Two novel 3D Zn(II)/Cd(II) MOFs with tri- or di-nuclear cluster units for multifunctional sensing applications in aqueous media

With flexible 2-methylenesuccinate acid (H(2)MSA) and rigid 4, 4'-bipyridine (bpy) as mixed ligands, two three-dimensional (3D) metal-organic frameworks (MOFs), {[Zn-3(mu(2)-OH)(2)(MSA)(2)(bpy)(2)]center dot 4H(2)O}(n), (1) and {[Cd (MSA)(bpy)]center dot 2H(2)O}(n) (2), were obtained solvothermally. Complexes 1 and 2 both have a 3D framework structures, which include respectively a linear trinuclear [Zn-3] or a rare dinuclear [Cd-2] cluster node that consisting of two seven-coordinated Cd(II) ions. The adjacent [Zn-3] or [Cd-2]( )nodes in 1 and 2 are firstly linked together by the MSA(2-) ligand to form a 1D chain or a 2D layer unit respectively, which are further bridged by the bpy linkers to produce the 3D framework structures. If treating the [Zn-3] and [Cd-2] cluster as 4- and 6-connected nodes, the 3D frameworks of 1 and 2 can be simplified into a CdSO4 topological network with a Schlaflisymbol of (6 (5).8) and a rob network with a Schlafli symbol of (4(8).6(6).8), respectively. The PXRD patterns suggest that 1 and 2 have good stability when soaked in water for at least 48 h. The fluorescence sensing properties of 1 and 2 toward different metal inorganic ions were investigated, and two complexes both could sense Fe3+, MnO4- and Cr2O72- in aqueous solution with high sensitivity and selectivity (the LODs were 3.20 mu M, 1.54 mu M and 1.95 mu M for 1, 1.15 mu M, 0.48 mu M and 1.23 mu M for 2, respectively) as well as good recircularity. In addition, the mechanism of the selective luminescence quenching response for Fe3+, MnO4- and Cr2O72- could be attributed to the energy competition between the excitation of complex 1/2 and the ultraviolet absorption of responsive substances. With flexible 2-methylenesuccinate acid (H(2)MSA) and rigid 4, 4'-bipyridine (bpy) as mixed ligands, two three-dimensional (3D) metal-organic frameworks (MOFs), {[Zn-3(mu(2)-OH)(2)(MSA)(2)(bpy)(2)]center dot 4H(2)O}(n), (1) and {[Cd (MSA)(bpy)]center dot 2H(2)O}(n) (2), were obtained solvothermally. Complexes 1 and 2 both have a 3D framework structures, which include respectively a linear trinuclear [Zn-3] or a rare dinuclear [Cd-2] cluster node that consisting of two seven-coordinated Cd(II) ions. The adjacent [Zn-3] or [Cd-2]( )nodes in 1 and 2 are firstly linked together by the MSA(2-) ligand to form a 1D chain or a 2D layer unit respectively, which are further bridged by the bpy linkers to produce the 3D framework structures. If treating the [Zn-3] and [Cd-2] cluster as 4- and 6-connected nodes, the 3D frameworks of 1 and 2 can be simplified into a CdSO4 topological network with a Schlafli symbol of (6 (5).8) and a rob network with a Schlafli symbol of (4(8).6(6).8), respectively. The PXRD patterns suggest that 1 and 2 have good stability when soaked in water for at least 48 h. The fluorescence sensing properties of 1 and 2 toward different metal inorganic ions were investigated, and two complexes both could sense Fe3+, MnO4- and Cr2O72- in aqueous solution with high sensitivity and selectivity (the LODs were 3.20 mu M, 1.54 mu M and 1.95 mu M for 1, 1.15 mu M, 0.48 mu M and 1.23 mu M for 2, respectively) as well as good recircularity. In addition, the mechanism of the selective luminescence quenching response for Fe3+, MnO4- and Cr2O72- could be attributed to the energy competition between the excitation of complex 1/2 and the ultraviolet absorption of responsive substances.

Automated summary

The fluorescence sensing properties of two three-dimensional metal-organic frameworks (MOFs) were investigated, and they exhibited high sensitivity and selectivity towards Fe3+, MnO4- and Cr2O72-. The MOFs showed good stability and recircularity.