Ligand effect on Ru-centered species toward methane activation.

Ligands have been known to profoundly affect the chemical transformations of methane, yet significant challenges remain in shedding light on the underlying mechanisms. Here, we demonstrate that the conversion of methane can be regulated by Ru centered cations with a series of ligands (C, CH, CNH, CHCNH). Gas-phase experiments complemented by theoretical dynamic analysis were performed to explore the essences and principles governing the ligand effect. In contrast to the inert Ru+, [RuC]+, and [RuCNH]+ toward CH4, the dehydrogenation dominates the reaction of ligand-regulated systems [RuCH]+/CH4 and [RuCHCNH]+/CH4. In active cases, CH acts as active sites, and regulates the activation of CH4 assisted by the "seemingly inert" CNH ligand.

Iridium Dimer Anion-Mediated C≡C Triple Bond Cleavage and Successive Dehydrogenation of Acetylene in the Gas Phase.

The reactions of the iridium dimer anion [Ir2]- with acetylene have been studied by mass spectrometry in the gas phase, which indicate that the [Ir2]- anion can consecutively react with C2H2 molecules to form the [Ir2C2x]- (x = 1, 2) and [Ir2C2yH2]- (y = 3-5) anions as major products with the successive release of H2 molecules at room temperature. The reactions are confirmed by the reactions of the mass-selected product [Ir2C2]- anion with C2H2 to produce [Ir2C4]- and [Ir2C2yH2]- (y = 3-5). Photoelectron spectra and quantum chemistry calculations confirm that the [Ir2C2x]- (x = 1, 2) product anions possess cyclic [Ir(µ-C)2Ir]- and [Ir(µ-C)(µ-C3)Ir]- structures, implying that the robust C≡C triple bond of acetylene can be completely cleaved by the [Ir2]- anion.

Quadruple C-H Bond Activations of Methane by Dinuclear Rhodium Carbide Cation [Rh2C3].

The structure of the [Rh2C3]+ ion and its reaction with CH4 in the gas phase have been studied by infrared photodissociation spectroscopy and mass spectrometry in conjunction with quantum chemical calculations. The [Rh2C3]+ ion is characterized to have an unsymmetrical linear [Rh-C-C-C-Rh]+ structure existing in two nearly isoenergetic spin states. The [Rh2C3]+ ion reacts with CH4 at room temperature to form [Rh2C]+ + C3H4 and [Rh2C2H2]+ + C2H2 as the major products. In addition to the [Rh2C]+ ion, the [Rh2 13C]+ ion is formed at about one-half of the [Rh2C]+ intensity when the isotopic-labeled 13CH4 sample is used. The production of [Rh2 13C]+ indicates that the linear C3 moiety of [Rh2C3]+ can be replaced by the bare carbon atom of methane with all four C-H bonds being activated. The calculations suggest that the overall reactions are thermodynamically exothermic, and that the two Rh centers are the reactive sites for C-H bond activation and hydrogen atom transfer reactions.

The Reactive Sites of Methane Activation: A Comparison of IrC3+ with PtC3.

The activation reactions of methane mediated by metal carbide ions MC3+ (M = Ir and Pt) were comparatively studied at room temperature using the techniques of mass spectrometry in conjunction with theoretical calculations. MC3+ (M = Ir and Pt) ions reacted with CH4 at room temperature forming MC2H2+/C2H2 and MC4H2+/H2 as the major products for both systems. Besides that, PtC3+ could abstract a hydrogen atom from CH4 to generate PtC3H+/CH3, while IrC3+ could not. Quantum chemical calculations showed that the MC3+ (M = Ir and Pt) ions have a linear M-C-C-C structure. The first C-H activation took place on the Ir atom for IrC3+. The terminal carbon atom was the reactive site for the first C-H bond activation of PtC3+, which was beneficial to generate PtC3H+/CH3. The orbitals of the different metal influence the selection of the reactive sites for methane activation, which results in the different reaction channels. This study investigates the molecular-level mechanisms of the reactive sites of methane activation.

H-shaped oxalate-bridging lanthanoid-incorporated arsenotungstates.

