Triangular Ligand Research Articles

Two Cd(II) complexes: Fluorescence performances and loaded with paclitaxel-hydrogel on oral cancer treatment

In this study, two unique three-dimensional Cd(II)-based coordination polymers, [Cd3L12(H2O)4]∙(CH3CN)∙(H2O) (1) and [Cd3L22(H2O)2] (2), were successfully synthesized under solvothermal conditions. The organic linkers selected were two tricarboxylic acid ligands, H3L1 and H3L2 (H3L1 = 4,4′,4″-((benzene-1,3,5-tricarbonyl) tris(azanediyl)) tribenzoic acid, H3L2 = 4,4′,4″-(benzene-1,3,5-triyltris(azanediyl))tribenzoic acid). Furthermore, fluorescence performance tests of the complexes indicated that through coordination with the metal center and the semi-rigid triangular ligand, as well as the formation of a highly rigid network involving the framework and free solvent molecules in a hydrogen bond network, complexes 1 and 2 exhibited excellent blue fluorescence. Building upon this, given the poor biocompatibility of metal–organic frameworks (MOFs) as carriers, we employed hyaluronic acid (HA)/carboxymethyl chitosan (CMCS) hydrogel for encapsulation and paclitaxel loading. A novel paclitaxel drug delivery system, HA/CMCS-MOFs@paclitaxel, was developed, and the effects of the two systems on the expression of the cancer proliferation marker gene Ki-67 in OSCC cells (CAL27) were evaluated. Results demonstrated that the synthesized paclitaxel-loaded metal gel particles exhibited potent inhibitory activity against Ki-67, showcasing their potential as therapeutics for oral cancer.

Cage-Space-Partitioned Metal–Organic Frameworks for Efficient Carbon Dioxide Capture and Conversion

Metal–organic frameworks (MOFs) have demonstrated potential for CO2 capture and conversion, which are of great importance to alleviate current global environmental problems. Considering that MOFs with large pores are not conducive to adsorption under atmospheric environments, it is critical to control MOF materials with suitable pore sizes and catalytic sites to facilitate CO2 adsorption and fixation. Based on this, cage space partition (CSP), a new strategy to precisely regulate the pore sizes of MOFs, is proposed herein. The feasibility of the CSP strategy is demonstrated in an extra-large metal–organic cage ([M60(BTC)24], M = Co or Ni, BTC = benzene-1,3,5-tricarboxylate), which connects adjacent small cages ([M12(BTC)12]) to form a parent skeleton. For the first CSP process, four typical pyridine-based triangular ligands (TPT, 2,4,6-tris(4-pyridyl)-1,3,5-triazine) are symmetrically inserted into the M60-cage via open metal sites, which transfer the parent skeleton into a novel CSP-MOF (SNNU-337). Furthermore, two larger tri-pyridine ligands (TPHAP, 2,5,8-tri(40-pyridyl)-1,3,4,6,7,9-hexaazaphenalene) are involved to fulfill the second CSP process through residue open metal sites distributed on the inner cage surface, which lead to another isostructural CSP-MOF material (SNNU-338). Oriented by the continuous π–π interactions, the trapped TPT and TPHAP partitioners are divided into two groups, which finally divided the whole large pore into seven small sections. Benefiting from the two-step CSP process, the low-pressure CO2 adsorption capacity of MOFs is remarkably enhanced. Grand canonical Monte Carlo simulations clearly indicate that the introduction of partition agents successfully regulates the internal aperture of the cage and thus enhances the interactions between the MOF skeleton and CO2 molecules. Moreover, the synergistic effects of CSP in large M60-cages and open metal sites in M12-cages make SNNU-337/338 MOFs excellent catalysts to catalyze CO2 cycloaddition with various epoxides.

