Xu-Jia Hong

Temperature-/solvent-dependent low-dimensional compounds based on quinoline-2,3-dicarboxylic acid: structures and fluorescent properties.

A series of 0-D, 1-D, and 2-D metal-organic compounds through reactions of quinoline-2,3-dicarboxylic acid (2,3-H(2)qldc) with transition metal salts MCl(2), namely, M(2,3-Hqldc)(2)(H(2)O)(2) (M = Co(1), Zn(4) and Cd(7)), [M(3-qlc)(2)(H(2)O)(2)](n) (M = Co(2), Zn(5) and Cd(8)), M(2-qldc-3-OCH(3))(2)(CH(3)OH)(2) (M = Co(3) and Zn(6)) and [Cd(2,3-qldc-OCH(3))(μ(2)-Cl)](2n) (9) (where, 3-Hqlc = quinoline-3-carboxylic acid and 2-qldc-3-OCH(3) = 3-(methoxycarbonyl)quinoline-2-carboxylic acid), were synthesized and characterized by elemental analysis, IR, thermogravimetric analysis (TG), and single-crystal X-ray diffraction. When the temperature ranged from room temperature to 70 °C, three isomorphous mononuclear complexes 1, 4 and 7 were obtained in H(2)O/H(2)O + CH(3)OH. As the temperature rose further to above 90 °C, due to the decomposition of 2-position carboxyl group in ligand 2,3-H(2)qldc, the same reactions, respectively, produced three isomorphous 2-D layer-like structures 2, 5 and 8 with 4(4) topology in water. By contrast, when the mixed solvent of H(2)O + CH(3)OH at a 1 : 1 ratio (v/v) was applied, the three above-mentioned reactions respectively gave compounds 3, 6 and 9 with the 3-position esterification of 2,3-H(2)qldc. Compounds 3 and 6 are mononuclear and isomorphous, while complex 9 has a 1-D double-stranded chain-like structure connected by two μ(2)-Cl bridges. Obviously, these results reveal that the reaction temperature and solvent play a critical role in structural direction of these low-dimensional compounds. Meanwhile, the photoluminescent property of the selected compounds is also investigated.

Construction of four 3d–4f heterometallic pillar-layered frameworks containing left- and right-handed helical chains and a I− chemosensor

Four new heterometallic coordination complexes, namely, {[Zn4Ln2(imdc)4(SO4)(H2O)8]·4H2O}n [Ln = Nd (1), Sm (2), Eu (3), Gd (4); H3imdc = imidazole-4,5-dicarboxylic acid], were hydrothermally synthesized by the reactions of Ln2O3 with imidazole-4,5-dicarboxylic acid and ZnSO4·7H2O and characterized by single-crystal X-ray diffraction, infrared spectroscopy (IR), elemental analysis (EA), thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD). The single-crystal X-ray diffraction analyses reveal that these polymers are isostructural and possess an interesting 3D pillar-layered architecture with 424·64 topology, in which 2D layers constructed by alternately arranged 1D right-/left-handed helical chains of [Zn2(μ5-imdc)]n bridged via dimeric Eu2 units are pillared by μ2-SO42− and μ3-imdc3− anions. The liquid fluorescence of compounds 1–3 at room temperature shows that these complexes are very good chemosensors for I− ion, and the response of the sensor is based on fluorescence quenching of Zn–Ln MOFs by iodine ions.

2-Fold Interpenetrating Bifunctional Cd-Metal–Organic Frameworks: Highly Selective Adsorption for CO2 and Sensitive Luminescent Sensing of Nitro Aromatic 2,4,6-Trinitrophenol

A robust primitive diamond-type topology 3-D metal-organic framework (MOF) of {[Cd4(hbhdpy)2(bdc)3(DMA)2]·(H2O)4}n (1, DMA = N,N-dimethylacetamide) was constructed from the planar secondary building units of the dinuclear cadmium clusters, Cd2(μ2-O)2, and two linear organic linkers of the new multidentate Schiff base of 4-(2-hydroxy-3-methoxy-benzyli-denehydrazino-carbonyl)-N-pyridin-4-yl-benzamide (Hhbhdpy) through the solvothermal reaction. 1 presents a 2-fold interpenetrating network along with confined narrow channels and rich acylamide groups as well as potential metal open sites for excellent selective CO2 uptake over CH4/N2 and high luminescent response for 2,4,6-trinitrophenol (TNP) in DMA solution under ambient conditions. With 2-amino-1,4-dicarboxy-benzene (H2bdc-NH2) replacing H2bdc, an amine-functionalized MOF of {[Cd4(hbhdpy)2(bdc-NH2)3 (DMA)2]·(H2O)4}n (1-NH2) as an isomorphism of 1, was synthesized under the same reaction conditions. Compared with 1, the corresponding bifunctional features of 1-NH2 is more obvious. To the best of our knowledge, it is the first reported interpenetrating Cd-MOFs with highly sensitive luminescence response for TNP molecules combined with excellent selectivity for CO2/N2 and CO2/CH4.

