Xiang Xia Wu

Heterometallic Alkaline Earth–Lanthanide BaII–LaIII Microporous Metal–Organic Framework as Bifunctional Luminescent Probes of Al3+ and MnO4–

In this work a rigid asymmetrical tricarboxylate ligand p-terphenyl-3,4″,5-tricarboxylic acid (H3L) has been employed, and a unique heterometallic alkaline earth-lanthanide microporous luminescent metal-organic framework (MOF) {[Ba3La0.5(μ3-L)2.5(H2O)3(DMF)]·(3DMF)}n (1·3DMF) (DMF = dimethylformamide) has been isolated under solvothermal conditions. Single-crystal X-ray structural analysis demonstrates that 2D inorganic Ba-O-La connectivity can be observed in 1, which are further bridged via rigid terphenyl backbones of L(3-), forming a unique I(2)O(1)-type microporous luminescent framework. A 1D microporous channel with dimensionality of 9.151(3) Å × 10.098(1) Å can be observed along the crystallographic a axis. PXRD patterns have been investigated indicating pure phases of 1. The luminescence explorations demonstrated that 1 exhibits highly selective and sensitive sensing for Al(3+) over other cations with high quenching efficiency Ksv value of 1.445 × 10(4) L·mol(-1) and low detection limit (1.11 μM (S/N = 3)). Meanwhile 1 also exhibits highly selective and sensitive sensing for MnO4(-) over other anions with quenching efficiency Ksv = 7.73 × 10(3) L·mol(-1) and low detection limit (0.28 μM (S/N = 3)). It is noted that, when different concentrations of MnO4(-) solutions (0.5 to 100 μM) were dropped into the suspension of 1, the bright blue luminescence of the suspension observed under UV light can gradually change into pink color, indicating visually luminescent sensing, which makes the detection process of MnO4(-) more convenient in practical. The result also reveals that 1 represents the first example of bifunctional heterometallic alkaline earth-lanthanide MOF-based luminescent probes for selectively detecting Al(3+) and MnO4(-) in the water solutions.

A series of multi-dimensional metal–organic frameworks with trans-4,4′-azo-1,2,4-triazole: polymorphism, guest induced single-crystal-to-single-crystal transformation and solvatochromism

In this work, a flexible multi-dentate trans-4,4′-azo-1,2,4-triazole (atrz) ligand has been employed, and a series of novel coordination polymers, namely [Fe(μ-atrz)(NCS)2(H2O)2]n (1), [Fe(μ-atrz)(NCS)2(H2O)2]n (2), {[Fe(μ-atrz)(μ-Cl)(H2O)2]·Cl·H2O}n (3), {[Fe(μ-atrz)(atrz)2(H2O)2]·2Br·4H2O}n (4), {[Fe(μ-atrz)(atrz)2(H2O)2]·(BF4)2·2H2O}n (5), {[Cu(μ-atrz)3]·(BF4)2·2H2O}n (6), {[Cu(μ-atrz)3]·(BF4)2}n (7), {[Cu2(μ4-atrz)(μ2-OH)2(H2O)4]·SO4·3.75H2O}n (8), {[Zn(μ-atrz)(NCS)2]·0.5H2O}n (9) and {[Zn(μ-atrz)(NCS)2]}n (10) have been isolated. 1 and 2 present one-dimensional (1D) polymorphic iron(II)–triazole frameworks, in which bicycle-pedal motion of the azo moieties of atrz can be observed. Further, when different iron(II) salts are used, 1D iron(II)–triazole frameworks 3–5 with different 1D bridging motifs can be isolated. 6 has a 3D nano-porous CuII framework with dimensions of 11.709(1) A × 12.201(1) A. Interestingly, 6 exhibits guest induced single-crystal-to-single-crystal (SC-SC) structural transformation to obtain another 3D nano-porous CuII framework 7 with dimensions of 11.621(6) A × 16.674(1) A. 8 has a 2D cationic CuII framework constructed with infinite (CuO)n chains and unique μ4-bridging atrz ligands. Anion exchange experiment indicates an anion-induced structural transformation from the 3D CuII framework 6 to the 2D CuII framework 8 confirmed by PXRD patterns. Further, when Zn(NCS)2 is used in the reaction system, 9 can be isolated which exhibits guest induced SC-SC transformation to obtain 10 accompanied by a color change from red (9) to pale pink (10). Variable temperature magnetic susceptibility measurements (2–300 K) reveal anti-ferromagnetic interactions between central iron(II) ions for 1–5. The polymorphic iron(II) frameworks, guest induced single-crystal-to-single-crystal transformation and solvatochromism also reveal great potential for the construction of flexible frameworks employing 4,4′-azo-1,2,4-triazole as basic building blocks.

