The structures of uncommon cationic N-alkenyl purine and pyrimidine bases

The structures of 1,3 bis-(allyl)cytosinium bromide (1), 7,9 bis-(allyl)adeninium bromide hydrate (2) and 3-(butenyl)adeninium bromide (3) have been determined. 1 is dimeric via N?H...Br hydrogen bonds, which further associate into ribbons via weaker C?H...Br interactions. 2 is also dimeric, now from N?H...N hydrogen bonds, which build up further through a complex array of hydrogen bonds involving both the anion and water of crystallization (O?H...N, O?H...Br, C?H...Br). 3 does not dimerise but forms polymeric sheets via a series of N?H...N, C?H...N and C?H...Br hydrogen bonds.