NbO Topology Research Articles

Can NbO Keep nbo Topology under Electrons? -Unveiling Novel Aspects of Niobium Monoxide at the Atomic Scale.

A precise investigation of NbO has been carried out by advanced electron microscopy combined with powder and single crystal X-ray diffraction (XRD). The structure of pristine NbO has been determined as Pm-3 m space group (SG) with a = 4.211 Å and the positions of Nb and O at the 3c and 3d Wyckoff positions, respectively, which is consistent with previous report based on powder XRD data. Electron beams induced a structural transition, which was investigated and explained by combining electron diffraction and atomic-resolution imaging. The results revealed that the electron beam stimulated both Nb and O atom-migrations within each fcc sublattice, and that the final structure was SG Fm-3 m with a = 4.29 Å, Nb and O at the 4a and 4b with 75 % occupancy and same chemical composition. Antiphase planar defects were discovered in the pristine NbO and related to the structural transformation. Theoretical calculations performed by density functional theory (DFT) supported the experimental conclusions.

A fluorescence zinc metal-organic framework for the effective detection of Fe3+ and Fe2+ in water

A novel MOF of Zn-APT can be used as the fluorescence probe to detect Fe 3+ in aqueous solution with the high sensitivity and selectivity. It can absorb hemoporphyrin dihydrochloride on its surface to form red crystal Zn-APT-PH, which can also be used as the fluorescence probe to detect Fe 2+ in aqueous solution with the high sensitivity and selectivity. • A fluorescence metal–organic framework of Zn-APT was synthesized. • Zn-APT has the novel and compact structure with a nbo topology type. • Zn-APT can be used as a fluorescent probe to detect Fe 3+ effectively. • Zn-APT can adsorb hemoporphyrin dihydrochloride to form a red-brown crystal Zn-APT-PH. • Zn-APT-PH can be used as a fluorescent probe to detect Fe 2+ effectively. A fluorescence metal-organic framework [Zn 3 (APT) 4 ]·2H 2 O (Zn-APT) was synthesized from Zn(NO 3 ) 2 ·6H 2 O and 2-amino-6-purinethiol (ATP) by the solvothermal reaction. Zn-APT has a novel compact structure with a nbo topology type. The analyses of single-crystal diffraction reveal that Zn-APT crystallizes in a cubic crystal system and F d 3 ¯ c space group. Based on a large amount of π-conjugated organic ligands of ATP and d 10 metal center of Zn 2+ , Zn-APT can emit strong luminescence. It can be used as a fluorescent probe to detect Fe 3+ ion effectively. The detection limit is 0.28 μM and K sv (quenching efficiency) is 2.1 × 10 4 M −1 . In addition, Zn-APT can adsorb hemoporphyrin dihydrochloride to produce a red-brown crystal Zn-APT-PH. Interestingly, it can also be used to detect Fe 2+ ion efficiently with the detection limit of 0.12 μM and K sv of 1.9 × 10 4 M −1 .

Effect of Unsaturated Metal Site Modulation in Highly Stable Microporous Materials on CO2 Capture and Fixation.

We have designed and synthesized two unprecedented microporous three-dimensional metal-organic frameworks, {[Cd6(TPOM)3(L)6]·12DMF·3H2O}n (1) and {[Zn2(TPOM)(L)2]·2DMF·H2O}n (2), based on a flexible quadritopic ligand, tetrakis(4-pyridyloxymethylene)methane (TPOM), and a bent dicarboxylic acid, 4,4'-(dimethylsilanediyl)bis-benzoic acid (H2L). The networks of 1 and 2 share a 4-c uninodal net NbO topology but exhibit different metal environments due to coordination preferences of Cd(II) and Zn(II). The Cd(II) center in 1 is six-coordinated, whereas the Zn(II) center in 2 is only four-coordinated, making the latter an unsaturated metal center. Such modulation of coordination atmosphere of metal centers in MOFs with the same topology is possible due to diverse binding of the carboxylate groups of L2-. Both 1 and 2 have relatively high thermal stability and exhibit permanent porosity after the removal of guest solvent molecules based on variable temperature powder X-ray diffraction and gas adsorption analysis. These materials exhibit similar gas adsorption properties, especially highly selective CO2 uptake/capture over other gases (N2 and CH4). However, because of the presence of an unsaturated Lewis acidic metal site, 2 acts as a very efficient heterogeneous catalyst toward the chemical conversion of CO2 to cyclic carbonates under mild conditions, whereas 1 shows very less activity. This work provides experimental evidence for the postulate that an unsaturated metal site in MOFs enhances adsoprtion of CO2 and promotes its conversion via the Lewis-acid catalysis.

