Cooperative effects in FH/Li⋯HCCX⋯OH2 complexes (X = F, Cl, Br, H)

• A combination of H⋯π bonds and halogen bonds yield stable T-shaped trimers.
• Cooperative effects enhance trimer stability by 7–10%.
• Dimers of FH and C2H2 are T-shaped.
• Dimers of FLi and C2H2 have the monomers lying side by side.

The dimers with general formula FH/FLi⋯HCCX and HCCX⋯OH2, and the trimers FH⋯HCCX⋯OH2 (X = F, Cl, Br, H), were optimized computationally to stable structures. These model systems derive their strength from a combination of H⋯π (or Li⋯π) electrostatic interactions in the T-shaped FH/FLi⋯HCCX dimers and halogen bonding between the X and the O atom of H2O (or CH⋯O hydrogen-bonding in HCCH complexes). These cooperative interactions in the trimer clusters yield a non-additive energy which enhances the stability by between 7% and 10%. The variation in the interaction energies, as well as other selected properties, for different X is rationalized and discussed.

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