Devising Mixed-Ligand Based Robust Cd(II)-Framework From Bi-Functional Ligand for Fast Responsive Luminescent Detection of Fe3+ and Cr(VI) Oxo-Anions in Water With High Selectivity and Recyclability

Environmental issue related applications have globally surfaced as hottest areas of research, wherein luminescent metal-organic frameworks (LMOFs) with functionalized pores put unique signature in real-time monitoring of multiple classes of toxic compounds, and overcome many of the challenges of conventional materials. We report a two-fold interpenetrated, mixed-ligand Cd(II)-organic framework (CSMCRI-11) [Cd_1.5(L)₂(bpy)(NO₃)]·DMF·2H₂O (CSMCRI = Central Salt and Marine Chemical Research Institute, HL = 4- (1H-imidazol-1-yl)benzoic acid, bpy = 4,4'-bipyridine) that exemplifies bipillar-layer structure with two different Cd(II) nodes, and displays notable robustness in diverse organic solvents and water. Intense luminescence signature of the activated MOF (11a) is harnessed in extremely selective and fast responsive sensing of Fe³⁺ ions in aqueous phase with notable quenching constant (1.91 × 10⁴ M^-1) and impressive 166 ppb limit of detection (LOD). The framework further serves as a highly discriminative and quick responsive scaffold for turn-off detection of two noxious oxo-anions (Cr₂O₇ ^2- and CrO₄ ^2-) in water, where individual quenching constants (CrO₄ ^2-: 1.46 × 10⁴ M^-1; Cr₂O₇ ^2-: 2.18 × 10⁴ M^-1) and LOD values (CrO₄ ^2-: 179 ppb; Cr₂O₇ ^2-: 114 ppb) rank among best sensory MOFs for aqueous phase detection of Cr(VI) species. It is imperative to stress the outstanding reusability of the MOF towards detection of all these aqueous pollutants, besides their vivid monitoring by colorimetric changes under UV-light. Mechanism of selective quenching is comprehensively investigated in light of absorption of the excitation/emission energy of the host framework by individual studied analyte.

Poly[bis(dimethylformamide-κO)-(μ8-5,5′′-dicarboxy-[1,1′:4′,1′′-terphenyl]-2′,3,3′′,5′-tetracarboxylato-κ8 O:O 1:O 2:O 3:O 4:O 5:O 6:O 7)dizinc(II)] — dimethylformamide (1/2), C18H19N2O8Zn

C18H19N2O8Zn, orthorhombic, Pbca (no. 61), a = 17.4714(12) Å, b = 10.9180(7) Å, c = 20.0697(14) Å, V = 3828.4(4) Å3, Z = 8, R gt(F) = 0.0449, wR ref(F 2) = 0.1492, T = 100 K.

Pore-Functionalized and Hydrolytically Robust Cd(II)-Metal-Organic Framework for Highly Selective, Multicyclic CO2 Adsorption and Fast-Responsive Luminescent Monitoring of Fe(III) and Cr(VI) Ions with Notable Sensitivity and Reusability