Porous Metal Organic Framework for the Chemical Fixation of CO2 and Operation Nursing Application Values on Postoperative Infection

A porous 3D metal–organic framework (MOF) with NbO topology was prepared at ambient temperature by utilizing the paddle wheel dinuclear secondary building units of Co2(COO)4 and tertiary amine groups as an active center. Its chemical formula is {[Co2(L)(H2O)2]·(3DMF)(4H2O)}n (1, H4L is 5, 5′-(piperazine-1,4-diyl)diisophthalic acid). The activated MOF 1 possesses a rich porous structure, high Langmuir and BET surface areas, and abundant Lewis acid (CoII) catalytic sites and tertiary amino groups. This catalyst is suitable for the synthesis of cyclic carbonates from epoxides and CO2 with TBAB catalyst under a no solvent or mild reaction. Its treatment activity on postoperative bacterial infection was also determined, and bacterial survival was calculated. Relative ftsZ expression in bacteria was measured by real time RT-PCR.

A Cubic 3D Covalent Organic Framework with nbo Topology.

The synthesis of three-dimensional (3D) covalent organic frameworks (COFs) requires high-connectivity polyhedral building blocks or the controlled alignment of building blocks. Here, we use the latter strategy to assemble square-planar cobalt(II) phthalocyanine (PcCo) units into the nbo topology by using tetrahedral spiroborate (SPB) linkages that were chosen to provide the necessary 90° dihedral angles between neighboring PcCo units. This yields a porous 3D COF, SPB-COF-DBA, with a noninterpenetrated nbo topology. SPB-COF-DBA shows high crystallinity and long-range order, with 11 resolved diffraction peaks in the experimental powder X-ray diffraction (PXRD) pattern. This well-ordered crystal lattice can also be imaged by using high-resolution transmission electron microscopy (HR-TEM). SPB-COF-DBA has cubic pores and exhibits permanent porosity with a Brunauer-Emmett-Teller (BET) surface area of 1726 m2 g-1.

Oxalamide-Functionalized Metal Organic Frameworks for CO2 Adsorption.

Metal-organic frameworks (MOFs) have received great attention in recent years as potential adsorbents for CO2 capture due to their unique properties. However, the high cost and their tedious synthesis procedures impede their industrial application. A series of new CO2-philic oxalamide-functionalized MOFs have been solvothermally synthesized: {[Zn3(μ8-OATA)1.5(H2O)2(DMF)]·5/2H2O·5DMF}n (Zn-OATA), {[NH2(CH3)2][Cd(μ4-HOATA)]·H2O·DMF}n (Cd-OATA), and {[Co2(μ7-OATA)(H2O)(DMF)2]·2H2O·3DMF}n (Co-OATA) (H4OATA = N,N'-bis(3,5-dicarboxyphenyl)oxalamide). In Zn-OATA, the [Zn2(CO2)4] SBUs are connected by OATA4- ligands into a 3D framework with 4-connected NbO topology. In Cd-OATA, two anionic frameworks with a dia topology interpenetrated each other to form a porous structure. In Co-OATA, [Co2(CO2)4] units are linked by four OATA4- to form a 3D framework with binodal 4,4-connected 42·84 PtS-type topology. Very interestingly, Cu-OATA can be prepared from Zn-OATA by a facile metal ions exchange procedure without damaging the structure while the CO2 adsorption ability can be largely enhanced when Zn(II) metal ions are exchanged to Cu(II). These new MOFs possess channels decorated by the CO2-philic oxalamide groups and accessible open metal sites, suitable for highly selective CO2 adsorption. Cu-OATA exhibits a significant CO2 adsorption capacity of 25.35 wt % (138.85 cm3/g) at 273 K and 9.84 wt % (50.08 cm3/g) at 298 K under 1 bar with isosteric heat of adsorption (Qst) of about 25 kJ/mol. Cu-OATA presents a very high selectivity of 5.5 for CO2/CH4 and 43.8 for CO2/N2 separation at 0.1 bar, 298 K. Cd-OATA exhibits a CO2 sorption isotherm with hysteresis that can be originated from structural rearrangements. Cd-OATA adsorbs CO2 up to 11.90 wt % (60.58 cm3/g) at 273 K and 2.26 wt % (11.40 cm3/g) at 298 K under 1 bar. Moreover, these new MOFs exhibit high stability in various organic solvents, water, and acidic or basic media. The present work opens a new opportunity in the development of improved and cost-effective MOF adsorbents for highly efficient CO2 capture.

