A Biphenol-Based Chemosensor for ZnII and CdII Metal Ions: Synthesis, Potentiometric Studies, and Crystal Structures

We synthesized and characterized the ligand N,N′-bis[(2,2′- dihydroxybiphen-3-yl)methyl]-N,N′-dimethylethylenediamine (L), which contains two biphenol moieties linked as side arms to an N,N′- dimethylethylenediamine scaffold. The ligand is highly soluble in a 50/50 (v/v) water/ethanol mixture and, in its deprotonated form H−2L2−, is able to coordinate transition-metal ions such as NiII, ZnII, CuII, CdII, and PdII. The crystal structures of [Ni(H−2L)·2n-BuOH], [Ni(H−2L)·2MeOH], [Cd- (H−2L)·2DMF], [Cu(H−2L)(DMF)], and [Pd(H−2L)(DMF)] were also determined and described. Potentiometric titrations were carried out in a mixed solvent with ZnII, CuII, and NiII metal ions to determine the acid− base and stability constants. L was highly fluorescent in the visible range (400 nm). Moreover, its emission intensity increased upon the addition of ZnII or CdII ions in an ethanol/water solution and behaved as a chemosensor for the presence of these ions in the solution.