A pyrazole-functional 3D cobalt-organic framework for fluorescence detection of Cu2+ and Hg2+

A new MOFs luminescent probe with the formula of [Co3(L)2(H2O)6]n (1) was synthesized via a solvothermal reaction with a triangular ligand 1,3,5-(tris(1-(4-carboxyphenyl)-1H-pyrazol-3-yl))benzene (H3L) and Co nitrate. Single-crystal X-ray diffraction analysis revealed compound 1 features a 3D network, which was constructed by 1D Co-O chains and μ5-connected L3− ligands. It is noteworthy that pyrazole N atoms of the ligand were uncoordinated in the framework. Detailed luminescent investigations reveal that compound 1 could sever as a highly selective and sensitive “turn off” luminescent probe toward Cu2+ or Hg2+ in DMA solution. The possible luminescent quenching mechanism of compound 1 by Cu2+ or Hg2+ can be attributed to the weak Lewis acid-base interaction between Cu2+ or Hg2+ and pyrazole N atoms.

Construction of new multi-cage-based MOFs using flexible triangular ligands for efficient gas adsorption and separation

Designing efficient absorbents for multi-gas adsorption and separation is of critical significance for gas purification in chemical engineering. Multi-cage structure enables sufficient interactions with multi-gas through the restriction effects, which is promising to achieve high multi-gas separation performance. In this work, two isomorphic metal-organic frameworks (MOFs) (SNNU-275, M ​= ​Cu, and SNNU-276, M ​= ​Ni) with three types of cages (octahedral M6L4, cuboctahedral M12L8, and M12L24), which are (3,4)-linked three-dimensional microporous structures formed by stacking M6(TPA)4 octahedral coordination molecular cages are synthesized by using tri(4-pyridyl) amine (TPA) ligands and Cu/Ni metals. TPA is selected as the central ligand due to the small size and flexible characteristics. The synthesized SNNU-275 exhibits a good combination of high C2H2/CO2 adsorption selectivity (28), while high C2H2 uptake capacity (68 ​cm3 ​g−1) is achieved for SNNU-276 with high stability. In addition, SNNU-275 and SNNU-276 exhibited superior uptake capacity for benzene and water vapor. Overall, this work not only provides new triangular tripyridine-based MOFs with multiple cages for efficient gas purification, but also demonstrated that the multicage engineering is a promising strategy for the multicomponent gas separation.

Porous amorphous metal-organic frameworks based on heterotopic triangular ligands for iodine and high-capacity dye adsorption.

The research on amorphous metal-organic frameworks (aMOFs) is still in its infancy, and designing and constructing aMOFs with functional pores remains a challenge. Two aMOFs based on Co(II) and heterotopic triangular ligands with large conjugated aromatic planes, namely aMOF-1 and aMOF-2, were constructed and characterized by IR, XPS, EA, ICP, XANS and so on. aMOF-1 possesses mesopores, whereas aMOF-2 possesses micropores. The porosity, conjugated aromatic plane and uncoordinated N atoms in the framework allow these aMOFs to adsorb iodine and dyes. The iodine adsorption capacity of aMOF-1 is 3.3 g per g, which is higher than that of aMOF-2 (0.56 g per g), mainly due to the expansion or swelling of aMOF-1 after iodine adsorption. The uptake of cationic dyes by aMOF-2 showed more rapid kinetics and a higher removal rate than that by aMOF-1, mainly due to the difference in the porosity and surface charge. Although the surface charges of aMOF-1 and aMOF-2 are negative, both of them showed significantly faster adsorption kinetics toward anionic dyes, among which methyl orange (MO) and Congo red (CR) can be removed in 5 min. This occurs possibly because the quick adsorption of Na+ ions alters the surface charge of the framework and promotes dye uptake. The adsorption capacities of aMOF-1 for MO and CR reached 921 and 2417 mg g-1, respectively. The correlation data for aMOF-2 are 1042 and 1625 mg g-1, respectively. All adsorption capacities are among the highest compared to many cMOFs. Adsorption in mixed dye solution is found to be charge-dependent, kinetic-dependent, and synergetic in these systems. The porosity, surface charge regulation during adsorption, weak interactions and multiple adsorption processes contribute to the dye adsorption performance.

