Boron Tunneling in the “Weak” Bond-Stretch Isomerization of N−B Lewis Adducts

Ashim Nandi, Naziha Tarannam, Daniela Rodrigues Silva, Célia Fonseca Guerra, Trevor A. Hamlin, Sebastian Kozuch

Research output: Contribution to journalArticlepeer-review


Some nitrile-boron halide adducts exhibit a double-well potential energy surface with two distinct minima: a “long bond” geometry (LB, a van der Waals interaction mostly based on electrostatics, but including a residual charge transfer component) and a “short bond” structure (SB, a covalent dative bond). This behavior can be considered as a “weak” form of bond stretch isomerism. Our computations reveal that complexes RCN−BX3 (R=CH3, FCH2, BrCH2, and X=Cl, Br) exhibit a fast interconversion from LB to SB geometries even close to the absolute zero thanks to a boron atom tunneling mechanism. The computed half-lives of the meta-stable LB compounds vary between minutes to nanoseconds at cryogenic conditions. Accordingly, we predict that the long bond structures are practically impossible to isolate or characterize, which agrees with previous matrix-isolation experiments.

Original languageAmerican English
Pages (from-to)1857-1862
Number of pages6
Issue number18
StatePublished - 15 Sep 2021


  • Lewis adduct
  • bond stretch isomerism
  • dative bond
  • heavy-atom tunneling
  • kinetic isotope effect

All Science Journal Classification (ASJC) codes

  • Atomic and Molecular Physics, and Optics
  • Physical and Theoretical Chemistry


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