Structural polymorphism of pyrazinium hydrogen sulfate: extending chemistry of the pyrazinium salts with small anions

Two polymorphs (alpha, beta) of pyrazinium hydrogen sulfate (pyzH(+)HSO(4)(-), abbreviated as PHS) with distinctly different hydrogen-bond types and topologies but close electronic energies have been synthesized and characterized for the first time. The alpha-polymorph (P2(1)2(1)2(1)) forms distinct blocks in which the pyzH(+) and HSO(4)(-) ions are interconnected through a network of NH...O and OH...O hydrogen bonds. The beta-form (P1) consists of infinite chains of alternating pyzH(+) and HSO(4)(-) ions connected by NH...O and OH...N hydrogen bonds. Density functional theory (DFT) calculations indicate the possible existence of a hypothetical polar P1 form of the beta-polymorph with an unusually high dipole moment.