A Multi‐Center Energy Analysis of the Tunable Proton Affinity of Hydrogen Bonded Cluster Ions

The proton affinity (PA) of the [Tca–H^βMim]^? ion (Tca^?: trichloroacetate ion, HMim: 4‐Methyl‐1H‐imidazole) is a nearly linear function of the position (r₃) of H^β using the rigid framework approximation. This useful property of the ion is caused by an unusually large four‐center interaction term revealed by the multi‐center energy (MCE) analysis of PA(r₃). The MCE analysis shows further that despite the general stabilization of the [Tca–HMim–HAc]^? ion by cooperative effects, the individual hydrogen bonds carry a strong anti‐cooperative element caused by the rivalry of the two bases for the proton linking them.