Dušan P. Malenov

Stacking of Benzene with Metal Chelates: Calculated CCSD(T)/CBS Interaction Energies and Potential-Energy Curves

Accurate values for the energies of stacking interactions of nickel- and copper-based six-membered chelate rings with benzene are calculated at the CCSD(T)/CBS level. The results show that calculations made at the ωB97xD/def2-TZVP level are in excellent agreement with CCSD(T)/CBS values. The energies of [Cu(C3H3O2)(HCO2)] and [Ni(C3H3O2)(HCO2)] chelates stacking with benzene are -6.39 and -4.77 kcal mol(-1), respectively. Understanding these interactions might be important for materials with properties that are dependent on stacking interactions.

Stacking of Metal Chelates with Benzene: Can Dispersion‐Corrected DFT Be Used to Calculate Organic–Inorganic Stacking?

CCSD(T)/CBS energies for stacking of nickel and copper chelates are calculated and used as benchmark data for evaluating the performance of dispersion-corrected density functionals for calculating the interaction energies. The best functionals for modeling the stacking of benzene with the nickel chelate are M06HF-D3 with the def2-TZVP basis set, and B3LYP-D3 with either def2-TZVP or aug-cc-pVDZ basis set, whereas for copper chelate the PBE0-D3 with def2-TZVP basis set yielded the best results. M06L-D3 with aug-cc-pVDZ gives satisfying results for both chelates. Most of the tested dispersion-corrected density functionals do not reproduce the benchmark data for stacking of benzene with both nickel (no unpaired electrons) and copper chelate (one unpaired electron), whereas a number of these functionals perform well for interactions of organic molecules.

Unexpected Importance of Aromatic–Aliphatic and Aliphatic Side Chain–Backbone Interactions in the Stability of Amyloids

The role of aromatic and nonaromatic amino acids in amyloid formation has been elucidated by calculating interaction energies between β-sheets in amyloid model systems using density functional theory (B3LYP-D3/6-31G*). The model systems were based on experimental crystal structures of two types of amyloids: (1) with aromatic amino acids, and (2) without aromatic amino acids. Data show that these two types of amyloids have similar interaction energies, supporting experimental findings that aromatic amino acids are not essential for amyloid formation. However, different factors contribute to the stability of these two types of amyloids. In the former, the presence of aromatic amino acids significantly contributes to the strength of interactions between side chains; interactions between aromatic and aliphatic side chains are the strongest, followed by aromatic-aromatic interactions, while aliphatic-aliphatic interactions are the weakest. In the latter, that is, the amyloids without aromatic residues, stability is provided by interactions of aliphatic side chains with the backbone and, in some cases, by hydrogen bonds.

Stacking of cyclopentadienyl organometallic sandwich and half-sandwich compounds. Strong interactions of sandwiches at large offsets

Stacking interactions of organometallic sandwich and half-sandwich compounds with cyclopentadienyl (Cp) were studied by searching and observing the crystal structures in the Cambridge Structural Database and performing density functional calculations. The strongest calculated interactions are at an offset of 1.5 A with energies for sandwich and half-sandwich dimers of −3.37 and −2.87 kcal mol−1, respectively, somewhat stronger than the stacking interaction between two benzene molecules, −2.73 kcal mol−1. At large offsets of 5.0 A, 74% of the strongest energy is preserved for the sandwich dimer and only 29% for the half-sandwich dimer. In crystal structures, for sandwich compounds, the stacking at large offsets is dominant (73%), since the interaction at large offsets is relatively strong, and the geometries enable additional simultaneous interactions with Cp faces. The stacking at large offsets between half-sandwich compounds is less dominant, since the interaction is weaker. However, Cp half-sandwich compounds stack at large offsets unexpectedly often (almost 60%), since the branching of their other ligands in the compound favors more simultaneous interactions with Cp faces. Strong interaction at large offsets for sandwich compounds is the consequence of favorable electrostatic interaction, which is not the feature of stacking between half-sandwich compounds.

Strong Stacking between Organic and Organometallic Molecules as the Key for Material Design

Very attractive properties of organic-inorganic materials consisting of planar molecules, namely magnetism, conductivity, non-linear optics and catalysis, are highly dependent on the stacking interactions. Metal-chelate rings and aromatic molecules are very common constituents of these materials. The search of Cambridge Structural Database has shown that stacking interactions of chelates and aromatic molecules occur very often in crystal structures; these interactions are of very similar geometries to stacking between two aromatic molecules. The energies of these interactions have been calculated at high theoretical levels, showing much stronger stacking of six-membered chelate with benzene that stacking of two benzene molecules. The stacking interaction between two benzene molecules is -2.73 kcal/mol, while the interaction between benzene and chelate ring dependent on the metal type, being stronger for copper(II)-chelate (-6.08 kcal/mol) than for nickel(II)-chelate (-4.68 kcal/mol). The energies of interactions are calculated at CCSD(T)/CBS level and the benchmark study was performed to find Minnesota functionals that can reproduce this data.