Synthesis and characterization of noble-metal-substituted Dawson-type polyoxometalates

Polyoxometalates substituted by noble metal cations (PdII, RuIII, IrIV) of general formula (Bu4N)n[P2W17M(OH2)O61] are prepared by refilling the vacant site of the lacunary precursor 2-K10P2W17O61. Both 31P- and 183W-n.m.r. studies provide convincing evidence for the above structural assignment. The u.v.-vis and i.r. spectra are consistent with the first row transition metal substituted homologues. Electrochemical investigations by cyclic voltammetry in MeCN revealed four reversible one-electron redox couples, which are ascribed to the tungsten(VIV) process of the tungsten-oxo framework.     

一种具有Keggin结构的有机-无机复合的单铈取代夹心型磷钨酸盐的合成及其结构表征(英文)

在水热条件下合成了一种具有Keggin结构的有机-无机复合的单铈取代夹心型磷钨酸盐[H2dap]2.5H5-[Ce(α-PW11O39)2].11.5H2O(1);利用元素分析、红外光谱和单晶X射线衍射表征了其结构.结果表明,化合物1属于三斜晶系,P-1空间群,晶胞参数为:a=1.254 9(7)nm,b=1.915 9(11)nm,c=2.129 0(12)nm,α=68.426(10)°,β=88.320(10)°,γ=89.853(10)°,V=4.758(5)nm3,Z=2,Dc=4.116g/cm3,GOOF=1.022,R1=0.111 2,wR2=0.218 9.化合物1分子由1个晶体学独立单铈取代夹心型[Ce(α-PW11-O39)2]10-磷钨酸多阴离子,2.5个双质子化的[H2dap]2+阳离子,5个质子及11.5个结晶水分子组成.     

Decomposition of a-type sandwiches. Synthesis and characterization of new polyoxometalates incorporating multiple d-electron-centered units

The controlled decomposition of the sandwich-type polyoxometalates K(12)[(M(OH(2))(2))(3)(A-alpha-PW(9)O(34))(2)] (where M = Mn(II) or Co(II)) in 0.5 M NaCl yields a new family of transition metal substituted POMs of the general formula [((MOH(2))M(2)PW(9)O(34))(2)(PW(6)O(26))](17)(-) (where M = Mn(II) (1Mn) or Co(II) (1Co)). The structure of 1Mn, determined by single-crystal X-ray diffraction (a = 17.4682(10) A, b = 22.3071(12) A, c = 35.1195(18) A, beta = 95.898(1) degrees, monoclinic, P2(1)/c, Z = 4, R(1) = 6.19%, based on 50264 independent reflections), consists of two B-alpha-(Mn(II)OH(2))Mn(II)(2)PW(9)O(34)(3)(-) units joined by a B-type hexavacant PW(6)O(26)(11)(-) fragment to form a C-shaped polyoxometalate. A low resolution X-ray structure of the Co(II) analogue, 1Co, was also obtained. The UV-visible spectrum of 1Co shows the characteristic charge-transfer bands of polyoxometalates as well as a new Co-centered peak (560 nm, epsilon = 416 M(-)(1) cm(-)(1)) which appears at a higher wavelength relative to that exhibited by the parent A-type sandwich, K(12)[(Co(OH(2))(2))(3)(A-alpha-PW(9)O(34))(2)]. The methyltricaprylammonium salt of 1Mn is an effective catalyst for the H(2)O(2)-based epoxidation of cis-cyclooctene, cyclohexene, and 1-hexene.     

Synthesis and characterization of two charge-transfer salts based on Keggin-type polyoxometalates and morpholinebiguanide

Two new inorganic-organic salts, formulated as (C₆H₁₃N₅OH)₂ [HPMo₁₂O₄₀] · 5H₂O and (C₆H₁₃N₅OH)₃[PW₁₂O₄₀], were synthesized and characterized by elemental analysis, IR, ESR, diffuse reflectance spectra, thermogravimetry, and X-ray photoelectron spectroscopy. Solid diffuse reflectance spectra showed charge-transfer interactions between the inorganic and organic moieties in the solid state. Salt I had strong photosensitivity for UV light or X-ray irradiation, and its photochromic reaction under UV light was found to exhibit first-order kinetics. The article is published in the original.     

