R-substituents Induced Structural diversity, Synergistic Effect and Highly selective Luminescence Sensing for Fe3+ Detection By Postsynthetically Modified Cd-MOF

The self-assembly of 5-substituted isophthalic acid (R-H2BDC, R=H, NO2, Me, OH and tBu), CdII ions and 2,4,6-tris(3-pyridyl)-1,3,5-triazine (3-TPT) or 2,4,6-tris(4-pyridyl)-1,3,5-triazine (4-TPT) under solvothermal conditions yield six Cd-MOFs: {[Cd(BDC)(4-TPT)]•1.5H2O}n (Cd-MOF-1), {[Cd(NO2-BDC)(4-TPT)]•2H2O}n (Cd-MOF-2), {[Cd(Me-BDC)(4-TPT)]•2H2O}n (Cd-MOF-3),{[Cd(OH-BDC)(4-TPT)]•2.5H2O}n (Cd-MOF-4), {[Cd(tBu-BDC)(4-TPT)2/3]•DMF}n (Cd-MOF-5), {[Cd(BDC)(3-TPT)2/3]•3H2O}n (Cd-MOF-6), (where H2BDC = isophthalic acid, NO2-BDC = 5-nitroisophthalic acid, Me-BDC = 5-methylisophthalic acid, OH-BDC = 5-hydroxyisophthalic acid, tBu-BDC = 5-tert-butylisophthalic acid, 3-TPT = 2,4,6-tris(3-pyridyl)-1,3,5-triazine and 4-TPT = 2,4,6-tris(4-pyridyl)-1,3,5-triazine). All compounds are constructed from the dimeric Cd2(OCO)2 unit, and connected by the mixed R-H2BDC and n-TPT ligands into three-dimensional frameworks. Cd-MOF-1, 2 and 3 are iso-structural, in which the Cd2(OCO)2 units are bridged into 1D chains extended along [1 1 0] and [-1 1 0] directions, respectively, and are then further interlinked by 4-TPT ligands into three-dimensional network with CdS net topology. Cd-MOF-4 exhibits three-dimensional framework with pcu topology, in which the dimeric Cd2(OCO)2 units are firstly connected into two-dimensional Cd(OH-BDC)n sheet, and further “pillared” by 4-TPT into three-dimensional network. In Cd-MOF-5 and 6, the Cd2(OCO)2 units are firstly linked into three-dimensional NbO net by tBu-BDC/BDC ligands, which are further accommodated by the size-matching trigonal 3-TPT/4-TPT ligands into novel (3,8)-connected three-dimensional net. Interestingly, via the synergistic effect of open hydroxyl and pyridyl groups, the Cd-MOF-4 can be functionalized by Eu3+ ions by post synthetic modification, and the resulting 0.001Eu3+@Cd-MOF-4 phospher shows highly selective and sensitive probe for detection and recognition to Fe3+ ion through luminescence quenching effect in aqueous solution.