Progressive Cation Triggered Anion Binding by Electron-Rich Scaffold: Case Study of a Neutral Tripodal Naphthyl Thiourea Receptor

Abstract

A neutral tripodal electron-rich anion receptor L, decorated from a tren building block, has been deliberately synthesized from acetonitrile for thorough investigation of host− guest binding aptitude in the solid state especially. The naphthylbased tris-thiourea scaffold, without the presence of any π-acidic or electron-withdrawing aryl terminals, has been established as a potential system that can efficiently bind anions of varied dimensionality consistently triggered by the size of the countercation, as regularly observed from single crystal X-ray analysis, and well supported by solution state NMR binding studies. The newness of this report is the systematic and consistent solid state anion binding within the inner tripodal receptor cleft of highly electron-rich naphthyl terminals. Although the receptor L was first synthesized in the 19th century, no solid state binding studies have been reported until now. However, numerous tren-based urea/thiourea ligands with several terminal functionalizations having a more acidic tripodal hydrophobic pocket were extensively reported as anion receptors in the solid state over the past decades. In contrast, even within the less hydrophobic and very small inner tripodal cleft, the naphthyl thiourea receptor L still effectively entraps spherical fluoride (1a, 1b), relatively larger spherical chloride (2a, 2b) and bromide (3a, 3b), planar nitrate (4), and tetrahedral sulfate (5) anions via a 1:1 host−guest complexation mode, regularly triggered by n-TBA/TEA countercations.

Self-Assemblies of Positional Isomeric Linear Bis-Urea Ligands with Oxyanions/Hydrated Oxyanions: Evidence of F– and OH– Induced Atmospheric CO2 Fixation

“…Continuing our group’s pursuit in the field of substituent driven anionic/hydrated anionic supramolecular self-assemblies of acyclic receptors, − herein we develop a class of nitro-phenyl functionalized comparatively less cooperative and more challenging positional isomeric linear bis-urea receptors L 1 – L 3 (Scheme ), derived from the least converging aromatic diamine ( para -phenylenediamine) to investigate the coordination behavior with anions/hydrated anions in neutral form. Structural studies reveal that both para -isomer ( L 1 ) and meta -isomer ( L 1 ) are capable of (HCO 3 ) 2 -dimer entrapment either by fluoride or hydroxide induced fixation of atmospheric CO 2 in complexes 1a , 2a , and 2b .…”

Urea- and Thiourea-Based Receptors for Anion Binding

“…Anion coordination chemistry has began its journey in 1968 with the pioneering work of Park and Simmons with the discovery of diazabicyclic compounds, known as katapinands. 14 Since then, a decent amount of work has been published on anion binding with artificial receptors based on a variety of functional groups, such as amine, 15,16 amide, 17,18 thioamide, 19,20 urea, 21,22 thiourea, 23,24 pyrrole, 25,26 indole, 27,28 and transitionmetal complexes. 29,30 Among the various receptors, urea-and thiourea-based compounds serve as good fits as anion receptors due to their ability to coordinate an anion by utilizing directional H bonds.…”

Trapped Cyclic Dimeric Oxyanion Assembly by a Urea-Functionalized Receptor: Potent Application in Linear Discriminant Analysis and as Antibacterial Agents

“…Bisulfates also are known to affect human health by causing breathing difficulties, burning pain in the mouth, chest pain, burning of the esophagus, diarrhea, etc. To date, various neutral and protonated anion receptors, having multiple NH units, have been reported with topological complementarities in their molecular assemblies. − In this regard, tactically synthesized urea-derived polytopic neutral receptors seem to be potentially significant to researchers for the complete encapsulation or trapping of monomeric, dimeric, or polymeric oxyanions. In the area of supramolecular chemistry, of late, the roles of hydrogen bonds (HBs), which facilitate favorable hydrogen bonds between anions, have gained much attention.…”