A unique multi-functional cationic luminescent metal–organic nanotube for highly sensitive detection of dichromate and selective high capacity adsorption of Congo red

In this work a flexible multi-dentate 1-(4-aminobenzyl)-1,2,4-triazole (abtz) ligand has been employed, a unique cationic triazole–Ag(I) metal–organic nanotube {[Ag(μ3-abtz)]·(NO3)·(0.125H2O)}n (MONT-1) has been isolated under solvo-thermal conditions. The abtz ligands adopt tri-dentate coordination modes via triazole nitrogen atoms and aromatic amino nitrogen atoms, which bridge neighboring AgI centers in a syn conformation, leading to MONT formation. PXRD patterns have been investigated indicating pure phases of MONT-1. Solid-state luminescence properties indicate strong fluorescent emissions of MONT-1 at room temperature. Further, interestingly MONT-1 exhibits visually highly selective and sensitive luminescence sensing for Cr2O72− ions in aqueous solutions with high quenching efficiency Ksv = 1.97 × 104 L mol−1 and low detection limit (0.19 μM (S/N = 3)), which make it a promising candidate for visually sensing Cr2O72− anion pollutants in practice. On the other hand, the absorption of environmental pollutants by MONT-1 has also been investigated. MONT-1 has a high absorption capacity for Cr2O72− (211.8 mg g−1), and these absorbed Cr2O72− anion pollutants can be gradually released in the presence of nitrate. Additionally MONT-1 also can selectively adsorb Congo Red (CR) dye molecules in aqueous solutions with a high absorption capacity of 823.3 mg g−1. Therefore MONT-1 can be used a unique multi-functional 1D nano-tubular metal–organic material in sensitive detection and effective adsorption/removal of these environment pollutants in industrial waste water solutions.

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

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]·(ClO4)2·H2O}n (1), {[Cd(abtz)2(H2O)2]·(SiF6)}n (2), {[Cd(abtz)2(H2O)2]·(ClO4)1.64·(HSO4)0.36·1.36H2O}n (3), {[Cd(abtz)2(NCS)]·(ClO4)}n (4) and {[Ag2(μ2-abtz) (μ3-abtz)(ClO4)]·(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]·(ClO4)2·H2O}n (1) and{[Cd(abtz)2(H2O)2]·(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]·(ClO4)1.64·(HSO4)0.36·1.36H2O}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)]·(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 {[Ag2(μ2-abtz)(μ3-abtz) (ClO4)]·(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.

Triazole based Ag coordination clusters: synthesis, structural diversity and anion exchange properties

In this work two new multi-dentate 1,2,4-triazole derivate ligands 4-(4-methyl-2-pyridine)-1,2,4-triazole (L1), 4-(5-methyl-3-pyridine)-1,2,4-triazole (L2) have been designed and synthesized. Three novel cluster-based cationic silver(I) coordination compounds with L1 and L2, namely [Ag2(H2O)4(L1)2](CF3CO2)2 (1), [Ag4(L1)6](BF4)4 (2) and {[Ag2(H2O)(L2)2]·(BF4)2}n (3) have been isolated. When L1 and different Ag(I) salts are used, the bi-nuclear Ag(I) cluster 1 and the tetra-nuclear Ag(I) cluster 2 can be isolated indicating anion induced structural diversity. Further when L2 is used, 3 can be isolated. 3 is a 2D clustered-based coordination compound based on bi-nuclear Ag(I) clusters. PXRD patterns and solid state luminescent properties of 1–3 have been investigated. Further anion exchange properties 2 and 3 also have been investigated. 2 and 3 present novel examples of triazole–silver(I) coordination compounds for effectively capturing the anion pollutants Cr2O72−, MnO4− in water solutions and Congo Red in methanol solutions through the anion exchange process.

