Charge-Assisted Complexation of Anions of Different Dimensionality by Benzimidazole-Based Receptors Bearing -OH Functionality

Abstract

Two benzimidazole-based receptors (L¹ and L²) bearing -OH functionality form crystalline salts with different organic and inorganic acids viz. [L¹H⁺]­[Cl^–] (<b>1</b>), [L¹H⁺]­[NO₃^–] (<b>2</b>), [L¹H⁺]­[OAc^–] (<b>3</b>), [L¹H⁺]­[DNB^–]·DMF (<b>4</b>), [L¹H⁺]­[H₂PO₄^–] (<b>5</b>), [L²H⁺]­[OAc^–]·AcOH (<b>6</b>), [L²H⁺]­[DNB^–] (<b>7</b>), and [L²H⁺]­[HSO₄^–]·H₂O (<b>8</b>) where the shape of the counteranion drives the solid structure from a one-dimensional polymeric chain to a three-dimensional structure. Structural analyses show that the anion binding in all eight complexes is attributable entirely to NH⁺<b>···</b>anion, NH<b>···</b>anion, OH<b>···</b>anion, and multiple CH<b>···</b>anion hydrogen bonding interactions. In the solid structure the planar nitrate anion forms a cyclic structure with receptor L¹, whereas the acetate anion with the same receptor leads to a molecular barrel type structure. Again the tetrahedral dihydrogen phosphate anion forms a polymeric interanionic chain structure with L¹, and the other tetrahedral hydrogen sulfate anion forms hydrogen sulfate–(water)₂–hydrogen sulfate adducts with charged L²