Here we study the effects that the halogen atom identity and electron withdrawing capability have on the σ-hole in dihalogen, halomethane, haloethynyl, halobenzene, and haloethynyl benzene halogen bond (XB) donors (X2, XY, XCH3, XCF3, RBX, and RBAX; where R = F1-5, CN1-5, (NO2)2, and CF3 and X = At, I, Br, Cl, and F). Full geometry optimizations and harmonic vibrational frequency computations were performed with the M06-2X density functional in conjunction with a double-ζ correlation consistent basis set augmented with diffuse functional on all atoms with a pseudopotential for bromine, iodine, and astatine centers (aug-cc-pVDZ for H, C, N, O, F, Cl and aug-cc-pVDZ-PP for Br, I, At; denoted as aVDZ). Full natural bond orbital (NBO) analyses are performed on the M06-2X/aVDZ optimized structures to gain insight into how modifications in the halogen atom and the electron withdrawing groups affect the size and magnitude of the σ-hole and the C-X and C≡C vibrational stretching frequencies. Connections between the structural, energetic, and vibrational properties of the XB donors adopted in this work will be discussed.

Probing the electron withdrawing effects in the σ-holes of halogen bond donors

ACS Fall 2021

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