Anion‐Templated Supramolecular C₃ Assembly for Efficient Inclusion of Charge‐Dispersed Anions into Hydrogen‐Bonded Networks

Abstract

The binding properties and conformational adaptability of a known nitrate/sulfate receptor N,N'-3-azapentane-1,5-bis[3-(1-aminoethylidene)-6-methyl-3H-pyran-2,4-dione] (L) toward various charge-dispersed monoanions (HSO(3)(-), ClO(4)(-), IO(4)(-), PF(6)(-), and SbF(6)(-)) are considered. These anions template the folding of three HL(+) species through a self-assembly process into a new hollow supramolecular trication. During the self-assembly, all strong hydrogen-bond donors of the podand become coordinatively saturated by interactions with the oxo functionalities from other HL(+) molecules. In that way, only the weak hydrogen-bond-donating groups in the exterior part of the receptor are accessible for anion binding. The investigated anions are accommodated in the hydrophobic pockets of the isomorphous hydrogen-bonded frameworks, which serve as a basis for selective crystallization from the highly competitive anion/solvent systems. This behavior is discussed in terms of size and geometry of the anions as well as the receptor's coordination capabilities to provide the most favorable surroundings for guest inclusion both in solution and in the solid state.

Intramolecular Hydrogen Bonding Involving Organic Fluorine: NMR Investigations Corroborated by DFT-Based Theoretical Calculations

“…Voluminous information is available on the self-assembly of molecules driven by HB [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. HB interaction is responsible for the three-dimensional conformation of proteins, synthetic foldamers [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ], peptide catalysis, peptidomimetic design [ 34 , 35 , 36 , 37 , 38 , 39 ], double helical structure of DNA [ 40 , 41 ], unique properties of water [ 42 ], etc. Thus, in-depth knowledge of HB interaction aids in understanding the chemical properties of many organic and bio-macromolecules [ 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ].…”

Regioselective Conjugate Addition of Nitriles to α,β‐Unsaturated Imines: Synthesis of Fluorinated Primary Enamines and 2‐Aminopyridine Derivatives

“…The anions are bound by NH⋅⋅⋅O hydrogen bonds involving the protonated NH of both conformers. HL in the C conformation was not observed in the previously described supramolecular complexes11, 12 so it seems that the formation of tweezers is particularly beneficial for planar HB acceptors. Nearly identical supramolecular architectures in 4 a / 1 b and 2 c / 3 c pairs suggest also a templating role of the acid, since the carboxylic groups in Hmal/Hopa and Hfum/Hsuc pairs are in similar relative arrangements (Scheme ).…”

“…Among several equilibria in methanol solution (including deprotonation of the acid, protonation of L and binding of the anion), changes in the UV/Vis spectra observed upon addition of acid solutions into the solution of L were mainly caused by complexation 12. Spectrophotometric titrations revealed that binding affinities in solution matched those observed by crystallization, with the steepest titration curve obtained for complexation of Hmal (Figure 2 c).…”

“…The study of anion binding has traditionally been performed in solution9 where the host often experiences conformational freedom to form complexes with a wide range of guests. However, selectivity in separation has usually been achieved only upon crystallization,10–12 emphasizing the importance of intermolecular interactions in rigid crystal environment which lock the conformation of the host giving rise to its selectivity. In this context, recent advances in chemical reactivity achieved using mechanochemistry indicate that the concepts of supramolecular chemistry, such as templating,13 may be applicable also to solvent‐free reactions 14.…”

Protonation and Anion Binding Properties of Aromatic Bis‐Urea Derivatives—Comprehending the Proton Transfer

“…As the field of anion coordination chemistry has evolved, new levels of complexity of the related systems have been explored, which has increased the need for thorough research of all processes related to anion coordination . In this field, urea derivatives have been among the most studied receptors, and numerous studies of their complexation with diverse anionic species have been reported .…”