A quantum crystallographic approach to short hydrogen bonds

Area of Science:

• Solid-state chemistry
• Supramolecular chemistry
• Crystallography

Background:

• Short hydrogen bonds (approx. 2.45 Å) are crucial in molecular complexes.
• Their behavior is temperature-dependent and can be tuned.
• Understanding these bonds is key to material properties and pharmaceutical applications.

Purpose of the Study:

• To investigate the nature of short O-H⋯O and O+-H⋯O- hydrogen bonds.
• To analyze their position within the salt-cocrystal continuum.
• To correlate hydrogen bond characteristics with molecular structure and environment.

Main Methods:

• High-resolution synchrotron X-ray diffraction for electron density mapping.
• Ab initio modeling for theoretical analysis.
• Study of substituted urea and organic acid molecular complexes (N,N'-dimethylurea complexes).

Main Results:

• Complexes fall within the salt-cocrystal continuum, exhibiting strong electrostatic or very strong covalent character.
• Electron density is sensitive to proton transfer, aiding in salt-cocrystal continuum studies.
• Calculated potentials show a zero barrier to proton migration, forming an 'energy slide'.

Conclusions:

• Short hydrogen bonds exhibit characteristics of both strong interactions and covalent bonds.
• Proton position and migration are influenced by the molecular environment.
• This fundamental understanding has implications for regulating pharmaceutical materials.