Xing-Po Wang

Single-Crystal to Single-Crystal Phase Transition and Segmented Thermochromic Luminescence in a Dynamic 3D Interpenetrated AgI Coordination Network

A new 3D Ag(I)-based coordination network, [Ag2(pz)(bdc)·H2O]n (1; pz = pyrazine and H2bdc = benzene-1,3-dicarboxylic acid), was constructed by one-pot assembly and structurally established by single-crystal X-ray diffraction at different temperatures. Upon cooling from 298 to 93 K, 1 undergo an interesting single-crystal to single-crystal phase transition from orthorhombic Ibca (Z = 16) to Pccn (Z = 32) at around 148 K. Both phases show a rare 2-fold-interpenetrated 4-connected lvt network but incorporate different [Ag2(COO)2] dimeric secondary building units. It is worth mentioning that complex 1 shows red- and blue-shifted luminescences in the 290-170 and 140-80 K temperature ranges, respectively. The variable-temperature single-crystal X-ray crystallographic studies suggest that the argentophilic interactions and rigidity of the structure dominated the luminescence chromism trends at the respective temperature ranges. Upon being mechanically ground, 1 exhibits a slight mechanoluminescence red shift from 589 to 604 nm at 298 K.

Three mixed-ligand coordination networks modulated by flexible N-donor ligands: syntheses, topological structures, and temperature-sensitive luminescence properties

Three new mixed-ligand metal–organic coordination networks based on tetrabromoterephthalic acid and different bis-imidazole or bis-triazole ligands, [Zn2(bmib)(tbtpa)2·2H2O]n (1), [Cd(ditb)(tbtpa)(H2O)2·2H2O]n (2), and [Zn(ditp)(tbtpa)]n (3) (bmib = 1,4-bis(2-methyl-1H-imidazol-1-yl)butane, ditb = 1,4-di(1H-1,2,4-triazol-1-yl)butane, ditp = 1,3-di(1H-1,2,4-triazol-1-yl)propane, H2tbtpa = tetrabromoterephthalic acid), have been synthesized under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction analyses, infrared spectroscopy (IR), elemental analyses, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Single-crystal X-ray diffraction analysis reveals that 1 features a 4-fold class IIIa interpenetrated dia framework strengthened by Br⋯Br halogen bonds. Complex 2 possesses an infinite 2D layer structure with a 44-sql topology, and the 2D sheets were further packed into the 3D supramolecular framework in an –ABAB– fashion which is reinforced by hydrogen bonds and Br⋯Br halogen bonds. Complex 3 is a 2D 63-hcb network incorporating [Zn2(tbtpa)2] cyclic subunits, and the 2D layers were further extended to a 3D supramolecular framework incorporating π⋯π interactions and Br⋯Br and Br⋯O halogen bonds. In 1–3, all flexible N-donor ligands and dicarboxylates are 2-connected linkers, but networks with diverse topologies are formed, which indicates the coordination preferential geometries of the central metal ion and that the coordination conformations and modes of the ligands have important influences on the resultant structures. Furthermore, there is no solid-state photoluminescence observed for 1–3 at 298 K, and only 2 and 3 are emissive when cooled to liquid nitrogen temperature. The nanosecond range of lifetimes of 2 and 3 in the solid state at 77 K reveals that their emission is fluorescent in nature.

Pb(II) metal–organic nanotubes based on cyclodextrins: biphasic synthesis, structures and properties

Two chiral lead metal–organic nanotubes (CD-MONT-2 and CD-MONT-3) based on β-cyclodextrin (β-CD) and γ-cyclodextrin (γ-CD) were synthesized through a biphasic solvothermal reaction. The lead ions were connected by two β-CD or γ-CD molecules through their glycosidic oxygen atoms to generate a discrete metal–organic nanotube containing a {Pb14} or {Pb16} metallamacrocycle, respectively. Guest solvents of cyclohexanol molecules were trapped in the cavity of the β-CD-based nanotube, whereas there were no solvents in the cavity of the γ-CD-based nanotube. These differences directly led to the formation of different 3D packing structures. Their properties including temperature-dependent photoluminescence, adsorption of I2 molecules and thermal-decomposition behaviors were studied.

