Crystalline central-metal transformation in metal-organic frameworks

π-Type halogen bonding enhanced the long-lasting room temperature phosphorescence of Zn(ii) coordination polymers for photoelectron response applications

Long-lasting phosphorescence emission was achieved via π-type halogen bonding in Zn(ii) based coordination polymers. The delocalized H-aggregates afforded large electron channels for efficient charge transport and high photoelectron response.

Solution-mediated and single-crystal to single-crystal transformations of cucurbit[6]uril host–guest complexes with dopamine

The structural transformations of cucurbit[6]uril–dopamine complexes are associated with loss of water molecules either from the macrocyclic cavity or from the crystal lattice.

The crystal structure of poly[(m4-4-bromoisophthalato-κ4O: O′:O′′:O′′′)zinc(II)], C8H3BrO4Zn

C8H3BrO4Zn, monoclinic, P21/c (no. 14), a = 4.7134(4) Å, b = 15.4354(13) Å, c = 12.0064(9) Å, β = 98.942(8)°, V = 862.89(12) Å3, Z = 4, Rgt(F) = 0.0445, wRref(F2) = 0.1193, T = 292.67(10) K.

Crystal structure of tetraaqua-bis(μ2-5-aminoisophthalato-κ3 N:O,O′)-bis(4,4′-dipyridylsulfide-κ1 N)dizinc(II), C36H34N6O12S2Ni2

C36H34N6O12S2Ni2, monoclinic, C2/c (no. 15), a = 29.642(4) Å, b = 6.2241(4) Å, c = 21.667(2) Å, β = 108.592(13)°, V = 3788.9(7) Å3, Z = 4, R gt(F) = 0.0907, wR ref(F 2) = 0.1605, T = 293(2) K.

Enhanced Water Stability and Photoresponsivity in Metal-Organic Framework (MOF): A Potential Tool to Combat Drug-resistant Bacteria

In this work, we have successfully synthesized a bimetallic (Zinc and Cobalt) Zeolitic Imidazolate Framework (Zn50Co50-ZIF), a class in a wider microporous Metal-Organic Framework (MOF) family. The synthesized nanostructures maintain both water stability like ZIF-8 (solely Zn containing) and charge transfer electronic band in the visible optical spectrum as ZIF-67 (solely Co containing). Crystal structure from XRD, high resolution transmission electron microscopy (HRTEM) followed by elemental mapping (EDAX) confirm structural stability and omnipresence of the metal atoms (Zn and Co) across the nanomaterial with equal proportion. Existence of charge transfer state consistent with ZIF67 and intact ultrafast excited state dynamics of the imidazolate moiety in both ZIF-8 and ZIF-67, is evidenced from steady state and time resolved optical spectroscopy. The thermal and aqueous stabilities of Zn50Co50-ZIF are found to be better than ZIF-67 but comparable to ZIF-8 as evidenced by solubility, scanning electron microscopy (SEM) and XRD studies of the material in water. We have evaluated the photoinduced ROS generation by the mixed ZIF employing dichloro-dihydro-fluorescein diacetate (DCFH-DA) assay. We have also explored the potentiality of the synthesized material for the alternate remediation of methicillin resistant Staphylococcus aureus (MRSA) infection through the photoinduced reactive oxygen species (ROS) generation and methylene blue (MB) degradation kinetics.

Metal-Organic Framework (MOF)-based Nanomaterials for Biomedical Applications

BACKGROUND

Metal-organic frameworks (MOFs), as a new class of porous organic-inorganic crystalline hybrid materials that governed by the self-assembled of metal atoms and organic struts have attracted tremendous attention because of their special properties. Recently, some more documents have reported different types of nanoscale metal-organic frameworks (NMOFs) as biodegradable and physiological pH-responsive systems for photothermal therapy and radiation therapy in the body.

DISCUSSION

In this review paper aims at describing the benefits of using MOF nanoparticles in the field of biomedicine, and putting into perspective their properties in the context of the ones of other NPs. The first section briefly reviews the biomaterial scaffolds of MOFs. The second section presents the main types of stimuli-responsive mechanisms and strategies from two categories: intrinsic (pH, redox state) and extrinsic (temperature, light irradiation and magnetic field) ones. The combinations of photothermal therapy and radiation therapy have been concluded in detail. Finally, clinical applications of MOFs, future challenges and perspectives are also mentioned.

CONCLUSION

This review outlines the most recent advances MOFs design and biomedical applications, from different synthesis to their use as smart drug delivery systems, bioimaging technology or a combination of both.