Highly efficient and bifunctional Cd(II)-Organic Framework platform towards Pb(II), Cr(VI) detection and Cr(VI) photoreduction

Lead and chromate/dichromate are widely used in manufacturing industry, but Pb(II) and Cr(VI) ions pose fatal threats to human health and the water ecological environment. It is thus highly desirable to develop novel and valid strategies for rapid detection and effective decontamination of these heavy metal ions. Design and assembly of luminescent Metal-Organic Framework (LMOFs) for effective recognition and removal of Pb(II) and/or Cr(VI) from water provide a feasible avenue to address this issue. Herein, a novel Cd(II)-MOF, [(Cd3L2)]·(solvent)x (labeled as compound 1) with bright blue fluorescence was assembled under the solvothermal reaction of triangular ligand 5'-(5-carboxy-1H-benzo [d]imidazole-2-yl)-[1,1':3′,1″-terphenyl]-4,4″-dicarboxylic acid (H3L) and Cd(NO3)2. Given that the unique structure features of 3D stacking framework, i. e. strong π···π conjugative effects of organic linkers, plentiful free imidazole N atoms and carboxyl O atoms, Cd-MOF of 1 was deliberately deployed as bifunctional platform to sense Pb(II)/Cr(VI) and photochemically reduce Cr(VI) to Cr(III). Notably, 1 emits durable bright blue fluorescence and performs rapid quenching sense for Pb2+, Cr2O72− and CrO42−, with ultra low detection limits of 1.89, 4.83 and 2.84 ​ppb, respectively. Moreover, highly toxic Cr(VI) could be rapidly and thoroughly reduced to Cr(III) ions by 1 under the irradiation of mercury lamp, with reliable recycling ability. The possible photoluminescence, quenching and photocatalytic reduction mechanisms also were tentatively proposed.

Highly sensitive detection of nitrobenzene by a series of fluorescent 2D zinc(ii) metal-organic frameworks with a flexible triangular ligand.

Four fluorescent zinc(ii) metal–organic frameworks, namely [Zn(HCIA)(4,4′-bipy)] (1), [Zn2(CIA)(OH)(1,4-bibz)1.5]·H2O (2), [Zn(CIA)(OH) (4,4′-bbpy)] (3), and [Zn2(HCIA) (4,4′-bimp)]·H2O (4), were prepared hydrothermally with a flexible triangular ligand (H3CIA) and a series of linear N-donor ligands (H3CIA = 5-(2-carboxybenzyloxy) isophthalic acid, 4,4′-bipy = 4,4′-bipydine, 1,4-bibz = 1,4-bis(1-imidazoly)benzene; 4,4′-bbpy = 4,4′-bis (imidazolyl) biphenyl; 4,4′-bimp = 4,4′-bis (imidazole-1-ylethyl) biphenyl). Structural analyses revealed that complex 1 exhibited a 2D brick-like network structure based on the basic bimetallic ring, 2 was also a 2D interspersed structure from the 1D tubular structure, compound 3 possessed a 2D (4,4) network with 4,4′-bbpy occupying the holes, and complex 4 displayed a 2D network from the 1D ladder-like chain. The thermal stabilities and fluorescent properties of these complexes were investigated in the solid state. The fluorescent sensing experiments revealed that all Zn-MOFs could highly sensitively detect nitrobenzene in aqueous solution, which indicated that these materials can be used as fluorescent probes for the detection of nitrobenzene.

Suite of Organoplatinum(II) Triangular Metallaprism: Aggregation-Induced Emission and Coordination Sequence Induced Emission Tuning.

A series of triangular metallaprisms with a kinetically inert Pt-N bond have been synthesized from the stepwise assembly of a Pt-corner, linear linker 4,4'-bipy (4,4'-bipy = 4,4'-bipyridine) and triangular ligand [tpb or tpt, tpb = tris(4-pyridyl)benzene, tpt = tris(4-pyridyl)triazine]. The use of an unsymmetrical [Pt(HL)]-corner (H2L = 2,6-diphenylpyridine) leads to novel isostructural products. Phenyl rotation at the metal-corners endows these complexes with good aggregation-induced emission (AIE) function, with varied activities across the isostructural complexes. The coordination sequence of electron-deficient ligand tpt also imparts significant influence on the complex emission. These organoplatinum triangular metallaprisms thus provide a good model to study the influence of building blocks and coordination sequence on the luminescence of supramolecules.

Bpytrisalen/Bpytrisaloph: A Triangular Platform That Spatially Arranges Different Multiple Labile Coordination Sites.

