Probing the structures and chemical bonding of boron-boronyl clusters using photoelectron spectroscopy and computational chemistry: B(4)(BO)(n) (-) (n = 1-3)

The electronic and structural properties of a series of boron oxide clusters, B(5)O(-), B(6)O(2) (-), and B(7)O(3) (-), are studied using photoelectron spectroscopy and density functional calculations. Vibrationally resolved photoelectron spectra are obtained, yielding electron affinities of 3.45, 3.54, and 4.94 eV for the corresponding neutrals, B(5)O, B(6)O(2), and B(7)O(3), respectively. Structural optimizations show that these oxide clusters can be formulated as B(4)(BO)(n) (-) (n = 1-3), which involve boronyls coordinated to a planar rhombic B(4) cluster. Chemical bonding analyses indicate that the B(4)(BO)(n) (-) clusters are all aromatic species with two π electrons.     

2D sheet-like architectures constructed from main-group metal ions, 4,4'-bpno and 1,2-alternate p-sulfonatothiacalix[4]arene

Two novel 2D sheet-like complexes 1 and 2 have been prepared by reaction of p-sulfonatothiacalix[4]arene (TC4AS) with main-group metal ions (lead(II) or barium(II)) and 4,4'-bipyridine-N,N'-dioxide (4,4'-bpno). In both complexes 1 and 2, TC4AS molecules prefer 1,2-alternate conformation, forming 2D sheet-like layers in the presence of divalent ions and 4,4'-bpno ligand. The layers extend to 3D architectures via strong hydrogen bonding interactions. In addition, complexes 1 and 2 are thermally stable up to ca. 335 and 305 °C, respectively. It seems that the strong hydrogen bonds between the sheet-like layers impart the extraordinarily high degrees of stability to the structures. Further analysis indicates that complexes 1 and 2 are significantly different: (a) the divalent ions have different coordination environments due to the nature of the different ions; (b) TC4AS within complexes 1 and 2 connects to four Pb(II) or six Ba(II) ions, respectively; (c) 4,4'-bpno shows different connection modes; (d) in the solid state, complex 1 exhibits intense orange luminescence with triexponential decays, while complex 2 does not exhibit any obvious luminescence at cryogenic temperatures.     

Three novel organic-inorganic complexes based on decavanadate [V10O28]6- units: special water layers, open 3D frameworks and yellow/blue luminescences

Three unusual polyoxovanadate-based inorganic-organic hybrid complexes, [Zn(Im)(2)(DMF)(2)](2)[H(2)V(10)O(28)]·Im·DMF (1), [Zn(3)(Htrz)(6)(H(2)O)(6)][V(10)O(28)]·10H(2)O·Htrz (2) and {[Zn(3)(trz)(3)(H(2)O)(4)(DMF)](2)[V(10)O(28)]·4H(2)O}(n) (3) (Im = imidazole, Htrz = 1,2,4-triazole, DMF = N,N'-dimethylammonium) have been synthesized at room temperature via evaporative crystallization, and characterized by single-crystal X-ray diffraction. Complex 1 shows the structure of a discrete [V(10)O(28)](6-) cluster grafted by two [Zn(Im)(2)(DMF)(2)](2+) fragments through two bridged oxygen atoms, representing a rarely observed coordination mode. Complex 2 consists of a linear trinuclear Zn(II) unit bridging six Htrz ligands and a [V(10)O(28)](6-) cluster as the counter anion, where the extensive hydrogen-bonding interactions lead to {Zn(3)-V(10)}(SMF) and a special water layer involving (H(2)O)(36) rings, and consequently forms a unique 3D metal-organic-water supramolecular network. Complex 3 can be described as a 3,4-connected fsc-type network, and is the first example of open coordination 3D framework based on [V(10)O(28)](6-) and the other two different secondary building units, involving mononuclear and binuclear Zn(II)-Htrz motifs. The optical properties of complexes 1-3 in the solid state are investigated at room temperature. The results show that complexes 1 and 3 emit intense blue luminescences attributed to the ligands, while complex 2 exhibits an infrequent fluorescent property, emitting both blue and yellow luminescences at 472 and 603 nm simultaneously. Furthermore, powder X-ray diffraction and thermogravimetric analyses of 1-3 are also investigated, which demonstrate their high purities and thermal stabilities.     

Electrochemical performance of B and M phases VO2 nanoflowers

VO₂ exists in four phases, among which, the M/R phase VO₂ is well known for its reversible metal‐semiconductor phase transition at about 68 °C, and VO₂ (B) is a promising candidate cathode material to be applied in aqueous lithium‐ion battery owing to its proper electrode potential and layered structure. In this study, VO₂ (B) nanoflowers was synthesized via one‐step hydrothermal process and then successfully transformed into the VO₂ (M) by heat treatment. Electrochemical behaviors of the two samples were evaluated by cycling discharge and cyclic voltammetry (CV). The results showed that flower‐like VO₂ (B) had the first discharge capacity of 180.33 mAhg‐1, an outstanding value of 52.8% for the capacity retention after 50 cycles. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and Crystal Structure of a Pure Inorganic Network Based Tetra-Sodium Capped Sandwich-Type Polyanion

Abstract  

The synthesis and single-crystal structure of a Na-salt compound Na₁₀[Co₄(OH₂)₂(AsW₉O₃₄)₂]·32H₂O (1) was reported. Compound 1 crystallizes in triclinic system, space group P−1, with the lattice parameters: a = 11.6040(10) ?, b = 12.9361(13) ?, c = 17.396(2) ?, α = 97.4120(10)°, β = 106.8590(10)°, γ = 111.867(2)° and Z = 1. Compound 1 consists of a pure inorganic network based on tetra-sodium capped sandwich-type anionic clusters [Co₄(OH₂)₂(AsW₉O₃₄)₂]¹⁰⁻ bridged through Na–OH₂ subunits. The thermogravimetric and electrochemistry measurements had also been studied.     

