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.