The appearance of a bright yellow color signals the inclusion of a halide ion (X=Cl, Br, I) into the dicopper(II) cryptate 1 in aqueous solution at pH 5.2. The X− ion bridges the two metal centers, as is shown by the crystal structure of the bromide inclusion complex. At pH 8, X− is replaced by the smaller OH− ion, and the solution turns emerald green. The cage can adjust its intermetallic cavity to include polyatomic anions as large as N3− and NCS−.
Crystals of the title compound are orthorhombic with a = 11 .I 16(11), b = 12.043(9), c = 7.646(5) 8, space group Pbca, Z = 8. The structure was solved from three-dimensional diffractometer data by Patterson and Fourier methods and refined by block-diagonal least-squares to R 0.029 for 1029 observed reflections. The structure consists of protonated cations in the cis-conformation, i.e. with the -NH-NH2 group bent towards the C=S bond, and of chloride anions. Packing is determined by hydrogen-bonds formed by the -NH:, -NH,, and >NH groups with CI-and S.
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