New sandwich-type polymeric potassium-dicyanoargentate(I) complex: synthesis,characterization and enzymatic activity

Coordination compounds containing dicyanoargentate(I) have remarkable biological potential due to their therapeutic antibacterial, antifungal, antibiofilm, and anticancer properties. In this study, a new dicyanoargentate(I)-based complex was synthesized and characterized by various procedures (elemental, thermal, FT-IR for complex) involving crystal analysis of the complex. In addition, the biological activity of this new compound on the acetylcholinesterase (AChE) enzyme, an important enzyme for the nervous system, was investigated. When the infrared (IR) spectrum of the complex is examined, the OH vibration peak resulting from H₂O molecules in the structure at 3948-3337 cm⁻¹ and at 2138 cm⁻¹, along with a CN peak coordinated to Ag, can be seen, indicating that the mass remaining in the thermal degradation of the complex at 1000 ◦ C is the weight corresponding to the metal mixture consisting of K+Ag (calc.: 68.06). The crystal method revealed that the complex has a sandwich-like, polymeric chemical structure with layers formed by K⁺ cations and [Ag(CN)₂H₂O]⁻ anions. Therefore, the AChE enzyme has potential therapeutic uses in improving ACh levels in brain cells, in reducing various side effects, and in improving cognitive impairment, especially in advanced Alzheimer’s disease patients. In this study, the activity of this newly synthesized complex on AChE was also investigated. As a result of this research, [Ag(CN)₂(H₂O)K] had 0.0282 ± 0.010 μM Ki values against AChE. The compound was therefore a good inhibitor for the AChE enzyme. This type of compound can be used for the development of novel anticholinesterase drugs.     

Synthesis, characterization, and crystal structures of two novel high-nuclear nickel-substituted dimeric polyoxometalates

Two novel high-nuclear Ni-substituted polyoxometalates Na9K[Ni7(OH)4(H2O)(CO3)2(HCO3)(A-alpha-SiW9O34)(beta-SiW10O37)].5H3O.18H2O (1) and K6Na4[{Ni6(H2O)4(mu2-H2O)4(mu3-OH)2}(x-SiW9O34)2].17.5H2O (2) have been obtained by reaction of K(8)[gamma-SiW10O36] with NiCl2.2H2O in basic conditions. Compounds 1 and 2 all represent the first polyoxometalates substituted by seven and six Ni centers, respectively. Also, compound 1 exhibits a novel asymmetric dimeric structure, composed of [A-alpha-SiW9O34]10- and [beta-SiW10O37]10- units linked by a Ni7 cluster and three carbonates, which exhibit tri- and bidentate coordination modes in 1.     

Synthesis, characterization, and reactivity of Ti(IV)-monosubstituted Keggin polyoxometalates

Ti(IV)-monosubstituted Keggin-type polyoxometalates (Ti-POMs), mu-oxo dimer [Bu4N]8[(PTiW11O39)2O] (1), and three monomers [Bu4N]4[PTi(L)W11O39], where L = OH (2), OMe (3), and OAr (4, ArOH = 2,3,6-trimethylphenol (TMP)), have been prepared starting from mu-hydroxo dimer [Bu4N]7[(PTiW11O39)2OH] (5) or heteropolyacid H5PW11TiO40 or both. The compounds have been characterized by elemental analysis, IR, UV-vis, and multinuclear (31P, 1H, 183W) NMR. The interaction of 1 and 3-5 with H2O in MeCN produces 2. The hydrolysis constants, estimated from 31P and 1H NMR data, are 0.006 and 0.04 for 1 and 3, respectively. Studies by 31P NMR, IR, potentiometric titration, and cyclic voltammetry revealed that 1-3 and 5 afford the same protonated titanium peroxo complex [Bu4N]4[HPTi(O2)W11O39] (I) upon interaction with aqueous H2O2 in MeCN. The rates of formation of I correlate with the rates of hydrolysis of the Ti-POMs and follow the order of 5 > 1 > 3. A two-step mechanism of the reaction of Ti-POMs with H2O2, which involves hydrolysis of the Ti-L bonds to yield 2 followed by fast interaction of 2 with hydrogen peroxide producing I, is suggested. The equilibrium constant for the reaction of 2 with H2O2 to yield I and H2O, estimated using 31P NMR, is 10. The interaction of the Ti-POMs with TMP follows the trends similar to their interaction with H2O) and requires preliminary hydrolysis of the Ti-L bonds. All of the Ti-POMs catalyze the oxidation of TMP with H2O2 in MeCN to give 2,3,5-trimethyl-p-benzoquinone and 2,2',3,3',5,5'-hexamethyl-4,4'-biphenol. The product distribution is similar for all of the Ti-POMs. The catalytic activities of the Ti-POMs correlate with the rates of formation of I and follow the order of 2 > 5 > 1 > 3. The findings lay a basis for a better understanding of the nature of the reactivity of titanium in Ti-catalyzed oxidations.     