A 3D MOF based on Adamantoid Tetracopper(II) and Aminophosphine Oxide Cages: Structural Features and Magnetic and Catalytic Properties.

This work describes an unexpected generation of a new 3D metal–organic framework (MOF), [Cu4(μ-Cl)6(μ4-O)Cu(OH)2(μ-PTA=O)4]n·2nCl-EtOH·2.5nH2O, from copper(II) chloride and 1,3,5-triaza-7-phosphaadamantane 7-oxide (PTA=O). The obtained product is composed of diamandoid tetracopper(II) [Cu4(μ-Cl)6(μ4-O)] cages and monocopper(II) [Cu(OH)2] units that are assembled, via the diamandoid μ-PTA=O linkers, into an intricate 3D net with an nbo topology. Magnetic susceptibility measurements on this MOF in the temperature range of 1.8–300 K reveal a ferromagnetic interaction (J = +20 cm–1) between the neighboring copper(II) ions. Single-point DFT calculations disclose a strong delocalization of the spin density over the tetranuclear unit. The magnitude of exchange coupling, predicted from the broken-symmetry DFT studies, is in good agreement with the experimental data. This copper(II) compound also acts as an active catalyst for the mild oxidation and carboxylation of alkanes. The present study provides a unique example of an MOF that is assembled from two different types of adamantoid Cu4 and PTA=O cages, thus contributing to widening a diversity of functional metal–organic frameworks.

MOFs with acs and Nbo topologies using flexible diisophthalate ligands: Influence of dihedral angle between phenyl rings on the crystal structure

Research on the design, synthesis, and application of metal organic frameworks (MOFs) based on flexible ligands has attracted significant attention in recent years owing to their superior performance in applications such as gas adsorption and molecular separation. In this work, two acs-type MOFs and an Nbo-type MOF derived from three different flexible diisophthalate ligands were solvothermally prepared and structurally characterized by single crystal X-ray diffraction, powder X-ray diffraction, and thermogravimetric analysis. Analyses of the data revealed that the topologies of the MOFs were correlated to the dihedral angle between the phenyl rings in the ligands.

The ligand effect resulted in different fluorescence responses of two similar zinc-based MOFs to high-valence metal ions and amino acids

Abstract The strategy of ligand functionalization can be used to adjust and control the properties of Metal-Organic Frameworks (MOFs). Based on these considerations, we chose two similar ligands (bpta = 3,5-bis(4-pyridyl)-1,2,4-triazole, bpat = 3,5-bis (4-pyridyl)-4-amino-1,2,4-triazole) and synthesized two MOFs with similar structures, {Zn2(bpta)2(hpta)(H2O)2·6H2O}n (1), {Zn2(bpat)2(hpta)(H2O)4·4H2O}n (2), by introduction of Zn(NO3)2·6H2O and pyromellitic dianhydride (pmda) coligand. X-ray single-crystal diffraction reveals that two MOFs both crystallized in triclinic systems with NbO topology. We systematically studied their fluorescence sensing performance. The results reveal that they both show obvious fluorescence enhancement effect to high-valence metal ions (Fe3+, Al3+, Cr3+, In3+ and Zr4+) and some amino acids. Unlike compound 1, the change of fluorescence property is not only reflected in the intensity, but also in the emission peak position for compound 2 with amino group. In addition, 2-H2O has a high selectivity and sensitivity to tryptophan, and there is no shift of emission peak. We verified the mechanism for the difference in fluorescence response between compounds 1 and 2 by IR and X-ray photoelectron spectrum.

