A flexible bis(pyridylcarbamate) anion receptor: Binding of infinite double-stranded phosphate, [-sulfate-(H₂O)₂-]_n, and hydrogen-bridged helical perchlorate chain

Anion complexation of a flexible bis(pyridylcarbamate) receptor, 3-pyridinyl-carbamic-acid-1,2-ethanediylester (L), is reported. Upon addition of a series of inorganic acids (H₃PO₄, H₂SO ₄, HClO₄, HCl and HBr), the ligand L can be doubly protonated and bind the anions through hydrogen bonding interactions, affording the adducts 1-5. The binding modes of the protonated ligand ([LH ₂]²⁺) with anions in 1-5 in the solid state are established by X-ray single crystal diffraction. Of particular interest is that the three oxoanion complexes (1-3) feature intriguing anionic polymer fashions, such as the novel double-stranded dihydrogen phosphate chain in 1, the infinite [-sulfate-(H₂O)₂-]_n chain in 2, and hydrogen-bridged helical perchlorate chain in 3. For complexes 4 and 5, the packing diagram displays a layered structure with the halide anions located between the adjacent cationic arrays. Receptor L can selectively crystallize with the sulfate anion from the acid mixture H₃PO₄, H ₂SO₄, HClO₄, HCl and HBr.