Xiao-Shan Zeng

Syntheses, structures and properties of five entangled coordination polymers constructed with trigonal N-donor ligands

Based on the mixed-ligand system, five new entangled coordination polymers have been synthesized, namely, [Co1.5(1,3-bdc)1.5(tib)(H2O)] (1), [Ni(1,3-bdc)(tib)(H2O)2]·0.5H2O (2), [Cu(Hbtc)(Htpim)] (3), [Co(bpndc)(pytpy)(H2O)]·0.5H2O (4), and [Ni(bpndc)(pytpy)(H2O)]·0.5H2O (5), (1,3-bdc = 1,3-benzenedicarboxylate, btc = 1,3,5-benzenetricarboxylate, bpndc = 4,4′-benzophenone dicarboxylate, tib = 1,3,5-tris(1-imidazolyl)benzene, Htpim = 2,4,5-tri(4-pyridyl)-imidazole, pytpy = 2,4,6-tris(4-pyridyl)pyridine). Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectroscopy and TG analyses. Compound 1 exhibits a new trinodal (3,4,4)-connected 3D self-penetrating framework with (83)2(63.82.9)2(84.9.10) topology. Compound 2 displays an interesting 2D → 3D polythreading framework constructed from sidearm-containing 2D 63-hcb nets. Compound 3 exhibits an unusual (2D → 3D) entangled array with the coexistence of polythreading and interdigitation self-assembled from sidearm-containing 2D double-edged nets. Compounds 4 and 5 both show an intriguing 3-fold interpenetrated PtS-type (4,4)-connected 3D framework containing meso-helices. In addition, the magnetic properties of compounds 1–5 have been investigated in the temperature range 2–300 K.

Metal nuclearity affects network connectivity: a series of highly connected metal–organic frameworks based on polynuclear metal clusters as secondary building units

Seven novel highly connected metal–organic frameworks (MOFs), formulated as [Co7(aobtc)3(bpy)2(μ3-OH)2(μ2-OH2)2(H2O)4]·4H2O (1), [Ni5(aobtc)2(bpy)2(μ3-OH)2(H2O)6]·4H2O (2), [Zn3(aobtc)2]·H2bpy·H2O (3), [Zn3(aobtc)2]·H2bpp·H2O (4), [Cd3(aobtc)2]·[Me2NH2]2·3H2O (5), [Co3(aobtc)2]·H2bpp·H2O (6) and [Mn3(aobtc)2]·H2bpy·2H2O (7) (H4aobtc = azoxybenzene-3,3′,5,5′-tetracarboxylic acid, bpy = 4,4′-bipyridine, bpp = 1,3-bis(4-pyridyl)propane) have been synthesized and characterized by elemental analyses, IR spectra, single-crystal X-ray diffraction, powder X-ray diffraction, and thermal analyses. Compound 1 is a 3D (4,4,14)-connected self-penetrating framework with (46)2(45·6)(430·526·631·74) topology based on hexanuclear clusters as 14-connected nodes. To our knowledge, compound 1 represents the highest connected self-penetrating topology presently known in the entangled system. Compound 2 displays a trinodal (4,4,10)-connected network with (46)(45·5)(410·518·612·75) topology based on tetranuclear clusters as 10-connected nodes. Compounds 3–7 exhibit (4,8)-connected flu nets based on trinuclear clusters as 8-connected nodes, and these five MOFs show similar structures but different pore volumes mainly associated with the change of the species of guest molecules. Structural analyses of 1–7 demonstrate that increasing the metal nuclearity is a practical method to obtain highly connected coordination networks based on metal clusters as nodes. In addition, the magnetic properties of 1, 2, 6, and 7 and the luminescence properties of compounds 3–5 have also been studied.

The impact of metal ions on photoinduced electron-transfer properties: four photochromic metal–organic frameworks based on a naphthalenediimide chromophore

