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<p>This paper reports six crystal structures of five calix[<i>n</i>]arenes (<i>n</i> = 4, 6, or 8), highlighting the remarkable ability of this molecular class to self-assemble into diverse architectures and conformations, and rationalizing which structural features predispose calixarenes to act as supramolecular hosts. The structures of <i>p</i>-sulfonatocalix[4]arene and 1,3-bis(carboxymethyl)calix[4]arene reveal open-crown conformations accessible to guest molecules, both in the calcium salt and DMSO solvate forms, respectively. Closed-crown conformations were identified in two conformational polymorphs of hexakis(carboxymethyl)calix[6]arene methyl ester and in a lower-rim <i>n</i>-butyl-functionalized <i>p-tert</i>-butylcalix[8]arene derivative, in which their first crystal structures are reported here. Meanwhile, the <i>p-tert</i>-butylcalix[8]arene without lower-rim functionalization crystallizes with two structurally similar pleated-loop conformers that display distinct packing motifs. Hirshfeld surface analyses and DFT help us also to understand the interactions patterns and conformerism, such as the finding of an atypical high-energy 1,2,3-alternate conformer in which the closed crown is kept by π···π interactions between phenyl rings in one of the two polymorphs of hexakis(carboxymethyl)calix[6]arene methyl ester.</p>

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Polymorphism and structural diversity in calix[n]arenes (n = 4, 6 or 8)

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月19日

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  • Marcelo Augusto Moraes da Luz,
  • Meiry Edivirges Alvarenga,
  • Bárbara Júlia Gonçalves Dutra,
  • Guilherme Martins Fernandes,
  • Freddy Fernandes Guimarães,
  • Ângelo de Fátima,
  • Cleiton Moreira da Silva,
  • Felipe Terra Martins

摘要

This paper reports six crystal structures of five calix[n]arenes (n = 4, 6, or 8), highlighting the remarkable ability of this molecular class to self-assemble into diverse architectures and conformations, and rationalizing which structural features predispose calixarenes to act as supramolecular hosts. The structures of p-sulfonatocalix[4]arene and 1,3-bis(carboxymethyl)calix[4]arene reveal open-crown conformations accessible to guest molecules, both in the calcium salt and DMSO solvate forms, respectively. Closed-crown conformations were identified in two conformational polymorphs of hexakis(carboxymethyl)calix[6]arene methyl ester and in a lower-rim n-butyl-functionalized p-tert-butylcalix[8]arene derivative, in which their first crystal structures are reported here. Meanwhile, the p-tert-butylcalix[8]arene without lower-rim functionalization crystallizes with two structurally similar pleated-loop conformers that display distinct packing motifs. Hirshfeld surface analyses and DFT help us also to understand the interactions patterns and conformerism, such as the finding of an atypical high-energy 1,2,3-alternate conformer in which the closed crown is kept by π···π interactions between phenyl rings in one of the two polymorphs of hexakis(carboxymethyl)calix[6]arene methyl ester.