Chemistry of Tantalum Clusters in Solution and on SiO<sub>2</sub> Supports:  Analogies and Contrasts

Nemana, Sailendra; Okamoto, Norihiko L.; Browning, Nigel D.; Gates, Bruce C.

doi:10.1021/la063769j

Cited by 7 publications

(3 citation statements)

References 47 publications

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“…As presented in Figure , a lithiation process for BTT and SBT gives rise to slight red-shifts of peaks A and B by ∼0.2−0.5 eV, reflecting the reduction of tantalum ion. Taking into account the fact that an energy change by ∼1 eV in Ta L III -edge region corresponds to a change of ∼0.7 electronic charge on Ta, the observed red shift suggests only a slight decrease of the Ta oxidation state (i.e., ∼0.15−0.35) upon the lithiation. In addition to the variation of Ta oxidation state, the energies of peaks A and B are dependent on the strength of crystal field around the Ta ions.…”

Section: Resultsmentioning

confidence: 95%

Effect of Bond Covalency on the Lattice Stability and Fatigue Behavior of Ferroelectric Bismuth Transition-Metal Oxides

et al. 2008

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The effects of bond covalency on the chemical bonding nature and lattice stability of ferroelectric bismuthbased transition-metal oxides have been investigated systematically through comparative X-ray absorption spectroscopic studies for several Aurivillius-structured materials and their chemically reduced derivatives. According to Ti K-edge X-ray absorption near-edge structure (XANES) analysis, Bi 3 TaTiO 9 shows a weaker strength of (Ti IV -O) bonds than Bi 4 Ti 3 O 12 , which could be interpreted as a result of the bond competition with highly covalent (Ta V -O) bonds. Also, it was found that a lithiation process gives rise to a remarkable variation of Ti local structure commonly for Bi 3 TaTiO 9 and Bi 4 Ti 3 O 12 . In contrast, there is only a slight spectral change in the Ta L III -edge XANES spectra of Bi 3 TaTiO 9 and SrBi 2 Ta 2 O 9 upon the chemical reduction, underscoring the higher stability of more covalent (Ta V -O) bonds than (Ti IV -O) bonds. Alternatively, an energy difference between the peaks corresponding to Ta 2p 3/2 f Ta 5d t 2g and Ta 2p 3/2 f Ta 5d e g transitions appears to be greater for Bi 3 TaTiO 9 than for SrBi 2 Ta 2 O 9 , indicating that the bond competition between collinear (Ta-O) and (Ti-O) bonds has a greater influence on the crystal field of TaO 6 octahedra than an interaction between perpendicularly aligned (Ta-O) and (Bi/Sr-O) bonds. On the basis of the present experimental findings, we are able to conclude that the highly resistive nature of the (Ta V -O) bonds against the increase of electronic charge is responsible for the excellent cycle characteristics of the SrBi 2 Ta 2 O 9 phase. In this regard, the incorporation of highly covalent metal ions into the octahedral sites of the Aurivillius-structured lattice is supposed to be effective in improving the lattice stability and memory performance of this ferroelectric metal oxide.

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Section: Resultsmentioning

confidence: 95%

Effect of Bond Covalency on the Lattice Stability and Fatigue Behavior of Ferroelectric Bismuth Transition-Metal Oxides

et al. 2008

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“…The samples were prepared by adsorption of Ta(CH 2 Ph) 5 on nonporous powder SiO 2 that had been calcined at 773 K; the resultant material was treated in flowing H 2 at 423 K for 3 h; details regarding the treatment are given in the Experimental Section. Complementary results pertaining to this sample are given elsewhere . A summary of the sample treatments and characterizations is given in Table .…”

Section: Resultsmentioning

confidence: 98%

Reactivity of Binuclear Tantalum Clusters on Silica: Characterization by Transient Time-Resolved Spectroscopy

Nemana

Gates

2008

J. Phys. Chem. C

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Binuclear tantalum clusters were synthesized from Ta(CH2Ph)5 (Ph is phenyl) on the surface of nonporous SiO2 (Aerosil), and their reactions with H2, D2, and ethylene were characterized by time-resolved infrared (IR), extended X-ray absorption fine structure (EXAFS), and X-ray absorption near edge spectroscopies. The EXAFS data indicate the formation in H2 of clusters with a Ta−Ta coordination number of approximately 1 and a bonding distance of 2.74 Å. Reactions of the supported clusters with D2 and H2 facilitate the interconversion of O−H and O−D groups on the SiO2 surface. Reaction of these clusters with ethylene led to their rapid fragmentation to give mononuclear tantalum complexes, as the tantalum was oxidized and new ligands formed, suggested by IR spectra to be ethyl. The results demonstrate a rough analogy between the chemistry of tantalum clusters on the SiO2 surface and their chemistry in solution. Because alkenes are suggested intermediates in the catalytic disproportionation of alkanes on supported tantalum, our results indicate how these intermediates might influence the nature of the catalytically active species.