Three oxalate-bridging lanthanide-based polyoxometalates (Ln-POMs) K17Na2H5[{(As2W19O67(H2O))Ln(H2O)2}2(C2O4)]·50H2O. [Ln = Sm3+ (1), Pr3+ (2), and Ce3+ (3)] were successfully synthesized. The structures were further characterized by single-crystal X-ray diffraction analyses, Raman spectroscopy, elemental analyses, powder X-ray diffraction (PXRD), IR spectra, UV/vis diffuse reflectance spectroscopy, and thermogravimetric analysis (TGA). The structural characterization study reveals that Ln-POMs 1-3 crystallize in the form of the triclinic space group P1[combining macron] and consist of an oxalate bridging di-Ln3+-incorporated H-shaped dimer, which can also be viewed as a combination of two half-units {Ln(As2W19O67(H2O))(H2O)2}222- related by an inversion center. It is worth noting that the opening angle (33.01°) from the [As2W19O67(H2O)]14- fragment in 1-3 is less than that of the [As2W19O67(H2O)]14- precursor (40.99°). Furthermore, the stability of 1-3 in aqueous solution and their solid-state photoluminescence properties have also been investigated in this work.

C/C Exchange in Activation/Coupling Reaction of Acetylene and Methane Mediated by Os+: A Comparison with Ir+, Pt+, and Au.

The activation and coupling reactions of methane and acetylene mediated by M+ (M = Os, Ir, Pt, and Au) have been comparatively studied at room temperature by the techniques of mass spectrometry in conjunction with theoretical calculations. Studies have shown that Os+ and Ir+ can mediate the activation/coupling reaction of CH4 and C2H2, while Pt+ and Au+ cannot, which could be explained by the number of empty valence orbitals in the metal atom. In addition, there are different competition channels for the reaction mediated by Os+ and Ir+: an expected dehydrogenation and an unexpected C/C exchange. We find that if the rare C/C exchange reaction takes place, there are symmetric carbon atoms in the reaction intermediate and the C/C exchange reaction is favored kinetically. The C/C exchange reaction must be considered, which will affect the yield of the products in the primary reaction. This study shows the molecular-level mechanisms which include the C/C exchange reaction in the activation and coupling reaction of organic compounds mediated by different metals.

Reactions of Transition-Metal Carbyne Cations with Ethylene in the Gas Phase.

The reactions of iridium- and osmium-carbyne hydride cations [HIrCH]+ and [HOsCH]+ with ethylene have been studied using mass spectrometry with isotopic-labeling in the gas phase. The carbyne reactivity is compared with that of the rhodium, cobalt, and iron analogues [TMCH2]+ (TM = Fe, Co, and Rh), which were determined to have the carbene structures. Besides the cycloaddition/dehydrogenation reaction in forming the [TMC3H4]+ + H2 (TM = Ir and Os) products, a second reaction pathway producing the [TMC2H2]+ ion and CH4 via triple hydrogen atom transfer reactions to the carbyne carbon is observed to be the major channel. The latter channel is not observed in the rhodium, cobalt, and iron carbene cation reactions. Quantum-chemical calculations indicate that the distinct reactivity is not due to different initial structures of the reactants. Both reaction channels are predicted to be thermodynamically exothermic and kinetically facile for the carbyne cations, and the reactions proceed with the initial formation of a carbene intermediate via hydride-carbyne coupling. The latter channel is also exothermic but kinetically unfavorable for the rhodium, cobalt, and iron carbene cations.

An organic chromophore -modified samarium-containing polyoxometalate: excitation-dependent color tunable behavior from the organic chromophores to the lanthanide ion.

Here, an organic-inorganic hybrid lanthanide-based polyoxometalate (Ln-POM) [N(CH3)4]3K2Sm(C7H5O2)(H2O)2(α-PW11O39)·11H2O (1) was successfully synthesized and characterized well by several physicochemical techniques. In the polyanion of 1, the benzoic acid ligand directly binds a Sm3+ ion for the formation of an organic-inorganic hybrid polyanion. This organic-inorganic hybrid structure can effectively sensitize the emissions of the Sm3+ ion, which was confirmed by the photoluminescence and time-resolved emission spectroscopy of 1. The photoluminescence study demonstrates that the Sm3+ ion possesses a relatively high-symmetry coordination geometry, which is consistent with the structural analysis of Sm3+ in 1. Furthermore, the polyanion of 1 can form a 3D 4,8-topology framework through the linkage of K1 and K2 ions. In addition, the photoluminescence properties of 1 have been explored, revealing that 1 shows reversible color-tunable photoluminescence based on the excitation from 260 nm to 350 nm, and emitting colors from blue to pink.

