Dinuclear oxomolybdate(v) species with oxalato and pyridine ligands revisited: cis/trans isomerization of [Mo2O42-C2O4)2(R-Py)2] 2- (R-Py = pyridine, alkyl-substituted pyridine) in water evidenced by NMR spectroscopy

Barbara Modec, Darko Dolenc, Jurij V. Brenčič, Jože Koller, Jon Zubieta

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Abstract

The simple oxohalomolybdate(V) ions [MoOCl4(H 2O)]- and [MoOBr4]- were reacted with oxalic acid in mixtures containing an alcohol and a pyridine (R-Py) to form the dinuclear anions [Mo2O42-C 2O4)2(R-Py)2)2] 2- based on the {Mo2O4}2+ structural core. The dinuclear anion exists in two isomeric forms - as a trans and as a cis isomer. A trans arrangement of the pyridine ligands relative to the Mo 22-O)2 bridge was observed for (PyH) 2[Mo2O42-C2O 4)2Py2] (1), (PyH)2-[Mo 2O42-C2O4) 2(3,5-Lut)2] (2), [MeNC5H3(Me) 2]2[Mo2O4-(η2-C 2O4)2(3,5-Lut)2]·H 2O (3), (4-MePyH)2[Mo2O42-C2O4)2-(4-MePy) 2]·1/2(4-MePy) (5), and [(C6H5) 4P]2[Mo2O42-C 2O4)2-Py2]·H2O (7) [Py = pyridine; 3,5-Lut = 3,5-lutidine; MeNC5H3(Me) 2+ = N-methyl-3,5-lutidinium cation and 4-MePy = 4-methylpyridine], while a cis arrangement was found in only two compounds, namely (4-EtPyH)2[Mo2O42- C2O4)2(4-EtPy)2] (4) (4-EtPy = 4-ethylpyridine) and (4-MePyH)3[Mo2O42-C2O4)2(4-MePy)2]Br (6). The solution chemistry of the trans-[Mo2O42-C2O4)2Py2] 2- anion was monitored by 1H and 13C variable temperature NMR spectroscopy and showed evidence of two processes: the substitution of a pyridine ligand for water, coupled with cis/trans isomerization. Both reactions were exploited in the preparation of trans-(PyH)2[Mo2O42-C 2O4)2(H2O)2] (8) from a water/methanol solution of cis-(4-EtPyH)2[Mo2O 42-C2O4)2(4-EtPy) 2] (4). trans-(PyH)2[Mo2O42-C2O4)2(H2O) 2] (8) was seen to react with methanol with the rupture of the molybdenum-to-oxalate bonds resulting in the cyclic octanuclear anion which crystallizes as a pyridinium salt, (PyH)2[Mo8O 16(OCH3)88-C2O 4)]·2CH3OH (9). The compounds were fully characterized by X-ray structural analysis and IR spectroscopy. MO calculations were performed on the isomeric pair of [Mo2O42-C2O4)2(4-MePy)2] 2- in order to establish their relative energies.

Original languageEnglish (US)
Pages (from-to)3224-3237
Number of pages14
JournalEuropean Journal of Inorganic Chemistry
Issue number16
DOIs
StatePublished - Aug 19 2005

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Keywords

  • Isomerization
  • Molybdenum
  • N ligands
  • NMR spectroscopy
  • Polyoxometalates

ASJC Scopus subject areas

  • Inorganic Chemistry

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