Metallogel of bis(tetrazole)-appended pyridine derivative with CoBr2 as a chemoprobe for volatile gases containing chloride atom

A bis(tetrazole)-appended ligand 1 formed the metallogel efficiently by mixing with Co2+ ion. Interestingly, the metallogel 1 with CoBr2 showed the orange yellow colour, which has octahedral structure. The rheological properties of metallogel obtained with CoBr2 were ca. 1.5-fold larger than that for the metallogel obtained with CoCl2. Upon addition of HCl, SOCl2, (COCl)2 and COCl2 containing chloride atoms in the metallogel 1 prepared with CoBr2 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, HNO3 and H2SO4. These findings indicate that the metallogel 1 with CoBr2 is useful as a chemoprobe for gases containing chloride atom.