Topological effects on separation of alkane isomers in metal−organic frameworks

Polymorphism in metal−organic frameworks (MOFs) means that the same chemical building blocks (nodes and linkers) can be used to construct isomeric MOFs with different topological networks. The choice of topology can substantially impact the pore network of the MOF, changing the sizes and shapes of the pores, which has implications for adsorption and separation applications. In this work, we look at the influence of topology in 38 polymorphic MOFs on the separation of linear and branched C4–C6 alkane isomers, a separation of great importance to the petrochemical industry. We find that the MOF Cu2(1,4-benzenedicarboxylate) in nbo topology (nbo-Cu2BDC) has particularly high affinity for linear alkanes due to its small pore size, which excludes the branched isomers. Upon studying this MOF in further detail, we find that it can take either of two conformations: a cubic conformation, which is typical of nbo MOFs, and a unique star conformation that contains 1D triangular and hexagonal channels. The determination of which conformation the MOF will adopt depends on steric effects between the nodes and linkers.

A Gold Quartet Framework with Reversible Anisotropic Structural Transformation Accompanied by Luminescence Response

Summary Hierarchy and chirality are the fundamental characteristics of biomolecules. Chemistry on hierarchical self-assembly and spontaneous symmetry breaking helps to uncover the mechanism of living activities and the origin of chirality in nature. Herein, we describe a chiral gold quartet framework (GQF) with C4-symmetric structure hierarchically aggregated from an achiral anionic [Au10(dpptrz)4S4]2− (dpptrz-Au10), which was acquired via click-reaction-induced and Au(I)⋅⋅⋅Au(I)-interaction-directed cluster-to-cluster transformation (CCT) from the rationally designed [(dppa)6Au18S8]2+ (dppa-Au18). Inter-cluster hydrogen bonding and alkali ion coordination were observed to assist the hierarchical self-assembly and chiral self-organization of the GQF. Upon exposing the crystal to vacuum, the bottom-up constructed GQF showed an anisotropic structural transformation accompanied by a visual luminescence change in a single-crystal-to-single-crystal (SCSC) manner that became reversible upon removal of vacuum. This research largely advances the potential of polynuclear gold(I)-sulfido clusters in hierarchical self-assembly and luminescent materials.

Applicability of NBO and AIM Topology Analyses to Chemical Bonding in Some Diacetylplatinum(II) Complexes

The geometrical structures of six square-planar diacetylplatinum(II) complexes ([Pt(Ac)2L], L = hydrazine-type ligand) were calculated using six (B3LYP, CAM-B3LYP, B3PW91, M06, M06HF and PBE) DFT methods and one post-Hartree–Fock (MP2) method combined with 6-31G(d,p) basis sets for nonmetal atoms and LANL2DZ for Pt. Using percent relative errors, M06HF and MP2 are best for predicting Pt–N bond distances, but worst for Pt–C bond distances, whereas B3PW91 is best. Pt–N(pyridine) bonds have higher electron density at the bond critical points than Pt–N(hydrazone) bonds, and the former are more covalent than the latter. Further, Pt–C bonds trans to hydrazone moieties are more covalent than Pt–C bonds trans to Pt–N(pyridine) bonds. Pt–C bonds are mainly due to Pt→Ac back donation rather than Ac→Pt donation; σ-bonding is less important in this case, consistent with the high π-acidity and strong trans effect of acetyl groups. In contrast, Pt→N back donation is negligible and Pt–N bonds are mainly due to N→Pt σ-donation, which stabilizes trans Pt–C bonds.

A three-dimensional Cu-MOF with strong π-π interactions exhibiting high water and chemical stability

A novel Cu paddle-wheel based metal-organic framework, [Cu(byia)(DMF)]·1.5DMF·7H2O (compound 1, byia = 5-(benzimidazol-2-yl) isophthalic acid), has been solvothermally synthesized. Compound 1 possesses a three-dimensional framework and unusual quadruple π-π interactions between two neighboring byia ligands, its structure can be described as nbo topology or fog topology by using different simplifications. It should be noted that compound 1 exhibits high chemical stability in strong acid and alkaline aqueous solutions, and outstanding water stability (at least half a year in water).

