Synthesis of Crystalline Calcium Bicarbonate

Area of Science:

• Geochemistry
• Crystallography
• Biogeochemistry

Background:

• Bicarbonate reactions, particularly with calcium, are vital to Earth's carbon cycle and biochemical processes.
• Calcium bicarbonate (Ca(HCO3)2) has been hypothesized for over 200 years but never isolated, with attempts invariably yielding carbonates.

Purpose of the Study:

• To synthesize and determine the crystal structure of calcium bicarbonate (Ca(HCO3)2).
• To understand the factors inhibiting the isolation of metal bicarbonates.

Main Methods:

• Crystal synthesis by modifying the bonding environment to stabilize bicarbonate ions.
• X-ray crystallography to determine the crystal structure of synthesized Ca(HCO3)2.

Main Results:

• Successfully synthesized Ca(HCO3)2 crystals with direct calcium-bicarbonate bonds.
• The Ca(HCO3)2 crystal structure is rhombohedral, identical to calcite.
• Polarization in aqueous environments destabilizes calcium-bicarbonate pairing, preventing isolation.

Conclusions:

• The first resolved crystal structure of Ca(HCO3)2 provides fundamental insights into metal-bicarbonate interactions.
• Understanding these interactions advances the control of CO2-involved reactions and ionic compound formation.