Oral Presentation The 35th Biennial Conference of the Society of Crystallographers in Australia and New Zealand 2024 (Crystal 35)

Investigations of chalcogen bonding in Ebselen-DMAP co-crystals using terahertz spectroscopy   (108673)

Catriona Thomson 1 2 , Dominique Appadoo 3 , Courtney Ennis 4 , Thomas Fellowes 5 , Tze Cin Owyong 6 , Adam W. E. Stewart 1 2 , Jonathan M. White 1 2
  1. The University of Melbourne, Parkville, VIC, Australia
  2. The Bio21 Institute of Molecular Science and Biotechnology, Parkville, VIC, Australia
  3. Australian Synchrotron, ANSTO, Clayton, VIC, Australia
  4. University of Otago, Dunedin, Otago, New Zealand
  5. The University of Liverpool, Liverpool, United Kingdom
  6. La Trobe University, Melbourne, VIC, Australia

Chalcogen bonding describes the attractive, non-covalent interaction between a partially polarised chalcogen atom (S, Se, Te) and a Lewis Base. Previous work in our group has illustrated the presence of chalcogen bonding interactions between the organoselenium drug Ebselen and the Lewis base DMAP, as evident by the co-crystal structure.1 Although commonly characterised crystallographically, we are interested in the synergistic characterisation of chalcogen bonding in co-crystals via terahertz spectroscopy. The absorption of light in the terahertz (THz) region of the electromagnetic spectrum is attributed to relatively weak non-covalent interactions (e.g. hydrogen bonding and van der Waals interactions). As such, THz spectroscopy has proven to be a very sensitive technique to characterise weak intermolecular interactions especially relevant to the field of crystallography. Although some work in the literature has used THz spectroscopy to characterise hydrogen bonding vibrational modes, the same cannot be said for chalcogen bonding. This presentation will outline our collaboration with the THz beamline at the Australian Synchrotron to characterise chalcogen bonding between Ebselen and DMAP.  Investigations thus far have been conducted on crystalline powders and single crystal samples using a polarised THz source. Informed by face indexing from single crystal XRD/THz experiments, the THz beam can be oriented along the axis of the chalcogen bond and orthogonal to it, hence enabling the comparison of signals from the two orientations to aid in the assignment of the Se…N vibration. The CRYSTAL14 program was used to calculate lattice vibrations in the co-crystals of Ebselen-DMAP also occurring in the THz region so they can be eliminated as candidates for the signal associated with the N…Se vibration. The solid-state investigations are complemented by solution studies in addition to DFT calculations. The results of our investigations have allowed us to identify a band at ca. 80 cm-1 as a likely signature for the N...Se chalcogen bond between Ebselen and DMAP.

  1. Fellowes, T.; White, J. M. New Insights into Chalcogen Bonding Provided by Co-Crystal Structures of Benzisoselenazolinone Derivatives and Nitrogen Bases. CrystEngComm 2019, 21 (10), 1539–1542.