A banana-shaped iron(III)-substituted tungstogermanate containing two types of lacunary polyoxometalate units

A novel polyoxotungstate cluster (H₂en)_2.5H₉[Fe₆Ge₃W₂₄O₉₄(H₂O)₂] · 14H₂O (1) (en = ethylenediamine) has been hydrothermally synthesized and structurally characterized by IR, TGA and single-crystal X-ray diffraction. The polyoxoanion skeleton of 1 is composed of two tri-Fe^III substituted B-α-(Fe₃GeW₉O₄₀) Keggin units connected by an unique hexavacant GeW₆O₂₆ Keggin fragment, leading to the first Fe(III)-containing banana-shaped tungstogermanate. Magnetic measurements of 1 reveal that the exchange interactions within the trimetal clusters are antiferromagnetic.     

A tetranuclear oxofluorovanadium(IV) cluster encapsulating a Na(H2O)n+ subunit

Hydrothermal reactions of sodium vanadate, methylenediphosphonic acid, hydrogen fluoride and the appropriate organoamine yielded the vanadium(IV)-oxyfluoride compounds [NH₃(CH₂)₂(NH₂)(CH₂)₂NH₃]₃[{Na(H₂O)} ⊂ {V₄O₄F₂(O₃PCH₂PO₃)₄}]·8H₂O (1·8H₂O) and [NH₃(CH₂)₂(NH₂)(CH₂)₂(NH₂)(CH₂)NH₃]₂[{Na(H₂O)} ⊂ {V₄HO₄F₂(O₃PCH₂PO₃)₄}]·7H₂O (2·7H₂O). The vanadium-oxyfluoride cationic unit {V₄O₄F₂(O₃PCH₂PO₃)₄}^10 − of the compounds consists of pairs of fluoride bridged {VFO₅} octahedra linked through η⁴-diphosphonate ligands into a three polyhedra thick band. The {Na(H₂O)_n}⁺ groups occupy the interior of the band but are displaced from the centroid toward one face so as to project the aqua ligands into the extra-annular domain. The fluoride ligands bridge two vanadium sites as well as coordinating to the sodium cation.     

Ligand substitution in sandwich-type complexes of germanotungstates: Syntheses,crystal structures and magnetic properties

Two new sandwich-type germanotungstates K₂H₂{Zn(en)₂}{Zn(en)₂}₂{(GeW₉O₃₄)₂Zn₄(Hen)₂}·17H₂O (1) and K₂H₂{Ni(en)₂}{Ni(en)₂}₂{(GeW₉O₃₄)₂Ni₄(Hen)₂}·12H₂O (2) (en = ethylenediamine) have been hydrothermally synthesized. The polyanions of the two compounds are composed of a [Ge₂W₁₈M₄(Hen)₂O₆₈]^10? (M = Zn, Ni) group decorated by two [M(en)₂(H₂O)]²⁺ units. The luminescence of compound 1 exhibits an intense UV radiation emission maximum at λ ≈ 449 nm upon excitation of 372 nm. The magnetic investigation of compound 2 demonstrates the presence of ferromagnetic interactions between the Ni²⁺ ions of the Ni₄O₁₄(Hen)₂ clusters in 2.     

A novel transition-metal-linked hexaniobate cluster with photocatalytic H2 evolution activity

A novel transition-metal (TM) complex based on Lindqvist polyoxoniobate K₁₀[(Nb₆O₁₉)Cr^III(H₂O)₂]₂·28H₂O (1) has been synthesized by a new two-pot synthesis strategy and structurally characterized by single crystal X-ray diffraction analysis, IR spectrum, UV–vis spectroscopy, XRPD and TG analysis. Compound 1 crystallizes in the C2/m space group with a = 32.143(19) Å, b = 10.030(6) Å, c = 12.878(8) Å, β = 110.611(9)°, and V = 3886(4) ų. X-ray structure analysis reveals that polyanion [(Nb₆O₁₉)Cr^III(H₂O)₂]₂^10 − (1a) represents the first example of two nuclear dimeric polyoxoniobate, in which two Lindqvist anions [Nb₆O₁₉]⁸ are sandwiched by two {Cr^III(H₂O)₂} groups. Further, 1 exhibits photocatalytic H₂ evolution activity.     

