Amide Functionalized Mesoporous MOF LOCOM-1 as a Stable Highly Active Basic Catalyst for Knoevenagel Condensation Reaction

Acyl-amide is extensively used as functional group and is a superior contender for the design of MOFs with the guest accessible functional organic sites. A novel acyl-amide-containing tetracarboxylate ligand, bis(3,5-dicarboxy-pheny1)terephthalamide, has been successfully synthesized. The H₄L linker has some fascinating attributes as follows: (i) four carboxylate moieties as the coordination sites confirm affluent coordination approaches to figure a diversity of structure; (ii) two acyl-amide groups as the guest interaction sites can engender guest molecules integrated into the MOF networks through H-bonding interfaces and have a possibility to act as functional organic sites for the condensation reaction. A mesoporous MOF ([Cu₂(L)(H₂O)₃]·4DMF·6H₂O) has been prepared in order to produce the amide FOS within the MOF, which will work as guest accessible sites. The prepared MOF was characterized by CHN analysis, PXRD, FTIR spectroscopy, and SEM analysis. The MOF showed superior catalytic activity for Knoevenagel condensation. The catalytic system endures a broad variety of the functional groups and presents high to modest yields of aldehydes containing electron withdrawing groups (4-chloro, 4-fluoro, 4-nitro), offering a yield > 98 in less reaction time as compared to aldehydes with electron donationg groups (4-methyl). The amide decorated MOF (LOCOM-1-) as a heterogeneous catalyst can be simply recovered by centrifugation and recycled again without a flagrant loss of its catalytic efficiency.

Structure and 119Sn Mössbauer-spectroscopic characterization of BaRhSn2

The stannide BaRhSn2 was synthesized by induction melting of an arc-melted RhSn2 precursor compound with barium in a sealed tantalum ampoule. The structure of BaRhSn2 was refined from single-crystal X-ray diffractometer data: MgCuAl2 type, Cmcm, a = 437.56(4), b = 1242.35(10), c = 767.30(6) pm, wR2 = 0.0845, 469 F 2 values and 16 variables. The rhodium and tin atoms form a two-dimensional [RhSn2] δ− polyanionic network with short Rh–Sn (273–274 pm) and Sn–Sn (303–312 pm) distances. The large barium atoms lead to a substantial orthorhombic distortion of the (lonsdaleite-related) tin substructure, forcing a break of the Sn–Sn bond in b direction. This change in the tin substructure is reflected in the 119Sn Mössbauer spectrum. The tin atoms exhibit a higher s electron density which is expressed in an increased isomer shift of δ = 2.08(1) mm s−1 as compared to the previously reported stannide CaRhSn2 with a three-dimensional [RhSn2] δ− polyanionic network and δ = 1.96(4) mm s−1.

Synthesis of 3D Cadmium(II)-Carboxylate Framework Having Potential for Co-Catalyst Free CO2 Fixation to Cyclic Carbonates

Metal-organic frameworks (MOFs) are porous coordination polymers with interesting structural frameworks, properties, and a wide range of applications. A novel 3D cadmium(II)-carboxylate framework, CdMOF ([Cd2(L)(DMF)(H2O)2]n), was synthesized by the solvothermal method using a tetracarboxylic bridging linker having amide functional moieties. The CdMOF crystal structure exists in the form of a 3D layer structure. Based on the single-crystal X-ray diffraction studies, the supramolecular assembly of CdMOF is explored by Hirshfeld surface analysis. The voids and cavities analysis is performed to check the strength of the crystal packing in CdMOF. The CdMOF followed a multistage thermal degradation pattern in which the solvent molecules escaped around 200 °C and the structural framework remained stable till 230 °C. The main structural framework collapsed (>60 wt.%) into organic volatiles between 400–550 °C. The SEM morphology analyses revealed uniform wedge-shaped rectangular blocks with dimensions of 25–100 μm. The catalytic activity of CdMOF for the solvent and cocatalyst-free cycloaddition of CO2 into epichlorohydrin was successful with 100% selectivity. The current results revealed that this 3D CdMOF is more active than the previously reported CdMOFs and, more interestingly, without using a co-catalyst. The catalyst was easily recovered and reused, having the same performance.