A hexadecanuclear silver alkynyl cluster based NbO framework with triple emissions from the visible to near-infrared II region.

Compared to emissive silver-thiolate clusters, their alkynyl cousins are, however, usually luminescence silent. Herein we report a novel silver-alkynyl cluster based NbO-type framework (SD/Ag18) showing unprecedented triple emission spanning from the visible to near-infrared (NIR) region. It is a 3D framework constructed from a [Cl@Ag16] cluster based unit, which is further quadruply bridged by the surrounding four Ag atoms through AgAg interactions, giving a 4-connected NbO topology. Although SD/Ag18 exhibits weak orange-red emission at room temperature, its emission becomes strong upon cooling, with three emission maxima at 524, 647 and 1036 nm, respectively, covering both the visible and NIR regions. The visible emissions involve triplet alkynyl-to-metal charge transfer mixed with a cluster-centered state, whereas the participation of cPrC[triple bond, length as m-dash]C- in the frontier orbitals of the cluster may be responsible for the NIR emission. The unusual emissions, especially in the NIR-II region, are observed, for the first time, in silver complexes.

Partially Interpenetrated NbO Topology Metal–Organic Framework Exhibiting Selective Gas Adsorption

We report on the first partially interpenetrated metal–organic framework (MOF) with NbO topology for its ability to separate methane from carbon dioxide and permanently sequester the greenhouse gas CO2. The MOF, Cu2(pbpta) (H4pbpta = 4,4′,4″,4‴-(1,4-phenylenbis(pyridine-4,2-6-triyl))-tetrabenzoic acid), crystallizes in the monoclinic C2/m space group and has a 2537 m2/g Brunauer, Emmett and Teller surface area with an 1.06 cm3/g pore volume. The MOF exhibits selective adsorption of CO2 over CH4 as well as that of C2H6 and C2H4 over CH4. Cu2(pbpta) additionally shows excellent catalytic efficacy for the cycloaddition reaction of CO2 with epoxides to produce industrially important cyclic carbonates using solvent-free conditions.

Synthesis of a NbO Type Homochiral Cu(II) Metal-Organic Framework: Ferroelectric Behavior and Heterogeneous Catalysis of Three-Component Coupling and Pechmann Reactions.

A chiral tetracarboxylic acid ligand, H4L, incorporating the (S)-(+)-2-methylpiperazine moiety in its middle, solvothermally forms a homochiral Cu(II) framework, {[Cu2(L)(H2O)2]·(4DMF)(4H2O)}n (LCu). It forms a non-interpenetrated structure consisting of [Cu2(COO)4] paddle-wheel secondary bonding units (SBUs) with NbO topology. Interestingly, the framework LCu exhibits excellent ferroelectric properties. It shows a remnant polarization (Pr) of ∼3.5 μC cm-2 and a coercive field (Ec) of ∼12 kV cm-1 with a distinct electric hysteresis loop. Dielectric studies of LCu reveal almost frequency-independent behavior with a dielectric constant (εr) of ∼42 and a low dielectric loss (tan δ) of ∼0.04 up to 106 Hz, for potential use in high-frequency applications. In addition, activated framework LCu' having uncoordinated metal sites acts as an efficient heterogeneous catalyst in the three-component coupling of amines, aldehydes, and alkynes, as well as in Pechmann reactions of phenols with β-ketoesters.

A comparative study of C2H2 adsorption properties in five isomeric copper-based MOFs based on naphthalene-derived diisophthalates.

In this work, five positional isomeric ligands consisting of two peripheral isophthalate moieties attached to the central naphthyl core in different ways, namely, 5,5'-(naphthyl-1,3-diyl) diisophthalate (H4L1), 5,5'-(naphthyl-1,4-diyl) diisophthalate (H4L2), 5,5'-(naphthyl-1,5-diyl) diisophthalate (H4L3), 5,5'-(naphthyl-1,6-diyl) diisophthalate (H4L4) and 5,5'-(naphthyl-2,6-diyl) diisophthalate (H4L5), have been used to generate five copper-based MOF isomers. As revealed by single-crystal X-ray diffraction studies, they adopted two different types of topologies depending on the organic ligands: ssa topology for the MOFs ZJNU-71 and ZJNU-74 based on the ligands H4L1 and H4L4, respectively, and nbo topology for the MOFs ZJNU-72, ZJNU-73 and NOTT-103 derived from the ligands H4L2, H4L3 and H4L5, respectively. Furthermore, their C2H2 adsorption properties were systematically investigated, revealing that their different C2H2 uptake capacities can be mainly related to their different pore sizes since they possess the same chemical compositions and gravimetric densities of open metal sites. In particular, among these five MOF compounds investigated, ZJNU-71 exhibits the highest gravimetric C2H2 uptake of 208.1 cm3 (STP) g-1 at 295 K and 1 atm. The value is also among the highest reported for MOF compounds under the same conditions. This work provides a fundamental understanding of the impact of the positional isomerism of the organic ligands on the structures as well as gas adsorption properties of the resulting MOFs.

