A series of two-dimensional microporous triazole-functionalized metal-organic frameworks with the new multi-dentate ligand 1-(4-aminobenzyl)-1,2,4-triazole: single-crystal-to-single-crystal transformation, structural diversity and luminescent sensing

摘要

In this work a new flexible multi-dentate 1-(4-aminobenzyl)-1,2,4-triazole (abtz) ligand has been designed and synthesized, and a series of two-dimensional (2D) triazole-functionalized metal-organic frameworks, namely {[Cd(abtz)(2)(H2O)(2)]center dot(ClO4)(2)center dot H2O}(n) (1), {[Cd(abtz)(2)(H2O)(2)]center dot(SiF6)}(n) (2), {[Cd(abtz)(2)(H2O)(2)]center dot(ClO4)(1.64)center dot(HSO4)(0.36)center dot 1.36H(2)O}(n) (3), {[Cd(abtz)(2)(NCS)]center dot(ClO4)}(n) (4) and {[Ag-2(mu(2)-abtz) (mu(3)-abtz)(ClO4)]center dot(ClO4)}(n) (5) have been isolated. Firstly, when abtz and corresponding cadmium(II) salts are employed, new rectangular-grid 2D coordination frameworks containing free ClO4- or SiF62- anions, {[Cd(abtz)(2)(H2O)(2)]center dot(ClO4)(2)center dot H2O}(n) (1) and{[Cd(abtz)(2)(H2O)(2)]center dot(SiF6)}(n) (2), can be isolated. Furthermore, in 1 weakly H-bonded ClO4- anions present within the voids can be partly exchanged by HSO4- anions to generate the anion exchanged crystalline product {[Cd(abtz)(2)(H2O)(2)]center dot(ClO4)(1.64)center dot(HSO4)(0.36)center dot 1.36H(2)O}(n) (3) in single-crystal-to-single- crystal (SC-SC) manner. On the other hand, 1 can be used as a precursor to react with NH4NCS to obtain the 2D bilayer framework {[Cd(abtz)(2)(NCS)]center dot(ClO4)}(n) (4) under hydrothermal conditions. This also presents a novel example of structural transformation with bond rupture/formation from a mono-layer framework 1 to a 2D bi-layer framework 4. Furthermore, when AgClO4 is used to replace Cd(ClO4)(2) in the reaction system, another 2D layer framework {[Ag-2(mu(2)-abtz)(mu(3)-abtz) (ClO4)]center dot(ClO4)}(n) (5) with unique (2,4,5) connected topology can be isolated. The solid state luminescence properties and PXRD patterns of 1-5 have been investigated. Additionally, luminescence measurements illustrate that complexes 4 and 5 represent novel examples as luminescent probes of new sensing materials. 4 shows highly sensitive response to acetone and Fe3+. Besides, 5 is the first report of multidimensional polymers based on triazole derivatives with luminescent response to small biological molecules such as vitamin C in water solutions.