Anhydrous Adenine: Crystallization, Structure, and Correlation with Other Nucleobases

The crystal structure of anhydrous adenine has been determined using a single crystal grown by a unique approach using a sublimation process. Anhydrous adenine crystallizes in the monoclinic space group P21/c with a = 7.891(3) Å, b = 22.242(8) Å, c = 7.448(3) Å, β = 113.193(5)°, V = 1201.6(3) Å3, and Z = 8. The two molecules in the asymmetric unit are connected via two N−H···N hydrogen bonds, and the crystal structure is stabilized by two sets of N−H···N hydrogen bonds, one across the center of symmetry connecting the imidazole moiety to the pyridine moiety and the other linking the next asymmetric unit resulting in a "sheet" motif.