Recent developments on zinc(ii) metal-organic framework nanocarriers for physiological pH-responsive drug delivery

The high storage capacities and excellent biocompatibilities of zinc(ii) metal-organic frameworks (Zn-MOFs) have made them outstanding candidates as drug delivery carriers. Recent studies on the pH-responsive processes based on carrier-drug interactions have proven them to be the most efficient and effective way to control the release profiles of drugs. To satisfy the ever-growing demand in cancer therapy, great efforts are being devoted to the development of methods to precisely control drug release and achieve targeted use of an active substance at the right time and place. In this review article, we discuss the diverse stimuli based on Zn-MOFs carriers that have been achieved upon external activation from single pH-stimulus-responsive or/and multiple pH-stimuli-responsive viewpoints. Also, the perspectives and future challenges in this type of carrier system are discussed.

Ion exchange collaborating coordination substitution: More efficient Cr(VI) removal performance of a water-stable CuII-MOF material

An unusual water-stable cationic metal-organic framework {[Cu(L)_0.5(bpe)(H₂O)](NO₃)•(H₂O)_0.5}_n (1) (H₄L = bis(3,5-dicarboxypyridinium)-p-xylylene) was synthesized, which was developed into an effective capture material for removal chromate from water. The results show that this material efficiently traps HCrO₄^- pollutant ions via single-crystal to single-crystal (SCSC) coordination substitution process. The HCrO₄^- uptake capacity of 1 is high to 190 mg/g. Meaningfully, the structure of 1-HCrO₄ ({[Cu(L)_0.5(bpe)(HCrO₄)]}_n) can be accurately obtained by single-crystal X-ray diffraction, where the chromate enter the framework to form stable coordination with central metal ions Cu²⁺. This is the first example of a stable coordination between chromate and the framework during the capture process. The captured HCrO₄^- are not dissociated easily into the solution due to the coordination bond. This interaction makes the enrichment of HCrO₄^- more stable and the capture capacity excellent. Furthermore, the HCrO₄^- releasing process displays good regeneration in a single crystal state, which further elaborates the reversible SCSC transformation. The mechanism of Cr(VI) removal was also confirmed by DFT calculation studies. This work provides a new way to design and develop efficient MOF capture materials.

Directed Structural Transformations of Coordination Polymers Supported Single-Site Cu(II) Catalysts To Control the Site Selectivity of C-H Halogenation

A main difficulty in C-H bond functionalization is to undertake the catalyst control accurately where the reaction takes place. In this work, to achieve highly effective and regioselective single-site catalysts, a three-dimensional (3D) rhombus-like framework of {[Mn(Hidbt)DMF]·H₂O}_n (1) [H₃idbt = 5,5'-(1H-imidazole-4,5-diyl)-bis(2H-tetrazole)] containing coordinated DMF molecules was constructed. For the dissolution-recrystallization structural transformation process, attractive structural transformations proceeded from 1 to a new crystalline species formulated as {[Mn₃(idbt)₂(H₂O)₂]·3H₂O}_n (2) with a 3D windowlike architecture, and then the Mn ions in 2 could be exchanged with Cu ions through cation exchange in a single-crystal to single-crystal fashion to produce the Cu-exchanged product {[Mn₂Cu(idbt)₂(H₂O)₂]·3H₂O}_n (2a), which had a windowlike framework like that of 2. Furthermore, 2 and 2a were used as heterogeneous catalysts for the regioselective C-H halogenation of phenols with N-halosuccinimides (NCS and NBS) to produce the site selective single monohalogenated products. It was found that the catalytic activity and site selectivity of 2a were much higher than those of 2, because the unique structural features of 2a with the uniformly dispersed Cu^II active centers served as a single-site catalyst with a site-isolated and well-defined platform to promote the C-H halogenation reaction in regiocontrol and guide an orientation that favored the para selectivity during the reaction process.

Reversible Structural Transformations of Metal-Organic Frameworks as Artificial Switchable Catalysts for Dynamic Control of Selectively Cyanation Reaction

