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(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···N bond. This bond is quite strong, with interaction energies exceeding 35 kcal/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 0.2 eV.
Michalczyk, M., Zierkiewicz, W. & Scheiner, S. Struct Chem (2019) 30: 1003. https://doi.org/10.1007/s11224-019-01337-6