Synthesis and Study of a novel supramolecular 'host-guest' complex based on cucurbit[6]uril and 1,4-bis(2-hydroxyethyl)piperazine dihydrochloride

Abstract

A novel supramolecular complex C₄₄H₇₁Cl₂N₂₆O₂₂ (CB[6]@Pipa·2HCl) of the "host-guest" type has been synthesized. It is based on cucurbit[6]uril (CB[6]) with dihydrochloride 1,4-bis(2-hydroxyethyl)piperazine (Pipa·2HCl) localized within the portals of the macrocycle. Based on ¹H NMR and X-ray crystallography, the host-guest ratio in the complex under the specified conditions was determined to be 1:1. Further evidence of complex formation was observed through IR spectroscopy, where a splitting and shift in the absorption band of carbonyl vibrational frequencies of cucurbit[6]uril by 36 cm^-1 and 12 cm^-1 towards the side of smaller wave numbers was detected in CB[6]@Pipa·2HCl compared to the original CB[6]. TGA/DSC analysis results indicated an increase in thermal stability by 55°C for the obtained CB[6]@Pipa·2HCl complex compared to the initial 1,4-bis(2-hydroxyethyl)piperazine dihydrochloride. The structure of the synthesized CB[6]@Pipa·2HCl complex was confirmed using single-crystal XRD