Characterizing Hydrogen-Bond Interactions in Pyrazinetetracarboxamide Complexes: Insights from Experimental and...

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Dipalladium(II) complexes are investigated for their unique structural and bonding properties.
• Pyrazinetetracarboxamide ligands offer versatile coordination environments.
• Short hydrogen bonds can significantly influence molecular properties and reactivity.

Purpose of the Study:

• To experimentally and computationally analyze dipalladium(II) complexes with functionalized pyrazinetetracarboxamide ligands.
• To investigate the nature and strength of short O---O distances and associated hydrogen bonds.
• To understand the influence of ligand substituents and counterions on hydrogen bond characteristics.

Main Methods:

• Synthesis and single-crystal X-ray diffraction of dipalladium(II) complexes.
• Solution studies including spectroscopic analysis.
• Quantum topological analyses: electron localization function (ELF), noncovalent interaction (NCI) analysis, and Bader's quantum theory of atoms in molecules (QTAIM).

Main Results:

• Complexes with tetraethyl, tetrahexyl, and tetrakis(2-hydroxyethyl) ethyl ether ligands were synthesized.
• Crystal structures revealed very short O---O distances (2.413(5)–2.430(3) Å) between adjacent amide carbonyl groups.
• Quantum chemical analyses confirmed the presence of low barrier hydrogen bonds and provided insights into proton delocalization.

Conclusions:

• The short O---O separations are indicative of strong, potentially low barrier, hydrogen bonding.
• The ligand environment and, notably, the counterion at the fourth coordination site, exert a subtle but significant influence on the hydrogen bond strength and proton distribution.
• These findings contribute to understanding hydrogen bonding in coordination complexes and the role of non-covalent interactions in molecular design.