A robust porous pillar-chained Cd-framework with selective sorption for CO2 and guest-driven tunable luminescence

A robust porous pillar-chained 3-D Cd-framework, {[Cd2(μ3-OH)2(cpt)2]·(H2O)}n (1) (Hcpt = 4-(4-carboxyphenyl)-1,2,4-triazole), containing 1-D square nanotubular channels with impressive selective sorption for CO2 over N2/H2 and interesting guest-driven tunable luminescence is reported.

Construction of three pH-dependent luminescent metal–organic frameworks with 3-(4-carboxyphen-yl)-1,3-benzoimidazole

Three luminescent metal–organic frameworks (MOFs) with 3-(4-carboxyphenyl)-1,3-benzoimidazole (HCPBm), named [Er(CPBm)3]n (1), [Zn(CPBm)2]n (2) and {Zn[Er(CPBm)(OH)(H2O)4]4·(ClO4)4·Cl2}n (3), have been synthesized using zinc(II) chloride, erbium(III) perchlorate and the ligand HCPBm under different pH conditions. Complex 1 obtained at pH = 5.5 exhibits a 1-D chain structure based on Er(III). At pH = 7.0, a 2-D Zn(II)-based layer 2 forms. The reaction at pH = 8.5 leads to a 2-D heteronuclear square grid layer 3 with a rare stacking fashion of ⋯ABCD⋯ in a 3-D supramolecular network. Compound 1 shows typical lanthanide Er(III) near-infrared emission, and compound 2 has strong fluorescent emission based on the ligand HCPBm. However, compound 3 presents sensitized near-infrared emission (λmax = 1500 nm) upon excitation of the Zn(II) unit in the visible region (400 nm) due to efficient energy transfer from the Zn(II) ion to the Er(III) units.

Anion-Dependent Assembly of Four Sensitized Near-Infrared Luminescent Heteronuclear ZnII–YbIII Schiff Base Complexes from a Trinuclear ZnII Complex

Four anion-dependent 0D Zn(II)-Yb(III) heterometallic Schiff base complexes, [YbZn2L2(OAc)4]·ClO4 (2), YbZnL2(NO3)3 (3), [(YbL)2(H2O)Cl(OAc)]2·[ZnCl4]2 (4), and YbZnL(OAc)4 (5), were assembled through central metal substitution or reconstruction from homotrinuclear Zn(II) complex {[(Zn(OAc)(H2O)L]2Zn}(ClO4)2·4H2O [1; HL = 2-ethoxy-6-[(pyridin-2-ylmethylimino)methyl]phenol] with different Yb(III)X3 salts [X = ClO4 (2), NO3 (3), Cl (4), and OAc (5)], in which the Zn(II)-sensitized near-infrared luminescent performances in the four complexes 2-5 are closely related to their structural models.

Two low-dimensional Schiff base copper(I/II) complexes: synthesis, characterization and catalytic activity for degradation of organic dyes

Two low-dimensional oxime-containing Schiff base copper(I/II) complexes with iodine–copper cluster [Cu2I4]2− bridges, namely, {[CuII4I3(pop)4]2(CuI2I4)}·(CH3CN)2·H2O (2) and [CuII4I2(pop)4(CuI2I4)·(CH3CN)]n (3) (Hpop = 2-(hydroxyimino)-N′-[1-(2-yridyl)ethylidene]propanehydrazone), have been synthesized from the reaction of [2 × 2] grid-like compound {[CuIII(pop)]4}2·4H2O (1) with equivalent CuI2I2 (iodine–copper clusters) under solvothermal conditions and characterized by elemental analysis (EA), infrared spectroscopy (IR), thermogravimetric analysis (TGA), and X-ray single-crystal/powder diffraction. The results show that 2 is a 0-D discrete structure from an assembly of one [Cu2I4]2− unit and two [2 × 2] molecular grids (1) via μ3-I atoms coordinating to CuI/CuII atoms. However, compound 3 presents a 1-D wave-like chain, which is constructed by coordination of μ2-I atoms from [CuI2I4]2− units with CuII atoms in [2 × 2] molecular grids (1). Moreover, catalytic experiments demonstrated that compounds 2 and 3 have promising visible-light-driven catalytic activity in degrading various organic dyes.

