Yan-Li Gai's research while affiliated with Jiangsu Normal University and other places

Two novel compounds, named [Ti2Na4(BTC4A)2(μ6-O2−)(CH3O−)2·2H2O·2DMA] (1) and [Ti4(BTC4A)(OH−)4(EtO−)6(iPrO−)2] (2) (H4BTC4A= p-tert-Butylthiacalix [4] arene), have been synthesized and characterized. Single crystal diffraction shows that compound 1 features a dumbbell-like molecule based on an octahedral Ti2Na4 core and two BTC4A4− ligands with cone conformation. Compound 2 is composed of a bi-titanium(IV) unit and a BTC4A4− ligand with 1,2-alternate conformation. The estimated optical bandgaps of compounds 1 and 2 are 2.87 and 1.97 eV, respectively, which are smaller than that of TiO2. Moreover, compounds 1 and 2 display much higher and more efficient photocatalytic degradation abilities for methylene blue than TiO2 under visible light irradiation.

Two novel lead-based coordination polymers, namely [Pb(cbdcp)]·0.5H2O·0.5CH3OH (1) and [Pb(cbdcp)] (2), have been solvothermally constructed by using a zwitterionic ligand 4-carboxy-1-(3,4-dicarboxy-benzyl)-pyridinium chloride (abbreviated as H3cbdcpCl). Compound 1 has a three-dimensional framework displaying a valence-bonded SrAl2 topology with the 4²·6³·8 symbol, while compound 2 has a two-dimensional sheet structure that can be simplified into a three-dimensional π⋯π interaction-connected topology with the {4⁴·6²}2{4⁸·6¹⁵·8⁵} symbol. Notably, compound 1 proved to be a promising potential luminescent sensor capable of selectively detecting anions, cations and small organic molecules, especially Cr2O7²⁻, CrO4²⁻, Fe³⁺ and nitrobenzene.

A novel silicotungstate-based silver(I) compound, formulated as [{Ag8(H3mtz)12}{SiW12O40}2]·8H2O (1) (H3mtz = 3-Mercapto-1,2,4-triazole) has been hydrothermally synthesized. This compound was identified by the single-crystal X-ray diffraction, and also characterized by FT-IR, UV, TG, PXRD and elemental analyses. The data show that it possesses the octanuclear silver(I) clusters and the anionic silicotungstates, which were connected via the hydrogen bonds and weak Ag–O bonds. Interestingly, the estimated optical bandgap of compound 1 is 1.95 eV, which falls into the range of semiconductors.

Five d10 transition-metal clusters, {[Zn15(2,6-Hbptp)- (2,6-bptp)7(μ2-O)4(μ2-OH)4(HCOO)2(NO3)(H2O)2]·20H2O} (1), {[Zn8(2,6-Hbptp)(2,6-bptp)5(μ3-O)2]·(ClO4)·7H2O} (2), {[Cd8(2,6-Hbptp)2(2,6-bptp)4(μ3-O)2]·(NO3)2·10H2O} (3), {[Ag7(2,6-Hbptp)(2,6-bptp)3]·4H2O·CH3OH}n (4), and {[Ag6(2,6- Hbptp)2(2,6-bptp)2][Ag6(2,6-Hbptp)2(2,6-bptp)2]2·30H2O·4CH3OH} (5), based on bent ligand 2,6-bis[3-(pyrazin-2-yl)-1,2,4- triazolyl]pyridine (2,6-H2bptp) have been synthesized. Compound 1 exhibits a novel fanlike Zn15 cluster, which is the highest-nuclearity Zn cluster with 2,6-H2bptp reported thus far. In 2 or 3 (M = Zn/Cd), each ligand coordinates to three M2+ ions, to form an M8L6 cluster. The structure of compound 4 is a Ag6 cluster-based 1D chain, where each hexanuclear [Ag6(2,6-Hbptp)(2,6-bptp)3]− cluster links its equivalent ones via sharing the Ag atom. Compound 5 contains two kinds of Ag6 clusters, and the alternating arrangement of them gives the final structure. It is worth mentioning that the Ag−Ag bond distances in 4 and 5 are relatively very short and suggest a closed-shell d10−d10 argentophilic interaction. The luminescence properties of compounds 1−5 have been researched at ambient and low temperatures. Interestingly, the emission intensities of 1−5 increase gradually upon cooling. A new strong emission band for 4 appears at 610 nm exhibiting red-orange luminescence. The low-energy emissions (620 nm) of 5 gradually blue shift to shorter wavelengths.

An example of structural evolution from inclined polycatenation to parallel polyrotaxane-like interpenetration is demonstrated by modifying the (6,3) layer. Notably synergies of co-ligand binding mode and metal coordination geometry provide the appropriate constituent motifs necessary to instill this entanglement variation.

Reaction of europium sulfate octahydrate with p-terphenyl-3,3″,5,5″-tetracarboxylic acid (H4ptptc) in a mixed solvent system has afforded three new coordination polymers formulated as {[Eu(ptptc)0.75(H2O)2]·0.5DMF·1.5H2O}n (1), {[Me2H2N]2 [Eu2(ptptc)2(H2O)(DMF)]·1.5DMF·7H2O}n (2), and {[Eu(Hptptc)(H2O)4]·0.5DMF·H2O}n (3). Complex 1 exhibits a three-dimensional (3D) metal-organic framework based on {Eu2(μ2-COO)2(COO)4}n chains, complex 2 shows a 3D metal-organic framework constructed by [Eu2(μ2-COO)2(COO)6](2-) dimetallic subunits, and complex 3 features a 2D layer architecture assembling to 3D framework through π···π interactions. All complexes exhibit the characteristic red luminescence of Eu(III) ion. The triplet state of ligand H4ptptc matches well with the emission level of Eu(III) ion, which allows the preparation of new optical materials with enhanced luminescence properties. The luminescence properties of these complexes are further studied in terms of their emission quantum yields, emission lifetimes, and the radiative/nonradiative rates.

