Structures and Spectra of Halide Hydrate Clusters in the Solid State: A Link between the Gas Phase and Solution State

Area of Science:

• Chemistry
• Solid-state chemistry
• Hydrate chemistry

Background:

• Halide hydrates are crucial in various chemical processes.
• Understanding their solid-state structures provides insights into their behavior in solution.
• Discrete halide hydrates, particularly chloride hydrates, exhibit diverse structural motifs.

Purpose of the Study:

• To review and assess known discrete solid-state halide hydrates.
• To analyze structural characteristics and water-to-halide ratios.
• To establish connections between gas-phase, solid-state, and solution structures.

Main Methods:

• Literature review of solid-state halide hydrate structures.
• Analysis of structural data, focusing on discrete clusters and polymeric forms.
• Comparison of experimental solid-state data with computed gas-phase structures and vibrational spectra.

Main Results:

• Most discrete halide hydrates are chloride-based, often dihalides.
• Polymeric chloride hydrates predominantly form 2D layered structures.
• Distinct chloride:water ratios exist for isolated clusters (1-3 waters), 2D layers (2-8 waters), 1D chains (1-2 waters), and 3D semiclathrates (20-38 waters).
• A notable gap in chloride:water ratio exists between 8-20 waters.
• [Cl(H2O)]- is unique as it exists in solid, gas, and solution phases and possesses a free OH group.
• Infrared spectroscopy is valuable for identifying these species.

Conclusions:

• Discrete halide hydrates in the solid state serve as a bridge between gas-phase species and solution behavior.
• Structural diversity is observed across different hydration levels and dimensionalities.
• The findings enhance our understanding of microsolvated ion-pairs.