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Probing Halogen Bonding via Paramagnetic NMR
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry. (Erdélyi Group)ORCID iD: 0000-0002-7945-5504
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry. (Erdélyi Group)ORCID iD: 0000-0003-0359-5970
2018 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Halogen Bonding is a spectacle that has recently received widespread attention, despite the fact that it was discovered over 200 years ago. This fundamental interaction is vastly abundant in today’s world, and a better understanding of it would enable us to both design and improve upon existing drugs, materials and catalysts, to name a few. Halogen bonds (XB) are roughly 180°, non-covalent interactions that exploit the anisotropic electron density of a halogen atom. Analogous to hydrogen bonding, a halogen bond acceptor (being an electron donor in the form of a Lewis base (LB)) and a halogen bond donor (being an electron acceptor consisting of a halogen with a σ-hole) must exist. σ-Holes are electrophilic regions that arise on the opposite tip of an R-X bond in the anti-bonding orbital and to maximise these holes, one can make ‘R’ more electron withdrawing and/or ‘X’ larger with a more diffuse outer electron shell (I > Br > Cl > F).Halogen bonding, like many other weak bonding interactions, is incredibly difficult to measure accurately in solution. Thus, we hypothesize that paramagnetic NMR techniques are potentially useful for their detection and characterization. This involves the use of a compound containing free electrons, and when these are subjected to the large magnetic field of an NMR spectrometer, they exhibit unique qualities that one can fruitfully exploit. In these studies, we mainly focus on measuring Pseudocontact Shifts (PCS) that arise from vast spectral broadening due to the free electrons. With this technique, we are able to assess very weak bonding interactions by the detection of small chemical shift differences due to a much larger spectral window than commonly detected.In this work, building upon previous studies carried out within the group,1 we synthesise cyclen-based organic ligands which complex a paramagnetic lanthanide (Ln3+) species. Attached to one amine in the cyclen core is a Lewis Base (or halogen bond acceptor) which is utilised in probing halogen bonding between itself and a free halogen bond donor in solution. Expected PCS measurements will give an accurate value of the weak bonding interaction between donor and acceptor in solution- the resolution of which is something that is simply not possible via classical NMR studies.

Place, publisher, year, edition, pages
2018.
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-357811OAI: oai:DiVA.org:uu-357811DiVA, id: diva2:1240487
Conference
1ST NATIONAL MEETING OF THE SWEDISH CHEMICAL SOCIETY, Lund, June 17-20, 2018
Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2019-01-09Bibliographically approved

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Wilcox, ScottErdélyi, Máté

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