Two novel 3D porous metal–organic frameworks, {[Zn2(bpt)(btc)]·4H2O}n (1) and {[Cd2(bpt)(btc)(H2O)]·(DMA)2}n (2) (DMA = N,N-dimethylacetamide), were prepared based on 3,5-bis(pyrazinyl)-1,2,4-trizole (Hbpt) with the auxiliary ligand 1,3,5-benzenetricarboxylic acid (H3btc). Complex 1 could be described as a (3,6)-connected binodal 3D network with rutile topology and Schläfli symbol of (4.62)2(42.610.83), where its coordination framework exhibits a high thermal stability up to 420 °C as well as excellent boiling-water resistance. Complex 2 shows a (3,6,8)-connected trinodal 3D framework with a Schläfli symbol of (4.62)2(414.612.82)(44.610.8), which has not been reported previously. Interestingly, the gas-adsorption investigation discloses that complex 1 possesses a high enthalpy of H2 adsorption (9.6 kJ mol−1). Intensive solid-state fluorescence spectra of complexes 1 and 2 have also been determined.

Hydrothermal synthesis has afforded five divalent zinc coordination polymers containing 4-(4-carboxyphenyl)-2,2':6',2''-terpyridine (HL1) or its isomer 4-(4-carboxyphenyl)-2,2':4',4''-terpyridine (HL2), with or without the addition of auxiliary ligands, 1,3,5-benzenetricarboxylic acid (H3btc) and 1,4-benzenedicarboxylic acid (H2bdc). Their structures have been characterized by single crystal X-ray analyses and further characterized by infrared spectra, elemental analyses, powder X-ray diffraction, thermogravimetric analyses and photoluminescent spectra. Across this series, the ππ interactions have a dramatic impact on the self-assembly of these entanglement structures, in either case it can exert an important structure-directing role. In addition, the disposition of pyridine nitrogen atoms in ligands also plays a large role in structure direction in this system. Complex is a 2D + 2D→3D inclined polycatenated coordination polymer based on the resulting array of 2D (6,3) layers constructed by 1D→2D ππ directed self-assembly. Complex is assembled into a 3D framework by means of 1D + 1D→3D mutual interdigitation based on 1D→1D self-assembly driven by ππ stacking interactions. Complex shows a 2D + 2D→3D interdigital network involving 2D + 2D→2D parallel interpenetrated and 2D + 2D→2D interdigital (4,4) layer motifs. Complex displays a 2D + 2D→3D polythreaded framework based on a 2D (4,4) network comprised of alternating rings and rods. Complex is a (3,4)-connected 3D framework with topology (4.8(2).10(3))(4.8(2)). In comparison with covalently connected entanglements, such ππ directing self-assembly of entanglements are far less explored, especially, polycatenane based on 1D chain motifs and polythread based on 2D layer motifs are rarely reported. Furthermore, the luminescent properties of complexes at room temperature have also been studied in detail herein.

Two new bismuth arsenites with two different structural types, namely, Bi2O(AsO3)Cl (1), Bi8O6(AsO3)2(AsO4)2 (2), have been synthesized by the solid-state reactions. Compound 1 exhibits novel 2D bismuth arsenite layers with Bi4O4 rings capped by oxide anions, which are further interconnected by Bi–Cl–Bi bridges into a 3D network. Compound 2 contains both arsenite and arsenate anions, its 3D structures are based on 1D bismuth arsenite and 1D bismuth arsenate chains both along b-axis, which are interconnected by oxide anions via Bi–O–Bi bridges, forming 1D tunnels of Bi4As4 8-membered rings (MRs) along b-axis, the lone pairs of the arsenite groups are orientated toward the centers of the above tunnels. Thermogravimetric analysis indicated that both compounds display high thermal stability. Optical property measurements revealed that they are wide band-gap semiconductors. Both compounds display broad green-light emission bands centered at 506 nm under excitation at 380 and 388 nm.

A series of novel two-dimensional (2D) lanthanide coordination polymers with 4-hydroxyquinoline-2-carboxylate (H(2)hqc) ligands, [Ln(Hhqc)(3)(H(2)O)](n)·3nH(2)O (Ln = Eu (1), Tb (2), Sm (3), Nd (4), and Gd (5)) and [Ln(Hhqc)(ox)(H(2)O)(2)](n) (Ln = Eu (6), Tb (7), Sm (8), Tm (9), Dy (10), Nd (11), Yb (12), and Gd (13); H(2)ox = oxalic acid), have been synthesized under hydrothermal conditions. Complexes 1-5 are isomorphous, which can be described as a two-dimensional (2D) hxl/Shubnikov network based on Ln(2)(CO(2))(4) paddle-wheel units, and the isomorphous complexes 6-13 feature a 2D decker layer architecture constructed by Ln-ox infinite chains cross-linked alternatively by bridging Hhqc(-) ligands. The room-temperature photoluminescence spectra of complexes Eu(III) (1 and 6), Tb(III) (2 and 7), and Sm(III) (3 and 8) exhibit strong characteristic emissions in the visible region, whereas Nd(III) (4 and 11) and Yb(III) (12) complexes display NIR luminescence upon irradiation at the ligand band. Moreover, the triplet state of H(2)hqc matches well with the emission level of Eu(III), Tb(III), and Sm(III) ions, which allows the preparation of new optical materials with enhanced luminescence properties.