Hydrothermal syntheses and structural characterization of two sandwich-type arsenotungstates

Two new organic–inorganic composite sandwich-type arsenotungstates [H₂dap]₆H₈[Ni₄(H₂O)₂(B-α-AsW₉O₃₄)₂]₂ · 33H₂O (1) and {[Ni(dap)₂(H₂O)]₂[Ni(dap)₂]₂[Ni₄(Hdap)₂(B-α-AsW₉O₃₄)₂]} · 4H₂O (2) (dap = 1,2-diaminopropane) have been hydrothermally synthesized by reaction of Na₈[A-α-HAsW₉O₃₄] · 11H₂O with NiCl₂ · 6H₂O in the presence of 1,2-diaminopropane and characterized by elemental analysis, IR spectra, X-ray single-crystal diffraction, and thermogravimetric analysis. 1 crystallizes in the triclinic P 1 space group with a = 16.351(6) Å, b = 16.423(6) Å, c = 19.894(7) Å, α = 110.630(6)°, β = 92.684(7)°, γ =104.946(7)°, V = 4774(3) ų, Z = 1, GOOF = 1.033, R ₁ = 0.0517, wR ₂ = 0.1086. 2 also crystallizes in the triclinic P 1 space group with a = 13.305(4) Å, b = 13.882(4) Å, c = 17.031(5) Å, α = 68.109(5)°, β = 71.511(4)°, γ = 88.407(5)°, V = 2753.5(14) ų, Z = 1, GOOF = 1.051, R ₁ = 0.0491, wR ₂ = 0.1150. Notably, 1 is a discrete structure, composed of two tetra-Ni^II substituted sandwich-type polyoxoanions [Ni₄(H₂O)₂(B-α-AsW₉O₃₄)₂]^10? with different spatial orientation, whereas 2 displays a organic–inorganic composite 2-D sheet architecture constructed by tetra-Ni^II sandwiched [Ni₄(H₂O)₂(B-α-AsW₉O₃₄)₂]^10? units by means of [Ni(dap)₂]²⁺ bridges. Some previously reported transition-metal-substituted sandwich-type polyoxotungstates have been summarized.     

Synthesis and photocatalytic activity assessing of the TiO<Subscript>2</Subscript> nanocomposites modified by some lanthanide ions and tin-derivative sandwich-type polyoxometalates

New nanocomposites containing sandwich-type polyoxometalate of [(PW₉O₃₄)₂(HOSn^IVOH)₃]^12? (P₂W₁₈Sn₃) loaded onto Ln-doped TiO₂ (Nd, Sm, Dy, Tb) nanoparticles were synthesized and their catalytic activities were assessed. The Ln–TiO₂ nanoparticles and Ln–TiO₂/P₂W₁₈Sn₃ nanocomposites were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction, field emission scanning electron microscope, energy dispersive analysis of X-rays spectra and diffuse reflectance spectra. The photocatalytic efficiency of the Ln–TiO₂ and Ln–TiO₂/P₂W₁₈Sn₃ were examined in the photodegradation of methyl orange and methylene blue solutions. It was revealed through different characterization techniques that the P₂W₁₈Sn₃ was successfully loaded on the lanthanide-doped anatase phase TiO₂ nanoparticles and the particles diameter were relatively 20–30 nanometers. It was revealed that doping by the lanthanide ions followed by loading of polyoxometalates improves the photocatalytic performance of TiO₂ effectively. The effects of operational parameters and the kinetics of photocatalytic degradation under UV light were discussed. The prepared nanocomposites were stable and could be easily separated from the reaction system.     

