Hydrogen bonding. Part 86: DFT molecular orbital study of the first hydration shell of N,N,N-trimethyl-1-adamantylammonium ion

Consecutive addition of H2O to the N,N,N-trimethyl-1-adamantylammonium ion (3MAA+) follows an orderly pattern. The first H2O binds to the triangular face formed by the three methyl groups. Subsequently three sets of three H2O bind sequentially to form, in order, (H2O)3, (H2O)6, and (H2O)9 subgroups with C3 symmetry about the z-axis of the ion. The result is a closed C3 (H2O)9 ring about the ion in the region adjacent to the α-CH3 and β-CH2 carbons, to give a first shell stoichiometry of 3MAA+·10H2O. These 10H2O are bound to the ion by a combination of CHO hydrogen bonds and ion–dipole forces. The eleventh H2O accepts a hydrogen bond from a ring H2O but is otherwise unconnected to the ion, and is assumed to represent the first member of a larger solvent shell.