Complexes that possess multiple metals in their proximity exert useful functions such as multivalent capture and catalytic activities. However, it is often challenging to arrange multiple metals with regular distances and to maintain the reactive coordination sites. We have now designed and synthesized organic macrocyclic ligands, bpytrisalen and bpytrisaloph, as platforms to spatially arrange different kinds of metals and their coordination sites. Metals coordinating to the bpy N2 units of the triangular ligands are assembled in the cavity with their labile coordination sites directed inward. Meanwhile, the metals at the salen/saloph N2O2 units have axial coordination sites that are vertically pointing out of the triangle. As a result, planar homo- and heterohexanuclear complexes with different kinds of coordination sites are obtained. Furthermore, a double-decker structure was selectively constructed upon coordinating a ditopic linker ligand to the axial coordination sites of the salen units, which shows the orthogonality of the coordination sites at the bpy and salen units. The consistency in the array of metal centers and their coordination sites irrespective of the elements is a desirable feature in the pursuit of applications for the multinuclear complexes.

Pore Space Partition within a Metal-Organic Framework for Highly Efficient C2H2/CO2 Separation.

The pore space partition (PSP) approach has been employed to realize a novel porous MOF (FJU-90) with dual functionalities for the challenging C2H2/CO2 separation under ambient conditions. By virtue of a triangular ligand (Tripp = 2,4,6-tris(4-pyridyl)pyridine), the cylindrical channels in the original FJU-88 have been partitioned into uniformly interconnected pore cavities, leading to the dramatically reduced pore apertures from 12.0 × 9.4 to 5.4 × 5.1 Å2. Narrowing down the pore sizes, the resulting activated FJU-90a takes up a very large amount of C2H2 (180 cm3 g-1) but much less of CO2 (103 cm3 g-1) at 298 K and 1 bar, demonstrating it to be the best porous MOF material for this C2H2/CO2 (50%:50%) separation in terms of the C2H2 gravimetric productivity. IAST calculations, molecular modeling studies, and simulated and experimental breakthrough experiments comprehensively demonstrate that the pore space partition strategy is a very powerful approach to constructing MOFs with dual functionality for challenging gas separation.

A Trinuclear Iron(III) Complex of a Triple Noninnocent Ligand for Spin-Structured Molecular Conductors.

N,N',N'',N''',N'''',N'''''-(Triphenylene-2,3,6,7,10,11-hexayl)hexapicolinamide (H6 hptp), a triangular ligand containing three noninnocent coordination sites, and its trinuclear iron(III) complex (PPh4 )3 [FeIII 3 (hptp)6 (CN)6 ] were prepared. In this complex, three low-spin Fe3+ ions are coordinated by the triangular hptp6- bridging ligand at its apices. Cyclic voltammetry of (PPh4 )3 [FeIII 3 (hptp)6 (CN)6 ] in PhCN solution showed one reductive wave for 3 Fe2+ /3 Fe3+ and three oxidative waves for the hptp6- ligand. The controlled-potential electronic spectra of the solution presented broad absorption bands in the near-IR (NIR) region for oxidations because a π-radical is generated on the hptp6- ligand. The EPR spectra of frozen solutions also showed large oxidization-state dependent differences caused by the strong exchange interactions between the electrons in the d orbitals of the Fe3+ ions and those of the π-radicals in the hptp6- ligand. The electronic and magnetic states of the oxidized species were investigated using density functional theory.

Solvent-Induced and Temperature-Promoted Aggregation of Bipyridine Platinum(II) Triangular Metallacycles and Their Near-Infrared Emissive Behaviors.

A series of bipyridine platinum(II) complexes with different sizes of triangular metallacycles and alkyl/oligoether chains has been synthesized and characterized. They are packed in a zig-zag fashion with the formation of dimeric structures according to their X-ray crystal structures. Different emission origins are observed due to the different sizes of the triangular ligands. Their morphologies could be tuned by the modification of the molecular structures with different metallacyclic alkynyl ligands and alkyl/oligoether chains and solvents. More interestingly, unusual electronic absorption changes and upfield shifts of the aromatic proton resonances are observed upon increasing the temperature, suggesting further aggregation of the architectures. Near-infrared (NIR) emission is also realized through the tuning of the π-π stacking, Pt⋅⋅⋅Pt interactions, and the packing of planar metallacycles.

