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From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
Ability of Peripheral H Bonds to Strengthen a Halogen Bond
1Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300, United States.
Abstract:
Quantum calculations study the manner in which the involvement of a halogen atom as a proton acceptor in one or more H bonds (HBs) affects the strength of the halogen bond (XB) it can form with a nucleophile aligned with the X σ-hole. A variety of Lewis acids wherein X = F, Cl, Br, and I are attached to a tetrel atom C or Ge engaged in a XB with nucleophile NH3. One, two, and three HF molecules were positioned perpendicular to the XB axis so that they could form a HB to the X atom. Each such HB strengthened the XB by an increment of 1 kcal/mol or more that does not attenuate as each new HB is added, potentially increasing the interaction energy manyfold. Additionally, the presence of one or more HBs facilitates the formation of a XB by molecules which are reluctant to engage in such a bond in the absence of these auxiliary interactions. Even the F atom, which avoids such a XB, can be coaxed to participate in a XB of moderate strength by one or more of these external HBs.
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