4. H. Bolvin (pages 417 – 427) studied the Creutz-Taube ion, [(NH3)5Ru-pyrazine-Ru(NH3)5]5+ (pyrazine is shown below). Estimate the LFSE for each Ru ion and determine the spin only magnetic moment.

 

Answer

In the limit of localized charges, the Ru have different oxidation states: Ru2+ and Ru3+. All of the ligands are strong field, so the electron configurations are t2g6 for the Ru2+ with LFSE = –24Dq + 2P and t2g5 for the Ru3+ with LFSE = –18Dq + 2P. Magnetic moments can not be separated onto the individual ions but the entire complex has 1 unpaired spin so μ = [1(1+2)]½ = 1.73 Bohr-magnetons.