Interactions of (MY)6 (M = Zn, Cd; Y = O, S, Se) quantum dots with N-bases

(MY)(6) clusters, with M = Zn and Cd and Y = O, S, Se, form double-layer drum-like structures containing M-Y covalent bonds. The positive regions near the M atoms attract the N atom of both NH3 and NMe3 so as to form a noncovalent M<bold>N bond</bold>. This bond is quite strong, with interaction energies exceeding 35kcal/mol. The bond strength diminishes with reduced electronegativity of the Y atom (O > S > Se) and is stronger for M = Zn than for Cd. Trimethylation of the base enhances the bond strength. The interaction is dominated by the electrostatic component which accounts for some 60-70% of the total attractive force. The interaction increases the highest occupied molecular orbital-lowest unoccupied molecular orbital gap by between 0.1 and 0.2eV.