Hydrogen Bonds of Coordinated Ethylenediamine and a Water Molecule: Joint Crystallographic and Computational Study of Second Coordination Sphere

Abstract

In the study of hydrogen bonds between noncoordinated and metal-coordinated ethylenediamine and a water molecule, the data in the Cambridge Structural Database (CSD) were analyzed and DFT calculations were performed. For coordinated ethylenediamine in the CSD, the analyzed distributions of dOH distances show a maximum in the range of 2.0–2.1 Å, while the angle α shows a maximum in the range of 150–160°. The DFT calculations were done for octahedral geometries of cobalt(III), copper(II), and nickel(II) complexes and square-planar geometry of palladium(II) complexes. The coordination of ethylenediamine to the metal ions strengthens its hydrogen bond with the water molecule. Namely, noncoordinated ethylenediamine and the water molecule have an interaction energy of −2.3 kcal/mol, while for coordinated ethylenediamine, the interacting energy spans from −4.0 to −28.0 kcal/mol depending on the metal ion and charge of the complex. The hydrogen bond energies have a good correlation with the calculated electrostatic potential on the interacting hydrogen atom. The coordination number and oxidation states of the metal have a significant influence on the electrostatic potential on the interacting hydrogen atom and the energy of hydrogen bonds.