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Diagnostic features such as [ν(SiH) versus ν(NH2, in IR spectra and [δ(SiH) versus δ(NH2, in 1H-NMR spectra of the final solid allow extrapolation of the relative, ≡SiO)2Ta(=NH)(NH2, ≡SiO) 3TaIII] ratio and agree with this estimate. Furthermore, control experiments performed on, ≡SiO)2TaH] and, ≡SiO)2TaH3] under the same conditions as Fig. 2C, but with dinitrogen replaced by helium, showed the conversion of ∼50% of the surface tantalum hydrides to, ≡SiO)3TaIII, in agreement with the estimate. Independent experiments have shown that, ≡SiO)3TaIII] does not react with dinitrogen under the conditions of Fig. 2C
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III] does not react with dinitrogen under the conditions of Fig. 2C.
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19
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34548244039
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3 (16). Furthermore, the reaction in Fig. 3D accounts for the further increase of surface heterogeneity.
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3 (16). Furthermore, the reaction in Fig. 3D accounts for the further increase of surface heterogeneity.
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20
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34548268559
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Materials and methods and additional data are available as supporting material on Science Online.
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Materials and methods and additional data are available as supporting material on Science Online.
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2 coordination motifs to the tantalum center of 1a and 1b are possible, some of which are expected to show no IR absorption or have such absorption obscured by the opaque region of the silica support under study (32).
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2 coordination motifs to the tantalum center of 1a and 1b are possible, some of which are expected to show no IR absorption or have such absorption obscured by the opaque region of the silica support under study (32).
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32
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34548271417
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We have independently assessed that (i) the hydrazido complex, ≡SiO)2TaHx(NH-NH2, can be an intermediate in the synthesis of 2 and (ii) if formed, it cannot be detected under our experimental conditions because it leads directly to the final product 2. We have exposed starting hydrides 1 directly to hydrazine, N2H4 (10 torr, five-fold excess with respect to tantalum, 80°C) and observed the direct formation of 2 (20, Under the assumption that the primary reaction product between hydrazine and 1 is due to N-H activation by tantalum-hydrides, thus leading to the transient hydrazido complex, this result shows that a single-metal hydrazido complex of type, ≡SiO)2Ta(N2H3)H x] leads directly to 2. The IR spectroscopic evidence presented in the text for the formation of intermediates with reduced N-N bond order upon heating the
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2)].
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34
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35
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34548263653
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Some of the solid-state NMR spectra were recorded at the Rhone-Alpes European Large Scale Facility for NMR. Centre Informatique National de l'Enseignement Supérieur (CINES) and Institut du Développement et des Ressources en Informatique Scientifique (IDRIS) French national computing centers are thanked for generous donation of computing time. We are grateful to S. Fiddy of Council for the Central Laboratory of the Research Councils (CCLRC) Daresbury Laboratory for help in the EXAFS studies. The Centre National pour la Recherche Scientifique (CNRS) and Ecole Supérieure de Chimie Physique Electronique de Lyon (ESCPE-Lyon) are gratefully acknowledged for funding, the French Ministère délegué à la recherche for a Ph.D. fellowship to P.A, and CNRS for an associate research position to X.S.M
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Some of the solid-state NMR spectra were recorded at the Rhone-Alpes European Large Scale Facility for NMR. Centre Informatique National de l'Enseignement Supérieur (CINES) and Institut du Développement et des Ressources en Informatique Scientifique (IDRIS) French national computing centers are thanked for generous donation of computing time. We are grateful to S. Fiddy of Council for the Central Laboratory of the Research Councils (CCLRC) Daresbury Laboratory for help in the EXAFS studies. The Centre National pour la Recherche Scientifique (CNRS) and Ecole Supérieure de Chimie Physique Electronique de Lyon (ESCPE-Lyon) are gratefully acknowledged for funding, the French Ministère délegué à la recherche for a Ph.D. fellowship to P.A., and CNRS for an associate research position to X.S.M.
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