The competition of C-X⋯O=P halogen bond and π-hole⋯O=P bond between halopentafluorobenzenes C₆F₅X (X=F, Cl, Br, I) and triethylphosphine oxide.

Calculation predicted the interacting forms of halopentafluorobenzene C6F5X (X=F, Cl, Br, I) with triethylphosphine oxide which is biologically interested and easily detected by (31)P NMR. The interaction energy and geometric parameters of resultant halogen or π-hole bonding complexes were estimated and compared. Moreover, the bonding constants were determined by (31)P NMR. Both theory and experiments indicated the C6F6 and C6F5Cl interact with triethylphosphine oxide by π-hole bonding pattern, while C6F5I by halogen/σ-hole bonding form. For C6F5Br, two interactions are comparative and should coexist competitively. The calculated interaction energies of σ-hole bonding complexes, -5.07 kcal mol(-1) for C6F5Br⋯O=P and -8.25 kcal mol(-1) for C6F5I⋯O=P, and π-hole bonding complexes, -7.29 kcal mol(-1) for C6F6⋯O=P and -7.24 kcal mol(-1) for C6F5Cl⋯O=P, are consistent with the changing tendency of bonding constants measured by (31)P NMR, 4.37, 19.7, 2.42 and 2.23 M(-1), respectively.