Metal-organic frameworks (MOFs) show a distinctive pre-eminence over other heterogeneous systems for adsorption of carbon dioxide (CO₂) gas and fluorescence detection of water contaminating ions, where integration of both these attributes along with enhancement of pore functionality and water stability is crucial for potential applications related to environmental remediation. Pore functionalization has been achieved in a 2-fold interpenetrated, mixed-ligand Cd(II)-framework [Cd_1.5(L)₂(bpy)(NO₃)]·2DMF·2H₂O (CSMCRI-5) (HL = 4-(4-carboxyphenyl)-1,2,4-triazole, bpy = 4,4'-bipyridine, DMF = dimethylformamide, CSMCRI = Central Salt & Marine Chemicals Research Institute) by utilizing a bifunctional ligand HL. The bpy-pillared framework, containing diverse Cd(II) nodes, optimum sized voids, and free N-atom affixed one-dimensional porous channels, shows notable structural robustness in diverse organic solvents and water. In spite of a negligible surface area, the activated MOF (5a) exhibits good CO₂ uptake and highly selective CO₂ adsorption over N₂ (259.94) and CH₄ (14.34) alongside minor loss during multiple CO₂ adsorption-desorption cycles. Luminescence studies demonstrate extremely selective and ultrafast sensing of Fe³⁺ ions in the aqueous phase with notable quenching (1.13 × 10⁴ M^-1) as well as an impressive 98 ppb limit of detection (LOD). Importantly, Fe³⁺ detection is exclusively retained under simulated physiological conditions. The framework further serves as a quick-responsive scaffold for toxic CrO₄^2- and Cr₂O₇^2- anions, where individual quenching constants (CrO₄^2-: 1.73 × 10⁴ M^-1; Cr₂O₇^2-: 5.42 × 10⁴ M^-1) and LOD values (CrO₄^2-: 280 ppb; Cr₂O₇^2-: 320 ppb) rank among the best sensory MOFs for aqueous phase detection of Cr(VI) species. It is imperative to stress vivid monitoring of all these aqueous pollutants by a handy paper-strip method, besides outstanding applicability of 5a toward their recyclable detection. Mechanism of selective quenching is comprehensively investigated in light of the absorption of the excitation/emission energy of the host framework by an individual studied analyte.

Three-in-one is really better: exploring the sensing and adsorption properties in a newly designed metal-organic system incorporating a copper(ii) ion

A 2-D copper(ii)-based coordination polymer, [Cu(SCN)(hmp)]_n CP (1), was crystallized via the slow evaporation method after the reaction of CuSO₄·5H₂O, 2-pyridinemethanol (hmpH), sodium thiocyanate and sodium hydroxide in water for functional applications. CP (1) was characterized via elemental analysis, FTIR, PXRD, magnetic, EPR, crystallographic and TGA studies. The crystal structure and EPR data confirmed a square pyramidal geometry around the Cu(ii) ions. The topological analysis revealed that CP 1 has a {6^{^}3} point symbol with a [6.6.6] extended point symbol and 3-c net, uninodal net having hcb and Shubnikov hexagonal plane net/(6,3) type of uncommon topology. The magnetic studies suggested the strong antiferromagnetic nature of CP (1). The fluorescence sensing property of CP (1) was investigated with different nitro aromatic compounds and hazardous metal ions. CP (1) demonstrated high selectivity and sensitivity towards nitrobenzene, even in the presence of other competitive nitro aromatics. In addition, CP (1) showed excellent selectivity and sensitivity toward Fe³⁺ over other metal ions. The possible detection mechanisms were proposed employing UV-visible and fluorescence spectroscopy and DFT calculations. CP (1) also showed excellent recyclability towards both analytes, and its initial intensity was almost regained after several washings. Moreover, CP (1) acted as an excellent adsorbent material for natural dyes with different charges and sizes, i.e., methylene blue (MB), methyl orange (MO) and Rhodamine-B. Furthermore, CP (1) was utilized repeatedly for the effective adsorption of MB from wastewater without significant loss in its adsorption capacity. Hence, the present CP (1) was designed to relate coordination chemistry with various functional applications of interest.

Guest-Induced Ultrasensitive Detection of Multiple Toxic Organics and Fe3+ Ions in a Strategically Designed and Regenerative Smart Fluorescent Metal-Organic Framework