A series of temperature-dependent CdII-complexes containing an important family of N-rich heterocycles from in situ conversion of pyridine-type Schiff base

An efficient method for the synthesis of a wide variety of N-rich heterocycles has been systematically explored. The synthetic protocol involves a solvothermal in situ metal–ligand reaction of pyridine-type Schiff base N-(2-pyridylmethyl)-pyridine-2-carbaldimine (L) with Cd2+ ions, resulting in the efficient formation of nine temperature-dependent CdII-complexes 1–9 supported by six types of N-rich heterocycles L1–6. To the best of our knowledge, both the synthetic strategy with solvothermal in situ CdII-mediated Schiff base-conversion and N-rich heterocycle rings L1–2 as well as cis-L6 are reported for the first time. Meanwhile, plausible in situ formation mechanisms of L1–6 are also proposed.

Two samarium(III) complexes with tunable fluorescence from in situ reactions of 2-ethoxy-6-((pyridin-2-ylmethylimino)methyl)phenol with Sm3+ ion

Two samarium(III) complexes showing different luminescent intensity, namely Sm(HL1)2·NO3·2H2O (1) and [SmL2(C2H5OH)2·NO3]2 (2), were constructed via the solvothermal in situ lanthanide metal–ligand reactions of 2-ethoxy-6-((pyridin-2-ylmethylimino)-methyl)phenol (HL) from pyridin-2-ylmethanamine and 3-ethoxy-2-hydroxybenzaldehyde with Sm3+ ion at different temperatures, in which H2L1 resulted from C–C coupling dimerization of HL, while H2L2 from C–C coupling of HL and pyridin-2-ylmethanamine.

Efficient Encapsulation of Small S2-4 Molecules in MOF-Derived Flowerlike Nitrogen-Doped Microporous Carbon Nanosheets for High-Performance Li–S Batteries

Lithium-sulfur (Li-S) battery is regarded as one of the most promising next-generation efficient energy storage systems because of its ultrahigh theoretical capacity of 1675 mAh/g and energy density of 2600 Wh/kg accompanied by the environmental benignity and abundance from natural sulfur. However, the insulating nature of sulfur and the dissolution of the polysulfides Li2S n (4 ≤ n ≤ 8) seriously restrict its practical application. The metastable small sulfur molecules (S2-4) stored in microporous carbon (pore size of <0.6 nm) as the active materials can avoid the production of the soluble polysulfide and solve the shuttle effect thoroughly. In addition, the conductivity of sulfur can be also improved. However, the preparation of microporous carbon materials with reasonable pore size and unique morphology for efficiently encapsulating S2-4 is still challenging. Herein, three flowerlike microporous nitrogen-doped carbon nanosheets with the pore size of <0.6 nm (namely, FMNCN-800, -900, and -1000) as the cathode materials in Li-S batteries were obtained from temperature-dependent carbonization of the metal-organic framework (MOF), Zn-TDPAT, which was from the simply reflux reaction of N-rich ligand H6TDPAT with Zn(II) salt. Our study showed that the FMNCN-900 from carbonization of Zn-TDPAT at 900 °C has suitable pore volume and nitrogen content, accommodating small S2-4 molecules in its micropores with the mass uptake of about 45%. Meanwhile, the appropriate amount of the nitrogen doping and the unique nanostructure of the flowerlike carbon nanosheet in the FMNCN-900 can effectively support its fast electronic transmission and lithium-ion conduction. The resulting S@FMNCN-900 composite cathode material presents the excellent electrochemical property in the Li-S battery (here the carbonate as electrolytes) with a reversible capacity of about 1220 mAh/g at 0.1C after 200 cycles and even 727 mAh/g at 2C after the long-term cycle of 1000 with only around 0.02% capacity loss per cycle. Obviously, the results indicate that the delicate construction of MOF-derived nitrogen-doped microporous carbon nanosheet is a promising strategy to develop novel electrode material for high-performing Li-S batteries.