A dye encapsulated zinc-based metal-organic framework as a dual-emission sensor for highly sensitive detection of antibiotics

Self-assembly of two Zn-MOFs, [Zn₂L(DMF)₃]·H₂O·5DMF (1) and [Zn₂L(H₂O)₂]·4H₂O·3DMF (2), was achieved with an amide-functionalized tetracarboxylate ligand under similar conditions. Incorporated amide groups make the tetratopic linkers exhibit different configurations, tetrahedron and square, and subsequently combine tetrahedral [Zn₂(CO₂)₄] clusters or square paddle-well [Zn₂(CO₂)₄] clusters to afford a lon net for 1 and a nbo net for 2. Remarkably, 2 demonstrated high porosity and amide group decorated cages, and thereby proved to be a good capturing agent for a fluorescent dye molecule (DMASM). Consequently, a dual-emitting DMASM@2 sensor was successfully fabricated based on effective energy transfer from the host framework to DMASM with the variable luminescent color being visible to the naked eye. DMASM@2 could be used for the detection of metronidazole (MDZ) and dimetridazole (DTZ) with high sensitivity and remarkable recyclability.

Mg(II) Coordination Polymers Based on Flexible Isomeric Tetracarboxylate Ligands: Syntheses, Structures, Structural Transformation and Luminescent Properties

By using a new flexible tetracarboxylic acid, bis(3,5-dicarboxyphenyl) adipoamide, H₄L¹, and its isomer, bis(2,5-dicarboxyphenyl)adipoamide, H₄L², three Mg(II) coordination polymers, {[Mg₂(L¹)(H₂O)₂]·2EtOH·3H₂O}_n, 1, [Mg₂(L¹)(H₂O)₈]_n, 2, and {[Mg₂(L²)(H₂O)₆]·H₂O}_n, 3, have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Complexes 1 and 2 are the solvent ratio-dependent hydrothermally stable products. The tetracarboxylate ligand of complex 1 connects eight Mg(II) ions through nine oxygen atoms, resulting in a three-dimensional (3D) 5-connected uninodal net with a rare non-interpenetrating (4⁴.6⁶)-pcu-5-Pmna topology, whereas those of 2 and 3 link four Mg(II) ions through four oxygen atoms and six Mg(II) ions through six oxygen atoms, forming a 1D linear chain and a 3,6-connected 2-nodal 3D net having {4.6²}₂{4².6¹⁰.8³}-rtl topology, respectively. Complex 1 shows a series of structural transformations on heating to 200 °C and almost reversible structural transformation when the activated products were immersed in a mixture of ethanol and water or on hydrothermal. Likewise, complex 2 exhibits a reversible structural transformation on heating/hydrothermal, while 3 exhibits irreversible structural transformations. All three complexes exhibit blue light emissions, with that of complex 3 being much more intense.

Controllable synthesis of isoreticular pillared-layer MOFs based on N-rich triangular prism building units: gas adsorption and luminescent properties

Isoreticular 1–4 MOFs with rare lon topologies have been rationally synthesized based on novel trigonal-prism building units.

Enhancement of CO2 Adsorption and Catalytic Properties by Fe-Doping of [Ga2(OH)2(L)] (H4L = Biphenyl-3,3',5,5'-tetracarboxylic Acid), MFM-300(Ga2)

