Binding of inorganic oxoanions to macrocyclic ligands: interactions of sulfate and dithionate with protonated forms of [18]aneN6

Abstract

Three sulfate-macrocycle adducts [H₆L(HSO₄)₄(SO₄)]·H₂O (1), [H₆L(SO₄)₃] (2) and [H₆L(HSO₄)₂Cl₄]·2H₂O (3) (where L = [18]aneN₆) were crystallized from solutions containing the macrocycle and the appropriate inorganic acids, and [H₄L(S₂O₆)₂]·2H₂O (4) from an aqueous solution of the macrocycle and sodium dithionate. All four structures show that the polyammonium groups on the protonated macrocycle participate in ‘co-ordination’ or supramolecular interactions with one or more oxygen atoms from the polyoxoanions (i.e., SO₄²⁻, HSO₄⁻ or S₂O₆²⁻). In 3, the protonated macrocyclic cavity holds the two chloride anions in preference to the oxoanions. The sulfate anions show remarkable versatility in their interactions with the macrocycle. Of particular note is a unique η-5 N–H⋯O cluster involving the sole sulfate anion in 1, but there are many common features throughout the structures, such as the inclusion of one anion on either side of the macrocycle and the participation of all ammonium protons in H-bonding interactions.