Solvent-free synthesis of new metal phosphate-oxalates with helical-chain and slablike structures

Two metal phosphate-oxalate, namely, H₃pmdeta ⋅ Ga₂(HPO₄)(H₂PO₄)(C₂O₄)₃ (1) and H₂mpip ⋅ Mn₂(H₂PO₄)₂(C₂O₄)₂ ⋅ H₂O (2), were prepared under solvent-free conditions, where pmdeta = N′,N″,N″-pentamethyldiethylenetriamine and mpip = 1-methylpiperzaine. Compound 1 features a helical-chain structure containing cyclic inorganic building block. Compound 2 has a slablike structure with a kgd net. The magnetic and proton-conducting properties of compound 2 were also investigated.     

A novel organic-inorganic hybrid polyoxometalate-based 3D framework constructed by organo-functionalized [As2W21O72(mal)2]18 − units and Ce3 + ions

A novel organic-inorganic hybrid polyoxometalate-based 3D framework K₅H₄{Ce₃(H₂O)₉[As₂W₂₁O₇₂(mal)₂]}·20H₂O (1) (mal = malic acid) has been synthesized by the metastable precursor [As₂W₁₉O₆₇(H₂O)]^14 −, which was further characterized by IR spectrum, thermogravimetric analysis (TGA), and X-ray single-crystal diffraction. Structural analysis revealed that 1 consists of the organo-functionalized [As₂W₂₁O₇₂(mal)₂]^18 − units linked together by the Ce^3 + ions resulting in 3D network-like architecture. Magnetic property studies indicate that obvious antiferromagnetic interactions exist in three Ce^3 + ions.     

Microstructure and mechanical properties of Al2O3 ceramic and TiAl alloy joints brazed with Ag–Cu–Ti filler metal

Al₂O₃ ceramic was reliably joined to TiAl alloy by active brazing using Ag–Cu–Ti filler metal, and the effects of brazing temperature, holding time, and Ti content on the microstructure and mechanical properties of Al₂O₃/TiAl joints were investigated. The typical interfacial microstructure of joints brazed at 880 °C for 10 min was Al₂O₃/Ti₃(Cu,Al)₃O/Ag(s.s)+AlCu₂Ti+Ti(Cu,Al)+Cu(s.s)/AlCu₂Ti+AlCuTi/TiAl alloy. With increasing brazing temperature and time, the thickness of the Ti₃(Cu,Al)₃O reaction layer increased, and the blocky AlCu₂Ti compounds aggregated and grew gradually. The Ti dissolved from the TiAl substrate was sufficient to react with Al₂O₃ ceramic to form a thin Ti₃(Cu,Al)₃O layer when Ag–Cu eutectic alloy was used, but the dissolution of TiAl alloy was inhibited with an increase in Ti content in the brazing filler. Ti and Al dissolved from the TiAl alloy had a strong influence on the microstructural evolution of the Al₂O₃/TiAl joints, and the mechanism is discussed. The maximum shear strength was 94 MPa when the joints were brazed with commercial Ag–Cu–Ti filler metal, while it reached 102 MPa for the joint brazed with Ag–Cu+2 wt% TiH₂ at 880 °C for 10 min. Fractures propagated primarily in the Al₂O₃ substrate and partially along the reaction layer.     

Multiple functions of amines in the synthesis of anionic,cationic, and neutral indium oxalates

Three new indium oxalates, formulated as H₃dpta·In(C₂O₄)(H₂O)₃·2SO₄ (1), In(qd)(C₂O₄)_1.5·1.5H₂O (2), and H₂bpp·In₂(C₂O₄)₄ (3) in which dpta = dipropylenetriamine, qd = quinoxaline-2,3(1H,4H)-dione, and bpp = 1,3-bis(4-piperidyl)propane, were prepared in the presence of different amines. These compounds have cationic, neutral, and anionic frameworks, respectively. Topological analyses reveal that compound 2 has an hcb net, while compound 3 has a dia net. The photoluminescent property of compound 2 was also investigated.     

