![](https://d3ilqtpdwi981i.cloudfront.net/EdbISRGgO1uGOQwF-rlFDgWD5Rc=/425x550/smart/https://bepress-attached-resources.s3.amazonaws.com/uploads/0c/bf/f8/0cbff807-a7c4-497f-a9e6-df4b607b34f6/thumbnail_42f196d7-99c0-49a8-b904-f67c5cdd2708.jpg)
(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.