Synthesis, characterization, and photoluminescence properties of three two-dimensional lanthanide-containing Dawson-type polyoxometalates.

Three [α2-P2W17O61]10--based lanthanide-containing polyoxometalates (LCPs) [N(CH3)4]3H8{Ln(H2O)7[Ln(H2O)3Ln(H2O)4(α2-P2W17O61)2]}·48H2O [Ln = La3+ (1), Ce3+ (2), and Pr3+ (3)] were successfully obtained by the reaction of a trivacant Dawson-type precursor [P2W15O56]12- and lanthanide ions under hydrothermal conditions. The compounds 1-3 were fully characterized by single-crystal X-ray diffraction and a series of analytical methods, including elemental analyses, powder X-ray diffraction (PXRD), IR spectroscopy, Raman spectroscopy, UV/vis diffuse reflectance spectroscopy, and thermogravimetric analysis (TGA). Single-crystal X-ray diffraction analyses indicated that 1-3 were isostructural and exhibited a 2D network architecture through the alternative connection of [α2-P2W17O61]10- and lanthanide ions. The photoluminescence properties of 1-3 were investigated at room temperature, and 3 displayed the characteristic emissions of a Pr3+ emitting center, indicating that POMs can transfer energy and sensitize Pr3+ emissions. The reason for the weak emission intensity of Pr3+ emitting ions was because the radiationless losses via a charge-transfer Pr → W state negatively affected the emission of the Pr3+ ions in LCPs.

Assembly of Lanthanide-Containing Polyoxotantalate Clusters with Efficient Photoluminescence Properties.

Eight novel lanthanide-containing polyoxotantalates, Cs3[Ln(H2O)6{H4(TaO2)6As4O24}]·7H2O (Ln = Sm (1), Eu (2), Tb (3), Dy (4), Er (5), Tm (6), Yb (7), Lu (8)), have been obtained via a one-pot reaction methodology. Each of these compounds is made up of the new type polyanion [(TaO2)6As4O24]10- with Ln3+ linkers, giving a one-dimensional chain. The compounds represent the first family of "pure" Ta-based polyoxometalate lanthanide derivatives. These architectures were characterized by various physicochemical analyses. Furthermore, the photoluminescence properties of compounds 2-Eu and 8-Lu were also explored, and meanwhile time-resolved emission spectroscopy indicated that the {As4Ta6} segment makes a contribution to the energy transfer of compound 2 from the polyoxotantalate to the EuIII center, which efficiently facilitates emissions of the Eu3+ center.

Pyrazine dicarboxylate-bridged arsenotungstate: synthesis, characterization, and catalytic activities in epoxidation of olefins and oxidation of alcohols.

A praseodymium(iii)-containing arsenotungstate K16H15Li7[Pr2(H2O)3(pzdc)As3W29O103]2·38H2O (1) (pzdc = pyrazine-2,3-dicarboxylic acid) was synthesized by a conventional aqueous solution method and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and single crystal X-ray diffraction. Structural analysis revealed that compound 1 was constructed by two identical subunits {Pr2(H2O)3(AsW9O33)3W2O4} bridged together by two pzdc ligands. In addition, compound 1 could act as an efficient catalyst for the epoxidation of olefins and oxidation of alcohols with hydrogen peroxide (H2O2) as the oxidant. In particular, the turnover frequency (TOF) in the oxidation of 1-phenylethanol reached up to 10 170 h-1, which is higher than that of previously reported catalysts.

Well-tuned white-light-emitting behaviours in multicenter-Ln polyoxometalate derivatives: A photoluminescence property and energy transfer pathway study.

