Two tautomeric polymorphs of 2,6-dichloropurine

Abstract

Two polymorphs of 2,6-dichloropurine, C(5)H(2)Cl(2)N(4), have been crystallized and identified as the 9H- and 7H-tautomers. Despite differences in the space group and number of symmetry-independent molecules, they exhibit similar hydrogen-bonding motifs. Both crystal structures are stabilized by intermolecular N-H···N interactions that link adjacent molecules into linear chains, and by some nonbonding contacts of the C-Cl···π type and by π-π stacking interactions, giving rise to a crossed two-dimensional herringbone packing motif. The main structural difference between the two polymorphs is the different role of the molecules in the π-π stacking interactions.

Solvatomorphism with polar protic/aprotic and non-polar solvents in a series of complexes derived from the 5-phenylimidazole/tetrafluoroborate/copper(ii) reaction system

“…The X-ray structure determination of all compounds (1-19) revealed that the initially used 4-phenylimidazole ligand (HL) is present as its 5-phenylimidazole tautomeric form. This rearrangement, termed as annular tautomerism of 4(5)-phenylimidazole, [65][66][67] is a result of the amphoteric character of the imidazole and involves the exchange of a proton from the pyrrole-type atom N1 to the pyridine-type atom N3. Tautomerism is accompanied by a significant change in ligand conformation and it is thus likely that the 5-phenyl form of the HL ligand is the most favourable one in terms of the formation of these complexes.…”

Influence of ligand positional isomerism on the molecular and supramolecular structures of cobalt(II)-phenylimidazole complexes

“…The X-ray analysis of compounds 5-8 showed that the initially used 4-phenylimidazole ligand ( L 0 the exchange of a proton from the pyrrole-type atom N1 to the pyridine-type atom N3 and is termed an annular tautomerism of 4(5)-phenylimidazole (Claramunt et al, 2002;Kubicki, 2004;García-Rubiñ o et al, 2011) (Fig. 1).…”