Multicomponent cluster ions. I. The proton solvated by CH3CN/H2O

Abstract

Experimental and ab initio dissociation energies of the (H₂O)_n(CH₃CN)_mH⁺ ions are reported. The experimental energies range from 10–35 kcal/mol. The proton is best stabilized by placing the maximum number of acetonitrile molecules close to the protonated center in such a way that the formation of a network of strong hydrogen bonds is still possible. Other results from this work are: (1) Distinct solvent shells can be distinguished in these complex ions. (2) Mixtures of several isomeric structures are unlikely for n≤4. (3) When a water or an acetonitrile molecule clusters with (H₂O)(CH₃CN)H⁺, the proton is transferred from the acetonitrile to the water. (4) Although electrostatic interactions make the dominant contribution to the bonding in these systems, polarization and charge‐transfer effects contribute also. (5) There is a cooperativity effect among the hydrogen bonds that leads to extensive changes in geometry and charge distribution as successive hydrogen bonds are formed. (6) The relative complexation energies along a series of reactions correlate with many properties of the electron donor and with several properties of the proton donor.