Stacking Interactions between Square-Planar Metal Complexes with 2,2′-Bipyridine Ligands. Analysis of Crystal Structures and Quantum Chemical Calculations

Abstract

Stacking interactions between square-planar metal complexes containing bipyridine ligands (bipy) were studied by analyzing data in the Cambridge Structural Database (CSD) and by density functional theory (DFT) calculations. In most of the crystal structures, two bipy complexes were head-to-tail oriented. On the basis of the data from CSD, we classified the overlaps of bipy complexes into six types. The types were defined by values of geometrical parameters, and the interactions of the same type have very similar overlap geometries. The most frequent are the structures with quite large overlap area including chelate rings and pyridine fragments. The overlap is often influenced by ligands coordinated at the third and fourth coordinating positions or by molecules (ions) from the environment in the crystal structure. The interaction energies of all types of overlap were calculated on model systems using the DFT (TPSS-D3) method. The strongest calculated interaction has an energy of −31.66 kcal/mol and large area of overlap. By decreasing the overlap area, the strength of interactions decreases. The weakest calculated interaction has an energy of −7.26 kcal/mol and the small overlap area of pyridine fragments. These results presenting the geometries and energies of stacking interactions can be very important for various molecular systems.

Can Stacking Interactions Exist Beyond the Commonly Accepted Limits?

“…47 Hence, all the calculations were also carried out using SCS(MI)-MP2 method (where MI is an abbreviated of "Molecular Interactions"). In this modification, the spin-component scaling factors were optimized, for a given basis set, against the intermolecular binding energies of the S22 test set, 38 which includes hydrogen-bonded systems, dispersion-dominated systems and mixed systems. All the calculations were performed with usage of Dunning's correlation consistent basis sets 55 and utilizing cc-pVDZ → cc-pVTZ extrapolation scheme (cc-pV(DT)Z).…”

“…The some limited studies were presented (e.g. for pyridine molecules 37 and square-planar metal coordination compounds containing bipyridine ligands 38 ), but they did not give any generalized rules about the geometrical parameters (including the possibility of existence of π•••π interactions for long d Cg•••Cg distances).…”

Electrochemical Oxidation of Glassy Carbon Provides Similar Electrochemical Response as Graphene Oxide Prepared by Tour or Hummers Routes

“…Metal‐chelate rings and their interactions with aromatic molecules are important in terms of conducting and magnetic materials, crystal engineering, and catalysis 14–17. Many crystal structures of metal chelates are described18–28 and their interaction patterns with aromatic rings are generally known 21–25. It has been notoriously difficult to calculate the energies of the noncovalent interactions of metal chelates at high theoretical levels due to the overall size of the systems and due to presence of the metal ion 29.…”

Robust Packing Patterns and Luminescence Quenching in Mononuclear [Cu(II)(phen)2] Sulfates

“…Chem. C XXXX, XXX, XXX−XXX thus indicating the slipping stacking interaction with offset 43,45. The consecutive metal···metal separations through the stacked ligands insignificantly differ now, being equal to 8.4555(9) and 8.7711(9) Å.…”