Herein we probe the effects of electron withdrawing and electron donating groups along with the identity of the halogen atom has on the electropositive σ-holes in halomethanes, haloethynes, halobenzenes, and haloethynyl benzene halogen bond (XB) donors (XCH3, XCCR, XCCR’, RBX, R’BX, RR’BX, RBAX, R’BAX, and RR’BAX; where R = –OH, –SH, –NH2, and –BH2, R’ = –F, –CN, and –NO2, and X = At, I, Br, Cl, and F). Full geometry optimizations and harmonic vibrational frequency computations are computed through the global hybrid M06-2X density functional in conjunction with a double-ζ quality correlation consistent basis set augmented with diffuse functions on all atoms and a pseudopotential on bromine, iodine, and astatine centers (aug-cc-pVDZ for H, C, N, O, B, S, F, Cl and aug-cc-pVDZ-PP for Br, I, At; denoted as aVDZ-PP). To gain insight into the role that different electron donating and electron withdrawing groups' cooperative interactions play on the size and magnitude of the σ-hole, natural bond orbital (NBO) and critical point (CP) analyses are performed on the M06-2X/aVDZ-PP optimized structures. Connections between the σ-hole properties and the structural, energetic, and vibrational properties of the XB donors will be discussed.

Fundamental observations behind the effects of electron donating and electron withdrawing groups on halogen bond donor σ-holes

ACS Spring 2022

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