Effect of Metal-Ligand Bond Distances on Rates of Electron-Transfer Reactions. The Crystal Structures of Hexaammineruthenium(II) Iodide, [Ru(NH3)6]I2, and Hexaammineruthenium(III) Tetrafluoroborate, [Ru(NH3)6][BF4]3

Helen C. Stynes, James A Ibers

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Abstract

The crystal and molecular structures of hexaammineruthenium(II) iodide and hexaammineruthenium((II) tetrafluoroborate have been determined from three-dimensional X-ray data collected at room temperature by counter methods. The two complexes both crystallize with four formula units in the cubic space group Oh6-Fm3m, with m3m site symmetry imposed on the cations RuII(NH3)62+ and RuII(NH3)63+. The ruthenium(II) complex has a unit cell edge a = 10.841 (4) Å. The structure has been refined by least-squares techniques to a conventional R factor of 2.1% on F, using 139 unique reflections for which F2 = 3σ(F2). The ruthenium(III) complex has a unit cell edge a = 11.385 (1) Å. The least-squares refinement on F, using 385 independent reflections for which F2 = 3σ(F2), converged to a conventional R factor of 4.7%. The Ru(II)-NH3 distance is 2.144 (4) Å and the Ru(III)-NH3 distance is 2.104 (4) Å, a significant difference of 0.040 (6) Å. This result in conjunction with the known difference of 0.178 (17) A between the Co(II)-NH3 and Co(III)-NH3 bond distances leads to the conclusion that the electrostatic effect on bond distances is significantly smaller than the effect of spin change. From a calculation of ligand field stabilization energy it is found that the anomalous slowness of the electron transfer between Co(NH))62+ and Co(NH3)63+ arises from the.difference in energy between the spin states of the two exchanging ions and not from the bond length reorganization energy.

Original languageEnglish (US)
Pages (from-to)2304-2308
Number of pages5
JournalInorganic Chemistry
Volume10
Issue number10
DOIs
StatePublished - Oct 1 1971

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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