The synthesis of molecular-level artificial switchable catalysts, of which activity in different chemical processes can be switched by controlling different stimuli, has provided a new paradigm to perform mechanical tasks and measurable work. In this work, to obtain highly effective and regioselective artificial switchable catalysts, a hierarchical anion-pillared framework {(H₃ O)[Cu(CPCDC)(4,4'-bpy)]}_n (1; H₃ CPCDC=9-(4-carboxyphenyl)-9H-carbazole-3,6-dicarboxylic acid, 4,4'-bpy=4,4'-bipyridine), including free [H₃ O]⁺ ions as guest molecules, was constructed. Upon dissolve-exchange-crystallization behavior, fascinating reversible structural transformations proceeded between anion framework 1 and neutral 2D stair-stepping framework {[Cu(CPCDC)(4,4'-bpe)]}_n (2; 4,4'-bpe=4,4'-vinylenedipyridine). Moreover, frameworks 1 and 2 can act as heterogeneous artificial switchable catalysts to selectively promote the direct cyanation reaction of terminal alkynes and azobisisobutyronitrile. The results indicated that 1 and 2 exhibited excellent selectivity to generate vinyl isobutyronitrile skeletons or propiolonitrile frameworks, respectively, as unique products. Furthermore, indicating paper, GC-MS, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy analysis demonstrated that the reversible structural transformations endowed 1 and 2 with well-defined platforms to stabilize the isobutyronitrile and CN sources through the different catalytic pathways.

Syntheses and photocatalytic properties of three new d10-based coordination polymers: effects of metal centres and ancillary ligands

Three d¹⁰-based coordination polymers with three different nitrogen-based ancillary ligands have been synthesized and their photocatalytic properties were explored in the decomposition of methyl violet.

Reversible dielectric switching behavior of a 1D coordination polymer induced by photo and thermal irradiation

Switchable dielectric relaxation is achieved through photocycloaddition/reversion within a 1D coordination polymer on thermal and photo irradiation.

Rare metal-ion metathesis of a tetrahedral Zn(ii) core of a noncentrosymmetric (3,4)-connected 3D MOF

An SHG-active framework of 1-Zn can undergo metal metathesis, in which the tetrahedrally coordinated Zn(ii) ions are completely exchanged with Cu(ii) ions while retaining the integrity of the network.

A quantitative transmetalation with a metal organic framework compound in a solid–liquid interface reaction: synthesis, structure, kinetics, spectroscopy and electrochemistry

A Zn(ii)-MOF (1) can be transformed to its isomorphous Cu(ii)-MOF (2) quantitatively in a single crystal to single crystal metal exchange process in a solid–liquid interface reaction.

Porous functionalized MOF self-evolution promoting molecule encapsulation and Hg2+ removal

Porous functionalized MOF self-evolution has successfully improved the Hg²⁺ removal performance and implemented dye molecule encapsulation.

Temperature tuned syntheses of two new d10-based Cd(ii) cluster metal–organic frameworks: luminescence sensing and photocatalytic properties

The solvothermal reactions of 5,5′-(1,4-phenylenebis(methyleneoxy))diisophthalic acid (H₄L) and the N-donor ancillary ligand 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (bpz) with cadmium(ii) salts at two different reaction temperatures yielded two new metal–organic frameworks (MOFs), viz., [Cd(H₂L)(bpz)]_n (1) and [Cd₂(H₄L)(L)(bpz)₂]_n (2), which have been characterized by FTIR and single crystal X-ray diffraction. The single crystal X-ray diffraction studies revealed that 1 displays a 3-periodic network with monometallic SBU, while 2 exhibits a 3-periodic network with a 2-fold interpenetration feature. The effects of variation in reaction temperature on the architecture of MOFs 1 and 2 have been discussed. The luminescence investigation indicates that both 1 and 2 displayed good turn-off luminescence sensing against nitroaromatic compounds (NACs), especially m-nitrophenol (MNP), via a decrease in their luminescence intensities with a K_sv value of 6.43 × 10³ for 1 and 2.03 × 10⁴ for 2 and LOD values of 1.09 and 0.81 ppm for 1 and 2, respectively. The plausible mechanism for the decline in luminescence intensity of the MOFs with NACs has been addressed using theoretical calculations. The photocatalytic properties for both the MOFs demonstrated that they display efficient photocatalytic performances to degrade methyl violet (MV) under UV irradiation. The plausible mechanism through which these MOFs exhibited photocatalytic properties has been suggested using band gap calculations.

Two new d¹⁰-based Cd(ii) MOFs were synthesized and their photoluminescence sensing to selectively detect m-nitrophenol (MNP) and ability to decompose the organic dye methyl violet (MV) were explored.

Metal-dependent photocatalytic activity and magnetic behaviour of a series of 3D Co–Ni metal organic frameworks

Mixed-metal systems in MOFs modulate their photocatalytic activity and magnetic behavior, which may open a new avenue for the preparation of functional materials with adjustable magnetic behaviors.

Ultra-highly selective trapping of perrhenate/pertechnetate by a flexible cationic coordination framework

This work presents a 3D cationic coordination framework, showing ultra-highly selective trapping of perrhenate/pertechnetate in the presence of sulfate 20 000 times in excess.

