Systematic size mediated trapping of anions of varied dimensionality within a dimeric capsular assembly of a flexible neutral bis-urea platform

Abstract

A rationally designed ortho-phenylenediamine based trifluoromethyl meta-disubstituted bis-urea receptor (L) exhibits effective, consistent and systematic binding in its neutral form towards smaller spherical halides (fluoride, chloride, bromide and iodide), and relatively larger planar carbonate and tetrahedral sulphate oxyanions. All the complexes are well characterized both in the solid-state and solution phase. In the presence of excess fluoride anions, the receptor L encapsulates a hydrated cyclic fluoride-water [F(HO)] tetramer inside the n-TBA cation sealed dimeric complementary cavity (complex 1). Whereas excess n-TBA/TEA salts of chloride, bromide and iodide result in unusual (Cl), (Br), and (I) doubly encapsulated 2 : 2 dimeric host-guest complexes (2a, 2b, 3 and 4). Two receptor units encapsulate a carbonate ion, via hydroxide induced aerial CO fixation (complex 5), and a sulphate anion (complex 6), respectively, in the presence of excess tetrabutylammonium hydroxide and bisulphate salt. H NMR titration and 2D NOESY experiments corroborate the solution-state binding and encapsulation of hydrated/non-hydrated halides and oxyanions via N-HA hydrogen bonding.

Recognition of Anions, Monoamine Neurotransmitter and Trace Amine Hydrochlorides by Ureido‐Hexahomotrioxacalix[3]arene Ditopic Receptors

“…The calculated N‐H ··· X – bond lengths (Table S2) are consistent with those found in the solid state for a bis‐urea receptor . The N‐H ··· F – coordination environment is distorted from octahedral, however, that around chloride is far less regular as a consequence of its larger size.…”

“…The calculated N-H···Xbond lengths (Table S2) are consistent with those found in the solid state for a bis-urea receptor. [37] The N-H···Fcoordination environment is distorted from octahedral, however, that around chloride is far less regular as a consequence of its larger size. The close approach of the three urea substituents to the smaller fluoride necessitates a more sterically constrained ligand geometry whereas the longer N-H···Clinteractions lower the steric energy.…”

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

“…These kinds of (HCO 3 ) 2 anionic dimer entrapped noncooperative self-assemblies by m -phenylenediamine based receptors via F – induced CO 2 fixation were recently reported by our group . However, aerial CO 2 fixation as carbonate or bicarbonate trapped complexes by several preorganized receptors containing cooperative binding modes was previously reported by Gunnlaugsson et al, Gale et al, , Ghosh et al, and our group ,,, also. In contrast, herein the linear p -phenylenediamine based isomeric para - and meta -bisurea neutral receptors are still capable of capturing dimeric association of bicarbonate created by donor–acceptor H-bonding interactions despite the absence of any receptor cooperativities or more number of coordinating sites.…”

“…The number of tren-based or benzene based tripodal acyclic podands with several -NH functionalities has been well-known as an established area for binding and recognition anions via formation of molecular capsules with topological complementarity, as they can readily offer a flexible and structurally preorganized cavity. − In contrast, recognition of anionic guests by entrapment or encapsulation within the self-assembled architectures of aromatic dipodal urea/thiourea based neutral receptors is not common in the literature due to the less flexible and less coordinating binding sites containing rigid scaffolds compared to the tripodal ligands. Several bisurea/thiourea derivatives of o -phenylenediamine were reported previously as an anion receptor or anion sensor in solid or solution states by Gale et al, − Wu et al, Das et al, Molina et al, Tarr et al, and our group , also, as the amine groups of o -phenylenenediamine become the most converging among ortho , meta , and p -phenylenediamine, and hence aromatic 1,2-diamine based receptors have much more tendency to form cooperative anion complexes compared to other isomeric rigid diamines. Very recently, we reported a class of meta -phenynenediamine based neutral bis-urea receptors with one or more terminal aryl substituents, and their self-assembled anion/hydratred-anion bound architectures have been studied extensively in solid and solution states, where the complexation phenomena are heavily governed by the anion dimension or substituent effect. − …”

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

“…The encapsulation of larger tetrahedral sulfate oxyanion is very much anticipated inside the unimolecular capsular assembly, as it is present as a contaminant in drinking water as well as acts as a pollutant in nuclear and radioactive waste, which hampers the vitrification process. , Thus far, numerous tripodal oxyurea/thiourea receptors consisting of one or more terminal aryl substitutions have been widely reported by Custelcean et al, Ghosh et al, Janiak et al., Gale et al, Das et al, and from our group also, − which can recognize an anionic guest in either 1:1, 2:2, or 2:1 host–guest complexation mode via topological complementarity in the solid state, based on the solution state anion binding studies of first tren-based urea/thiourea receptors reported by Morán et al in 1995 . In our ongoing effort in the field of anion-receptor chemistry to encapsulate the hydrated/solvated/cation-triggered anionic guests into the host capsules, − herein we report the cation-triggered systematic encapsulation of smaller (fluoride) to larger halides (chloride, bromide) as well as planar (planar) and tetrahedral (sulfate) oxyanions inside the tris-naphthyl thiourea receptor cavity via 1:1 unimolecular host–guest complexation mode. Most importantly, this report delivers the first anion binding crystallographic evidence of one of the simplest tren-based unsubstituted highly electron-rich thiourea derivatives L , which was first synthesized by Wu et al in 1999, that demonstrated the only solution state oxyanion binding.…”