Comparison of the effects of FePO4 and FePO4·2H2O as precursors on the electrochemical performances of LiFePO4/C

Carbon-coated LiFePO₄/C composite as cathode materials is synthesized by solid-state method using anhydrous FePO₄ and hydrous FePO₄·2H₂O as precursors.The effects of sintering temperature and carbon content on the properties of LiFePO₄/C composite are compared by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and charging–discharging test. The crystallinity, morphology, and particle size distribution of these two precursors are compared to investigate their effect on the electrochemical performances of LiFePO₄/C composite. Compared with hydrous FePO₄·2H₂O, anhydrous FePO₄ has good crystallinity, uniform particle morphology and symmetrical size distribution, contributing to LiFePO₄/C composite have excellent electrochemical performances. Due to the dehydration of hydrous FePO₄·2H₂O during synthesis, uneven distribution of carbon content and carbon layer is coated on LiFePO₄ surface, deteriorating the electrochemical performance of LiFePO₄/C composite. When anhydrous FePO₄ was used as the precursor, the LiFePO₄/C composite sintered at 700 °C with carbon content of 0.4 by molar ratio show high discharge capacity and stable cycling performance, with discharge capacity of 106.3 mA h g⁻¹ at 10 C, and a capacity retention rate of 99.2% after 200 cycles at 1 C.     

Polyaniline‐supported platinum‐hydrous ruthenium oxide nanocomposite as electrocatalyst for methanol oxidation

A novel composite electrode is fabricated through the electrodeposition of hydrous ruthenium oxide (RuO₂·xH₂O) and platinum (Pt) particles into the matrix of polyaniline (PANI). Scanning electron microscopy reveals that RuO₂·xH₂O and Pt particles are homogeneously distributed into the matrix of PANI. A comparison of the sizes of Pt and RuO₂·xH₂O particles incorporated into the PANI film reveals that Pt particles are smaller in sizes as compared with the sizes of RuO₂·xH₂O particles. The catalytic activity of composite electrodes was evaluated for the oxidation of methanol by using cyclic voltammetry and chronoamperometry. A relatively high catalytic current was noticed for the oxidation of methanol (2.37 mA/cm²) at PANI‐Pt‐RuO₂·xH₂O electrode (+0.6 V (V vs. Ag/AgCl) in comparison to oxidation current at PAN‐Pt (1.27 mA/cm²) electrode. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Effect of steam on the acid strength of H3PW12O40/SiO2 · nH2O and its application in skeletal isomerization of n-butane

The effect of steam on the acid strength of H₃PW₁₂O₄₀ (HPW)/SiO₂ · nH₂O was determined by the Hammett indicators. When the steam content in N₂ was 1.6%, the acidity (H₀ > −13.7) of HPW/SiO₂ · nH₂O could be kept for over 10 h at 300 °C, but for only 2 h when steam was lacking. When it was used as a catalyst for skeletal isomerization of n-butane to isobutane at 300 °C, the HPW/SiO₂ · nH₂O showed stability in the presence of steam (1.6% in feed) better than that without steam, due to a suppression of the loss of crystalline water.     

Hexachloroplatinate(IV) anion-induced cucurbit[5]uril and cucurbit[8]uril supramolecular assemblies with linear channels

Two Q[n]-based porous compounds, Q[5]·[PtCl₆]^2 −·2H₃O·12H₂O and 2Q[8]·[PtCl₆]^2 −·2H₃O·74H₂O in cooperating the hexachloroplatinate(IV) anion ([PtCl₆]^2 −) as an inorganic structure directing agent are demonstrated. The driving forces for the formation of such novel Q[n]-based porous compounds are considered to be the outer surface interactions of Q[n]s, including dipole interactions between Q[n]s and ion-dipole interactions between [PtCl₆]^2 − anions and Q[n]s. Moreover, the Q[5]-based porous compound displays absorption distinctness for tetrachloromethane, whereas the Q[8]-based porous compound displays absorption distinctness for methanol.     

Two corrugated 2D bilayer (63)(658) topological coordination polymers: Synthesis,structure, and water-induced reversible transformation

Two stable supramolecular microporous polymers with double-layer structures, [Co(AIP)(BPY)_0.5 · H₂O]_n · 2nH₂O (1) and [Ni(AIP)(BPY)_0.5 · H₂O]_n · 2nH₂O (2), were constructed from AIP (5-aminoisophthalate) and BPY (4,4′-bipyridine) under hydrothermal conditions. Both of them exhibit rarely reported (3,4)-connected (6³)(6⁵8) topology and interesting water-induced reversible transformation properties that are confirmed by PXRD studies.     

pH-controlled the formation of 4-sulfocalix[4]arene-based 1D and 2D coordination polymers