A superior fluorescent sensor for Al3+ and UO22+ based on a Co(II) metal–organic framework with exposed pyrimidyl Lewis base sites

A robust 3D pcu Co(II) metal–organic framework (MOF) based on a designed bent pyrimidyl–biimidazole ligand, [Co2(dmimpym)(nda)2]n (1; dmimpym = 4,6-di(2-methyl-imidazol-1-yl)-pyrimidine, H2nda = 1,4-naphthalenedicarboxylic acid), was successfully synthesized under solvothermal conditions and characterized using single-crystal X-ray diffraction. Compound 1 has a 2-fold interpenetrated 6-connected pcu network based on a [Co2(COO)4] paddle-wheel secondary building unit (SBU). It contains exposed pyrimidyl Lewis base sites, has porosity, and exhibits ligand-based blue emission in the solid state, which render it suitable as a fluorescent sensor for the detection of metal ions. Fluorescence titration experiments reveal that 1 is highly selective for Al3+ with exclusively enhanced emission as compared to other metal ions, and the limit of detection (LOD) reaches as low as 0.7 μM. Importantly, 1 can be cycled at least five times without the loss of emission signals. Moreover, 1 is able to detect low concentration of uranyl ions via fluorescence quenching. The present study sheds light on the realization of the practical application of MOFs as luminescent sensors via tailoring of the ligand and extends the way towards low-cost transition metal-based MOF sensors.

General Assembly of Twisted Trigonal-Prismatic Nonanuclear Silver(I) Clusters

A general class of C3 -symmetric Ag9 clusters, [Ag9 S(tBuC6 H4 S)6 (dpph)3 (CF3 SO3 )] (1), [Ag9 (tBuC6 H4 S)6 (dpph)3 (CF3 SO3 )2 ]⋅CF3 SO3 (2), [Ag9 (tBuC6 H4 S)6 (dpph)3 (NO3 )2 ] ⋅NO3 (3), and [Ag9 (tBuC6 H4 S)7 (dpph)3 (Mo2 O7 )0.5 ]2 ⋅2 CF3 COO (4) (dpph=1,6-bis(diphenylphosphino)hexane), with a twisted trigonal-prism geometry was isolated by the reaction of polymeric {(HNEt3 )2 [Ag10 (tBuC6 H4 S)12 ]}n , 1,6-bis(diphenylphosphino)hexane, and various silver salts under solvothermal conditions. The structures consist of discrete clusters constructed from a girdling Ag9 twisted trigonal prism with the top and bottom trigonal faces capped by diverse anions (i.e., S(2-) and CF3 SO3 (-) for compound 1, 2×CF3 SO3 (-) for compound 2, 2×NO3 (-) for compound 3, and tBuC6 H4 S(-) and Mo2 O7 (2-) for compound 4). This trigonal prism is bisected by another shrunken Ag3 trigon at its waist position. Interestingly, two inversion-related Ag9 trigonal-prismatic clusters are dimerized by the Mo2 O7 (2-) ion in compound 4. The twist is amplified by the bulkier thiolate, which also introduces high steric-hindrance for the capping ligand, that is, the longer dpph ligand. Four more silver-sulfur clusters (namely, compounds 5-8) with their nuclearity ranging from 6-10 were solely characterized by single-crystal X-ray diffraction to verify the above-described synergetic effect of mixed ligands in the construction of Ag9 twisted trigonal prisms. Surprisingly, only cluster 1 emits yellow luminescence at λ=584 nm at room temperature, which may be attributed to a charge transfer from the S 3p orbital to the Ag 5s orbital, or mixed with metal-centered (MC) d(10) →d(9) s(1) transitions. Upon cooling from 300 to 80 K, the emission intensity was enhanced along with a hypsochromic shift. The good linear relationship between the maximum emission intensity and the temperature for compound 1 in the range of 180-300 K indicates that this is a promising molecular luminescent thermometer. Furthermore, cyclic voltammetric studies indicated that the diffusion- and surface-controlled redox processes were determined for compounds 1 and 3 as well as compound 4, respectively.

Five MOFs with different topologies based on anthracene functionalized tetracarboxylic acid: syntheses, structures, and properties

Five coordination polymers based on 5,5′-(2,3,6,7-tetramethoxyanthracene-9,10-diyl)diisophthalic acid (H4LOMe): [Mn4(LOMe)(OAc)2(μ3-OH)2(NMP)4(H2O)2]·2H2O (1), [Ni2(LOMe)0.5(H2LOMe)0.5(μ3-OH)(H2O)3]·6H2O (2), [Cd2(LOMe)(H2O)2(NMP)]·2DMF·NMP·H2O (3), [Co2(LOMe)(H2O)2]·2NMP·DMA·2H2O (4), [Zn2(LOMe)(H2O)2]·2NMP·2H2O·DOE (5) (NMP = N-methylpyrrolidone, DMF = N,N′-dimethylformamide, DMA = N,N′-dimethylacetamide, DOE = 1,4-dioxane) were prepared by solvothermal methods and characterized by elemental analysis (EA), single-crystal X-ray crystallography, powder X-ray diffraction (PXRD), infrared spectroscopy (IR), and thermogravimetric analyses (TGA). X-ray crystallography analysis shows that complex 1 bears a two-dimensional (2D) (4,4) network based on tetranuclear secondary building units, which are further assembled into a three-dimensional supramolecular structure via π⋯π stacking interaction; complex 2 displays a 3D framework with fsc topology based on 2D 44-sql layers and tetranuclear SBUs; complex 3 reveals a 3D PtS network via the LOMe bridging dimetal {Cd2O11} units; complexes 4 and 5 possess 3D open frameworks with a rarely reported 3-nodal (4,4,4)-connected nou network. Moreover, magnetic susceptibility measurement of complexes 1 and 2 confirm the presence of magnetic exchange coupling among the metal ions of tetranuclear clusters, and fluorescent spectra of complexes 1, 3 and 5 show emission signals in the blue region.

