Cd2+-selective fluorescence response of TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine) derivatives bearing ether oxygen-binding sites.

Moderate Zn2+ selectivity over Cd2+ (IZn/ICd = 1.6) in the fluorescence enhancement of TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine) was changed to Cd2+ preference via the introduction of a methoxymethyloxy (MOMO) substituent at the 8-position of one of the four quinoline rings (IZn/ICd = 0.2). Thus, 8-MOMOTQEN (N-(8-methoxymethyloxy-2-quinolylmethyl)-N,N',N'-tris(2-quinolylmethyl)ethylenediamine) showed not only high Cd2+-selectivity but also an enhanced fluorescence quantum yield upon Cd2+ binding and high sensitivity for Cd2+ detection as shown by ϕCd = 0.065 and LOD (limit of detection) = 19 nM. The two oxygen atoms of the MOMO group in 8-MOMOTQEN play a crucial role in the fluorescent metal-ion selectivity because the corresponding hydroxy (8-OHTQEN) and methoxy (8-MeOTQEN) derivatives resulted in a poor fluorescent response and metal selectivity, respectively. Another N6O2 ligand, N,N'-bis(8-methoxy-2-quinolylethyl)-N,N'-bis(2-quinolylmethyl)ethylenediamine ((8-MeO)2TQEN) exhibited a Zn2+-selective fluorescence enhancement (IZn/ICd = 2.2), indicating the superiority of the MOMO group for the selective sensing of Cd2+.

Structure and electrochemical properties of (µ-O)2Mn2(iii,iii) and (µ-O)2Mn2(iii,iv) complexes supported by pyridine-, quinoline-, isoquinoline- and quinoxaline-based tetranitrogen ligands.

Seven new bis(µ-oxo)dimanganese complexes with Mn2(iii,iii) or Mn2(iii,iv) oxidation states were prepared using quinoline- and isoquinoline-based tetraamine ligands. The structures of the ligands include ethylenediamine, trans-1,2-cyclohexanediamine and tripodal amine, bearing two or three nitrogen-containing heteroaromatics. Regardless of the skeleton and number of aliphatic nitrogen atoms in the ligands, quinoline complexes stabilize the Mn2(iii,iii) oxidation state, whereas, isoquinoline ligands afford Mn2(iii,iv) complexes. A systematic comparison of the differences in structural parameters and redox potentials of a total of 14 complexes with a (µ-O)2Mn2 diamond core, which includes corresponding pyridine and quinoxaline derivatives as supporting ligands, highlights the distinct deviation of quinoline and tripodal amine motifs in this ligand series.