Comment on the ionization energy of B2F4.

The Gn test sets(1) of accurate (uncertainty ≤ 1 kcal mol–1 ≈ 4 kJ mol–1) experimental data are widely employed in the development and assessment of quantum chemistry procedures. However, while all the data in the Gn sets nominally carry a sub-kcal mol–1 uncertainty, several of the experimental values show uncharacteristically large discrepancies when compared with values determined by high-level theoretical calculations. One of these questionable values is the adiabatic ionization energy (IE) of B2F4, for which the theoretical values calculated, for example, with the high-level G2 (1133.9, kJ mol–1),(1b) G3 (1135.4 kJ mol–1),(2) and G4 (1127.2 kJ mol–1)(3) procedures differ significantly from the experimental value of 1164.6 ± 1.0 kJ mol–1.(4)