Three manganese/4-sulfocalix[4]arene complexes, namely, {H[(C₂₈H₂₀O₁₆S₄)Mn(H₂O)₄Mn_0.5(H₂O)₂]}_n ·6nH₂O (1), {NH₄[(C₂₈H₂₀O₁₆S₄)Mn(H₂O)₄Mn_0.5(H₂O)₂]}_n · 5nH₂O (2), [(C₂₈H₂₀O₁₆S₄)Mn₂(H₂O)₈]_n · 6nH₂O (3), have been synthesized under different pH conditions. Complex 1, which exhibits a one-dimensional (1D) structure, is formed at [H⁺] = 2.0 mol L⁻¹. Reaction at pH 4 leads to another one-dimensional (1D) coordination polymer of 2. At pH 5, a two-dimensional (2D) coordination polymer of complex 3 is formed, showing clearly structural effects on pH response.     

Synthesis of a graphene–carbon nanotube composite and its electrochemical sensing of hydrogen peroxide

Graphene, whose structure consists of a single layer of sp²-hybridized carbon atoms, provides an excellent platform for designing composite nanomaterials. In this study, we have demonstrated a facile process to synthesize graphene–multiwalled carbon nanotube (MWCNT) composite. The graphene–MWCNT composite material is endowed with a large electrochemical surface area and fast electron transfer properties in Fe(CN)₆^3?/4? redox species. A graphene–MWCNT composite modified electrode exhibits good performance in terms of the electrocatalytic reduction of H₂O₂; a sensor constructed from such an electrode shows a good linear dependence on H₂O₂ concentration in the range of 2 × 10^?5 to 2.1 × 10^?3 mol L^?1. The detection limit is estimated to be 9.4 × 10^?6 mol L^?1. This study provides a new kind of composite modified electrode for electrochemical sensors.     

Effects of substrates on the capacitive performance of RuOx·nH2O and activated carbon-RuOx electrodes for supercapacitors

The electrochemical energy storage and delivery on the electrodes composed of hydrous ruthenium oxide (RuO_x·nH₂O) or activated carbon-hydrous ruthenium oxide (AC-RuO_x) composites are found to strongly depend on the substrate employed. The contact resistance at the active material-graphite interface is much lower than that at the active material-stainless steel (SS) mesh interface. Thin films of gold plus RuO_x·nH₂O deposited on SS meshes (RuO_x/Au/SS) are found to greatly improve the poor contact between SS meshes and electrode materials. The maximum specific capacitance (C_S,RuOx) of RuO_x·nH₂O, 1580 F g⁻¹ (measured at 1 mV s⁻¹), very close to the theoretic value, was obtained from an AC-RuO_x/RuO_x/Au/SS electrode with 10 wt.% sol-gel-derived RuO_x·nH₂O annealed in air at 200 °C for 2 h. The highly electrochemical reversibility, high-power characteristics, good stability, and improved frequency response of this AC-RuO_x/RuO_x/Au/SS electrode demonstrate its promising application potential in supercapacitors. The ultrahigh specific capacitance of RuO_x·nH₂O probably results from the uniform size distribution of RuO_x·nH₂O nanoparticles, ranged from 1.5 to 3 nm which is clearly observed from the high-resolution transmission electron microscopy (HRTEM).     

Unusual metal–organic network constructed from Zn(II), benzenetricarboxylate and bis(1,2,4-triazolyl)pyridine

Hydrothermal reaction of ZnSO₄ · 7H₂O with 1,3,5-benzenetricarboxylic acid (H₃btc) and 2,6-bis(1,2,4-triazolyl)pyridine (btp) afforded a novel metal–organic network {[Zn₃(btc)₂(btp)₂(H₂O)₂] · 4H₂O}_n (1) with a supramolecular cocrystal [H₃btc · btp · H₂O]_n (2). The complex 1 exhibits an unusual network containing two molecular squares and a rectangle. The networks interpenetrate to make a 3D metal–organic framework, which is quite thermal stable. Compound 2 shows a 2D supramolecular network assembled through strong hydrogen bonds.     

Preparation of WC/Co composite powders by electroless plating

Ultra-fine WC/Co composite powders were prepared by electroless plating in this study. The Co layers with an average thickness of 50–100 nm were uniformly and completely covered on raw WC particles with a diameter of 0.3–0.5 µm. The influences of electroless plating conditions on the composites were investigated. The Co layer covering on WC particles was controlled by the content of CoSO₄·7H₂O, pH value and bath temperature. With increasing the content of CoSO₄·7H₂O up to 25 g/L, both the weight gain and the plating rate markedly increased. However, when the content of CoSO₄·7H₂O further increased to 30 g/L, while the weight gain displayed a slight decrease, the plating rate continued to increase moderately. Moreover, with the increase of pH value from 9.5 to 11, both the weight gain and the reaction time decreased. Furthermore, the plating rate exhibited an exponential relationship with the bath temperature. When the pH value, bath temperature and the concentration of CoSO₄·7H₂O are 10, 80 °C and 25 g/L respectively, the weight gain of Co-coated WC composite powders is 185.1 mg/g.     

