Influence of Noncovalent Interactions on Uracil Tautomer Selection: Coordination of Both N1 and N3 Uracilate to the Same Metal in the Solid State

The reaction of uracil and [Zn(H2O)6](NO3)2 in aqueous ammonia solution produces, after treatment with
iProOH, the complex [Zn(uracilate-κN)(uracilate-κN3)(NH3)2]. This compound in the solid state presents a complete set of
hydrogen bonds and electrostatic interactions including those mediating the self-recognition of the uracilate groups. The
unique characteristics of this complexsmall size and the presence of both N1 and N3 uracil tautomers among otherseliminate possible factors in uracil tautomer selection, demonstrating the overriding importance of noncovalent interactions
in tautomer selection during crystallization. This result can probably be extended to other, uracil-related ligands.