A macrocyclic dinuclear copper complex, [Cu 2 II (1)Br 3 (H 2 O)]Br has been synthesized and characterized by X-ray crystallography, in which the macrocycle is folded to form a bowl-shaped cavity. The sensing ability of the receptor has been studied for halides by UV-VIS spectroscopy in water-acetonitrile (1:3 v/v) and water. The results indicate that the new receptor exhibits strong affinity and selectivity for iodide.The field of anion coordination chemistry continues to expand with new synthetic molecules capable of recognizing anions with environmental and biomedical relevance. 1 Various types of synthetic receptors have been developed which employ hydrogen bonds offered by specific binding sites as in azamacrocyles, 2 amides, 3 thioamide, 4 urea 5 and pyrroles 6 to bind anions with size and shape selectivity in various media. Without the involvement of hydrogen bonds, quaternized ammonium hosts by electrostatic forces, 7 and azamacrocyles 8a and phosphonium hosts 8b by ion paring (in aqueous medium where hydrogen bonding is weak) 8 are known to form anion complexes in aqueous medium. An alternative approach is to use dinuclear metal complexes 9 as shown in seminal papers by Nelson 10 and Fabbrizzi 11 with two copper ions in cryptand-based receptors, providing vacant axial sites that are available to coordinate an anion through Lewis-acid base interactions. The presence of two metal ions further increases the rigidity of a cryptand, and the metal-metal distance within the cavity determines the binding strength, displaying selectivity for an anion with correct bite length. For example, the dicopper(II) complex of m-xylyl-based cryptand (Cu(II)-Cu(II) = 6.10 Å) showed strong affinity for an anion of comparable size as N 3 − or NCS − but failed to bind small halides. 10 The free macrocycle 1 was prepared as reported previously. 17 The synthesis of macrocyclic dinuclear copper complex was accomplished from the reaction of 1 with two equivalents of anhydrous CuBr 2 in H 2 O/CH 2 OH mixture. Crystals suitable for X-ray analysis were obtained by slow evaporation of a water solution of the complex.The X-ray analysis 18 reveals that the complex is crystallized in the space group, Pn to yield a molecular formula, C 26 H 44 Br 3 Cu 2 N 6 O·Br (R) in which two Cu(II) ions reside at both N 3 sites in the macrocycle. Each Cu(II) is coordinated with three macrocyclic nitrogens and one bromide at equatorial plane, but one has an axial bromide, while the other has an axial water, thus forming a square pyramidal geometry. Such effect leads to the macrocycle adopting a bowl-shaped cavity (Figure 1) with the Cu-Cu distance of 7.101 (4) Å. The Cu-N distances are 2.025(4) to 2.056(4) Å that are comparable to the corresponding Cu-N distances (1.973(5) to 2.056(5) Å) observed in m-xylyl-based macrocycle. 10 The Cu-Br axial distance, 2.959(4) Å is significantly longer than those observed in Cu-Br equatorial distances (Cu2-Br2 = 2.3890(7), and Cu1-Br1 = 2.4171(7) Å) -a phenomenon that is known as a Jahn-Teller distortion. 1...

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.

Structural characterization of a sulfate complex with an azamacrocycle suggests that one sulfate is encapsulated in the macrocyclic cavity with eight hydrogen bonds; a significant selectivity of the host was observed for sulfate over halides, nitrate and perchlorate as evaluated by 1 H NMR studies in water.Sulfate is present in the biological system and plays a crucial role in many biochemical processes, 1 such as in biosynthesis 2 and sulfate binding proteins. 3 Sulfate is also a known inorganic pollutant in the environment. 4 For example, contamination of the Hanford nuclear waste site by this anion has been a matter of increased concern, hampering the vitrification process. 5 However, as compared to other oxoanions, such as phosphate and nitrate, this anion has been less studied with synthetic hosts. 6 Therefore, the design of suitable hosts for selective recognition of sulfate remains a challenge in the area of anion binding chemistry. 7 Encapsulated sulfate was crystallographically characterized in self-assembled metal-organic cage hosts, polyamides, 8 ureas 9 or indoles. 10 In these cases, an encapsulation occurred within the crystal lattices formed by a host matrix or between hosts. Based on the theoretical † Electronic supplementary information (ESI) available: One crystallographic data in CIF format, the synthetic procedure in pdf format. CCDC 777812. For ESI and crystallographic data in CIF or other electronic format see

A p-xylyl-based macrocycle L has been synthesized and its binding properties with halides have been investigated by 1H NMR titrations, single crystal X-ray diffraction analysis, and density functional theory (DFT) calculations. As investigated by 1H NMR titrations, the ligand preferentially binds a halide in a 1:2 binding mode, with the association constants (in log K2) of 2.82, 2.70, 2.28, and 2.20 for fluoride, chloride, bromide, and iodide, respectively. The overall binding trend was found to be in the order of fluoride > chloride > bromide > iodide, reflecting that the binding strength correlates with the relative basicity and size of the respective halide. Crystallographic studies indicate that the ligand forms 1:2 complexes with chloride, bromide and iodide. In the chloride complex, the ligand is hexaprotonated and each chloride is held via three NH···Cl– bonds. The ligand is tetraprotonated for the other complexes, where each halide is H-bonded to two secondary ammonium NH+ groups via NH···X– bonds. The results of DFT calculations performed on [H6L]6+ at M062x/6-311G (d,p) level in both gas and solvent phases, suggest that the ligand binds halides with the binding energy in the order of F– > Cl– > Br– > I–, supporting the experimental data obtained from 1H NMR studies. Results from DFT calculations further indicate that a 1:2 binding is energetically more favorable than a 1:1 binding of the ligand.