Construction of three-dimensional Ln–Ag (Ln = Eu; Tm) coordination polymers based on isonicotinate and oxalate ligands

Hexanuclear 4d–4f heterometallic coordination polymers, [Ln₂Ag₄(IN)₅(ox)₂(NO₃)(H₂O)₂ · 3H₂O] [Ln = Eu (1), Tm (2); IN = isonicotinate and ox = oxalate], have been synthesized by hydrothermal reaction of mixed organic ligands and metal salts. Both structures display the same unusual 3D heterometallic coordination frameworks based on rare zigzag lanthanide–oxalate–silver chains, Ag₂(IN)₃ units and IN linkers. The photoluminescent properties of complex 2 were studied.     

Complexation and structural studies of a sulfonamide aza-15-crown-5 derivative

An aza-15-crown-5 derivative, N-[4-(phenyldiazo)benzenesulfonyl]-aza-15-crown-5, 1 was synthesised from commercially available starting materials in 55% yield. Compound 1, which contains a sulfonamide link between the crown ether macroring and the azobenzene, readily binds alkali metals in buffered ethanol–water (75:25 v/v, pH 6.66). Titration data for both sodium and potassium were readily fitted to a 1:1 metal ion/ligand binding model to obtain stability constants (log K) of 4.7 ± 0.4 and 4.8 ± 0.2 dm³ mol^? 1, respectively. We also investigated the structures of 1 and the sodium perchlorate salt of 1, [Na(1)(H₂O)]₂(ClO₄)₂, which were determined by X-ray crystallography. [Na(1)(H₂O)]₂(ClO₄)₂ is a dimer in the solid state whereby a sulfonamide oxygen atom from one of the [Na(1)(H₂O)] cations provides solvation of the adjacent macroring bound sodium cation. In the crystal structure, binding of a water molecule to the sodium cation is supported by hydrogen bonding to the sulfonamide oxygen, which represents a supramolecular lariat ether-like interaction.     

The first anion template cubic cyanometallate cage and its 3,5-dimethyltris(pyrazolyl)methane iron(II, III) tricyanide building blocks

Several 3,5-dimethyltris(pyrazolyl)methane iron(II, III) tricyanide building units have been prepared and characterized. Treatment of K[(HC(3,5-Me₂Pz)₃)Fe^II(CN)₂](K⁺1^-) with Fe^II(H²O)⁶(BF⁴)² affords a new anion template cubic cyanometallate cage [(BF₄) ⊂ {Fe^II(H₂O)}₄{(HC(3,5-Me₂Pz)₃)Fe^II (CN)₃}₄](BF₄)³ 3.     

Synthesis and crystal structures of two new inorganic–organic hybrid polyoxomolybdate complexes: [Himi]4[{Co(imi)2(H2O)2}Mo7O24] · 4H2O and [Zn(imi)4]2[(imi)2Mo8O26] · 6H2O

The two new inorganic–organic hybrid polyoxomolybdate complexes [Himi]₄[{Co(imi)₂(H₂O)₂}Mo₇O₂₄] · 4H₂O (1) and [Zn(imi)₄]₂[(imi)₂Mo₈O₂₆] · 6H₂O (2) (imi = imidazole) have been prepared by conventional aqueous solution synthesis. Compound 1 consists of heptamolybdate anions [Mo₇O₂₄]⁶⁻ covalently linked by [CoN₂O₄]²⁺ octahedra into one-dimensional zigzag-shaped chains. The zigzag-shaped chains are further linked together via the hydrogen-bonding interactions to form a 2D supramolecular framework. Compound 2 is build up of an imidazole-coordinated octamolybdate anion, two imidazole coordinating zinc cations and lattice water molecules to form a three-dimensional framework via complex hydrogen-bonding.     

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.     

