Crystal and molecular structure of [Ni{2-H₂NC(=O)C₅H₄N}₂(H₂O)₂][Ni{2,6-(O₂C)₂C₅H₃N}₂]·4.67H₂O; DFT studies on hydrogen bonding energies in the crystal

Abstract

<jats:p>[Ni{2-H<jats:sub>2</jats:sub>NC(=O)C<jats:sub>5</jats:sub>H<jats:sub>4</jats:sub>N}<jats:sub>2</jats:sub>(H<jats:sub>2</jats:sub>O)<jats:sub>2</jats:sub>][Ni{2,6-(O<jats:sub>2</jats:sub>C)<jats:sub>2</jats:sub>C<jats:sub>5</jats:sub>H<jats:sub>3</jats:sub>N}<jats:sub>2</jats:sub>]·4.67H<jats:sub>2</jats:sub>O, a new complex salt containing a bis(2,6-dicarboxypyridine)nickel(II) anion and a bis(2-amidopyridine)diaquanickel(II) cation, was synthesized and characterized. The crystal is stabilized by an extensive network of hydrogen bonds. Alternate layers of anions and cations/water molecules parallel to (010) can be distinguished. Computational studies of the network packing of the title compound by high-level DFT-D/B3LYP calculations indicate stabilization of the networks with conventional and non-conventional intermolecular O—H...O, N—H...O and C—H...O hydrogen bonds along with π-stacking contacts. Due to the presence of water molecules and the importance of forming hydrogen bonds with the involvement of water clusters to the stability of the crystal packing, the importance and role of these water clusters, and the quantitative stability resulting from the formation of hydrogen bonds and possibly other noncovalent bonds such as π-stacking are examined. The binding energies obtained by DFT-D calculations for these contacts indicate that hydrogen bonds, especially O—H...O and N—H...O, control the construction of the crystalline packing. Additionally, the results of Bader's theory of AIM for these interactions agree reasonably well with the calculated energies.</jats:p>