Ca(BF₄)₂·xH₂O redefined from powder diffraction as hydrogen-bonded Ca(H₂O)₄(BF₄)₂ ribbons.

Area of Science:

• Inorganic Chemistry
• Crystallography
• Materials Science

Background:

• Calcium bis(tetrafluoroborate) hydrate (Ca(BF4)2·xH2O) is a compound with an incompletely understood crystal structure.
• Hydrated salts often exhibit complex structures influenced by water molecule coordination and hydrogen bonding.

Purpose of the Study:

• To determine the precise crystal structure of calcium bis(tetrafluoroborate) hydrate using laboratory powder diffraction data.
• To elucidate the coordination environment of water molecules and their role in the overall structure.
• To reformulate the compound based on the determined structural arrangement.

Main Methods:

• Laboratory powder diffraction data collection.
• Crystal structure determination and refinement.
• Analysis of coordination polyhedra and hydrogen bonding interactions.

Main Results:

• The crystal structure was determined to be a mono-dimensional arrangement of infinite ribbons.
• Water molecules are integrated into [CaO4F4] square antiprisms, sharing fluorine corners with [BF4] tetrahedra.
• The compound is reformulated as Ca(H2O)4(BF4)2, indicating a specific coordination number for calcium and water.
• The structure is interconnected by hydrogen bonds (H...F and H...O).

Conclusions:

• The determined structure reveals a novel mono-dimensional network in calcium bis(tetrafluoroborate) hydrate.
• The reformulation Ca(H2O)4(BF4)2 accurately represents the compound's composition and structural role of water.
• The compound Ca(H2O)4(BF4)2 is isostructural with calcium perchlorate tetrahydrate, Ca(ClO4)2·4H2O, highlighting similarities in hydrated salt structures.