Exploring short strong hydrogen bonds engineered in organic acid molecular crystals for temperature dependent proton migration behaviour using single crystal synchrotron X-ray diffraction (SCSXRD)

Lucy K. Saunders, Harriott Nowell, Lauren E. Hatcher, Helena J. Shepherd, Simon J. Teat, David R. Allan, Paul R. Raithby, Chick C. Wilson

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Seven multi-component molecular crystals containing O-H⋯O/O+-H⋯O- and N+-H⋯O- short strong hydrogen bonds (SSHBs) have been engineered by combining substituted organic acids with hydrogen bond acceptor molecules N,N-dimethylurea and isonicotinamide. In these materials, the shortest of the SSHBs are formed in the N,N-dimethylurea set for the ortho/para nitro-substituted organic acids whilst a twisted molecular approach favours the shorter SSHBs N+-H⋯O- in the isonicotinamide set. Temperature dependent proton migration behaviour has been explored in these systems using single crystal synchrotron X-ray diffraction (SCSXRD). By using a protocol which considers a combination of structural information when assessing the hydrogen atom (H-atom) behaviour, including refined H-atom positions alongside heavy atom geometry and Fourier difference maps, temperature dependent proton migration is indicated in two complexes (2: N,N-dimethylurea 2,4-dinitrobenzoic acid 1 : 1 and 5: isonicotinamide phthalic acid 2 : 1). We also implement Hirshfeld atom refinement for further confidence in this observation; this highlights the importance of having corroborating trends when applying the SCSXRD technique in these studies. Further insights into the SSHB donor-acceptor distance limit for temperature dependent proton migration are also revealed. For the O-H⋯O/O+-H⋯O- SSHBs, the systems here support the previously proposed maximum limit of 2.45 Å whilst for the charge assisted N+-H⋯O- SSHBs, a limit in the region of 2.55 Å may be suggested.

Original languageEnglish
Pages (from-to)5249-5260
Number of pages12
Issue number35
Early online date12 Aug 2019
Publication statusPublished - 21 Sep 2019

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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