Expanding the Solid Form Landscape of Bipyridines

Area of Science:

• Solid-state chemistry
• Crystallography
• Coordination chemistry

Background:

• Bipyridine isomers (2,2'- and 4,4'-) are crucial in coordination chemistry as ligands and coformers.
• Understanding their solid-state behavior is essential for material design and pharmaceutical applications.

Purpose of the Study:

• To conduct solid-state screening and crystal structure prediction for 2,2'- and 4,4'-bipyridine isomers.
• To characterize and compare the diverse solid-state forms and crystallization behaviors of these isomers.

Main Methods:

• Experimental techniques: thermal analysis, isothermal calorimetry, X-ray diffraction, gravimetric moisture sorption, and IR spectroscopy.
• Computational approaches: crystal structure prediction and lattice/interaction energy calculations.

Main Results:

• 2,2'-Bipyridine formed one anhydrate and a formic acid disolvate.
• 4,4'-Bipyridine yielded multiple forms, including an anhydrate, dihydrate, and eight carboxylic acid solvates (seven new).
• Lattice energy calculations supported disolvate formation, while 4,4'-bipyridine showed higher conformational flexibility and faster hydrate interconversion kinetics.

Conclusions:

• The structural differences between 2,2'- and 4,4'-bipyridine isomers lead to distinct solid-state behaviors and crystallization patterns.
• The exposed nitrogen atoms in 4,4'-bipyridine facilitate greater solvate formation and conformational adaptability.
• Computational and experimental data provide a comprehensive understanding of bipyridine solid forms.