Octanuclear Zinc Research Articles

Octanuclear Zinc Clusters in Microporous Organic Polymers: Network-Enhanced Reductive CO2 Fixation to Formamides at Room Temperature.

A building block containing eight zincs and eight iodo groups (8Zn) is obtained by the Zn complexation of a salen ligand bearing two additional hydroxy groups. Through the Sonogashira-Hagihara coupling of 8Zn with 1,3,5,7-tetra(4-ethynylphenyl) adamantane, microporous organic polymers bearing octanuclear zinc clusters (MOP-8Zn) are prepared, exhibiting a high surface area of 562 m2g-1, microporosity, and a particulate morphology with an average diameter of 249nm. The MOP-8Zn exhibits significantly enhanced catalytic performance, compared to molecular counterparts, in the reductive carbon dioxide fixation to formamides, possibly due to the cooperative adsorption and confinement effect of networks on substrates.

A self-assembled metal–organic framework for enhanced UO22+ fluorescence sensing: integration of an octa-nuclear zinc cluster with hexakis(4-carboxyphenoxy)cyclotriphosphazene

A novel photoactive Zn-MOF was successfully synthesised by introducing a flexible cyclotriphosphonitrile hexacarboxylic acid, which achieves a sensitive fluorescence quenching response to radioactive UO22+ ions and the heavy metal Fe3+.

Design of a MOF based on octa-nuclear zinc clusters realizing both thermal stability and structural flexibility.

An octa-nuclear zinc (Zn8) cluster-based two-fold interpenetrated metal-organic framework (MOF) of [(CH3)2NH2]2[Zn8O3(FDC)6]·7DMF (denoted as Zn8-as; H2FDC = 9H-fluorene-2,7-dicarboxylic acid; DMF = N,N-dimethylformamide) was synthesized by the reaction of a hard base of a curved dicarboxylate ligand (H2FDC) with the borderline acid of Zn(II) under solvothermal conditions. Zn8-as shows significant crystal volume shrinkage upon heating, yielding a solvate-free framework of [(CH3)2NH2]2[Zn8O3(FDC)6] (Zn8-de). Zn8-de displays gated adsorption for C2H2 and type-I adsorption for CO2, attributed to the framework flexibility and the different interactions between the gas molecules and the host framework.

Sensitive and Specific Guest Recognition through Pyridinium-Modification in Spindle-Like Coordination Containers.

An elaborately designed pyridinium-functionalized octanuclear zinc(II) coordination container 1-Zn was prepared through the self-assembly of Zn2+ , p-tert-butylsulfonylcalix[4]arene, and pyridinium-functionalized angular flexible dicarboxylate linker (H2 BrL1). The structure was determined by a single-crystal X-ray diffractometer. 1-Zn displays highly sensitive and specific recognition to 2-picolylamine as revealed by drastic blueshifts of the absorption and emission spectra, ascribed to the decrease of intramolecular charge transfer (ICT) character of the container and the occurrence of intermolecular charge transfer between the host and guest molecules. The intramolecular charge transfer plays a key role in the modulation of the electronic properties and is tunable through endo-encapsulation of specific guest molecules.

Octanuclear zinc(II) carboxylate framework based on 1,4-naphthalenedicarboxylic acid

A novel Zn(II)-cluster-based coordination polymer-namely, {[Zn8(μ4-O)2(1,4-ndc)6(DMF)3]⋅DMF}n (1) was synthesized using Zn(NO3)2 with 1,4-naphthalenedicarboxylic acid (1,4-H2ndc) under solvothermal conditions using CH3OH/H2O/DMF (6:1:1) as solvents and characterized by single crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, and luminescent measurements. The complex 1 features a 3D structure based on the octanuclear metal cluster of [Zn8(μ4-O)2(OOCR)12(DMF)3] as secondary building unit, which possesses a (412·63) network topology considering the octanuclear cluster as 6-connected nodes. Thermal property and photoluminescence investigations revealed that the complex 1 displays a high thermal stability, and a strong emission spectrum peak at 403nm at room temperature, and the complex 1 may be a technically viable option for the luminescence materials.

Novel hexanuclear and octanuclear zinc alkyl cages derived from a bis-oxamidate ligand

1 and 2 were prepared by coordination self-assembly from reacting N,N′-bis(3,5-di-tert-buthyl-2-phenol)oxamide (L-H4) with ZnEt2 in toluene and THF, respectively. The molecular X-ray structures show 1 as an octanuclear Zn8 cage and 2 as a hexanuclear Zn6 cage. The nuclearity of these cages is driven by the solvent, in fact 1 gives 2 upon addition of THF. Good polymer conversions for the ROP of rac-lactide were achieved by using 1 and 2 with alcohols as co-catalysts.

