ChemInform Abstract: CITRAT‐KOMPLEXE VON NB(V)

Григорьева, В. В.; Golubeva, I. V.

doi:10.1002/chin.197530353

Cited by 1 publication

(2 citation statements)

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“…A similar band is also observed in the spectra of malato− and tartarato−niobates . Moreover, there are significant changes in the 1300−1000 cm -1 region in comparison to the spectra of Na 3 (C 6 H 5 O 7 ) 2 which could indicate the coordination of the secondary hydroxyl group to niobium and the presence of a planar five-membered chelate ring characteristic of α-hydroxycarboxylic acid−niobium complexes . This is consistent with the observation of Dengel and Griffith that only carboxylate ligands which form a five-membered chelate ring lead to ternary peroxocarboxylato complexes of Nb, Ta, W, and Mo.…”

Section: Discussionsupporting

confidence: 89%

“…The increase in the stability of complexes formed at high pH is attributed to the structural differences between the low pH and high pH citrato−niobium complexes. At low pH the protons of the central carboxyl and a terminal carboxyl group of citric acid are substituted by niobium leading to the formation of a seven membered chelate ring . At pH > 5 the deprotonated hydroxyl and the central carboxyl groups are coordinated to niobium 7 to form a unique but stable five-membered chelate ring .…”

Section: Discussionmentioning

confidence: 99%

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Synthesis, Decomposition and Crystallization Characteristics of Peroxo−Citrato−Niobium: An Aqueous Niobium Precursor

1997

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The synthesis of peroxo−citrato−niobium, a novel aqueous precursor of niobium, is reported. Niobium oxalate was decomposed with acidified H2O2 to form a peroxo−niobium complex, which was reacted with citric acid at pH ∼ 7.5 to form the stable peroxo−citrato−niobium complex. IR and Raman spectroscopy indicate that the peroxo−citrato−niobium complex consists of tridentate bridging citrato and bidentate peroxo ligands. The aqueous complex is binuclear with peroxo groups chelated to niobium and the precipitated complex is polynuclear with bridging type peroxo groups. Due to kinetic limitations during crystallization, the formation of seven-coordinated niobium in peroxo−citrato−niobium energetically favors the formation of niobium oxides with seven-coordinated niobium, viz. TT−Nb2O5 and T−Nb2O5. Consequently, nanocrystalline metastable TT−Nb2O5, with a particle size of ∼25 nm, crystallizes from the peroxo−citrato−niobium complex at 580 °C. On further heating, TT−Nb2O5 transforms to T−Nb2O5 at 800 °C, M−Nb2O5 at 1000 °C, and H−Nb2O5 at 1200 °C. The nanometric particle size is retained after heating to 1200 °C and H−Nb2O5 has an average crystallite size of 53 nm.

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Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%