Lanthanide-Aromatic Iminodiacetate Frameworks with Helical Tubes: Structure, Properties, and Low-Temperature Heat Capacity

A series of lanthanide coordination polymers [LnL(H₂O)₂] _n [Ln = Pr (1), Nd (2), Sm (3), Eu (4), and Gd (5), H₃L = N-(4-carboxy-benzyl)iminodiacetic acid] was hydrothermally prepared and structurally characterized. All the five compounds have been confirmed as 3D Ln-CPs with one-dimensional helical tunnels composed of four helical chains, although there are different coordination geometries around Ln³⁺. Enantiomeric helixes in 1-3, and absolute left-handed and right-handed helical chains in 4 and 5, respectively, lead to different tunnel spaces. Their conformations can also be featured by different space groups and unit cell dimensions. Photoluminescence measurement on 3 and 4 show characteristic emission peaks of Sm³⁺ and Eu³⁺ ions, respectively. The low-temperature heat capacity of 1-4 has been investigated in the temperature range of 1.9-300 K. Their heat capacity values are nearly equal below 10 K and display a crossover with the value order C _p,m(2) > C _p,m(1) ≈ C _p,m(4) > C _p,m(3) above 10 K. The measured heat capacities have been fitted, and the corresponding thermodynamic functions were consequently calculated based on the fitting parameters. The standard molar entropies at 298.15 K have been determined to be (415.71 ± 4.16), (451.32 ± 4.51), (308.53 ± 3.09), and (407.62 ± 4.08) J·mol^-1·K^-1 for 1, 2, 3, and 4, respectively.

Terpyridine-Based 3D Metal-Organic-Frameworks: A Structure-Property Correlation

Design, synthesis, and applications of metal-organic frameworks (MOFs) are among the most salient fields of research in modern inorganic and materials chemistry. As the structure and physical properties of MOFs are mostly dependent on the organic linkers or ligands, the choice of ligand system is of utmost importance in the design of MOFs. One such crucial organic linker/ligand is terpyridine (tpy), which can adopt various coordination modes to generate an enormous number of metal-organic frameworks. These frameworks generally carry physicochemical characteristics induced by the π-electron-rich (basically N-electron-rich moiety) terpyridines. In this minireview, the construction of 3D MOFs associated with symmetrical terpyridines is discussed. These ligands can be easily derivatized at the lateral phenyl (4'-phenyl) position and incorporate additional organic functionalities. These functionalities lead to some different binding modes and form higher dimensional (3D) frameworks. Therefore, these 3D MOFs can carry multiple features along with the characteristics of terpyridines. Some properties of these MOFs, like photophysical, chemical selectivity, photocatalytic degradation, proton conductivity, and magnetism, etc. have also been discussed and correlated with their frameworks.

A Bifunctional Luminescent Metal-Organic Framework for the Sensing of Paraquat and Fe3+ Ions in Water

The hydrothermal reaction of Zn²⁺ ions with a mixture of two ligands, Hcptpy and H₃ btc (Hcptpy=4-(4-carboxyphenyl)-2,2':4',4''-terpyridine; H₃ btc=1,3,5-benzenetricarboxylic acid), led to the formation of a 3D metal-organic framework (MOF) with 1D channels, [Zn₂ (cptpy)(btc)(H₂ O)]_n (1), which was structurally characterized by using single-crystal X-ray diffraction (SXRD). In MOF 1, two independent Zn²⁺ ions were interconnected by btc^3- ligands to form a 1D chain, whilst adjacent Zn²⁺ ions were alternately bridged by cptpy^- ligands to generate a 2D sheet, which was further linked by 1D chains to form a 3D framework with a new (3,3,4,4)-connected topology. Furthermore, compound 1 also exhibited excellent stability towards air and water and, more importantly, luminescence experiments indicated that it could serve as a probe for the sensitive detection of paraquat (PAQ) and Fe³⁺ ions in aqueous solution.

