Two novel complexes [ML]·(ClO4)2·EtOH·xH2O M = CuII, x = 3; M = NiII, x = 2; L = 1-R-4,7-bis(benzimidazole-2-yl-methyl)-1,4,7-triazacyclononane, [R = 1-(benzimidazole-2-yl-methyl)benzimidazole-2-yl-methy], were prepared by a one-pot method using the 1,4,7-triazacyclononane ligand (tacn) and 2-chloromethylbenzimidazole as starting materials. The ES-MS and u.v. spectra of the complexes indicate that they are very stable thermodynamically and kinetically in aqueous solution. The crystal structure of the CuII complex shows that the CuII centre is octahedrally coordinated by six nitrogen atoms of three benzimidazoles and tacn.