A chloride complex of a hexaprotonated azamacrocycle has been isolated, and its structure has been determined by X-ray crystallography showing two encapsulated chloride anions in the cavity. The two internal guests are coordinated at two binding sites on the opposite side of the macrocycle through trigonal recognition by hydrogen-bonding interactions. The other four chlorides are located outside the cavity, each with a single hydrogen bond from secondary amines. Ab initio calculations based on density functional theory (DFT) suggest that the encapsulation of two chlorides inside the cavity leads to a significant charge transfer from the anions to the protonated amines.

A macrocyclic-based fluorescence chemosensor has been designed and synthesized from the reaction of dansyl chloride and a hexaaminomacrocycle containing four secondary and two tertiary amines. The new chemosensor has been examined for its binding ability toward phosphate, sulfate, nitrate, iodide, bromide, chloride, and fluoride by fluorescence spectroscopy in DMSO. The results indicate that the compound binds each of the anions with a 1:1 stoichiometry, showing high affinity for the oxoanions, chloride and iodide with the binding constants up to four orders of magnitude. Ab initio calculations based on density functional theory (DFT) suggest that the ligand is deformed in order to encapsulate an anion, and each anion, except fluoride, is bonded to the macrocycle through two NH…X− and four CH…X− interactions.

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A hexaaminomacrocycle L, containing four secondary and two tertiary amines has been synthesized and crystallized with hydrobromic acid. Structural analysis of the bromide complex suggests that the ligand in its tetrtaprotonated form, is involved in coordinating two bromides from both sides via hydrogen bonding interactions with N…Br- distance of 3,351 Å, forming a ditopic complex. The other two bromides are outside the cavity, and singly bonded to the macrocycle. The molecules are packed showing layer structures in which the internal bromides are locked between the layers of macrocycles. The bromide anions are coordinated alternatively by one and two hydrogen bonds with the protonated amines from the two adjacent macrocycles.