Octanuclear zinc phosphates with hitherto unknown cluster architectures: ancillary ligand and solvent assisted structural transformations thereof.

Structural variations in zinc phosphate cluster chemistry have been achieved through a careful selection of phosphate ligand, ancillary ligand, and solvent medium. The use of 4-haloaryl phosphates (X-dippH2) as phosphate source in conjunction with 2-hydroxypyridine (hpy) ancillary ligand in acetonitrile solvent resulted in the isolation of the first examples of octameric zinc phosphates [Zn8(X-dipp)8(hpy)4(CH3CN)2(H2O)2]·4H2O (X = Cl 2, Br 3) and not the expected tetranuclear D4R cubane clusters. Use of 2,3-dihydroxypyridine (dhpy) as ancillary ligand, under otherwise similar reaction conditions with the same set of phosphate ligands and solvent, resulted in isolation of another type of octanuclear zinc phosphate clusters {[(Zn8(X-dipp)4(X-dippH)4(dhpyH)4(dhpyH2)2(H2O)2]·2solvent} (X = Cl, solvent = MeCN 4; Br, solvent = H2O 5), as the only isolated products. X-ray crystal diffraction studies reveal that 2 and 3 are octanuclear clusters that are essentially formed by edge fusion of two D4R zinc phosphates. Although 4 and 5 are also octanuclear clusters, they exhibit a completely different cluster architecture and have been presumably formed by the ability of 2,3-dihydroxypyridine to bridge zinc centers in addition to the X-dipp ligands. Dissolution of both types of octanuclear clusters in DMSO followed by crystallization yields D4R cubanes [Zn(X-dipp)(DMSO)]4 (X = Cl 6, Br 7), in which the ancillary ligands such as hpy, H2O, and CH3CN originally present on the zinc centers of 2-5 have been replaced by DMSO. DFT calculations carried out to understand the preference of Zn8 versus Zn4 clusters in different solvent media reveal that use of CH3CN as solvent favors the formation of fused cubanes of the type 2 and 3, whereas use of DMSO as the solvent medium promotes the formation of D4R structures of the type 6 and 7. The calculations also reveal that the vacant exocluster coordination sites on the zinc centers at the bridgehead positions prefer coordination by water to hpy or CH3CN. Interestingly, the initially inaccessible D4R cubanes [Zn(X-dipp)(hpy)]4·2MeCN (X = Cl 8, Br 9) could be isolated as the sole products from the corresponding DMSO-decorated cubanes 6 and 7 by combining them with hpy in CH3CN.

Luminescent Response of One Anionic Metal–Organic Framework Based on Novel Octa-nuclear Zinc Cluster to Exchanged Cations

Utilizing the flexible hexa-carboxylate ligand derived from cyclotriphosphazene, a novel anionic metal–organic framework based on an octa-nuclear zinc cluster has been synthesized, showing the variable luminescent properties controlled by different guest cations.

Syntheses, structures, photoluminescence, photocatalysis, and photoelectronic effects of 3D mixed high-connected metal–organic frameworks based on octanuclear and dodecanuclear secondary building units

Four novel metal-organic frameworks (MOFs) based on high-nuclear metal carboxylate clusters, namely, [Zn(4)(L)(2)(μ(3)-OH)(2)(H(2)O)(1.5)]·2H(2)O (1), [Zn(5)Na(L)(2)(μ(3)-OH)(4)(CH(3)CH(2)O)(H(2)O)(2)] (2), [Cd(4)(L)(2)(BIME)(0.5)(μ(3)-OH)(2)(H(2)O)(1.5)]·2H(2)O (3), and [Zn(4)(L)(2)(BET)(0.5)(μ(3)-OH)(2)(H(2)O)] (4), where H(3)L = (3,5-dicarboxyl-phenyl)-(4-(2'-carboxyl-phenyl)-benzyl)ether, BET = 1,1'-(2'-oxybis(ethane-2,1-diyl))bis(1,2,4-triazol-1-yl), BIME = 1,2-bis(imidazol-1-yl)ethane, have been synthesized under hydrothermal conditions. In 1, each planar octanuclear zinc cluster [Zn(8)(μ(3)-OH)(8)(CO(2))(12)(H(2)O)(3)] is linked by twelve L anions to give an unusual (3,12)-connected framework with (4(3))(2)(4(20)·6(28)·8(18)) topology. In 2, dodecanuclear heterometallic clusters [Zn(10)Na(2)(μ(3)-OH)(8)(CO(2))(12)(CH(3)CH(2)O)(2)(H(2)O)(4)] are surrounded by twelve L anions to form a (3,12)-connected net with the same topology as 1. However, 3 exhibits a rare (3,14)-connected (4(3))(3(2)4)(3(4)·4(20)·5(14)·6(34)·7(11)·8(8)) net based on octanuclear cadmium cluster [Cd(8)(BIME)(2)(μ(3)-OH)(4)(CO(2))(12)(H(2)O)(4)]·2H(2)O as a 14-connected node and H(3)L as a 3-connected node. In 4, each octanuclear zinc cluster [Zn(8)(BET)(2)(μ(3)-OH)(4)(CO(2))(12)(H(2)O)(2)] is linked by twelve L anions to furnish a (3,14)-connected net with the same topology as 3. The optical energy gaps and photoluminescence were investigated for the compounds. Moreover, compounds 1-4 exhibit good photocatalytic activities for degradation of methylene blue (MB) under UV irradiation and show good stability towards UV photocatalysis. In addition, 1 and 4 display a photocurrent density under several on-off cycles of illumination.