White light-emitting diodes (WLEDs) are of scientific significance in terms of their wide applications, and few uminescent materials based on white-light-emitting polyoxometalate (POM) derivatives have been reported till now. Herein, a series of organic chromophores modified POM derivatives [N(CH3)4]3K2Ln(C7H5O2)(H2O)2(α-PW11O39)]·11H2O (Ln3+ = Eu3+ (1), Tb3+ (2), Tm3+ (3), Lu3+ (4)) and multicenter-Ln analogues [N(CH3)4]3K2EuxTbyTm1-x-y(C7H5O2)(H2O)2(α-PW11O39)·11H2O (5-11) were synthesized successfully and were characterized by various physico-chemical analysis. The investigations indicate the white-light-emitting behavior can be well tuned by adjusting the molar ratio of Eu3+/Tb3+/Tm3+ = 0.06:0.10:0.84 in 9. The energy transfer process from organic benzoic and POM ligands to Eu3+, Tb3+ and Tm3+ emitting centers were detected through time-resolved emission spectroscopy (TRES) and the comparison of excitation of single-, double-, treble-Ln3+ mixed, indicating the energy can transfer from the photoexcitation O → M LMCT state of POM components and π → π* transition of organic ligand to sensitize the emissions of Ln3+ ions via intramolecular energy transition mechanism. The energy transfer between Eu3+ and Tb3+, Tm3+ and Eu3+, Tm3+ and Tb3+ ions also have been recorded and carefully studied by TRES and variations of Tm3+ luminescence lifetime in this context, and the results show a low-effectively process of energy transfer between Tm3+/Eu3+, Tm3+/Tb3+ ions and a relatively good energy transfer efficiency between Eu3+/Tb3+ ions.

Cobalt- and Nickel-Containing Germanotungstates Based on Open Wells-Dawson Structure: Synthesis and Characterization of Tetrameric Anion.

Two transition-metal-substituted compounds K10H10{[Co(H2O)2]2[Co(H2O)3]2(Ge4W36O130)}·32H2O (1Co) and K10H10{[Ni(H2O)2]2[Ni(H2O)3]2(Ge4W36O130)}·32H2O (2Ni), have been successfully synthesized, both of which consist of the S-shaped tetrameric structure {Ge4W36} constructed from trivacant Keggin-type germanotungstate precursor K8Na2[ A-α-GeW9O34]·25H2O. These compounds were characterized by single crystal X-ray diffraction crystallography, X-ray powder diffraction (XRD), Raman spectra, thermogravimetric analysis (TGA), electrochemistry, and IR spectra. In addition, the UV spectra and the electrospray-ionization mass spectra (ESI-MS) were employed to investigated the stable pH value range of 1Co and 2Ni in aqueous solution.

Utilizing the adaptive precursor [As2W19O67(H2O)]14- to support three hexanuclear lanthanoid-based tungstoarsenate dimers.

Three tartrate-bridging lanthanide-based tungstoarsenate dimers K11H13[Ln3(H2O)8(OH)2(AsW9O33)(AsW10O35(C4O6H3))]2·nH2O (Ln3+ = Eu3+ (1Eu), n = 50; Tb3+ (2Tb), n = 34; C4O6H6 = tartaric acid) and K15H9[Dy3(H2O)15(OH)2(AsW9O33)(AsW10O35(C4O6H3))]2·21H2O (3Dy) have been synthesized and further characterized by elemental analyses, X-ray powder diffraction, IR spectra, thermogravimetric analyses and single-crystal X-ray diffraction. Structural analyses indicate that all the polyanions of 1Eu-3Dy are isostructural, and are composed of two identical asymmetric sandwiched subunits [Ln3(H2O)8(OH)2(AsW9O33)(AsW10O35(C4O6H3))]12- interlinked by two tartrate ligands. Furthermore, the photoluminescence and variable-temperature magnetic properties of 1Eu, 2Tb and 3Dy have also been investigated.

Elucidating white light emissions in Tm3+/Dy3+ codoped polyoxometalates: a color tuning and energy transfer mechanism study.

