Anti-electrostatic hydrogen bonds.

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Chemical Bonding Theory

Background:

• Hydrogen bonding is typically understood to occur between species of opposite charges.
• Coulomb electrostatic forces are generally considered dominant in ionic interactions.
• The formation of stable complexes between like-charged ions has been a long-standing theoretical challenge.

Purpose of the Study:

• To investigate the possibility and characteristics of hydrogen-bonded complexes formed between ions of like charge.
• To explore the underlying interactions governing the stability of such "anti-electrostatic" hydrogen bonds (AEHBs).
• To challenge conventional models of hydrogen bonding and ionic interactions.

Main Methods:

• Utilized ab initio computational techniques.
• Employed hybrid density functional theory (DFT) methods.
• Analyzed theoretical, structural, and spectroscopic signatures of the studied complexes.

Main Results:

• Identified and characterized a new class of H-bonded complexes between like-charged ions (anion-anion and cation-cation).
• These AEHB species exhibit significant kinetic stability.
• Observed characteristic theoretical, structural, and spectroscopic evidence of hydrogen bonding.

Conclusions:

• Resonance-type covalency (charge transfer) interactions are dominant in AEHBs.
• These charge transfer interactions can overcome strong Coulomb electrostatic repulsion.
• Traditional assumptions about the essential role of ionic or dipole-dipole forces in H-bonding are challenged.