Anion binding to azamacrocycles: synthesis and X-ray crystal structures of halide adducts of [12]aneN4 and [18]aneN6

Abstract

An investigation into the halide binding properties of two polyazamacrocycles [12]aneN₄ (L1) and [18]aneN₆ (L2) has resulted in the determination of the molecular structure of five compounds [H₄L1(Br)₄]·2H₂O (1), [H₂L1(I₃)₂]·2I₂·2CH₃CN (2), [H₆L2(Cl)₆]·4H₂O (3), [H₄L2(Br)₄]·2H₂O (4) and [H₄L2(I)₂(I₃)₂] (5). [18]aneN₆ (L2) was generally found to bind two anions within the macrocyclic cavity. In the adducts formed by [12]aneN₄ (1 and 2), the anions and solvent of crystallization do not sit within the [12]aneN₄ cavity, instead preferring to occupy positions exterior to the macrocycle. Left- and right-handed helices are formed by the I₃⁻ and I₂ moieties in 2 that house acetonitrile solvent molecules in the centre of the spiral. In most cases, chloride and bromide adopt trigonal pyramidal co-ordination motifs with various degrees of distortion from a regular geometry. The ring size, conformational flexibility and level of protonation were found to influence the halide binding characteristics of the macrocycles.