Four super water-stable isostructural lanthanide-organic frameworks, [Ln(HL)(H2O)2]n·2H2O (1-Ln) (Ln = Eu, Tb, Nd and Sm), have been successfully synthesized under hydrothermal conditions with 3,5-di(2,4-dicarboxylphenyl)pyridine (H4L) and Ln(NO3)3·6H2O. 1-Ln shows a novel 2D layered structure with uncoordinated carboxylic and pyridyl groups pointing to the interior of interlayer channels. The luminescent properties of 1-Eu in the solid state and one steeped in aqueous solution have been measured, which show excellent luminescence and good luminescent stability in water. Next 1-Eu was chosen as a probe for sensing different metal ions. Consequently, 1-Eu exhibits a highly selective response to Fe(3+) through the luminescence quenching effect in aqueous solutions. The probable mechanisms of the quenching effects have been investigated in detail.

Four new metal-organic frameworks (MOFs), {[Zn(L)(OH)(HO)]·NMP·2HO} (1), {[HN(Me)][Zn(L)(HO)]·DMF·HO} (2), {[Co(L)(HO)]·2HO} (3) and {[Mn(L)(HO)]·6HO} (4), were assembled employing a symmetrical V-shaped rigid multicarboxylic acid ligand HL (HL = 2,4-di(3',5'-dicarboxylphenyl)benzoic acid) with different metal ions, resulting in versatile frameworks as well as various types of coordination modes of HL. 1 forms a three-dimensional (3D) 4-connected sra net based on trinuclear [Zn(μ-OH)(μ-COO)(μ-COO)] clusters, while 2 displays a 3D (4,6)-connected net based on two types of binuclear [Zn(μ-COO)(μ-COO)] and [Zn(μ-COO)] clusters. 3 and 4 contain similar [M(μ-COO)(μ-COO)] (3, M = Co; 4, M = Mn) clusters but result in different 4-connected 3D and 2D frameworks, respectively. 1 and 2 show solid-state luminescence properties at ambient temperature. Meanwhile, 1 shows high selectivity and sensitivity for not only Fe cations but also for CrO, CrO and MnO anions via a luminescence quenching effect with a low detection limit, which thus means that it could be a potential crystalline material for detecting these anions. The mechanisms of the quenching effect and sensing properties of 1 are discussed in detail. In addition, 3 and 4 have the presence of antiferromagnetic interactions between the metal ions.