Anion Binding Studies of Urea and Thiourea Functionalized Molecular Clefts.

Two rationally designed 4-nitrophenyl-based molecular clefts functionalized with thiourea (L 1 ) and urea (L 2 ) have been synthesized and studied for a variety of anions by UV-Vis and colorimetric techniques in DMSO. Results from the binding studies suggest that both L 1 and L 2 bind halides showing the order: fluoride > chloride > bromide > iodide; and oxoanions showing the order: dihydrogen phosphate > hydrogen sulfate > nitrate > perchlorate. Each receptor has been shown to form a 1:1 complex with an anion via hydrogen bonding interactions, displaying distinct color change for fluoride and dihydrogen phosphate in solution. As compared to the urea-based receptor L 2 , the thiourea-based receptor L 1 exhibits stronger affinity for anions due the presence of more acidic thiourea functional groups.

An Ideal C3-Symmetric Sulfate Complex: Molecular Recognition of Oxoanions by m-Nitrophenyl- and Pentafluorophenyl-Functionalized Hexaurea Receptors.

The anion-binding properties of two tripodal-based hexaureas appended with the m-nitrophenyl (1) and pentafluorophenyl (2) groups have been studied both experimentally and theoretically, showing strong affinities for sulfate over other inorganic oxoanions such as hydrogen sulfate, dihydrogen phosphate, bicarbonate, nitrate, and perchlorate. The structural analysis of the sulfate complex with 1 reveals that the receptor organizes all urea-binding sites toward the cavity at precise orientations around a tetrahedral sulfate anion to form an ideal C3-symmetric sulfate complex that is stabilized by 12 hydrogen-bonding interactions. The receptor and the encapsulated sulfate are located on the threefold axis passing through the bridgehead nitrogen of 1 and the sulfur atom of the anionic guest. The high-level density functional theory calculations support the crystallographic results, demonstrating that the C3-symmetric conformation of the sulfate complex is achieved due to the complementary NH···O between the receptor and sulfate.

1,3-Phenyl-enediammonium dinitrate.

In the title compound, C(6)H(10)N(2) (2+)·2NO(3) (-), the dication lies on a crystallographic twofold rotation axis. The nitrate ions are linked to the dications though N-H⋯O hydrogen bonds, forming a three-dimensional network.