Two trimeric tri-TiIV-substituted Keggin tungstogermanates based on tetrahedral linkers

Two trimeric nine-Ti^IV contained tungstogermanates K₁₄{K ⊂ [(Ge(OH)O₃)(GeW₉Ti₃O₃₈H₂)₃]} · 42H₂O 1 and K₁₀{K ⊂ [(SO₄)(GeW₉Ti₃O₃₈H₃)₃] · 40H₂O 2 have been conventionally synthesized and characterized by elemental analysis, IR, TG and single-crystal X-ray diffraction. They were constructed from three tri-substituted A-α-[GeW₉Ti₃O₃₈] and GeO₄/SO₄ tetrahedral linker. They display the first example of trimeric titanium-substituted tungstogermanates, which contain both Ti–O–Ti and Ti–O–Ge/Ti–O–S bridges.     

1D helical ZnII metal–organic polymers: Syntheses,structures and fluorescent properties

Hydrothermal reactions of 1,1′-(1,5-pentanediyl)bis-1H-benzimidazole (pbbm) with ZnCl₂ afford two 1D helical metal–organic polymers {[ZnCl₂(pbbm)] · (H₂O)_1/8}_n (1) and {[Zn(pbbm)₂] · Cl₂ · (H₂O)_1/2}_n (2). Polymer 1 features a 1D single helical architecture, whereas 2 possesses a 1D cationic double helical chain framework. Photoluminescence investigations reveal that both of them display strong emissions in the solid state at room temperature, which could originate from a ligand-to-ligand charge-transfer (LLCT) transition, as confirmed by the molecular orbital (MO) calculations.     

Three d10 coordination polymers based on rigid ligands with flexible functional groups: Syntheses,structures and luminescence

Three coordination polymers, namely, {[Zn(L)(BPY)]·DMF·H₂O}_n (1), {[Zn(L)(TPY)]·0.5H₂BDC·H₂O}_n (2), {[Cd(L)(H₂O)₂]·DMF}_n (3), have been synthesized based on a rigid linear carboxylate ligand (H₂L = 2′,5′-dimethoxy-[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid) and different lengths of pyridine ligands (TPY = 4,3′:5′,4″-terpyridine; BPY = 4,4′-bipyridine). These complexes have been characterized by single crystal X-ray diffraction, infrared spectroscopy, thermogravimetry, elemental analysis, and powder X-ray diffraction measurements. Complex 1 is a 6-connected 3-fold interpenetrating pcu net with point symbol {4¹² ∙ 6³}, 2 and 3 can be simplified as 4-connected sql nets with point symbol {4⁴ ∙ 6²}. In addition, their photoluminescent properties are also investigated in detail.     

A novel three dimensional 3d–4f heterometallic coordination framework with 2, 2′-bipyridine-3-carboxylate and oxalate ligands

The 3D heterometallic polymeric complex 1 {[Nd₂Cu₂(L)₂ (OXA)₄·2(2H₂O)]·2(3H₂O)}_n (HL = 2, 2′-bipyridine-3-carboxyic acid, OXA = oxalate) was obtained from hydrothermal reaction of Nd₂O₃, Cu(ClO₄)₂, HL and oxalic acid in the presence of ethanol and water. X-ray single crystal diffraction investigation of the polymeric complexes {[Nd₂Cu₂(L)₂(OXA)₄·2(2H₂O)]·2(3H₂O)}_n exhibits an interesting and novel topological structure.     

Conformational isomerism of a flexible fluorinated bis-pyridinecarboxamide ligand in the structural direction of two distinct layered CuII coordination polymers

Reaction of a flexible pyridinecarboxamide ligand N,N′-[(2,3,5,6-tetrafluoro-1,4-phenylene) bis(methylene)]bis(pyridine-4-carboxamide) (H₂tfpbbp) with Cu^II chloride or perchlorate affords two coordination polymers {[Cu(H₂tfpbbp)(tfpbbp)(H₂O)] · 2DMF · 4H₂O}_n (1) and {[Cu(H₂tfpbbp)₂(ClO₄)₂] · 3H₂O}_n (2). Both complexes have 2-D (4,4) layered networks extended by the exo-bidentate bridging ligands, which however consist of distinct [Cu–ligand]₄ meshes owing to the conformational difference of ligands. Their spectroscopic, thermal, and fluorescence properties have also been investigated.     