Syntheses, structural diversities and characterization of a series of coordination polymers with two isomeric oxadiazol-pyridine ligands

In this work two positional-isomeric oxadiazol-pyridine ligands 3-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L1) and 4-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L2) have been designed and synthesized. A series of novel coordination polymers, namely [Cd2(μ2-L1)2(μ2-NCS)4]n (1), {[Cd(L1)(μ2-dca)2(H2O)]·H2O}n (2), {[Cu(μ2-L1)2(NCS)2]·0.5H2O}n (3), {[Ag2(μ2-L1)(μ3-L1)2]·2PF6}n (4), {[Ag3(μ2-L1)4(μ2-CF3SO3)(CF3SO3)]·CF3SO3} (5), {[Cd(L2)2(μ2-NCS)2]}n (6), [Ag(μ2-L2)(μ2-CF3SO3)]n (7) and {[Ag(μ2-L2)]·BF4}n (8) have been isolated. Both 1 and 2 are 2D CdII coordination polymers containing infinite {Cd–NCS–Cd} chains (for 1) or infinite {Cd–dca–Cd} layers (for 2), respectively. 3 is a 2D CuII coordination polymer, in which central metal ions are bridged via a bidentate bridging L1 ligand. While when different AgI salts were introduced into the reaction system, 1D AgI coordination polymers 4 and 5 with diverse coordination modes can be isolated. Furthermore, when the isomeric oxadiazol-pyridine L2 is used to replace L1 in the reaction system, 6–8 can be isolated. 6 is a 2D CdII coordination polymer containing {Cd–NCS–Cd} layers. 7 is a 2D neutral AgI coordination polymer while 8 is a 2D cationic AgI coordination polymer. Variable temperature magnetic susceptibility measurements (2–300 K) reveal anti-ferromagnetic interactions between central copper(II) ions for 3. Solid-state luminescent properties of 1, 2 and 4–8 have been investigated indicating strong fluorescent emissions. Additionally, luminescent measurements illustrate that complex 8 exhibits highly sensitive luminescence sensing for Cr2O72− ions in aqueous solutions with high quenching efficiency Ksv = 2.08 × 104 L mol−1 and low detection limit (0.19 μM (S/N = 3)). 8 also represents the first report of a coordination polymer based on oxadiazol-pyridine derivatives with a luminescence response to Cr2O72− anion pollutants in aqueous solutions.

Solvo-thermal synthesis of a unique alkaline earth-transition Ba-Cd micro-porous coordination framework as hetero-metallic luminescent sensor for Cu 2+ and real-time detection of benzaldehyde

In this work a unique hetero-metallic alkaline earth-transition Ba-Cd luminescent micro-porous metal-organic framework {[BaCd(μ6-tp)1.5(μ2-Cl)(H2O) (DMF)2]·0.75H2O}n (H2tp=terephthalic acid) (1) has been prepared under solvo-thermal conditions. In 1 infinite 1D {Ba-X-Cd} (X=O, Cl) inorganic chains are linked via these full de-pronated tp2- ligands forming a unique 3D I1O2 type micro-porous coordination framework. PXRD patterns of 1 have been determined confirming pure phases of 1. Luminescence investigations suggested that 1 exhibits highly selective and sensitive sensing for trace amounts of benzaldehyde in ethanol, which provides a facile method for real-time detection of benzaldehyde. Meanwhile 1 also exhibits highly selective and sensitive sensing for Cu2+ over other cations with high quenching efficiency Ksv value 1.15×104L·mol-1. As far as we know, 1 represents the first example of alkaline earth-transition hetero-metallic Ba-Cd micro-porous coordination framework as bi-functional luminescent probes for Cu2+ and benzaldehyde.