Tetrahedral oxyanions-assisted supramolecular assemblies of pyridine-based tectons into hydrogen-bonding networks

The systematic research has been done into structural variations of supramolecular architectures by the self assembly of two pyridine-based potential anion receptors, 1-(4-pyridyl)piperazine (L₁) and 4-pyrrolidinopyridine (L₂), and different inorganic acids (HCl, HBr, HI, HNO₃, HClO₄, HIO₄, H₂SO₄ and H₃PO₄). The formation of four fascinating salts, i.e. (H₂L₁²⁺)•(H₂PO₄^-)₂ (1), (H₂L₁²⁺)•(ClO₄^-)₂ (2), (HL₂⁺)•(ClO₄^-) (3) and (HL₂⁺)•(IO₄^-) (4), indicates that N-heterocyclic L₁ and L₂ are prone to cocrystallize with tetrahedral oxyanions and anionic topologies play a crucial role in the crystallization process. Structural analyses reveal that various intermolecular ring motifs have been generated by robust hydrogen-bonding interactions in compounds 1-4. In particular, interesting substructures were observed in H₂PO₄^- from salts 1 due to its polytopic potential hydrogen-bonding donor and acceptor oxygen atoms, including ring motifs, 1D ribbons and 2D supramolecular framework. Much to our surprise, crystal 4 proves to be a member of few supramolecular salts crystallizing with IO₄^- anion according to the Cambridge Structure Database (CSD).