Shape-Persistent Octanuclear Zinc Salen Clusters: Synthesis, Characterization, and Catalysis

We describe a selective and template-controlled synthesis of a series of Zn(8) metal complexes based on a bis-nucleating salen ligand scaffold. Our results, a combination of X-ray analysis and solution studies, show that discrete, shape-persistent metal clusters can be prepared in high yield. Their activity in organic carbonate catalysis is a function of the metal-connecting fragment present in the exterior of the cluster complex. The high stability of the clusters has been confirmed by (1)H, (13)C (DEPTQ) and DOSY NMR, gel permeation chromatography, high-performance liquid chromatography, and mass spectrometry.

Two new pH-controlled metal–organic frameworks based on polynuclear secondary building units with conformation-flexible cyclohexane-1,2,4,5-tetracarboxylate ligand

By regulating the pH values, two new zinc(II) coordination polymers, formulated as [Zn4(μ7-CTAI)(μ3-OH)(μ2-OH)3(H2O)2]n·2n(H2O) (1), [Zn2(μ7-CTAII)(H2O)3]n (2) have been prepared by a flexible ligand, cyclohexane-1,2,4,5-tetracarboxylic acid (H4CTA) under hydrothermal conditions. Complex 1 exhibits a two-dimensional binodal (3,6)-connected topological network containing rare octanuclear zinc(II) clusters as the secondary building units (SBU1). Complex 2 displays a three-dimensional binodal (4,8)-connected topological network containing unusual Zn4(COO)6 secondary building units (SBU2). And importantly, the conformation of H4CTA in 1 exhibits (a,e,e,a) fashion and transforms to thermodynamically more stable conformation (e,a,e,e) type in 2 by pH-controlled. In addition, both of the complexes show strong photoluminescence at room temperature, and may be good candidates for potential luminescence materials.

Synthesis and structures of three d 10 metal coordination polymers constructed from flexible polycarboxylate and 1,10-phenanthroline ligands

Three novel d 10 metal coordination polymers, {[Cd(H 2odpa)(phen) 2]·H 2O} n ( 1), [Cd 2(odpa)(phen)(H 2O) 2] n ( 2), {[Zn 4(odpa) 2(phen) 2(H 2O) 2]·H 2O} n ( 3), (H 4odpa = 4,4′-oxydiphthalic acid, phen = 1,10-phenanthroline) were obtained with different metal/ligand ratios through hydrothermal method and characterized. Compound 1 forms a one dimensional zigzag chain, in which two phen ligands chelate to one cadmium atom. Compound 2 shows a three dimensional network structure comprised of new tetranuclear cadmium clusters as the nodes and (odpa) 4− anions as the linkers, exhibits an unusual topological structure. Compound 3 is an unprecedented three dimensional polymer based on octanuclear zinc clusters cross-linked by (odpa) 4− anions. In 1– 3, central Cd II/Zn II ions and (odpa) 4− ligand display completely different coordination modes and conformations. In addition, the thermal stabilities and photoluminescence properties of 1– 3 were also studied.

A (3,12)-Connected 3D Metal-Organic Framework Based on Nanosized Octanuclear Zinc Clusters

A (3,12)-connected 3D metal-organic framework has been synthesized based on octanuclear zinc clusters as 12-connected nodes and flexible carboxylate ligands as 3-connected nodes, and it represents the highest connected binodal network topology presently known for metal-organic frameworks.