Luminescent metal-organic frameworks (LMOFs) are promising functional materials for sustainable applications, where an analyte-induced multiresponsive system with good recyclability is beneficial for detecting numerous lethal pollutants. We designed and built the dual-functionalized, three-dimensional Zn(II)-framework [Zn₃( bpg)_1.5( azdc)₃]·(DMF)_5.9·(H₂O)_1.05 (CSMCRI-1) using an -OH group-integrated bpg linker and a -N═N- moiety containing H₂ azdc ligand, which functions as a unique tetrasensoric fluorescent probe. The activated CSMCRI-1 (1') represents the hitherto unreported pillar-layer framework for extremely selective fluorescence quenching by nitrofurazone antibiotics as well as explosive nitro-aromatic 2,4,6-trinitrophenol, where ultrasensitive detection is achieved for both the electron-lacking analytes. Impressively, 1' represents the first ever MOF for significant fluorescence "turn-on" detection of toxic and electron-rich 4-aminophenol in the concurrent presence of isomeric analogues. Density functional theory calculations highlight the specific importance of pillar functionalization in the "turn-on" or "turn-off" responses of 1' by electronically divergent toxic organics and provide further proof of supramolecular interactions between the framework and analytes. The fluorescence intensity of 1' dramatically quenches by a trace amount of Fe³⁺ ions over other competing metal ions, alongside visible colorimetric change of the framework in solid and solution phase upon Fe³⁺ encapsulation. The sensing ability of 1' remains unaltered for multiple cycles toward all lethal pollutants. The sensing mechanism is attributed to both dynamic and static quenching as well as resonance energy transfer, which strongly comply with the predictions of theoretical simulations. Considering the long-term and real-time monitoring, AND as well as OR molecular logic gates are constructed based on the discriminative fluorescence response for each analyte that provides a platform to fabricate smart LMOFs with multimode logic operations.

Syntheses, structures, luminescence and magnetic properties of seven isomorphous metal–organic frameworks based on 2,7-bis(4-benzoic acid)-N-(4-benzoic acid)carbazole

Seven isomorphous lanthanide metal–organic frameworks with special luminescence and magnetic properties are synthesized and characterized.

Two new luminescence cadmium coordination polymers constructed by 4,4′-di(4H-1,2,4-triazol-4-yl)-1,1′-biphenyl and polycarboxylic acids: syntheses, structures, Fe3+ identifying and photo-degradable properties

Two Cd centered coordination polymers (CPs) constructed from triazole derivative and different polycarboxylic acids exhibit diverse structures and different behaviors on Fe³⁺ identifying and photo-degradation of MB.

A new three-dimensional zinc-based metal-organic framework as a fluorescent sensor for detection of cadmium ion and nitrobenzene

In this study, a novel three-dimensional zinc-based metal-organic framework (Zn-MOF), i.e., {Zn₂(L)₂(DMF)₂H₂O}_n (L = 2,5-bis(phenylamino)-1,4-benzenedicarboxylic acid) was designed and developed under solvothermal condition. As a proof-of-principle, a π-conjugated framework of carboxylate ligand capable of "bottom up" synthesis was integrated with metal ion to construct a novel MOF for sensing applications. As expected, the synthesized Zn-MOF exhibited fluorescence enhancement for cadmium ion (Cd²⁺) and sensing of nitrobenzene (NB) through fluorescence quenching. The detection limits were calculated to be 0.12 μM for Cd²⁺ and 1.19 μg mL^-1 for NB based on signal-to-noise ratio of 3:1. Moreover, various techniques and density functional theory investigations verified that the possible sensing mechanisms for Cd²⁺ and NB included ion exchange and photoinduced electron transfer, respectively. Finally, their practical applications on real samples also demonstrated that the Zn-MOF-based sensor can be effectively utilized for detection and imaging of Cd²⁺ present in the real water samples and living cells. This study may inspire future research and design of target fluorescent MOFs with specific functions.