Effects of oxide buffer layers on the microstructure and electrical properties of PLZST 2/87/10/3 antiferroelectric thin films

In the present work, the effects of oxide buffer layers, such as ZrO₂, CeO₂ and TiO₂, on the microstructure and electrical properties of (Pb_0.97La_0.02)(Zr_0.87Sn_0.10Ti_0.03)O₃ (PLZST 2/87/10/3) antiferroelectric (AFE) thin films were investigated systematically. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) pictures illustrated that the crystalline orientation and surface microstructure of PLZST 2/87/10/3 AFE thin films had a close relation with these oxide buffer layers. As a result, the final electrical properties of AFE films were tuned by these buffer layers. Electrical measurements result showed that the dielectric properties, polarization characteristic and current–field curves of AFE thin films could be tailored by selecting a proper oxide buffer layer.     

Investigation of the structure evolution process in sol-gel derived CaO-B2O3-SiO2 glass ceramics

A sol-gel method was used to prepare CaO-B₂O₃-SiO₂ (CBS) glass powder for making low-temperature cofired ceramics. This paper was focused on the mechanism of hydrolysis and polymerization and also on the structural evolution of xerogel at various temperatures. The xerogel was transformed into glass ceramics containing CaSiO₃ and CaB₂O₄ crystalline phases through nucleation and crystallization processes. The results indicated that the xerogel exhibits [BO₄] or [SiO₄] based three-dimensional network structure whose interstices Ca ions fill in, which becomes more orderly and stable after heat treatments. The CBS glass ceramics through controlled crystallization have a potential as electronic packaging materials.     

Coordination Polymer Nanobelts as an Effective Sensing Platform for Fluorescence‐enhanced Nucleic Acid Detection

In this communication, the application of coordination polymer nanobelts (CPNs) assembled from H₂PtCl₆ and 3,3′,5,5′‐tetramethylbenzidine (TMB) are explored as an effective fluorescent sensing platform for nucleic acid detection for the first time. The suggested method has a high selectivity down to single‐base mismatch. DNA detection is accomplished by the following two steps: (1) CPN binds fluorecent dye‐labeled single‐stranded DNA (ssDNA) probe via both electrostatic attraction and π‐π stacking interactions between unpaired DNA bases and CPN. As a result, the fluorescent dye is brought into close proximity to CPN and substantial fluorescence quenching occurs due to photoinduced electron transfer from the nitrogen atom in CPN to the excited fluorophore. (2) The hybridization of adsorbed ssDNA probe with its target generates a double stranded DNA (dsDNA). The duplex cannot be adsorbed by CPN due to its rigid conformation and the absence of unpaired DNA bases, leading to an obvious fluorescence enhancement.

     

Effects of Carbon Black on Chain Mobility and Dynamic Mechanical Properties of Solution Polymerized Styrene-Butadiene Rubber

The structure of the bound rubber, the ¹H NMR (nuclear magnetic resonance) relaxation time, and the crosslink density of the physical network and the glass transition, were studied for solution polymerized styrene-butadiene rubber (SSBR) filled by carbon black, to investigate the effects of carbon black on the chain mobility and dynamic mechanical properties. It was found by ¹H NMR analysis that the rubber chains were adsorbed on the surface of carbon black to form physical crosslinks and restrict the mobility of the chains, especially for some high-mobility units such as chain ends. It was calculated, according to the molecular weight between adjacent crosslinks, that the main motion units of the tightly adsorbed chains appeared to be similar in size to the chain segments. The glass transition temperature (T _g) obtained by differential scanning calorimetry (DSC) could not be used to judge the effect of carbon black on chain mobility, while the appearance and change of the loss-tangent (tan δ) peak at high temperature in dynamic mechanical thermal spectrometry (DMTS) test showed that there were three chain states: free chains, loosely adsorbed chains, and tightly adsorbed chains. The dynamic rheology test showed that the unfilled SSBR compound had the rheological characteristics of entangled chain networks; however the nonlinear viscoelasticities of the filled SSBR were related to the gradual disentanglement of adsorbed chains and free chains. The peaks in tan δ vs. temperature curves implied that the motion unit size decreased with the increase of bound rubber content, and the modulus vs. temperature curve showed an apparently lower mobility of adsorbed chains than that of free chains through the very low dependence of modulus on temperature for the highly filled compounds. The extremely high tensile modulus of the vulcanizate with 63.6% carbon black at room temperature also implied that the adsorbed chains were in the glass state due to their restriction by the carbon black.     

Preparation and Properties of Poly(ethylene terephthalate)/Silica Nanocomposites

A kind of poly(ethylene terephthalate) (PET)/Silica nanocomposite (PETS) was synthesized via in situ polymerization using the compatibility between silica nanoparticles and ethylene glycol (EG). Transmission electron microscopy (TEM) micrographs revealed that the silica nanoparticles were well dispersed in the PET matrix, the particle size was about 10 nm with narrow distribution, and there existed strong interaction between the particles and the polymer chains. Differential scanning calorimetry (DSC) results indicated that the thermal properties of PETS with 2 wt% silica (PETS‐2) are different from those of pure PET (PETS‐0). The properties of the as‐spun fibers show that the tenacity and LASE‐5 (load at a specified elongation of 5%) of PETS‐2 were higher than those of PETS‐0, while the heat shrinkage of PETS‐2 was lower than that of PETS‐0. We suggest that the increasing of crystallinity and the strong interface interaction of the nanocomposite caused the fibers of PETS‐2 to not only have higher tenacity and LASE‐5 but also to have lower heat shrinkage.