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Titolo:
Solid and solution state NMR spectra and the structure of the gallium citrate complex (NH4)(3)[Ga(C6H5O7)(2)]center dot 4H(2)O
Autore:
Hawkes, GE; OBrien, P; Salacinski, H; Motevalli, M; Abrahams, I;
Indirizzi:
Univ London Queen Mary & Westfield Coll, Dept Chem, Struct Chem Grp, London E1 4NS, England Univ London Queen Mary & Westfield Coll London England E1 4NS S, England Univ London Imperial Coll Sci Technol & Med, Dept Chem, London SW7 2AY, England Univ London Imperial Coll Sci Technol & Med London England SW7 2AY gland
Titolo Testata:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY
fascicolo: 4, , anno: 2001,
pagine: 1005 - 1011
SICI:
1434-1948(200104):4<1005:SASSNS>2.0.ZU;2-C
Fonte:
ISI
Lingua:
ENG
Soggetto:
NUCLEAR-MAGNETIC-RESONANCE; CRYSTAL-STRUCTURE; ANTITUMOR ACTIVITY; AQUEOUS-SOLUTION; ALUMINUM; SPECTROSCOPY; DIFFUSION; TOXICITY; BINDING; SALTS;
Keywords:
gallium; NMR spectroscopy; structure elucidation; citrate speciation;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
36
Recensione:
Indirizzi per estratti:
Indirizzo: Hawkes, GE Univ London Queen Mary & Westfield Coll, Dept Chem, Struct ChemGrp, Mile End Rd, London E1 4NS, England Univ London Queen Mary & Westfield Coll Mile End Rd London England E1 4NS
Citazione:
G.E. Hawkes et al., "Solid and solution state NMR spectra and the structure of the gallium citrate complex (NH4)(3)[Ga(C6H5O7)(2)]center dot 4H(2)O", EUR J INORG, (4), 2001, pp. 1005-1011

Abstract

A gallium citrate complex (NH4)(3)[Ga(C6H5O7)(2)].4H(2)O (1) has been isolated from an aqueous mixture of gallium nitrate and citric acid at pH = 9. In the solid state 1 is monomeric and includes the near centrosymmetric ion[Ga(C6H5O7)(2)](3-) in the asymmetric unit, with each tridentate citrate coordinating to gallium through an alkoxide oxygen, an oxygen of the centralcarboxyl group and an oxygen of a terminal carboxyl group. The second terminal carboxyl group is not bound to the metal centre. The two alkoxide oxygen-gallium distances in the asymmetric unit are significantly shorter than the four carboxyl oxygen-gallium distances, indicating a stronger bond for the former, The number and intensities of the resolved resonances in the solid state C-13 MAS/NMR spectrum are consistent with the X-ray structure. Inaqueous solution near neutral pH (5.5 to 6.4) the complex partially dissociates to give an equilibrium of the 1:1 and 1:2 gallium/citrate species together with free citrate. Two sets of resonances are observed in both the H-1 and C-13 NMR spectra of solutions of the complex and these correspond to bound and free citrate; there is no resolution of resonances for the 1:1 and 1:2 species. The relative strength of the alkoxide oxygen-gallium bond inthe metal-bound citrate ligand leads to a slow intermolecular chemical exchange situation (rate < ca. 12 s(-1)) between the bound and free Ligand. The carboxylate oxygen-gallium bonds are quite labile and relatively rapid intramolecular chemical exchange occurs (rate > ca. 700 s(-1)) between the metal-bound and pendant terminal carboxyl groups, averaging their H-1 and C-13 NMR signals. The diffusion coefficients for the free and complexed citrate measured from the H-1 NMR spectra do not appear to be complicated by chemical exchange effects and, as expected, the diffusion coefficient for the complexed Ligand is smaller than for the free Ligand. In solution in the intermediate pH range (4.8 to 6.4) a new Ga-71 signal is observed at ca. delta= 27 (Delta nu (1/2) approximate to 10.6 kHz) which is assigned to the gallium citrate complexed species.

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Documento generato il 23/09/20 alle ore 05:27:44