⁹⁵Mo NMR study of the effect of structure on complexation of molybdate with alpha and beta hydroxy carboxylic acid ligands

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• 作者：Claude H. Yoder ; ^{cyoder@fandm.edu" class="auth_mail" title="E-mail the corresponding author} ; Emily L. Christie ; Jennifer L. Morford
• 关键词：Molybdate ; Hydroxy carboxylic acids ; 95Mo NMR ; Glycolic acid ; Lactic acid
• 刊名：Polyhedron
• 出版年：2016
• 出版时间：16 August 2016
• 年：2016
• 卷：114
• 期：Complete
• 页码：23-28
• 全文大小：674 K

文摘

The utility of the quadrupolar, spin 5/2 ⁹⁵Mo nucleus in NMR studies of complexation of molybdate have been demonstrated using model alpha hydroxy carboxylic acids. The ⁹⁵Mo NMR spectra show a down field shift of the resonance upon complexation, presumably due to the smaller 1/ΔE paramagnetic shift term for the octahedral molybdate complexes relative to the tetrahedral molybdate ion. The ⁹⁵Mo resonances are sufficiently distinct to establish three solution complexes for the reaction of lactic acid with molybdate. The effect of the structure of hydroxy carboxylic acids on complexation to molybdate (MoO₄²⁻) was studied with ¹³C and ⁹⁵Mo NMR spectroscopy. The use of the NMR spectra of both nuclei allows monitoring of the Lewis acidic molybdate site and the Lewis basic ligands. The beta hydroxy carboxylic acids, 3-hydroxypropanoic acid and salicylic acid, did not form complexes with molybdate, suggesting a preference for 5-membered chelated rings. The Lewis acidity of the negatively charged molybdate ion is rationalized with two schemes for the reaction with the chelating bidentate alpha hydroxy carboxylic acids.