Benchmarking of Halogen Bond Strength in Solution with Nickel Fluorides: Bromine versus Iodine and Perfluoroaryl versus Perfluoroalkyl Donors

Robin Noel Perutz, Sarah Jane Pike, Lee Brammer, Christopher A Hunter

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The energetics of halogen bond formation in solution have been investigated for a series of nickel fluoride halogen bond acceptors; trans-[NiF(2-C 5NF 4)(PEt 3) 2] (A1), trans-[NiF{2-C 5NF 3(4-H)}(PEt 3) 2] (A2), trans-[NiF{2-C 5NF 3(4-NMe 2)}(PEt 3) 2] (A3) and trans-[NiF{2-C 5NF 2H(4-CF 3)}(PCy 3) 2] (A4) with neutral organic halogen bond donors, iodopentafluorobenzene (D1), 1-iodononafluorobutane (D2) and bromopentafluorobenzene (D3), in order to establish the significance of changes from perfluoroaryl to perfluoroalkyl donors and from iodine to bromine donors. 19F NMR titration experiments have been employed to obtain the association constants, enthalpy, and entropy for the halogen bond formed between these donor-acceptor partners in protiotoluene. For A2–A4, association constants of the halogen bonds formed with iodoperfluoroalkane (D2) are consistently larger than those obtained for analogous complexes with the iodoperfluoroarene (D1). For complexes formed with A2–A4, the strength of the halogen bond is significantly lowered upon modification of the halogen donor atom from I (in D1) to Br (in D3) (for D1: 5≤K 285≤12 m −1, for D3: 1.0≤K 193≤1.6 m −1). The presence of the electron donating NMe 2 substituent on the pyridyl ring of acceptor A3 led to an increase in −ΔH, and the association constants of the halogen bond complexes formed with D1–D3, compared to those formed by A1, A2 and A4 with the same donors.

Original languageEnglish
Article numberchem.201900924R1
Pages (from-to)9237-9241
Number of pages5
JournalChemistry : A European Journal
Issue number39
Early online date15 Apr 2019
Publication statusPublished - 11 Jul 2019

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© 2019 WILEY‐VCH Verlag GmbH & Co. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.


  • NMR spectroscopy
  • halogen bonds
  • nickel fluorides
  • perfluoroaryl and perfluoroalkyl donors
  • solution

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