Two New Copper Borates with Mesoscale Cubic Supramolecular Cages Assembled from {Cu₄ @B₂₀ } Clusters

Area of Science:

• Inorganic Chemistry
• Materials Science
• Crystallography

Background:

• Supramolecular chemistry focuses on the design and synthesis of complex molecular assemblies.
• Metal borates are an important class of inorganic compounds with diverse structures and properties.
• Solvothermal synthesis is a versatile technique for creating crystalline materials.

Purpose of the Study:

• To synthesize and characterize novel copper borate compounds.
• To investigate the formation of 3D supramolecular frameworks and cubic cages.
• To explore the influence of boric acid on the resulting supramolecular architecture.

Main Methods:

• Solvothermal synthesis was employed to prepare the copper borate compounds.
• Single-crystal X-ray diffraction was used to determine the crystal structures.
• Characterization of the supramolecular framework and cage structures was performed.

Main Results:

• Two new copper borates, H₆[(μ₄-O)Cu₄@B₂₀O₃₂ (OH)₈]⋅25H₂O (1) and H₆[(μ₄-O)Cu₄@B₂₀O₃₂ (OH)₈]⋅34H₂O⋅8H₃BO₃ (2), were successfully synthesized.
• Both compounds exhibit 3D supramolecular frameworks built from novel cubic supramolecular cages with mesoscale cavities formed via hydrogen bonding.
• Compound 2, incorporating additional boric acid (H₃BO₃), displays larger cubic cage sizes and higher non-framework volume, resulting in mesoporous dimensions.

Conclusions:

• The study successfully synthesized novel copper borates with intricate 3D supramolecular architectures.
• The formation of mesoscale cubic cages is achieved through hydrogen bonding interactions.
• The incorporation of boric acid can effectively tune the size and porosity of the supramolecular cages.