Structural Transformations in the Thermal Dehydration of [Cu₂(bpa)(btec)(H₂O)₄]_n Coordination Polymer

Area of Science:

• Coordination Chemistry
• Materials Science
• Crystallography

Background:

• Pyridinic ligands and transition metals form coordination polymers like Metal-Organic Frameworks.
• Combining ligands can yield diverse structures and properties.
• 1,2,4,5-benzenetetracarboxylic acid (H4btec) is a versatile ligand in coordination chemistry.

Purpose of the Study:

• To synthesize and characterize a novel 2D coordination polymer using 1,2-bis(4-pyridyl)ethane (bpa) and H4btec.
• To investigate the thermal behavior and phase transformations of the synthesized compound.
• To perform a topological analysis of the bpa ligand in coordination polymers.

Main Methods:

• Microwave-assisted synthesis.
• Single crystal X-ray diffraction for structural characterization.
• Thermogravimetric analysis and variable temperature powder X-ray diffraction for thermal studies.
• Electronic paramagnetic resonance spectroscopy and magnetic susceptibility measurements.
• Analysis of over 1000 structures from the Cambridge Structural Database.

Main Results:

• A novel 2D coordination polymer, [Cu2(bpa)(btec)(H2O)4]n (1), was successfully synthesized and characterized.
• Compound 1 exhibits two sequential thermochromic phase transformations upon heating, influenced by coordinated water molecules.
• The anhydrous form, [Cu2(bpa)(btec)]n (1.ah), was also structurally determined.
• A comprehensive topological study classified the bpa ligand into 17 distinct topologies based on its role in coordination polymers.

Conclusions:

• The synthesized coordination polymer demonstrates interesting thermal and structural properties.
• Coordination water molecules play a crucial role in the thermal stability and phase transitions.
• The topological analysis provides a systematic classification of the bpa ligand's diverse coordination modes.