Metallogel of bis(tetrazole)-appended pyridine derivative with CoBr<sub>2</sub> as a chemoprobe for volatile gases containing chloride atom

<p>A bis(tetrazole)-appended ligand <b>1</b> formed the metallogel efficiently by mixing with Co<sup>2+</sup> ion. Interestingly, the metallogel <b>1</b> with CoBr<sub>2</sub> showed the orange yellow colour, which has octahedral structure. The rheological properties of metallogel obtained with CoBr<sub>2</sub> were ca. 1.5-fold larger than that for the metallogel obtained with CoCl<sub>2</sub>. Upon addition of HCl, SOCl<sub>2</sub>, (COCl)<sub>2</sub> and COCl<sub>2</sub> containing chloride atoms in the metallogel <b>1</b> prepared with CoBr<sub>2</sub> changed from orange yellow to blue-green colour. These results indicate that the octahedral structure of metallogel was converted into the tetrahedral structure. On the other hand, no significant colour changes were observed in the presence of an excess of other anions, namely HF, HBr, HI, HNO<sub>3</sub> and H<sub>2</sub>SO<sub>4</sub>. These findings indicate that the metallogel <b>1</b> with CoBr<sub>2</sub> is useful as a chemoprobe for gases containing chloride atom.</p>