Metal-organic frameworks (MOFs) are usually synthesized using a single type of metal ion, and MOFs containing mixtures of different metal ions are of great interest and represent a methodology to enhance and tune materials properties. We report the synthesis of [Ga2(OH)2(L)] (H4L = biphenyl-3,3',5,5'-tetracarboxylic acid), designated as MFM-300(Ga2), (MFM = Manchester Framework Material replacing NOTT designation), by solvothermal reaction of Ga(NO3)3 and H4L in a mixture of DMF, THF, and water containing HCl for 3 days. MFM-300(Ga2) crystallizes in the tetragonal space group I4122, a = b = 15.0174(7) Å and c = 11.9111(11) Å and is isostructural with the Al(III) analogue MFM-300(Al2) with pores decorated with -OH groups bridging Ga(III) centers. The isostructural Fe-doped material [Ga(1.87)Fe(0.13)(OH)2(L)], MFM-300(Ga(1.87)Fe(0.13)), can be prepared under similar conditions to MFM-300(Ga2) via reaction of a homogeneous mixture of Fe(NO3)3 and Ga(NO3)3 with biphenyl-3,3',5,5'-tetracarboxylic acid. An Fe(III)-based material [Fe3O(1.5)(OH)(HL)(L)(0.5)(H2O)(3.5)], MFM-310(Fe), was synthesized with Fe(NO3)3 and the same ligand via hydrothermal methods. [MFM-310(Fe)] crystallizes in the orthorhombic space group Pmn21 with a = 10.560(4) Å, b = 19.451(8) Å, and c = 11.773(5) Å and incorporates μ3-oxo-centered trinuclear iron cluster nodes connected by ligands to give a 3D nonporous framework that has a different structure to the MFM-300 series. Thus, Fe-doping can be used to monitor the effects of the heteroatom center within a parent Ga(III) framework without the requirement of synthesizing the isostructural Fe(III) analogue [Fe2(OH)2(L)], MFM-300(Fe2), which we have thus far been unable to prepare. Fe-doping of MFM-300(Ga2) affords positive effects on gas adsorption capacities, particularly for CO2 adsorption, whereby MFM-300(Ga(1.87)Fe(0.13)) shows a 49% enhancement of CO2 adsorption capacity in comparison to the homometallic parent material. We thus report herein the highest CO2 uptake (2.86 mmol g(-1) at 273 K at 1 bar) for a Ga-based MOF. The single-crystal X-ray structures of MFM-300(Ga2)-solv, MFM-300(Ga2), MFM-300(Ga2)·2.35CO2, MFM-300(Ga(1.87)Fe(0.13))-solv, MFM-300(Ga(1.87)Fe(0.13)), and MFM-300(Ga(1.87)Fe(0.13))·2.0CO2 have been determined. Most notably, in situ single-crystal diffraction studies of gas-loaded materials have revealed that Fe-doping has a significant impact on the molecular details for CO2 binding in the pore, with the bridging M-OH hydroxyl groups being preferred binding sites for CO2 within these framework materials. In situ synchrotron IR spectroscopic measurements on CO2 binding with respect to the -OH groups in the pore are consistent with the above structural analyses. In addition, we found that, compared to MFM-300(Ga2), Fe-doped MFM-300(Ga(1.87)Fe(0.13)) shows improved catalytic properties for the ring-opening reaction of styrene oxide, but similar activity for the room-temperature acetylation of benzaldehyde by methanol. The role of Fe-doping in these systems is discussed as a mechanism for enhancing porosity and the structural integrity of the parent material.

A luminescent metal–organic framework constructed using a tetraphenylethene-based ligand for sensing volatile organic compounds

A tetraphenylethene-based porous metal–organic framework with 1D rhombus channels and strong fluorescence is prepared and applied to detect volatile organic compounds.

Three Zn(ii)/Cd(ii)/Mn(ii) coordination polymers based on a 2-hydroxy-N-(1H-tetrazol-5-yl) benzamide ligand: structures, and magnetic and photoluminescence properties

Three transition metal complexes of the amide decorated tetrazolate are reported that include an interdigitated 3-D structure with 1-D channels.

Structural diversity of five new bitriazole-based complexes: luminescence, sorption, and magnetic properties

Employing a new bitriazole ligand, five complexes were assembled that display diverse structures, selective CO₂/CH₄ adsorption, luminescent sensing, and antiferromagnetic properties.