Four novel photochromic metal–organic frameworks (MOFs) self-assembled from a naphthalenediimide-based ligand and different metal cations, [Zn2(BINDI)(DMA)2]·2DMA (1), [Cd(H4BINDI)(H2BINDI)]·4DMF (2), [Ca2(HBINDI)Cl(DMA)3]·DMA (3), [Ba4(BINDI)2(DMF)7]·7DMF (4) (H4BINDI = N,N′-bis(5-isophthalic acid)naphthalenediimide), have been synthesized and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analyses, IR spectroscopy and TG analyses. Compound 1 exhibits a 3D porous framework with an lvt topology based on paddle-wheel Zn2(COO)4 clusters and BINDI as four-connected nodes. Compound 2 features a porous threefold interpenetrating diamondoid framework. Compound 3 shows a microporous 2D double-layer architecture and compound 4 displays a porous twofold interpenetrated 3D network. Interestingly, these four MOFs exhibit reversible photochromic behaviors with a concomitant eye-detectable color change, but different coloration degrees. The comparison of these MOFs indicates that the electron-withdrawing capabilities of metal cations play a significant role in tuning the photosensitive properties of photochromic MOFs; this result may provide a feasible route for the design and synthesis of photochromic MOFs with controllable photoinduced electron-transfer properties. Moreover, the photomodulated photoluminescence properties of compounds 1–4, as well as the solvatochromic behaviors of 3 and 4 were also investigated. Additionally, compounds 1–3 are found to be useful as indicators for the qualitative detection of nitrite by naked eye recognition of color change.

Highly Stable Mesoporous Luminescence-Functionalized MOF with Excellent Electrochemiluminescence Property for Ultrasensitive Immunosensor Construction

In this work, a novel mesoporous luminescence-functionalized metal-organic framework (Ru-PCN-777) with high stability and excellent electrochemiluminescence (ECL) performance was synthesized by immobilizing Ru(bpy)2(mcpbpy)2+ on the Zr6 cluster of PCN-777 via a strong coordination bond between Zr4+ and -COO-. Consequently, the Ru(bpy)2(mcpbpy)2+ could not only cover the surface of PCN-777 but also graft into the interior of PCN-777, which greatly increased the loading amount of Ru(bpy)2(mcpbpy)2+ and effectively prevented the leaching of the Ru(bpy)2(mcpbpy)2+ resulting in a stable and high ECL response. Considering the above merits, we utilized the mesoporous Ru-PCN-777 to construct an ECL immunosensor to detect mucin 1 (MUC1) based on proximity-induced intramolecular DNA strand displacement (PiDSD). The ECL signal was further enhanced by the enzyme-assisted DNA recycling amplification strategy. As expected, the immunosensor had excellent sensitivity, specificity, and responded wide linearly to the concentration of MUC1 from 100 fg/mL to 100 ng/mL with a low detection limit of 33.3 fg/mL (S/N = 3). It is the first time that mesoporous Zr-MOF was introduced into ECL system to assay biomolecules, which might expand the application of mesoporous metal-organic frameworks (MOFs) in bioanalysis. This work indicates that the use of highly stable mesoporous luminescence-functionalized MOFs to enhance the ECL intensity and stability is a feasible strategy for designing and constructing high-performance ECL materials, and therefore may shed light on new ways to develop highly sensitive and selective ECL sensors.

A series of porous interpenetrating metal–organic frameworks based on fluorescent ligands for nitroaromatic explosive detection

Four porous interpenetrating metal–organic frameworks (MOFs), namely, [Cd2(Tipb)2(btc)Cl]·Gx (1), [Cd(Tipb)(tdc)]·Gx (2), [Cd(Tipb)(fdc)]·Gx (3), and [Cd5(Tipb)4(btc)2Cl2(DMF)2(H2O)5]·Cl2·Gx (4) (G = guest molecules, Tipb = 1,3,5-tris(p-imidazolylphenyl)benzene, btc = benzene-1,3,5-tricarboxylic acid, tdc = thiophene-2,5-dicarboxylic acid, fdc = furan-2,5-dicarboxylic acid, and DMF = N,N′-dimethylformamide) have been assembled from π-electron-rich ligands and cadmium salts. These four MOFs exhibit strong fluorescent emissions upon excitation at room temperature. Due to the presence of π-electron-rich N-donor ligands, the sensing sensitivities of compounds 1–3 towards electron-deficient nitroaromatic explosives such as 2,4,6-trinitrophenol (TNP), 2,4-dinitrotoluene (2,4-DNT), 1,3-dinitrobenzene (1,3-DNB), and nitrobenzene (NB) have been studied by fluorescence quenching experiments. The results indicate that compounds 1–3 are highly sensitive to TNP owing to the electron and energy transfers between MOFs and TNP. Furthermore, compounds 1–3 remain stable after quenching and exhibit good recyclability. Moreover, the adsorption properties of 1–3 have also been investigated.