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“…23,32 The tantalum L III -edge EXAFS signal is acquired for the ( SiO) 3 Ta as prepared. As we know 2 is possibly decomposed by a surface "bimolecular" pathway, we analyzed the EXAFS data of 3 with increased k range to identify any possible cluster formed on the surface, since the detection of Ta−Ta contributions with a bond distance ranging from 2.9 to 3.1 Å is best resolved when k values are higher than 10.5 Å −1 (for a tantalum cluster supported on silica 33 ). Thus, the value of k range we used was up to 12.6 Å −1 , and no contribution attributed to the presence of a Ta−Ta bond could be found, illustrating that the formation of a tantalum cluster is negligible in the preparation of (SiO) 3 Ta.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Facile and Efficient Synthesis of the Surface Tantalum Hydride (≡SiO)₂Ta^IIIH and Tris-Siloxy Tantalum (≡SiO)₃Ta^III Starting from Novel Tantalum Surface Species (≡SiO)TaMe₄ and (≡SiO)₂TaMe₃

et al. 2014

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By grafting of TaMe 5 (1) on the surface of silica partially dehydroxylated at 500 °C (silica 500 ), a mixture of (SiO)TaMe 4 (2a; major, 65 ± 5%) and (SiO) 2 TaMe 3 (2b; minor, 35 ± 5%) was produced, which has been characterized by microanalysis, IR, and SS NMR ( 1 H, 13 C, 1 H− 13 C HETCOR, proton double and triple quantum). After grafting, these surface organometallic compounds are more stable than the precursor TaMe 5 . Treatment of 2a,b with water and H 2 resulted in the formation of methane in amount of 3.6 ± 0.2 and 3.4 ± 0.2 mol/grafted Ta, respectively. 2a,b react with H 2 (800 mbar) to form (SiO) 2 TaH. After (SiO) 2 TaH was heated to 500 °C under hydrogen or vacuum, [(SiO) 3 Ta][SiH] was produced, and the structure was confirmed by IR, NMR, and EXAFS. Considering the difficulty of the previous preparation method, these syntheses represent a facile and convenient way to prepare tantalum surface species (SiO) 2 TaH and (SiO) 3 Ta via the intermediate of the new surface organometallic precursors: (SiO)TaMe 4 /(SiO) 2 TaMe 3 . ( SiO) 2 TaH and (SiO) 3 Ta exhibit equal reactivities in alkane metathesis and ethylene polymerization in comparison to those in previous reports.

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Chemistry of Tantalum Clusters in Solution and on SiO₂ Supports: Analogies and Contrasts

Cited by 7 publications

References 47 publications

Effect of Bond Covalency on the Lattice Stability and Fatigue Behavior of Ferroelectric Bismuth Transition-Metal Oxides

Effect of Bond Covalency on the Lattice Stability and Fatigue Behavior of Ferroelectric Bismuth Transition-Metal Oxides

Reactivity of Binuclear Tantalum Clusters on Silica: Characterization by Transient Time-Resolved Spectroscopy

Facile and Efficient Synthesis of the Surface Tantalum Hydride (≡SiO)₂Ta^IIIH and Tris-Siloxy Tantalum (≡SiO)₃Ta^III Starting from Novel Tantalum Surface Species (≡SiO)TaMe₄ and (≡SiO)₂TaMe₃

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Chemistry of Tantalum Clusters in Solution and on SiO2 Supports: Analogies and Contrasts

Cited by 7 publications

References 47 publications

Effect of Bond Covalency on the Lattice Stability and Fatigue Behavior of Ferroelectric Bismuth Transition-Metal Oxides

Effect of Bond Covalency on the Lattice Stability and Fatigue Behavior of Ferroelectric Bismuth Transition-Metal Oxides

Reactivity of Binuclear Tantalum Clusters on Silica: Characterization by Transient Time-Resolved Spectroscopy

Facile and Efficient Synthesis of the Surface Tantalum Hydride (≡SiO)2TaIIIH and Tris-Siloxy Tantalum (≡SiO)3TaIII Starting from Novel Tantalum Surface Species (≡SiO)TaMe4 and (≡SiO)2TaMe3

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Chemistry of Tantalum Clusters in Solution and on SiO₂ Supports: Analogies and Contrasts

Facile and Efficient Synthesis of the Surface Tantalum Hydride (≡SiO)₂Ta^IIIH and Tris-Siloxy Tantalum (≡SiO)₃Ta^III Starting from Novel Tantalum Surface Species (≡SiO)TaMe₄ and (≡SiO)₂TaMe₃