Synthesis, characterization and catalytic application of SBA-15 immobilized rare earth metal sandwiched polyoxometalates

Rare earth metal sandwiched Keggin-type heteropolyoxometalates, K₁₁[RE(PW₁₁O₃₉)₂] (RE–PW₁₁, RE = La, Ce, Pr, Nd, Sm, Eu, Dy and Y), were anchored onto aminosilylated mesoporous silica SBA-15 and the resulting RE–PW₁₁/APTS/SBA-15 materials were characterized by ICP, FT-IR, XRD, N₂ adsorption, ³¹P MAS NMR and TEM. The RE–PW₁₁ clusters preserve their structure in the surface-modified mesopores. The catalytic activity of RE–PW₁₁ clusters was tested on heterogeneous oxidation of cyclohexene by H₂O₂. The interaction between RE–PW₁₁ and amino groups grafted on the channel surface of SBA-15 leads to strong immobilization of RE–PW₁₁ due to the introduction of the rare earth metal centre, which is against the leaching during the reaction.     

Synthesis and characterization of new nitridotechnetium-EDTA complex

TcN-EDTA has been synthesized for the first time starting from TcNCl₄ ^–. Elemental analysis shows that this compound has three molecules of water of crystallization: TcN(Hedta) · 3H₂O. Its optical spectrum has an absorption maximum at 505 nm with = 1060 dm³.mol^–1.cm^–1. It decomposed easily under alkaline conditions.     

Synthesis, characterization, and reactivity of a uranyl beta-diketiminate complex

Addition of 1 equiv of Li(Ar2nacnac) (Ar2nacnac = (2,6-(i)Pr2C6H3)NC(Me)CHC(Me)N(2,6-(i)Pr2C6H3)) to an Et2O suspension of UO2Cl2(THF)3 generates the uranyl dimer [UO2(Ar2nacnac)Cl]2 (1) in good yield. A second species can be isolated in low yield from the reaction mixtures of 1, namely [Li(OEt2)2][UO2(Ar2nacnac)Cl2] (2). The structures of both 1 and 2 have been confirmed by X-ray crystallography. Complex 1 reacts with Ph3PO to generate UO2(Ar2nacnac)Cl(Ph3PO) (3). In addition, 1 reacts with AgOTf and either 1 equiv of DPPMO2 or 2 equiv of Ph2MePO to provide [UO2(Ar2nacnac)(DPPMO2)][OTf] (4) and [UO2(Ar2nacnac)(Ph2MePO)2][OTf] (5), respectively. Both 4 and 5 have been fully characterized, including analysis by X-ray crystallography and cyclic voltammetry. Reduction of 4 with Cp2Co provides UO2(Ar2nacnac)(CH{Ph2PO}2) (6), a uranyl(VI) complex that is generated by the formal loss of H* from the DPPMO2 ligand. Labeling studies have been performed in an attempt to elucidate the mechanism of hydrogen loss. In contrast, reduction of 5 with Cp2Co provides UO2(Ar2nacnac)(Ph2MePO)2 (7), a rare example of a uranyl(V) complex. As expected, the solid-state molecular structure of 7 reveals slightly longer U-O(oxo) bond lengths relative to 5. Furthermore, complex 7 can be converted back into 5 by oxidation with AgOTf in toluene.     

Synthesis and characterization of a large bite angle iridium nixantphos complex

The complex (nixantphos)Ir(cod)Cl·CH₂Cl₂(0.5C₇H₈) 3 has been synthesized and structurally characterized by NMR, IR, and single crystal X-ray diffraction. The coordination around Ir is trigonal bipyramidal with both P groups of the nixantphos bound in a bis-equatorial mode. The bis-chelating cod (C₈H₁₂) occupies the remaining equatorial position and an axial position. This mode of bonding resulted in a large bite angle (P1—Ir—P2) of 106.49° (3) for 3. The IR and NMR data support the elucidated structure. Thermal analyses of 3 indicate that it is thermally stable up to decomposition greater than 400°C.     