Heteropolynuclear Schiff-base complexes Cu–Ln–Fe (Ln = Sm & Pr) with magnetic property

Two new complexes [{CuL}Sm(H₂O)₃{Fe(CN)₆}]₂·6H₂O (1) [{CuL}₂Pr(H₂O){Fe(CN)₆}]₂·4H₂O (2) (H₂L = N,N′-ethylenebis(3-methoxysalicylideneimine)) have been prepared by reactions of acyclic compartmental Schiff-base heterodinuclear 3d–4f compound [{CuL}Ln(NO₃)₃] (Ln = Sm & Pr) with K₃[Fe(CN)₆]. Crystal structures of both 1 and 2 reveal unique topology structures. 1 shows a dimeric heterotrinuclear [{CuL}Sm(H₂O)₃{Fe(CN)₆}]₂ while 2 displays a dimeric heterotetranuclear [{CuL}₂Pr(H₂O){Fe(CN)₆}] with distorted sandwich moieties [{CuL}₂Pr]. Both 1 and 2 form similar 1D ladder-like structure through the intermolecular double bridges of Cu–N bonds. The measurement of variable-temperature magnetic susceptibility reveals that both complexes 1 and 2 exhibit antiferromagnetic interaction between spin carriers.     

1-D networks formed by metal⋯sulfur van der Walls contacts: Novel tetrazole–thiolato Pd(II) and Pt(II) complexes

Pd(II)– and Pt(II)–azido complexes, [M(N₃)(PMe₃)₂(C–L)] {LH = 2-(2′)-thienyl pyridine; M = Pd (1), Pt(2)}, which contain σ-bonded heterocycles (L), were treated with aryl isothiocyanate (Me₂C₆H₃–NCS) to afford the corresponding Pd(II) and Pt(II) tetrazole–thiolato complexes, trans-{M[SCN₄(2,6-Me₂C₆H₃)](PMe₃)₂(C–L)} {M = Pd (3), Pt (4)}. Complexes 3 and 4 have a 1-D helical network formed by the intermolecular M?S van der Waals contacts.     

Impact of quenching process on the surface defect of titanium dioxide for hydrogen production from photocatalytic decomposition of water

Nanocrystalline titania was prepared by solvothermal reaction of titanium butoxide in toluene at 300 °C for 2 h. Thus obtained-powder was calcined at 300 °C in box furnace for 1 h and then quenched in various media at different temperature. The physiochemical properties of samples were investigated by using X-ray diffraction (XRD), nitrogen adsorption, CO₂-Temperature Programmed Desorption (CO₂-TPD), UV–visible scanning spectrophotometer, Transmission electron microscopy (TEM) and electron spin resonance spectroscopy (ESR) techniques. All physical properties such as phase, BET surface area and crystal size were not changed after quenching processes. While the CO₂-TPD and ESR results indicate the changing of Ti³⁺ contents on the surface of TiO₂ after quenching process. The amounts of Ti³⁺ increased as the quenching temperature decreased. Photocatalytic decomposition of water was carried out to evaluate the catalytic activity of quenched TiO₂. The activity of quenched-powder increased corresponding to the increasing of Ti³⁺ contents increased by following order: air at 77 K > air at RT > air at 373 K > 30 wt% H₂O₂ at RT = 30 wt% H₂O₂ at 373 K > H₂O at RT > H₂O at 373 K.     

An uncommon 3D Co5-cluster-based metal-organic framework: Synthesis,structure and magnetism

A highly connected metal–organic framework (MOF), namely, [Co₅(μ₃-OH)₂(iapt)₄(4,4′-bipy)_0.5(H₂O)·CH₃CN·3H₂O] (1) (H₂iapt = 5-aminoisophthalic acid and 4,4′-bipy = 4,4′-bipyridine), is reported. 1 shows a complicated pentanodal 4,4,4,4,13-c 3D net with (4³)(4³)(4³)(4³)(4²⁰·5¹⁴·6²³·7⁸·8¹³) topology based on an uncommon Co₅ cluster. The magnetic analysis reveals antiferromagnetic interactions in 1, and both the local spin–orbit coupling of octahedral Co(II) ions and the antiferromagnetic interactions are the primary factors in the magnetic behaviour.     