Lanthanide coordination polymers based on designed bifunctional 2-(2,2':6',2″-terpyridin-4'-yl)benzenesulfonate ligand: syntheses, structural diversity and highly tunable emission

Seven novel lanthanide coordination polymers, [Eu(STP)(glu)]_n (1), [Ln₄(STP)₂(glu)₅]_n·4nH₂O [Ln = Er (2), Yb (3)], [Ln(STP)(1,3-bdc)]_n·0.5nH₂O [Ln = Tb (4), Yb (5)], and [Ln(STP)(1,2-bdc)]_n [Ln = Eu (6), Tb (7)] [NaSTP = sodium 2-(2,2':6',2″-terpyridin-4'-yl)benzenesulfonate, H₂glu = glutaric acid, H₂(1,3-bdc) = benzene-1,3-dicarboxylic acid, H₂(1,2-bdc) = benzene-1,2-dicarboxylic acid], have been prepared under hydrothermal conditions and characterized by elemental analysis, IR and single-crystal X-ray diffraction. Compound (1) possesses a 2D layered structure based on 1D chains with STP^- and glu^2- anions acting as bridges. Compounds (2) and (3) are isomorphous and show a rare 3D tcj/hc net with a tetranuclear Ln³⁺ unit regarded as a seven-connected node and a glu^2- anion serving as a three-connected node. Compounds (4) and (5) are isomorphous and exhibit six-connected pcu nets by denoting binuclear units to six-connected nodes. Compounds (6) and (7) display 3D 3,5T1 nets with (1,2-bdc)^2- anions and dimetallic units serving as three- and five-connected nodes, respectively. The Eu compounds (1) and (6) demonstrate typically red emission, while the Tb compounds (4) and (7) exhibit characteristic green emission. The emission spectra of heteronuclear compounds [Eu_xTb_1-x(STP)(1,2-bdc)]_n (0 ≤ x ≤ 1) as efficient luminescent tags were investigated. The intermetallic energy transfer of Tb to Eu was also evaluated.

Zn(ii)-based coordination polymer: An emissive signaling platform for the recognition of an explosive and a pesticide in an aqueous system

A new emissive Zn(ii)-based coordination polymer (Zn-CP) bearing paddle-wheel clusters has been developed and the same has been demonstrated to have potential for recognising a nitroaromatic-based explosive (TNP) and a pesticide (2,6-DCNA) in aqueous solution. The structural integrity of this newly developed 2D material was established through single-crystal analysis, whereas the stability of Zn-CP in aqueous medium after the recognition process was investigated by the powder-XRD technique. A combination of experimental and theoretical studies revealed that the change in fluorescence intensity of Zn-CP while interacting with TNP and 2,6-DCNA was possibly due to simultaneous operation of PET and FRET. Experimentally, it was also established that Zn-CP can be reused in up to three cycles for the detection of TNP and 2,6-DCNA.

A Water-Stable Luminescent Metal-Organic Framework for Rapid and Visible Sensing of Organophosphorus Pesticides

Metal-organic frameworks (MOFs) have shown considerable prospects for sensing pesticide residues. However, the low stability of MOFs in water hinders them from testing food and environmental samples. Herein, we report an easy and cost-efficient synthesis of a water-stable zirconium luminescent MOF (Zr-LMOF) and its application for rapid, sensitive, and in situ detection of organophosphorous pesticides (OPPs). The Zr-MOF is prepared using Zr(IV) and 1,2,4,5-tetrakis(4-carboxyphenyl)benzene. The synthesized Zr-LMOF rapidly absorbs trace amounts of OPP parathion-methyl and indicates its presence. A low limit of detection of 0.115 μg kg^-1 (0.438 nM) with a wide linear range from 70 μg kg^-1 to 5.0 mg kg^-1 was achieved. Satisfactory recoveries ranging from 78% to 107% were obtained for spiked food and environmental samples. Further, the Zr-LMOF was applied to imitate rapid and in situ imaging detection of pesticide residue on fresh produce nondestructively; visual signals appeared under ultraviolet light within 5 min. These results suggest that the Zr-LMOF has the potential for low-cost, rapid, and in situ imaging detection of OPPs contamination via easy-to-read visual signal.

