Anion-templated synthesis of metallacages as a means for the colorimetric detection of chlorides.

In the presence of chloride or bromide in the appropriate mixture of solvents, 6 equiv of nickel(II) and 8 equiv of Hatu [Hatu=H2NC(=NH)NHC(=S)NH2] assemble to yield the metallacages [Ni6(atu)8X][ClO4]3 (atu=deprotonated form of Hatu; X=Cl, 5; Br, 6) where four "units" of the square-planar complex Ni(atu)2 are coordinated to two further nickel centers, forming an octahedral cage around an encapsulated chloride or bromide anion. Synthesis of the cages is highly dependent on the nature of the anions and the solvents used. In methanol, the cage only forms if chloride is present; in a mixture of acetone/methanol, the cage forms in the presence of either chloride or bromide. An interesting feature of the templation process is that there is a dramatic color change associated with assembly of the building blocks in the presence of the appropriate anion to yield the cages. This color change has been used as the basis for the colorimetric detection of chloride anions in methanol. The reaction of 4 equiv of nickel(II), 8 equiv of Hatu, and 2 equiv of platinum(II) has also been carried out, yielding the mixed-metal cage [Pt2Ni4(atu)8Cl][ClO4]3 (7a); the X-ray crystal structure of this compound is reported herein.