Crystal structure, magnetism, and luminescent properties of two isostructural pcu MOFs based on a triangular ligand

Two isomorphous metal-organic frameworks, {[M(TIPA) (btec)½]H2O}n, [M = Co (1) or Zn (2)] were synthesized hydrothermally based on a semi-rigid N-center triangular ligand TIPA, where TIPA = tris(4-(1H-imidazol-1-yl)-phenyl)amine, H4btec = 1,2,4,5-benzenetetracarboxylic acid. Single crystal structural analyses show that complexes 1 and 2 are isostructural and both feature a twofold interpenetrated pcu topology. In 1 and 2, the btec4− ligand adopting μ2-η2:η1 and μ1-η1:η0 coordination modes connect adjacent dinuclear Co/Zn units to form a 1D straight polymeric chain. Then these chains arranged in parallel/parallel fashion were further extended to a 3D network by exo-tridentate ligand TIPA with μ2-κ2N:N′ coordination mode. The magnetic property of 1 and the luminescent property of 2 were investigated. Furthermore, the structure and spectroscopic property of 2 were further investigated by DFT and TD-DFT calculations.

Ni3 versus Ni30 : A Truncated Octahedron Metal-Organic Cage Constructed with [Ni5 (CN)4 ]6+ Squares and Tripodal Tris-tacn Ligands That are Large and Flexible.

Reactions of trinickel complex of tripodal tris-tacn ligand N(CH2 -m-C6 H4 -CH2 tacn)3 (L, tacn=1,4,7-triazacyclononane) in acetonitrile-methanol solution with and without phosphate led to two complexes of distinct nuclearities, [(NiII Cl)3 (CH3 OH)3 (HPO4 )L](PF6 ) (Ni3 , 1) and [(NiII5 (CN)4 (H2 O)8 Cl)6 L8 ]Cl30 (Ni30 , 2). Ligand L takes upward and downward conformation in the structure of 1 and 2, respectively. It is proposed that phosphate directs the upward conformation of Ni3 L to form 1. In the absence of phosphate, Ni3 L assembles with cyanide ions, which are formed by Ni-catalyzed C-CN bond cleavage of acetonitrile, to give a nano-sized Ni30 cage. Complex 2 represents a discrete truncated octahedron cage assembled with [Ni5 (CN)4 ]6+ squares and large and flexible triangular ligands, which is scarcely observed for self-assembled metal-organic cages. The magnetic properties of 1 and 2 were examined, showing intriguing magnetic properties.

Construction of Noninterpenetrating and Interpenetrating (4-Fold and 8-Fold) 3-D Cd(II) Networks with Tris(1,2,4-triazol-4-yl)phenyl)amine Modulated by Aromatic Dicarboxylate Coligands

Three Cd(II)-based coordination polymers 1–3 with unique structures and topologies have been successfully constructed under solvothermal conditions by use of a newly designed N-containing rigid triangular ligand tris(4-(4H-1,2,4-triazol-4-yl)phenyl)amine (TTPA-4), wherein the structural interpenetration can be modulated by aromatic dicarboxylate coligands including thiophene-2,5-dicarboxylic acid (TDA) and terephthalic acid (TPA). Without using coligands, a noninterpenetrating porous 3-D network of 1 with nia topology was obtained. With the aid of the V-shaped TDA coligand, a 4-fold interpenetrating 3-D network of 2 resulted that is built from (2,3,7)-connecting (42.6)(44.6.88.104.124)(4)2 net. In the presence of the linear TPA auxiliary ligand, an 8-fold interpenetrating 3-D network of 3 was produced that is assembled by 3-connecting uninodal srs net. Particularly, compound 1 displays interesting dual function as the result of its unique structural attributes, which not only shows superb sensitivity for ...

Eight Zn(ii) and Cd(ii) complexes based on the aromatic C-centered triangular multicarboxylate and N-donor mixed ligands

Eight Zn(ii) and Cd(ii) complexes based on the C-centered triangular multicarboxylate and N-donor mixed ligands were synthesized. The coordination mode of ligands have obvious effects on the final structures. Luminescent properties were investigated.