A Cuprous [4 × 4] Grid: Single-Crystal to Single-Crystal Transformation and Fading of Luminescence by Solvent Inclusion

The subtle balance of the metrics of the highly supple 5,5'-pyridyl-3,3'-bis-1 H-pyrazolate and the variable coordination numbers of Cu(I) favor the stabilization of a [4 × 4] grid complex with all Cu(I). It has numerous cuprophilic bonds (Cu···Cu = 2.56-3.02 Å), and consequently, exhibits strong orange luminescence that fades upon insertion of solvents without loss of crystallinity.

Metal-Organic Framework (MOF)-Based Materials as Heterogeneous Catalysts for C-H Bond Activation

Converting light hydrocarbons such as methane, ethane, propane, and cyclohexane into value-added chemicals and fuel products by means of direct C-H functionalization is an attractive method in the petrochemical industry. As they emerge as a relatively new class of porous solid materials, metal-organic frameworks (MOFs) are appealing as single-site heterogeneous catalysts or catalytic supports for C-H bond activation. In contrast to the traditional microporous and mesoporous materials, MOFs feature high porosity, functional tunability, and molecular-level characterization for the study of structure-property relationships. These virtues make MOFs ideal platforms to develop catalysts for C-H activation with high catalytic activity, selectivity, and recyclability under relatively mild reaction conditions. This review highlights the research aimed at the implementation of MOFs as single-site heterogeneous catalysts for C-H bond activation. It provides insight into the rational design and synthesis of three types of stable MOF catalysts for C-H bond activation, that is, i) metal nodes as catalytic sites, ii) the incorporation of catalytic sites into organic struts, and iii) the incorporation of catalytically active guest species into pores of MOFs. Here, the rational design and synthesis of MOF catalysts that lead to the distinct catalytic property for C-H bond activation are discussed along with the post-synthesis of MOFs, intriguing functions with MOF catalysts, and microenvironments that lead to the distinct catalytic properties of MOF catalysts.

Stabilizing Metastable Polymorphs of Metal-Organic Frameworks via Encapsulation of Graphene Oxide and Mechanistic Studies

Polymorphic transition from a metastable phase to a stable phase often occurs in metal-organic frameworks (MOFs) under the action of external stimuli. However, these transitions sometimes result in deteriorating their special performances and can even lead to serious safety problems. Therefore, developing a simple and efficient strategy for enhancing the stabilities of metastable MOF polymorphs is very imperative and meaningful. Herein, we propose a simple graphene oxide (GO)-encapsulating strategy for improving the stabilities of metastable MOF polymorphs. To illustrate this strategy, we designed and synthesized two polymorphic MOFs [MOF(ATA-a) and MOF(ATA-b)] as examples, which are based on energetic 5-amino-1 H-tetrazole as ligands. Single-crystal X-ray diffraction showed that these two polymorphs have a same chemical composition [Zn₂(ATA)₃(ATA)_2/2] _n, but different space groups, space systems, and different stacking modes of the neighboring ligands. As expected, the metastable polymorph [MOF(ATA-a)] underwent a complete polymorphic transition at room temperature to form its stable polymorph [MOF(ATA-b)]. Using the proposed strategy, we successfully encapsulated a small amount of GO in the metastable polymorph [GO⊂MOF(ATA-a)]. The resultant composite exhibited better chemical stability, extremely higher thermal stability, and larger Brunauer-Emmett-Teller surface area compared to both its precursor and the physically mixed analogue. Remarkably, its onset decomposition temperature ( T_d) was as high as 377.4 °C, which is even higher than that of 1,3,5-triamino-2,4,6-trinitrobenzene ( T_d = 321 °C), making it a potential heat-resistant explosive. The mechanism of stabilization was investigated in detail using various analytical techniques. This work may not only provide new insights into the stabilization of functional MOF polymorphs but also open up a new field for the application of GO.

Elastically Flexible Crystals have Disparate Mechanisms of Molecular Movement Induced by Strain and Heat

Elastically flexible crystals form an emerging class of materials that exhibit a range of notable properties. The mechanism of thermal expansion in flexible crystals of bis(acetylacetonato)copper(II) is compared with the mechanism of molecular motion induced by bending and it is demonstrated that the two mechanisms are distinct. Upon bending, individual molecules within the crystal structure reversibly rotate, while thermal expansion results predominantly in an increase in intermolecular separations with only minor changes to molecular orientation through rotation.

