CCSD(T)/CBS and DFT methods are employed to study the stacking interactions of acetylacetonate-type (acac-type) chelates of nickel, palladium, and platinum with benzene. The strongest chelate-aryl stacking interactions are formed by nickel and palladium chelate, with interaction energies of 25.75 kcal mol 21 and 25.73 kcal mol 21 , while the interaction of platinum chelate is weaker, with interaction energy of 25.36 kcal mol 21 . These interaction energies are significantly stronger than stacking of two benzenes, 22.73 kcal mol 21 . The strongest nickel and palladium chelate-aryl interactions are with benzene center above the metal area, while the strongest platinum chelate-aryl interaction is with the benzene center above the C2 atom of the acac-type chelate ring. These preferences arise from very different electrostatic potentials above the metal ions, ranging from very positive above nickel to slightly negative above platinum. While the differences in electrostatic potentials above metal atoms cause different geometries with the most stable interaction among the three metals, the dispersion (correlation energy) component is the largest contribution to the total interaction energy for all three metals.density functional theory, dispersion, electrostatic potentials, metal chelates, stacking interactions 1 | I N TR ODU C TI ON Stacking interactions play very important roles in many important chemical and biological systems. [1] They are primarily recognized as one of the most important forces responsible for the structure of DNA [2,3] and for the stability of protein structure, [4][5][6] where they are established between aromatic moieties. Therefore, most of the studies on stacking interactions have dealt with aromatic molecules. [7][8][9][10][11][12][13][14][15][16][17] Several studies suggested that important and strong stacking interactions can be formed between aromatic and nonaromatic molecules or fragments [18][19][20][21][22][23][24] or between two nonaromatic moieties. [25,26] Most recently, the research on amyloids, that are considered responsible for Alzheimer's disease, showed that aromatic-aliphatic interactions are of greater importance than aromatic-aromatic interactions in amyloid-b polypeptides. [27] Several transition metal ions have been associated with amyloid-b polypeptide neurotoxicity, [28][29][30] and are the possible targets for Alzheimer's disease therapy with ligands that can form stable chelate rings with such ions. Chelate rings are also constituents in many materials [31,32] and play important roles in crystal engineering. [33,34] Moreover, chelate rings have a tendency to stack with aromatic rings, which was shown in searches of the Cambridge Structural Database. [23,35,36] Crystallographic studies showed a preference for stacking of aromatic rings with chelate rings over stacking with other aromatic rings. [36] These findings were supported by quantum chemical calculations, which showed stronger stacking interactions between metal chelate and aromatic rings than between two aromati...