Resorcarenes in the Boat Conformation as Building Blocks for Hydrogen-Bonded Assemblies Including Two Ammonium Cations

Abstract

Crystal structures are reported for various co-crystals of rccc-resorcarenes with triethylammonium chloride. Usually, two molecules of a C2v-symmetric tetraester 2 in the boat conformation are linked through four hydrogen-bonded chloride anions to give dimeric assemblies. Two of the chloride anions may be replaced by four hydrogen-bonded ethanol molecules in an otherwise similar structure. These assemblies, which consist of six or eight components, posses voluminous, negatively charged chambers in which two triethylammionium cations, 3+, are included as guests by strong electrostatic and hydrogen-bonding interactions. The host-guest N-H...Cl hydrogen bonds were clearly detected at 173 K. These are the first examples of hydrogen-bonded, solid-state capsules trapping two ions of the same charge in close proximity. In the 1:2 complex with 3+ Cl-, the molecule of the parent resorcarene 1 also adopts a boat conformation whose cavity is considerably extended by four hydrogen-bonded chloride anions. The pocket formed in this way again includes two 3+ ions as a result of electrostatic and hydrogen bonding host-guest interactions. All these structures show that the boat conformers of resorcarenes can be used as a novel motif for the construction of hydrogen-bonded assemblies capable of molecular inclusion and encapsulation.

Chemistry of calix[4]resorcinarenes

“…The boat conformers of calix [4]resorcinarene 52 form hydrogen-bonded, solid-state capsules that incorporate two triethylammonium cations simultaneously. 176 Two molecules of calix [4]resorcinarene in the boat conformation are linked through four hydrogen bonded chloride anions of Et 3 NH + Cl 7 to form dimers. The resulting large, negatively charged chambers may encapsulate two triethylammonium cations due to strong electrostatic and hydrogen-bonding interactions.…”

Crystallography and Crystal Engineering

“…The structure (CSD code QOFNOO, orthorhombic, space group P2 1 2 1 2 1 ) reveals a boat conformation of 2, the chloride anions are H-bonded to the upward pointing OH groups and the two cations are nesting inside the boat-like cavity [39] (Figure 10.21). The TriEA cation is bound to the cavity through cation-π interactions.…”

“…21 The host-guest complex, 2 × 2 (TriEACl) × 2 MeCN in QOFNOO with 2 in boat conformation, MeCN molecules omitted for clarity[39].…”

“…22 The host-guest complex, 2 × MeCN × TriEACl in QOFNUU with 2 in slightly distorted crown conformation[39].…”

Influence of lower rim C-methyl group on crystal forms and metal complexation of resorcinarene bis-crown-5

“…Inclusion of guests, such as ammonium cations or alcohols within the resorcinarene cavity has an important role in the formation of these assemblies. Hydroxyl group functionalization affects the ability of the resorcinarene to assume different conformations by interfering with the intramolecular hydrogen bonding, 10 or by restricting the conformation to a permanent crown or boat in resorcinarene cavitands 11 and in crown ether bridged resorcinarenes, respectively. 12,13 The lower rim alkyl chain length also has an effect on the resorcinarene conformation, since rccc C-methyl resorcinarene crystallizes in the boat conformation 3,6,14,15,16,17,18,19,20 more readily than C-ethyl or Cpropyl resorcinarenes, 21 and other, more rare conformations, such as scoop, 22 rctt chair 19,23 and rctt diamond 24 have been reported in addition to a typical crown conformation 25,26 .…”