A combined experimental and theoretical study of anion-π interactions in bis(pyrimidine) salts

We report the synthesis and X-ray characterization of an N,N'-tetramethylenebis(2-aminopyrimidinium) tetrafluoroborate salt that exhibits anion-pi interactions that are responsible for the crystal packing. The anion forms a sandwich complex with two pyrimidine rings. When the anion is nitrate, the crystal packing is governed by anion-pi interactions and hydrogen bonds, and the sandwich complex is not formed. Finally, a theoretical study of the anion-pi interactions in charged pyrimidine rings is in good agreement with the experimental findings. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)