In order to limit the mobility of impregnated Cu(II), an aromatic ligand was designed so as to contain a tridentate group capable of binding the Cu(II). The primary co-ordination sphere of the Cu(II) was not entirely filled by the amine so that the fourth site was able to bind to HCN. Since no Cr(VI) was used in order to facilitate the complete oxidation of HCN, it was anticipated that the toxic decomposition product cyanogen ((CN)2) would be observed [2]. 2,6-bis(benzoxazoyl)-4-hydroxypyridine (BBOP) was chosen because it is a tridentate ligand that is resistant to hydrolysis and has a hydroxyl group with which it can be grafted within siliceous matrices.