The double-tartaric bridging Tm-substituted POM derivative [N(CH3)4]6K3H7[Tm(C4H2O6)(α-PW11O39)]2·27H2O (1) was successfully synthesized and well characterized by various physico-chemical analyses. Furthermore, the mixed Dy3+/Tm3+ ion-based POM derivatives [N(CH3)4]6K3H7[DyxTm1-x(C4H2O6)(α-PW11O39)]2·27H2O (3-8) were first synthesized and confirmed by PXRD and IR spectra, indicating compounds 3-8 are isomorphic with 1. The detailed analyses of Ln-O-W bond angle and coordinated aqua ligands around emitting Ln3+ ions have revealed that the mentioned negative factors do not effectively affect the luminescence of emitting Ln3+ ions in 1-8. Investigations of PL emissions reveal that 3-8 can display color-tunable PL properties, emitting color from blue to white to yellow. The study of time-resolved emission spectroscopy of 6 indicates the energy can transfer from the LMCT excited state of POM fragments to Tm3+ and/or Dy3+ ions. Furthermore, the decreased luminescent lifetime of Tm3+ ions in 3-8 reasonably verifies the energy transfer from Tm3+ to Dy3+ ions to efficiently facilitate emissions of the Dy3+ centre.

Enhanced Photostability Luminescent Properties of Er3+-Doped Near-White-Emitting Dy xEr(1- x)-POM Derivatives.

A series of Dy xEr(1- x)-polyoxometalates (POMs) were successfully synthesized and characterized well by various physicochemical analysis. The structurally isolated compounds exhibit three characteristic emissions at 480 nm (blue, 4F9/2 → 6H15/2 transition), 573 nm (yellow, 4F9/2 → 6H13/2 transition), and 663 nm (red, 4F9/2 → 6H11/2 transition) whose luminescent color coordinates appear in the near-white area in the CIE 1931 chromaticity diagram. Time-resolved emission spectroscopy was used in Dy xEr(1- x)-POM to further authenticate energy transfer from the photoexcitation O → M ligand to the metal charge-transfer state of phosphotungstate components to active Dy3+/Er3+ ions and energy transfer between Dy3+ ion and Er3+ ion via intramolecular energy transitions. The relative emission intensity of ∼32%, ∼53%, and ∼85% for Dy-POM, Dy0.9Er0.1-POM, and Dy0.8Er0.2-POM respectively, were obtained under 300 min of UV irradiation, which indicates better photostability of Dy0.8Er0.2-POM. Furthermore, Dy xEr(1- x)-POM samples can emit macroscopic white light under blue irradiation.

A helical chain-like organic-inorganic hybrid arsenotungstate with color-tunable photoluminescence.

A 1-D infinite helical chain-like organic-inorganic hybrid arsenotungstate Na4H8[{Pr(H2O)2}2{As2W19O68}{WO2(mal)}2]·24H2O (mal = malate) (1) was prepared, which was characterized by elemental analyses, thermogravimetric (TG) analyses, IR spectroscopy, powder X-ray diffraction (PXRD) and X-ray single-crystal diffraction. Structural characterization revealed that 1 comprises the organo-functionalized [{As2W19O68}{WO2(mal)}2]18- polyanions hinged together by the Pr3+ ions forming a 1-D infinite helical chain-like architecture. The malate ligand may play a vital role to stabilize the structure of 1 by the formation of the five-membered W-O-C-C-O chelate ring. Solid state photoluminescence reveals that 1 features excitation wavelength-dependent emission properties, achieving a reversible emission color switching simply via changing the excitation wavelength. Time-resolved emission spectroscopy (TRES) indicates that the photoexcitation O → M ligand to metal charge transfer (LMCT) of arsenotungstate fragments can sensitize the Pr3+ ions through intramolecular energy transitions in 1.

Synthesis, crystal structure and biological evaluation of a main group seven-coordinated bismuth(III) complex with 2-acetylpyridine N4-phenylthiosemicarbazone.

Up to now, bismuth(III) complexes with thiosemicarbazones have been comparatively rare. Here, a main group seven-coordinated bismuth(III) complex [Bi(L)(NO3)2(CH3CH2OH)] (1) (HL = 2-acetylpyridine N(4)-phenylthiosemicarbazone) has been synthesized and characterized by elemental analysis, IR, (1)H NMR and single-crystal X-ray diffraction studies. The cytotoxicity data suggest that 1 exhibits higher in vitro antiproliferative activity in four human cancer cells tested. Its possible apoptotic mechanism has been evaluated in HepG2 cells. Compound 1 promotes a dose-dependent apoptosis in HepG2 cells and the apoptosis is associated with an increase in intracellular reactive oxygen species (ROS) production and reduction of mitochondrial membrane potential (MMP).