Smoothing the single-crystal to single-crystal conversions of a two-dimensional metal–organic framework via the hetero-metal doping of the linear trimetallic secondary building unit

Doping of Co²⁺ in the linear Cd₃ cluster secondary building units lowers the single-crystal to single-crystal conversion reactivity of the resulting metal–organic framework.

Enhanced glucose sensing based on a novel composite CoII-MOF/Acb modified electrode

A novel electrochemical sensor composed of a composite of Co^II-MOF/acetylene black exhibits enhanced sensing behavior for glucose detection.

Two MOFs as dual-responsive photoluminescence sensors for metal and inorganic ion detection

Two MOFs were synthesized and explored as dual-responsive photoluminescent sensors: 1 for Fe³⁺ and Cr₂O₇²⁻ ions, and 2 for Hg²⁺ and Cr₂O₇²⁻ ions.

Structures and single crystal to single crystal transformations of cadmium frameworks using a flexible tripodal ligand

Various cadmium coordination polymers were constructed using a flexible tris-imidazole ligand and they showed single crystal to single crystal transformations during anion exchange.

Four Mixed-Ligand Zn(II) Three-Dimensional Metal-Organic Frameworks: Synthesis, Structural Diversity, and Photoluminescent Property

Assemblies of four three-dimensional (3D) mixed-ligand coordination polymers (CPs) having formulas, {[Zn₂(bdc)₂(4-bpdh)]·C₂H₅OH·2H₂O}_n (1), [Zn(bdc)(4-bpdh)]_n (2), {[Zn₂(bdc)₂(4-bpdh)₂]·(4-bpdh)}_n (3), and {[Zn(bdc)(4-bpdh)]·C₂H₅OH}_n (4) (bdc²⁻ = dianion of 1,4-benzenedicarboxylic acid, 4-bpdh = 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene) have been synthesized and structurally characterized by single-crystal X-ray diffraction method. Structural determination reveals that the coordination numbers (geometry) of Zn(II) ions in 1, 2, 3, and 4 are five (distorted square-pyramidal (SP)), six (distorted octahedral (O_h)), five (trigonal-bipyramidal (TBP)), and four (tetrahedral (T_d)), respectively, and are bridged by 4-bpdh with bis-monodentate coordination mode and bdc²⁻ ligands with bis-bidentate in 1, chelating/bidentate in 2, bis-monodentate and bis-bidentate in 3, and bis-monodentate in 4, to generate two-fold interpenetrating 3D cube-like metal-organic framework (MOF) with pcu topology, non-interpenetrating 3D MOF, two-fold interpenetrating 3D rectangular-box-like MOF with pcu topology and five-fold interpenetrating diamondoid-like MOF with dia topology, respectively. These different intriguing architectures indicate that the coordination numbers and geometries of Zn(II) ions, coordination modes of bdc²⁻ ligand, and guest molecules play important roles in the construction of MOFs and the formation of the structural topologies and interpenetrations. Thermal stabilities, and photoluminescence study of 1–4 were also studied in detail. The complexes exhibit ligands based photoluminescence properties at room temperature.

Crystal structure of bis(μ 2-2-chlorobenzoato-κ3 O,O′:O′)-(2-chlorobenzoato-κO)-(2-chlorobenzoato-κO,O′)-bis(1,10-phenanthroline-κ2 N,N′)-dicadmium(II) monohydrate, C52H36Cd2Cl4N4O10

C52H36Cd2Cl4N4O10, triclinic, P1̄ (no. 2), a = 11.3651(8) Å, b = 12.9707(10) Å, c = 18.7281(14) Å, α = 79.327(1)°, β = 74.543(1)°, γ = 70.703(1)°, V = 2497.1(3) Å3, Z = 2, R gt(F) = 0.0393, wR ref(F 2) = 0.0933, T = 293 K.

Water-Mediated Structural Transformations of CuII 5-Halonicotinates Coordination Networks with Distinct Mechanisms

Currently, no unequivocal evidence is given for elucidation of "black box" during the structural transformations of dynamic crystalline materials. Here, three types of mechanisms are revealed for such transformations through X-ray diffraction and optical microscopy; namely, single-crystal to single-crystal (SC-SC), as well as "core-to-core" and "core-on-shell" processes. As confirmed by time-lapse optical microscopy, the latter two cases can be properly ascribed as partial recrystallization processes, while the former one is a continuous process with two different crystal lattices simultaneously maintained in one single crystal. Interestingly, these three distinct pathways can be exquisitely realized by changing only the halogen substituent (from -F, -Cl, to -Br) of the organic ligands in the coordination supramolecular systems.