Co-existence of heterometallic Zn2Er and ZnEr arrayed chromophores for the sensitization of near-infrared (NIR) luminescence

With the Zn-Schiff-base [ZnL(Py)] from the simple Salen-type Schiff-base ligand H₂L (H₂L = N,N′-bis(salicylidene)ethylene-1,2-diamine) as the precursor, two co-crystallized heterometallic (Zn₂Ln and ZnLn array) complexes [Zn₂Ln(L)₂(Py)₂(NO₃)₂]·[ZnLn(L)(Py)(NO₃)₃(H₂O)]·NO₃·mMeOH·nS (Ln = Er(1), S = CH₃CN, m = 2, n = 1 or Gd(2), S = H₂O, m = 1, n = 3) were obtained by the further reaction with Ln(NO₃)₃·6H₂O, respectively. The result of their photophysical properties shows the intramolecular effective energy transfer has been demonstrated in the Zn₂Er and ZnEr arrayed complex 1, and the co-existence of different chromophores should be a potentially new way to the fine-tuning properties of NIR luminescence from Er³⁺ ions.     

Synthesis and characterization of a new 2D trimetallic Mn/Ca/Na complex

A new tri-metallic Mn/Ca/Na coordination polymer, {[Mn₃NaCa(sal)₆(H₂O)₆]·7H₂O}_n (1·7H₂O), has been synthesized and characterized by single crystal X-ray diffraction, IR spectroscopy, and magnetic measurements. The X-ray analysis shows 1 consists of a 2D homochiral (6,3) network with chiral [Mn₃Na] clusters and chiral Ca ions as alternating nodes. Magnetic property study reveals the existence of weak antiferromagnetic couplings between Mn(III) ions with the interaction parameter J being ? 0.438 cm^? 1 within the complex.     

A helical salicyladoxime-based manganese triangle chain with single-molecule magnet behavior

The reaction of 2-hydroxyphenylpropanone oxime (Et-H₂salox) with Mn(NO₃)₂·4H₂O, NEt₃ and 1,3-bis(4-pyridyl)propane-N,N′-dioxide (bppo) in EtOH/H₂O mixture afforded a one-dimensional coordination polymer with the formula [Mn₃O(Et-salox)₃(bppo)(MeOH)(H₂O)₃](NO₃)_0.5(Et-Hsalox)_0.5·MeOH·H₂O (1·MeOH·H₂O). 1·MeOH·H₂O had a manganese triangle structure, [Mn^III₃O]^7 +, which was used as a building unit for a subsequent assembly of an oximate and central oxide. The flexible bppo ligand linked the units, resulting in the formation of a 1D helical structure. Variable temperature direct current magnetic susceptibility measurements of complex 1·MeOH·H₂O were carried out. Exchange interactions of the metal centers of complex 1·MeOH·H₂O were examined, and the results indicate that both ferro- and antiferromagnetic interactions simultaneously coexist in 1·MeOH·H₂O, resulting in an S = 2 ground state. Moreover, complex 1·MeOH·H₂O shows the frequency dependence of the out-of-phase component in alternating current magnetic susceptibility measurements, indicating single-molecule magnet behavior with U_eff = 28 K and τ₀ = 1.8 × 10^− 9 s.     

Novel heterobimetallic Cu/Mn coordination polymers prepared by “direct permanganate” synthesis

Two heterometallic Cu/Mn complexes [Cu(Me₂en)₂][Mn₂(ox)₃] · 2H₂O (1) (Me₂en = N,N-dimethylethylenediamine, H₂ox – oxalic acid) and [Cu(1,3-pn)(ox)(H₂O)][Mn(ox)(H₂O)₂] · H₂O (2) (1,3-pn = 1,3-diaminopropane) are prepared by the one-pot reaction of copper powder, tetrabutylammonium permanganate, oxalic acid and N-chelating ligands. Their structures are investigated by single-crystal X-ray analysis that reveals interesting variation in bridging motives of the oxalate groups composing the Mn-polymeric fragments.     

Two novel cadmium(II) coordination polymers based on bis-functionalized ligand 4′-(4-carboxyphenyl)-2, 2′:6′, 2″-terpyridine

Two novel cadmium(II) coordination polymers [Cd(cptpy)₂]_n·nH₂O (1) with a 1D double chain structure and [Cd₂(cptpy)₂(ox)]_n·2.5nH₂O (2) with an interesting 3-connected uninodal six-fold interpenetrating ths network (Hcptpy = 4′-(4-carboxyphenyl)-2,2′:6′,2″-terpyridine, H₂ox = oxalic acid) have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, single crystal X-ray diffraction and fluorescence spectra.