# Synthesis and X‑ray Structures of Bis-Functional Resorcinarene Crown Ethers

## TL;DR

Researchers synthesized and analyzed two new resorcinarene crown ethers, revealing their structural preferences and ion-binding properties.

## Contribution

The paper reports the synthesis and X-ray structures of novel bis-functional resorcinarene crown ethers with unique conformational and binding characteristics.

## Key findings

- TRC6 and TRC7 prefer boat conformation in the solid state with distinct crown ether arrangements.
- TRC6 forms 1:1 and TRC7 forms 1:2 complexes with potassium and rubidium cations in DMSO.
- NMR signal changes were more intense in acetonitrile with tetrafluoroborate salts.

## Abstract

Two resorcin[4]­arene-crowns
were synthesized with crown ether substituents
as the lower rim functionalities, with either the Crown-6 (TRC6) or Crown-7 (TRC7) moieties being incorporated. X-ray
crystallographic data show that both molecules prefer the boat conformation
in the solid state. The crown ethers were observed in an askew anti-arrangement in TRC6 and a syn-arrangement in TRC7. TRC6 crystallized
with four DMF and four H2O molecules. Two of the DMF solvent
molecules are hydrogen bonded to the resorcinolic OHs, and the other
two are entrapped as a dimer between two ether moieties from adjacent TRC6 molecules. In TRC7, four intramolecular
hydrogen bonds from the same resorcinol OH group to the crown ether
oxygens are observed, with O···O contact distances
of 2.742(2) Å and 2.872(2) Å and O–H···O
angles of 169.8° and 175.4°. Host–guest binding of
potassium and rubidium cations as their chloride and tetrafluoroborate
salts in highly competitive DMSO shows 1:1 and 1:2 host–guest
complexes for TRC6 and TRC7, respectively.
More intense NMR signal changes were observed in less competitive
acetonitrile solvent with the tetrafluoroborate salts.