Syntheses,structures and properties of a series of 3s–5d–4f mixed metal substituted sandwich-type arsenotungstates

A class of 3s–5d–4f mixed metal substituted sandwich-type arsenotungstates [H₂N(CH₃)₂]₈H₃[LnNa(H₂O)₄(OH)WO(H₂O) (B-α-AsW₉ O₃₃)₂]·8H₂O [Ln = La^III (1), Ce^III (2), Pr^III (3)] have been isolated from an aqueous solution reaction system (pH = 4) of Na₂WO₄·2H₂O, C₂H₇N·HCl, NaAsO₂ and Ln(NO₃)₃·6H₂O and structurally characterized by elemental analyses, IR spectra, UV spectra and single-crystal X-ray diffraction. It is the most prominent in 1–3 that the [LnNa(H₂O)₄(OH) WO(H₂O)(B-α-AsW₉O₃₃)₂]^11 − polyanion consists of two trivacant Keggin [B-α-AsW₉O₃₃]^9 − moieties linked by one [WO(H₂O)]^4 + group and a dimeric [LnNa(H₂O)₄(OH)]^3 + group resulting in the special 3s–5d–4f mixed metal substituted sandwich-type assembly. Interestingly, lanthanide and sodium ions simultaneously occupy the two positions located at the central belt of 1–3 with the site occupancy of 50% for each position. Moreover, the electrochemical and electrocatalytic properties of only 1 and 2 have been measured by cyclic voltammetry (CV) in 0.5 mol·L^− 1 Na₂SO₄ + H₂SO₄ aqueous solution. 1 and 2 illustrate electrocatalytic activities for the hydrogen peroxide reduction.     

Two 2-D 4-connected lanthanide coordination framework based on benzimidazole-5,6-dicarboxylate and acetate mixed ligands

Two 2-D polymers, [Ln(bidc)(Ac)·H₂O]_n (Ln = Tb(1), Dy(2) H₂bidc = benzimidazole-5,6-dicarboxylic acid, HAc = acetic acid), have been successfully synthesized under hydrothermal conditions at 150 °C and characterized by elemental analysis, infrared spectra and single-crystal X-ray diffraction. Single crystal X-ray diffraction analyses reveal that the two compounds are isomorphous and exhibit one new (4,4)-connected 2-nodal (4⁴·6²)(4⁴·6²) layer-like net, stabilized by the interchain hydrogen bonding N–H?O, O–H?O and π?π stacking interactions between two benzimidazole rings. 2-D layers are further connected by the interlayer O–H?O hydrogen-bonding interactions to form a 3-D supermoleculaer network. Moreover, the luminescent property of compound 1 and thermogravimetric analyses of the two complexes 1–2 are discussed in detail.     

Trinuclear cobalt(II) sandwiched polyoxotungstobismuthate with antennal copper(II)-complex: A new method to combine hetero–transition–metallic ions

A new sandwich-type hybrid complex, Na₈{Cu(im)₄(H₂O)}[Cu(im)₄ {Na(H₂O)₂Co(im)}₃(BiW₉O₃₃)₂] · 11H₂O (1) (im = imidazole), has been synthesized and structurally characterized. The polyoxoanion in 1 contains trinuclear Co²⁺ ions in the central belt and an antennal Cu(II)–imidazole supported complex, which firstly represents a copper(II)-complex mono-supported tungstobismuthate system containing sandwiched trinuclear cobalt(II) ions. Neighboring polyanions further connect each other by disodium ions to yield a dimeric complex. The successful synthesis of 1 opens a new approach to the combination of different kinds of transition–metal ions by virtue of lacunary Keggin-type polyoxoanions, [BiW₉O₃₃]^9?, as effective linkages. The magnetic investigation for 1 indicate weak antiferromagnetic interactions for trinuclear Co(II) clusters located in the polyanions.