Synthesis, X-ray characterization and DFT studies of bis-N-imidazolylpyrimidine salts: the prominent role of hydrogen bonding and anion–π interactions

Abstract

Five new proton transfer compounds, (bimipyrH₂)(Cl)₂ (1), (bimipyrH₂)[(NO₃)(NO₃HNO₃)] (2), (bimipyrH₂)(ZnCl₄) (3), (bimipyrH₂)(CdCl₄) (4) and (bimipyrH₂)(HgCl₄) (5) (bimipyr = 4,6-di(1H-imidazol-1-yl)pyrimidine), have been synthesized and characterized by elemental analysis, IR and NMR spectroscopy and single crystal X-ray diffraction. Crystallographic analysis revealed that the asymmetric unit of 1 consists of one doubly protonated bimipyr molecule, one solvent water molecule and two chloride anions. Conversely, 2 is anhydrous where one counterion is chelated by the (bimipyrH₂)²⁺ molecule and the other anion is solvated by the parent acid forming an independent ‘acid salt’ counterion [NO₃HNO₃]⁻. Both compounds exhibit diverse architectures involving hydrogen bonding and anion–π interactions. Compounds 3, 4 and 5 consist of outer sphere complexes of diprotonated bimipyr with [MCl₄]²⁻ as the counterion. They have the same molecular composition and compounds 4 and 5 (M = Cd and Hg, respectively) are essentially isomorphous and crystallized in the monoclinic space group P2₁/n. In the crystal structures of the five salts, N–H⋯Cl/O and C–H⋯Cl/O hydrogen bonds as well as anion–π, involving aromatic rings and inorganic anions, and π-stacking interactions are described and analysed by means of density functional theory (DFT) calculations since they play an important role in the construction of three-dimensional supramolecular frameworks. Finally, aggregation studies of compound 1 in solution (DMSO) are also described and discussed.