureas with strong meta-substituted electron-withdrawing substituents have the property to bond with strong acceptor solvents or reagents such as dimethyl sulfoxide (DMSO) and triphenylphosphine oxide (TPPO) in a 1:1 stoichiometry. − Later studies found that diarylureas could also recognize various anions including acid radicals, halides, and metal ions. − Yamasaki et al recently reported the formation of a diphenylurea cocrystal between different diphenylureas . In addition, the introduction of heteroaromatic substitutions (e.g., pyridine) , and more H-bond donors or acceptors (e.g., NO 2 , pyrrole, I, F) − in aromatic units would afford more diverse packing patterns. At the same time, Nanjia, Swift, and co-workers made great efforts to predict the cocrystallization and possible assembly styles from substitution environment, electronic effects, and with the help of computational energy calculation. ,− ,, …”