Observation of Contrary Thermo-responsive Trend for Single Crystal and Powder Samples in Mechano-, Thermo- and Solvato-responsive Luminescent Cubane [Ag4I4L4] Cluster

A new silver(I) iodide cluster [Ag₄I₄(TMP)₄] (TMP = tris(3-methylphenyl)-phosphine) 1 shows triply stimuli-responsive luminescent chromism, namely, mechano-, thermo- and solvent-responsive chromism, which is isostructural to our previously reported [Cu₄I₄(TMP)₄] 2 but shows quite different luminescence in response to the external stimuli. Especially, during the mechanical grinding, the relative intensities of HE and LE of 1 varied with a concomitant hypsochromic shift, and when the temperature was decreased from 300 to 5 K, unprecedented contrary thermo-responsive trend for single crystal and powered samples (blueshift of single crystals and redshift of powdered samples) was observed. These distinct characters of 1 should be due to the different molecular packing modes, metallic interactions and the unique character of Ag(I) ion.

Sonochemical synthesis of two new zinc(II) 1,10-phenanthroline coordination supramolecular compounds: New precursors to produce nano-sized zinc(II) oxide

Nanoparticles of two zinc(II) coordination supramolecule compounds (CSCs), [Zn(L)Cl2] (1) and [Zn(L)Br2] (2) L=1,10-phen=1,10-phenanthroline ligand, have been synthesized by use of a sonochemical process and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), Fourier transform infrared (FTIR) spectroscopy and elemental analyses. The single crystal X-ray data of compounds 1 and 2 imply that the Zn⁺² ions are four coordinated. Topological analysis shows that the compound 1 and 2 are new topology for net: 1,3M4-1. Nanoparticles of zinc(II) oxide have been prepared by calcination of two different zinc(II) CPs at 500°C that were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and IR spectroscopy.

Synthesis of several novel coordination complexes: ion exchange, magnetic and photocatalytic studies

Eight different novel polymers by the reactions of H₂L and metal ions (Zn²⁺, Cu²⁺, Co²⁺) in the presence or absence of auxiliary ligands were constructed. The Zn²⁺ in complexes 1–3 could be partially exchanged with Cu²⁺ ions.

Structural diversity, luminescence and photocatalytic properties of six coordination polymers based on designed bifunctional 2-(imidazol-1-yl)terephthalic acid

Six CPs, based on 2-(imidazol-1-yl)terephthalic acid, have been prepared and characterized.

An unusual (4,4)-connected 3D porous cadmium metal–organic framework as a luminescent sensor for detection of nitrobenzene

The MOF 1 shows an unusual (4,4)-connected 3D porous network. The high quenching efficiency of 1 is up to 98.2% at 160 ppm NBZ. 1 displays highly selectivity, sensitivity and recyclability in the detection of nitrobenzene.

A pair of homochiral porous metal–organic frameworks with a helical metal-carboxylate layer

By employment of predesigned proline derivative ligands ((R)-PIA and (S)-PIA) to assemble with bipy and Cd²⁺ ion, a pair of porous homochiral metal–organic frameworks (HMOFs) with a wavy Cd-PIA layer has been synthesized.

Zinc and cadmium complexes based on bis-(1H-tetrazol-5-ylmethyl/ylethyl)-amine ligands: structures and photoluminescence properties

Nine zinc and cadmium coordination compounds with bis-(1H-tetrazol-5-ylmethyl/ylethyl)-amine were synthesized and structurally characterized, and the fluorescent emission and fluorescence lifetime of complexes 1–9 have been investigated and discussed.

Assembly of a series of d10 coordination polymers based on W-shaped 1,3-di(2′,4′-dicarboxyphenyl)benzene: from syntheses, structural diversity, luminescence, to photocatalytic properties

Six d¹⁰ coordination polymers with different architectures based on W-shaped 1,3-di(2′,4′-dicarboxyphenyl)benzene (H₄DDB) have been prepared. Their photoluminescence and photocatalytic properties were also investigated.

Structural diversification and photocatalytic properties of zinc(ii) polymers modified by auxiliary N-containing ligands

Four zinc coordination polymers with different architectures based on 5-(1H-benzoimidazol-2-ylsulfanylmethyl)-isophthalic acid have been prepared. Their photoluminescence and photocatalytic properties were also investigated.