3 POLYMORPHS OF 2-AMINO-5-NITROPYRIMIDINE - EXPERIMENTAL STRUCTURES AND THEORETICAL PREDICTIONS

Three previously unknown crystal structures (polymorphs) of 2-amino-5- nitropyrimidine (I-III), as determined by single-crystal X-ray diffrac tion, are reported. Crystal packing, hydrogen-bond patterns, and inter molecular forces have been examined in detail, and theoretical studies were performed on I-III to estimate their lattice energies and to det ermine the role of changes in molecular conformation upon the resultin g crystal structure. Each structure is characterized by an extensive n etwork of hydrogen bonds (including C-H ... N and C-H ... O interactio ns) and short interlayer distances. This structural system has shown u p limitations of several assumptions that are generally made in curren t methods of predicting crystal structures and polymorphism, but withi n these limitations, the applied scheme has been successful.