Unusually strong hydrogen bond cooperativity in particular (H₂O)₂₀ clusters

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Chemical Physics

Background:

• Hydrogen bonding is fundamental to water's properties.
• Cooperativity effects in water clusters are not fully understood.
• Quantifying hydrogen bond strength is crucial for molecular simulations.

Purpose of the Study:

• To investigate the role of cooperativity in forming strong hydrogen bonds in neutral water clusters.
• To characterize the structural, vibrational, and NMR properties of a water cluster with a strong hydrogen bond.
• To quantify the energy of these unusually strong hydrogen bonds.

Main Methods:

• Utilized second-order perturbation theory and density functional theory.
• Analyzed a (H2O)20 pentagonal dodecahedron cluster.
• Employed symmetry-adapted perturbation theory for energy calculations.

Main Results:

• Identified hydrogen bond lengths shorter than 2.50 Å.
• Predicted a significant OH stretching frequency redshift (>2000 cm-1).
• Observed a large downfield shift (13.5 ppm) and anisotropy (49.9 ppm) in 1H magnetic shielding.
• Calculated hydrogen bond energy over three times stronger than in liquid water.

Conclusions:

• Cooperativity effects can indeed lead to unusually strong hydrogen bonds in neutral water clusters.
• The characterized strong hydrogen bond significantly alters vibrational and NMR properties.
• These findings provide insights into water's complex hydrogen bonding network.