A New Class of Ferromagnetically-Coupled Mixed Valence Vanadium(IV/V) Polyoxometalates.

MJ Manos, AJ Tasiopoulos, EJ Tolis, N Lalioti, John Derek Woollins, Alexandra Martha Zoya Slawin, MP Sigalas, TA Kabanos

Research output: Contribution to journalArticlepeer-review

51 Citations (Scopus)

Abstract

Reaction of [(VOCl2)-O-VI(thf)(2)] with a bidentate nitrogen-donor ligand (L: phen=1,10-phenanthroline, 5-mephen= 5-methyl-1,10-phenanthroline, bipy=2,2'-bipyridine, 5,5'-me(2)bipy=5,5'-dimethyl-2,2'-bipy) in methyl alcohol, in the presence of triethylamine, leads to the formation of hexameric [(V2V4V)-V-IV] oxo-alkoxo-vanadates of the general formula [V6O12-(mu(2)-OCH3)(4)(L)(4)].xH(2)O [L=phen (1 . 4H(2)O), 5-mephen (2 . 6H(2)O), bipy (3 . 4H(2)O), 5,5'-me(2)bipy (4 . H2O)]. X-ray structure analysis of 1 . 2H(2)O and 4. 8CH(3)OH revealed a pair Of V3O13N4 trimeric units sharing two corners, with a centrosymmetric planar V-6-core. In addition, a fully oxidized V-V species [(V4O8)-O-V(OCH3)(2)(mu(3)-OCH3)(2)(5,5'-me(2)bipy)(2)].3CH(3)OH (5 . 3CH(3)OH) was isolated from the reaction mixture used for the synthesis of 4 . H2O. The crystal structure of 5 . 3CH(3)OH revealed a dicubane-like framework with two missing vertices. Electron paramagnetic resonance (EPR) and variable temperature magnetic susceptibility studies for the hexamers 1 . 4 H2O and 3 . 4H(2)O showed the complete localization of the single 3d electrons on the V-IV ions and unusual ferromagnetic interaction between the two paramagnetic vanadium(iv) ions separated by a distance of about 5.1 Angstrom. Furthermore, intermolecular antiferromagnetic interactions through pi-contacts of phenyl rings were observed for these species below 8 K. The ferromagnetic exchange coupling observed in the hexanuclear compounds 1.4H(2)O and 3.4 H2O is also discussed using ab initio UHF calculations on a model compound. The value of the exchange coupling constant (3.7 cm(-1)) for this model compound, calculated using the broken symmetry approach, is in good agreement, both in sign and magnitude, with the experimental J values (6.00 cm(-1) for 1.4H(2)O and 8.54 cm(-1) for 3.4H(2)O).

Original languageEnglish
Pages (from-to)695-703
Number of pages9
JournalChemistry - A European Journal
Volume9
Issue number3
DOIs
Publication statusPublished - 3 Feb 2003

Keywords

  • ferromagnetism
  • intermolecular interaction
  • polyoxometalates
  • UHF calculations
  • vanadium
  • DENSITY-FUNCTIONAL THEORY
  • IRON-SULFUR CLUSTERS
  • HIGH-SPIN MOLECULES
  • BINUCLEAR COMPLEXES
  • MAGNETOSTRUCTURAL CORRELATIONS
  • STRUCTURAL CHARACTERIZATION
  • CARBOXYLATE CHEMISTRY
  • ORBITAL INTERACTIONS
  • MAGNETS
  • TETRANUCLEAR

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