Contrasting the Group 6 metal-metal bonding in sodium dichromate(II) and sodium dimolybdate(II) polymethyl complexes: synthetic, x-ray crystallographic and theoretical studies

Ross Campbell, Alan R. Kennedy, Ross McLellan, Stuart D. Robertson, Stephen Sproules, Robert E. Mulvey

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Abstract

Extending the class of group 6 metal-metal bonded methylate compounds supported by alkali metal counter-ions, the first sodium octamethylmolybdate(II) complex [(TMEDA)Na]4Mo2Me8 and heptamethylchromate(II) relations [(donor)Na]3Cr2Me7 (donor is TMEDA or TMCDA) are reported. The former was made by treating [(Et2O)Li]4Mo2Me8 with four equivalents of NaOtBu/TMEDA in ether; whereas the latter resulted from introducing TMEDA or TMCDA to ether solutions of octamethyldichromate [(Et2O)Na]4Cr2Me8. X-ray crystallography revealed [(TMEDA)Na]4Mo2Me8 is dimeric with square pyramidal Mo centres [including a short Mo–Mo interaction of 2.1403(3) Å] each with four methyl groups in a mutually eclipsed conformation. In dinuclear [(TMCDA)Na]3Cr2Me7 trigonal bi-pyramidal Cr centres each bond to three terminal methyl groups and one common Me bridge, that produces a strikingly short Cr–Cr contact of 1.9136(4) Å. Broken symmetry density functional theoretical calculations expose the multiconfigurational metal-metal bonding in these compounds with a Mo–Mo bond order of 3 computed for octamethylmolybdate(II). This is contrasted by the single Cr–Cr bond in heptamethylchromate(II) where the singlet ground state is derived by strong antiferromagnetic coupling between adjacent metal ions.
Original languageEnglish
Pages (from-to)6392-6403
JournalDalton Transactions
Volume46
Early online date26 Jan 2017
DOIs
Publication statusE-pub ahead of print - 26 Jan 2017

Keywords

  • group 6 metal-metal bonded methylate compounds
  • alkali metal counter-ions
  • metal-metal bonding
  • crystallographic characterisations
  • X-ray crystallography
  • synthesis

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