Two tautomeric polymorphs of 2,6-dichloropurine

Area of Science:

• Crystallography
• Solid-state chemistry
• Organic chemistry

Background:

• 2,6-dichloropurine is a purine derivative with potential biological and chemical applications.
• Polymorphism, the ability of a solid material to exist in more than one crystal form, can significantly impact material properties.

Purpose of the Study:

• To crystallize and characterize two distinct polymorphs of 2,6-dichloropurine.
• To elucidate the crystal structures and intermolecular interactions of these polymorphs.
• To compare the structural features and packing arrangements of the identified tautomers.

Main Methods:

• Single-crystal X-ray diffraction was employed to determine the crystal structures.
• Analysis of hydrogen bonding, nonbonding contacts (C-Cl···π), and π-π stacking interactions.
• Comparison of crystallographic data, including space groups and molecular arrangements.

Main Results:

• Two polymorphs of 2,6-dichloropurine were successfully crystallized and identified as the 9H- and 7H-tautomers.
• Both polymorphs exhibit similar hydrogen-bonding motifs (intermolecular N-H···N) forming linear chains.
• Crystal structures are further stabilized by C-Cl···π contacts and π-π stacking, resulting in a 2D herringbone packing.

Conclusions:

• The 9H- and 7H-tautomers of 2,6-dichloropurine represent distinct polymorphs with similar, yet differentiated, crystal packing.
• The primary structural distinction lies in the specific roles of molecules within the π-π stacking interactions.
• Understanding these structural nuances is crucial for predicting and controlling the properties of 2,6-dichloropurine in solid-state applications.