Synthesis and characterization of a Tc(V) glycolato complex

The preparation of the Tc(V) glycolato complex (C₄H₉)₄N[⁹⁹TcO(OCH₂CH₂O)₂] is described. On the basis of IR, ¹H-NMR and ¹³C-NMR spectra, a structure for the complex is postulated.     

Synthesis and physico-chemical characterization of a Schiff base and its zinc complex

Research on Chemical Intermediates - In the present studies, a Schiff base ligand and complex were synthesized by condensation reaction of 2-hydroxy-1-napthaldehyde and 4-methyl-1,3-phenyldiamine....     

Tin-derivative sandwich-type polyoxometalates supported on Nd-doped TiO2 nanoparticles as efficient and reusable catalysts in the oxidation of sulfides and alcohols

New nanocomposites, including different loading levels of sandwich-type polyoxometalates [(HOSn^IVOH)₃(XW₉O₃₄)₂]^n? (X = As (1), P (2) n = 12 and Si (3) n = 14) on Nd-doped TiO₂ nanoparticles were prepared by a simple impregnation method. The nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, Fourier transform infrared (FTIR), and energy-dispersive X-ray spectroscopy. Compounds 1–3 were successfully loaded on Nd-doped crystallized anatase-phase TiO₂ nanoparticles of 20–25 nm. Catalytic activities of nanocomposites were examined by carrying out the oxidation of sulfides and alcohols with H₂O₂. Simple synthesis method, reusability, and low amounts of the heterogeneous catalysts with a slight excess of H₂O₂ and mild reaction conditions make these oxidation reactions an environmentally benign chemical process.     

Structural characterization and magnetic properties of sandwich-type tungstoarsenate complexes. Study of a mixed-valent VIV2/VV heteropolyanion

Complexes K11Na1[As2W18(Mn(H2O))3O66]x27H2O (1) and Na12[As2W18(Co(H2O))3O66]x34H2O (2) have been characterized. 1 crystallizes in the orthorhombic space group Pnma, with a = 30.6484(4) A, b = 14.9946(2) A, and c = 19.17080(10) A (Z = 4), while 2 crystallizes in the monoclinic space group C2/c, with a = 14.124(2) A, b = 23.294(3) A, c = 32.247(3) A, and beta = 98.935(10) degrees (Z = 4). Structures of the anions of 1 and 2 are similar, the divalent metals adopting a square pyramidal environment. K11[As2W18(VO)3O66]x23H2O (3) crystallizes in the orthorhombic space group Pnma, with a = 30.6240(5) A, b = 14.9861(2) A, and c = 19.2651(3) A (Z = 4). The structure has revealed a disorder on two of the three metals linking the [alpha-AsW9O33]9- parts. For these two vanadium atoms, the V=O bonds are directed alternatively toward the inside or the outside of the [alpha-AsW9O33]9- cavity. The remaining vanadium shows a V=O bond always directed toward the outside of the cavity. Titration of VIV by CeIV revealed that 3 is the mixed-valent VIV2VV species. Magnetic measurements are in agreement with this formulation. The high-temperature molar magnetic susceptibility of a powdered sample of 3 clearly confirms the presence of two d1 centers. The two VIV are antiferromagnetically coupled, with J = -2.9 cm-1 and g = 1.93. Crystallographic data do not permit the location of the two VIV to be distinguished from the location of the VV. As expected, the Mn(II) are very weakly antiferromagnetically coupled in compound 1. The complex Na8[Ni(H2O)6]2[As2W18(Ni(H2O))3O66]x20H2O (4) has been synthesized. The anion crystallized with two octahedral [Ni(H2O)6]2+ as counterions. Magnetic data have been fitted assuming that the only exchange-coupled centers are the nickels of the polyanion. 4 exhibits an antiferromagnetic coupling with J = -1.7 cm-1, g = 2.27, and theta = -1.5 K.