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(H 2 O) 6 ](NO 3 ) 2 in aqueous ammonia solution produces, after treatment with i ProOH, the complex [Zn(uracilate-κ N 1 )(uracilate-κ N 3 )(NH 3 ) 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.