Preparation and Structure of Zinc(II) Complexes of Purine and 7-Azaindole

Trichloro(purinium)zinc(II) (1) and dichloro-bis-(7-azaindole)zinc(II) (2) have been prepared from respectively 1:1 (in acid solution) and 2:1 aqueous solutions of the parent base and zinc(II) chloride. In the latter case the salt di-[7-azaindolium]zinc(II) tetrachloride (3) is isolated under acid conditions. The structures of 1-3 have been established by X-ray structural analyses. Zinc coordinates the purine nitrogen N(7) in 1 and N(3) of 7-azaindole in 2. N(l) is protonated in 1. The bond length distribution of the cations 3 suggests a significant contribution from a resonance form in which N(9) carries the positive charge