Anisotropic Assembly of Ag52 and Ag76 Nanoclusters

Although there has been an upsurge of interest in anisotropic assembly of inorganic nanoparticles, atomically precise self-assembly of anisotropic metal clusters is extremely rare. Herein, we presented two novel silver nanoclusters, Ag52 (SD/Ag23) and Ag76 (SD/Ag24), which are interiorly templated by five MoO42- and a pair of Mo6O228- anions, respectively, and coprotected by bridging RSH and terminal diphosphine ligands exteriorly. Regiospecific distribution diphosphine ligands on the surface and the arrangement of multiple molybdate templates within the nanoclusters synergetically tailor their shapes to anisotropic oblate spheroid and elongated rod, respectively. This work not only open up new avenues for the synthesis of silver nanoclusters with novel metal skeleton shapes and anisotropic surface structures but also give important insights for the anisotropic growth of silver nanoclusters through surface modifications or/and template organizations.

A temperature-sensitive luminescent Ag20 nanocluster templated by carbonate in situ generated from atmospheric CO2 fixation

A drum-like Ag20 nanocluster, [(CO32−)@Ag20(SBut)10(DMF)6(NO3)8] (1), has been synthesized by the unexpected carbonate-templated self-assembly of AgNO3 and AgSBut precursor. Structural analysis reveals that 1 contains centrosymmetric drum-like Ag20S10 clusters constructed from two Ag5S5 pentagrams and a Ag10 ring. The CO32− in situ generated from fixation of atmospheric CO2 lies on the center of the cluster and acts as an anion template to direct the formation of 1. Interestingly, bright-green photoluminescence of 1 is switched on when cooled with liquid nitrogen.

Solvent-Controlled Phase Transition of a CoII-Organic Framework: From Achiral to Chiral and Two to Three Dimensions

An unprecedented reversible dynamic transformation is reported in a metal-organic framework involving bond formation, which is accompanied by two important structural changes; achiral to chiral and two- to three-dimensions. Using two bent organic ligands (diimpym=4,6-di(1H-imidazol-1-yl)pyrimidine; H2 npta=5-nitroisophthalic acid) and CoII (NO3 )2 ⋅6 H2 O the coordination polymer Co(diimpym)(npta)⋅CH3 OH, (1⋅CH3 OH), was obtained solvothermally. Its structure consists of knitted pairs of square layers (44 -sql net) of five-coordinated Co and disordered methanol, and it crystallized in the achiral Pbca space group at room temperature. It undergoes a single crystal to single crystal (SC-SC) transformation to a 3D interpenetrated framework (α-polonium-type net, pcu) of six-coordinated Co and ordered methanol in the chiral P21 21 21 space group below 220 K. Most unusual is the dynamic temperature-dependent shortening of a Co⋅⋅⋅O connection from a non-bonded 2.640 Å (298 K) to a bonded 2.347 Å distance (100 K) transforming the square pyramidal cobalt polyhedron to a distorted octahedron. The desolvated crystals (1) obtained at 480 K retain the full crystallinity and crystallize in the achiral Pbca space group between 100 and 298 K but the dynamic shortening of the Co⋅⋅⋅O distance connecting the layers into the 3D pcu framework structure is observed. Following post-synthetic insertion of ethanol (1⋅CH3 CH2 OH) it does not exhibit the transformation and retains the knitted 2D achiral Pbca structure for all temperatures (100-298 K) and the ethanol is always disordered. The structural analyses thus conclude that the ordering of the methanol induces the chirality while the available space controls the dynamic motion of the knitted 2D networks into the 3D interpenetrated framework. Consequently, 1 selectively adsorbs CO2 to N2 and exhibits Type-III isotherms indicating dynamic motion of the 2D networks to accommodate the CO2 at 273 and 298 K in contrast to the rigidity of the 3D framework at 77 K preventing N2 from penetrating the solid. The magnetic properties are also reported.

Atom-Precise Polyoxometalate–Ag2S Core–Shell Nanoparticles

Atomically precise polyoxometalate-Ag2 S core-shell nanoparticles were generated in a top-down approach under solvothermal conditions and structurally confirmed by X-ray single-crystal diffraction as an interesting core-shell structure comprising an in situ generated Mo6 O22 (8-) polyoxometalate core and a mango-like Ag58 S38 shell. This result demonstrates the possibility to integrate polyoxometalate and Ag2 S nanoparticles into a core-shell heteronanostructure with precisely controlled atomical compositions of both core and shell.