Six new inorganic–organic hybrids based on rigid triangular ligands: Syntheses, structures and properties

Six new inorganic–organic hybrids based on rigid triangular N-containing ligands, NaCuI2(tib)4(H2O)4[H2PWVWVI11O40][H2PWVI12O40]·6H2O (1), CuII3(tib)4Cl4[H2PWVI12O40]2·4H2O (2), Co(tib)2[PWV3WVI9O38]·5H2O (3), CuII3(tib)2[P2MoVI5O22(O2)]·4H2O (4), Mn(pytpy)2MoVI4O13 (5) and Co(pytpy)2MoVI4O13 (6) (tib=1,3,5-tris(1-imidazolyl)benzene, pytpy=4’-(4”-pyridyl)2,4’:6’,4”-terpyridine), have been hydrothermally synthesized. Single crystal X-ray diffraction studies revealed that compounds 1–4 display two-dimensional (2D) layered structures, and in compounds 1–3, the adjacent Keggin anions link with each other by W–O–W covalent interactions to form 1D inorganic chains. Compounds 5–6 are 3D “pillar-layer” frameworks based on bimetal–oxide layers pillared by the pytpy ligands. The compounds have been characterized by elemental analysis, powder X−ray diffraction, X-ray photoelectron spectroscopy and thermo gravimetric analyses. Moreover, the electrochemical and catalytic properties of compound 1 have been investigated as well.

Structural transition between a (4,4)-net and a CdI2-net in Cd(II) compounds and conversion from a mixture to a pure substance

The coordination of a rigid triangular ligand 2,4,6-tris[4-(1H-imidazole-1-yl)phenyl]-1,3,5-triazine (TIPT) with Cd(II) ions afforded two compounds with structural motifs of a CdI2-type and a (4,4) network for anions OTf− (CF3SO3−) and OTs− (p-CH3C6H5SO3−), respectively, between which structural transition can be induced by anion exchange via solvent-mediated recrystallization process. Using this method, a pure substance can be obtained from a mixture under the excess of certain kind of anions.

A Series of Highly Connected Metal–Organic Frameworks Based on Triangular Ligands and d10 Metals: Syntheses, Structures, Photoluminescence, and Photocatalysis

Four novel highly connected metal–organic frameworks (MOFs) based on d10 metals and triangular ligands, namely, [Ag7(4,4′-tmbpt)(HL)2(L)(H2O)] (1), [NaCd3(4,4′-tmbpt)(L)2(OH)]·H2O (2), [Cd3(3,3′-tmbpt)2(L)2(H2O)2]·3.5H2O (3), and [Cd3(3,4′-tmbpt)2(L)2(H2O)]·1.5H2O (4) (H3L = 5-(4-carboxybenzyloxy)isophthalic acid, 4,4′-tmbpt = 1-((1H-1,2,4-triazol-1-yl)methyl)-3,5-bis(4-pyridyl)-1,2,4-triazole, 3,3′-tmbpt = 1-((1H-1,2,4-triazol-1-yl)methyl)-3,5-bis(3-pyridyl)-1,2,4-triazole, and 3,4′-tmbpt = 1-((1H-1,2,4-triazol-1-yl)methyl)-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole) have been synthesized under hydrothermal conditions. Compound 1 features a three-dimensional (3D) (3,12)-connected net based on heptanuclear [Ag7(COO)7] units. Compound 2 displays a 3D (3,4,10)-connected net constructed by tetranuclear [NaCd3(μ3-OH)(COO)5]+ units. Compound 3 exhibits a 3D (3,4,8)-connected net based on binuclear [Cd2(COO)2] units. Compound 4 is a 3D binodal (3,9)-connected framework constructed by trinuclear [Cd3(COO)4] unit...

Triangular Trinuclear Metal-N4 Complexes with High Electrocatalytic Activity for Oxygen Reduction

A new class of macrocyclic metal-N(4) complexes [MN(4)](n) (M = Co and Fe) were designed and synthesized based on a triangular ligand. Their unique triangular trinuclear structure provides a high density of active sites and facilitates the reduction of dioxygen via a four-electron pathway. Among them, a [CoN(4)](3)/C catalyst (20 wt %) exhibits high catalytic activity and long-time stability for the oxygen reduction reaction (ORR) in alkaline conditions, superior to the commercial Pt/C catalyst. Such structurally well-defined [MN(4)](n) complexes provide a platform for a new generation of nonprecious metal catalysts (NPMCs) for fuel cell applications.