Anion Dependent Self-Assembly of Polynuclear Cd-Ln Schiff Base Nanoclusters: NIR Luminescent Sensing of Nitro Explosives

Two types of polynuclear Cd-Ln complexes [CdLnL(NO₃)Cl₂(DMF)₂] [Ln = La (1) and Nd (2)] and [Ln₂CdL₂(NO₃)₂(DMF)₂](OH)₂ [Ln = La (3) and Nd (4)] were constructed using a new Schiff base ligand which has a long backbone with two phenyl groups. The Schiff base ligands show a "twist" configuration in 1-4. The crystal structures show that the molecular dimensions of 3 and 4 are about 6 × 10 × 15 Å. The Cd-Nd complexes 2 and 4 exhibit the typical NIR luminescence of Nd³⁺. Interestingly, 4 shows the luminescent sensing of nitro explosives and exhibits a high sensitivity to 2-nitrophenol at the ppm level.

Sensing and capture of toxic and hazardous gases and vapors by metal–organic frameworks

This review summaries recent progress in the luminescent detection and adsorptive removal of harmful gases and vapors by metal–organic frameworks, as well as the principles and strategies guiding the design of these materials.

Exploration of fluorescent organotin compounds of α-amino acid Schiff bases for the detection of organophosphorous chemical warfare agents: quantification of diethylchlorophosphate

Fluorescent Schiff base organotin probes for the detection of chemical warfare agents.

Synthesis and characterization of a cadmium(II)-organic supramolecular coordination compound based on the multifunctional 2-amino-5-sulfobenzoic acid ligand

Much attention has been paid by chemists to the construction of supramolecular coordination compounds based on the multifunctional ligand 5-sulfosalicylic acid (H₃SSA) due to the structural and biological interest of these compounds. However, no coordination compounds have been reported for the multifunctional amino-substituted sulfobenzoate ligand 2-amino-5-sulfobenzoic acid (H₂asba). We expected that H₂asba could be a suitable building block for the assembly of supramolecular networks due to its interesting structural characteristics. The reaction of cadmium(II) nitrate with H₂asba in the presence of the auxiliary flexible dipyridylamide ligand N,N'-bis[(pyridin-4-yl)methyl]oxamide (4bpme) under ambient conditions formed a new mixed-ligand coordination compound, namely bis(3-amino-4-carboxybenzenesulfonato-κO¹)diaquabis{N,N'-bis[(pyridin-4-yl)methyl]oxamide-κN}cadmium(II)-N,N'-bis[(pyridin-4-yl)methyl]oxamide-water (1/1/4), [Cd(C₇H₆NO₅S)₂(C₁₄H₁₄N₄O₂)₂(H₂O)₂]·C₁₄H₁₄N₄O₂·4H₂O, (1), which was characterized by single-crystal and powder X-ray diffraction analysis (PXRD), FT-IR spectroscopy, thermogravimetric analysis (TG), and UV-Vis and photoluminescence spectroscopic analyses in the solid state. The central Cd^II atom in (1) occupies a special position on a centre of inversion and exhibits a slightly distorted octahedral geometry, being coordinated by two N atoms from two monodentate 4bpme ligands, four O atoms from two monodentate 4-amino-3-carboxybenzenesulfonate (Hasba^-) ligands and two coordinated water molecules. Interestingly, complex (1) further extends into a threefold polycatenated 0D→2D (0D is zero-dimensional and 2D is two-dimensional) interpenetrated supramolecular two-dimensional (4,4) layer through intermolecular hydrogen bonding. The interlayer hydrogen bonding further links adjacent threefold polycatenated two-dimensional layers into a three-dimensional network. The optical properties of complex (1) indicate that it may be used as a potential indirect band gap semiconductor material. Complex (1) exhibits an irreversible dehydration-rehydration behaviour. The fluorescence properties have also been investigated in the solid state at room temperature.

Eight rare earth metal organic frameworks and coordination polymers from 2-nitroterephthlate: syntheses, structures, solid-state luminescence and an unprecedented topology

An unprecedented report of eight lanthanide(iii) CPs and MOFs from 2-nitroterephthalate which feature four network types, including one novel topology.