A novel metal-organic framework for high storage and separation of acetylene at room temperature

A novel 3D microporous metal-organic framework with NbO topology, [Cu2(L)(H2O)2]∙(DMF)6·(H2O)2 (ZJU-10, ZJU = Zhejiang University; H4L =2′-hydroxy-[1,1′:4′,1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid; DMF =N,N-dimethylformamide), has been synthesized and structurally characterized. With suitable pore sizes and open Cu2+ sites, ZJU-10a exhibits high BET surface area of 2392m2/g, as well as moderately high C2H2 volumetric uptake capacity of 132cm3/cm3. Meanwhile, ZJU-10a is a promising porous material for separation of acetylene from methane and carbon dioxide gas mixtures at room temperature.

Shape-Asymmetry Supramolecular Isomerism in Asymmetrical Ligand PCPs and the Expression Method of Three-Level Isomerism.

We show here the supramolecular isomerism, with respect to shape-asymmetry of ligand and the new hierarchical classification for supramolecular isomerism, the three-level isomerism, which was advanced based on a thorough investigation for the four new Ni/dpt24 polymorphs [Hdpt24 = 3-(2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole)]. Compounds 1, 2, and 3 are three-dimensional twofold interpenetrated porous coordination polymers with NbO topology, while 4 with two-dimensional grid structure is termed as the primary isomer of 1/2/3 due to the difference of dimensionality. Complex 3 possessing different shape-asymmetry of single networks from 1 and 2, is called as the secondary isomer of 1 and 2. Complexes 1 and 2 possess the same topology, single shape-asymmetry networks, but different interpenetration-orientation and interpenetration-asymmetry, and are defined as the tertiary isomers. Distinct differences in H2 and CO2 adsorption capacity were observed among each level of isomers. In addition, the hierarchical classification's relationship with characteristic classifications has been discussed.

Synthesis of two metal-porphyrin frameworks assembled from porphyrin building motifs, 5, 10, 15, 20-tetrapyridylporphyrin and their base catalyzed property

Opening catalytically active sites in metal organic frameworks is an issue of fundamental importance for the development of effective and efficient catalysts. In this work, we first reported two metal metalloporphyrin–organic frameworks (MMPFs) with unoccupied pyridine groups as base catalysts. The reaction of Mn(II) and Co(II) with 5,10,15,20-tetrapyridylporphyrin produces two different metal metalloporphyrin–organic frameworks, {[(MnTPyP)]·H2O}n (MMPF-Mn) and [(CoTPyP)]n (MMPF-Co) (TPyP=5,10,15,20-tetrapyridylporphyrin) under hydrothermal conditions. These two MMPFs have been fully characterized by single-crystal X-ray diffraction, powder XRD, elemental analysis and thermogravimetry (TG). MMPF-Mn displays a 3D network with a nbo topology, large and open hexagonal channels, MMPF-Co reveals a 1D single zigzag chain architecture. Interestingly, both MMPFs have a high thermal stability and opening basic pyridine group, which have been tested for the base catalyzed Knoevenagel condensation reaction. The catalytic study has demonstrated that MMPF-Mn catalysts having exposed pyridine group within 1D channel displayed an excellent performance for Knoevenagel condensation reaction. When MMPF-Mn was recycled four times, its catalytic activity remained with an inconspicuous decrease. We attribute MMPF-Mn showing a better performance than MMPF-Co to its active sites being aligned in extra-large cavity with an interior diameter of 20Å.