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

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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.

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