Structural Diversity in Luminescent MOFs Containing a Bent Electron-rich Dicarboxylate Linker and a Flexible Capping Ligand: Selective Detection of 4-Nitroaniline in Water.

A combination of a bent bis(naphthalene) and hydroxy-based dicarboxylate linker and a flexible bis(tridentate)polypyridyl ligand has been employed to self-assemble with two different d metal centers, Zn and Cd , to form structurally diversified luminescent metal-organic frameworks, [Zn (tpbn)(mbhna) (H O) ]⋅4 H O⋅1.5DMF (1) and {[Cd (tpbn)(mbhna) ]⋅2DMF} (2), respectively (where, tpbn=N,N',N'',N'''-tetrakis(pyridine-2-ylmethyl)butane-1,4-diamine and H mbhna=4,4'-methylene-bis[3-hydroxy-2-naphthalene carboxylic acid]). Both 1 and 2 are characterized and analyzed by various analytical techniques including single-crystal X-ray diffractometry. Their excellent emissive nature is studied in different solvents and further utilized to selectively detect aromatic amines, particularly 4-nitroaniline in water with detection limits at sub-ppm level. The difference in sensing activity of 1 and 2 toward 4-NA is corroborated well with their structures. The mechanism of action has been established through Stern-Volmer plot, spectral overlap, time-resolved lifetime studies and HOMO-LUMO energy calculations. In addition, 1 and 2 are found to be recyclable and display good stability after sensing experiments.