Energetics and Structures of Adamantane and the 1- and 2-Adamantyl Radicals, Cations, and Anions

Equilibrium structures and harmonic vibrational frequencies were computed for adamantane (Ad), the 1- and 2-adamantyl radicals (1-Ad •, 2-Ad • ), cations (1-Ad +, 2-Ad + ), and anions (1-Ad -, 2-Ad - ). Ionization potentials and electron affinities of Ad, 1-Ad • and 2-Ad • have been predicted using four different density functional and hybrid Hartree−Fock/density functional methods. The equilibrium structure of adamantane ( T d symmetry) is in excellent agreement with electron diffraction experiments. 1-Ad • and 1-Ad - are predicted to lie about 4 kJ mol -1 below their 2-isomers, while 1-Ad + is predicted to lie 47 kJ mol -1 below 2-Ad + . For 1-Ad •, 1-Ad +, and 1-Ad -, C 3 v structures are found to be the minima, while a C s structure lies lowest for 2-Ad •, 2-Ad +, and 2-Ad - . The final predicted adiabatic ionization potentials for the radicals are 6.22 (1-Ad • ) and 6.70 eV (2-Ad • ). The vertical radical ionization potentials are necessarily larger: 6.85 (1-Ad • ) and 7.08 eV (2-Ad • ). The predicted adiabatic electron affinities are all negative: −0.13 (1-Ad • ) and −0.13 eV(2-Ad • ). The vertical electron affinities are −0.28 (1-Ad • ) and −0.37 eV(2-Ad • ). The vertical detachment energies are 0.07 (1-Ad - ) and 0.22 eV(2-Ad - ).