Ladders, rings and cubes as structural motifs in three new zinc(II) azide complexes: Synthesis, spectral and structural characterization

Three new zinc(II) azide complexes, namely {[Zn 2(N 3) 4(py-tetrazole) 2](py-tetrazole)} n ( 1), {[Zn 2(N 3) 4(3-OHpy)] · 2H 2O} n ( 2) and [Zn(N 3) 2(pym)] n ( 3), where py-tetrazole = tetrazolo[1,5- a]pyridine, 3-OHpy = 3-hydroxypyridine and pym = pyrimidine, have been synthesized by the hydrothermal methods and structurally characterized. The ligand py-tetrazole was obtained through the interaction of 2-chloropyridine with the azide ion under hydrothermal condition. The structure of 1 consists of a ladder-like arrangement of 1D double chain zinc(II) azide. In the coordination chain, each zinc atom binds di-EO azide bridges connecting another zinc atom in opposite chain, and two EO bridges, one on each side, and the fifth position is occupied by a N atom of py-tetrazole ligand. The structure of 2 features 2D sheets composed of tetranuclear zinc(II) ring and octanuclear zinc(II) ring interconnected by EO azide bridges. The 2D carrying into 3D supramolecular network by the help of several hydrogen bonding interactions. The 3-OHpy molecule acts in the tautomeric keto-form as O, O-bidentate bridging ligand. Complex 3 features distorted octahedral geometry around each zinc center, N, N′-bidentate pyrimidine ligand and EE azido bridges leading to 3D network structure. The IR spectra are measured and discussed. Complex 2 only exhibits photoluminescence properties whereas the other two complexes do not luminesce at room temperature.

CS 2 elimination and C–S bond cleavage in [Zn(dmpzdtc) 2] – Leading to formation of a cyclic octanuclear complex [Zn 4(μ-dmpz) 5(μ-OH)(μ 3-S)(py)] 2 · py(dmpzdtc = 3,5-dimethylpyrazole-1-dithiocarboxylate, dmpz = 3,5-dimethylpyrazolate)

Complex [Zn(dmpzdtc) 2] ( 1) (dmpzdtc = 3,5-dimethylpyrazole-1-dithiocarboxylate) in MeCN and pyridine underwent unique CS 2 elimination and C–S bond cleavage reactions to afford a novel cyclic octanuclear zinc sulfide complex [Zn 4(μ-dmpz) 5(μ-OH) (μ 3-S)(py)] 2 · py ( 2 · py) dmpz = 3,5-dimethylpyrazolate). Single-crystal X-ray diffraction revealed that 2 consists of two [Zn 4(μ-dmpz) 3(μ-OH)(μ 3-S)(py)] fragments linked by two pairs of μ-dmpz ligands, forming an unique metallocyclic structure. The luminescent property of this complex in solid state was also investigated.

Octanuclear Zinc(II) and Cobalt(II) Clusters Produced by Cooperative Tetrameric Assembling of Oxime Chelate Ligands

We have synthesized an octanuclear zinc(II) cluster [L4Zn8(H2O)3] by the complexation of 3-hydroxysalamo (H4L) with zinc(II) acetate. The complex crystallizes in the triclinic system, space group P, with unit cell parameters a = 18.233(10) A, b = 20.518(11) A, c = 21.366(11) A, alpha = 98.7557(2) degrees, beta = 99.191(11) degrees, gamma = 108.309(10) degrees, and Z = 4. The crystallographic analysis revealed the S4 symmetrical assembling of four ligands and that the tetrameric complex has three water molecules in an unsymmetrical fashion. Spectroscopic analysis of the complex strongly suggests that the octanuclear cluster also exists in solution and maintains a conformation similar to that in the crystal structure, although exchange of the coordinating water molecules presumably takes place. In addition, the formation process of the octanuclear complex is highly cooperative. A high coordinating ability of the [(salamo)Zn] unit as well as the catecholato2- moieties probably stabilizes the octanuclear assembly and makes the complexation process cooperative. The corresponding octanuclear cobalt(II) cluster [L4Co8(EtOH)3] was prepared in a similar manner. Complex [L4Co8(H2O)2X] (X = H2O or EtOH) was obtained by the recrystallization from chloroform/hexane. The complex crystallizes in the triclinic system, space group P, with unit cell parameters a = 15.2359(10) A, b = 16.9625(12) A, c = 18.9325(13) A, alpha = 101.9710(10) degrees, beta = 105.5410(10) degrees, gamma = 97.1290(10) degrees, and Z = 2. Temperature dependence of magnetic susceptibility showed a continuous decrease in the chi(M)T value with decreasing temperature, suggesting antiferromagnetic interaction among cobalt(II) ions. The magnetic susceptibility above 40 K obeys the Curie-Weiss law with a Weiss constant theta of -39 K and a Curie constant C of 19.7 cm(3) K mol(-1).