Which of the following complexes exhibit the highest paragmagnetic behavior? a. [Co(ox)2(OH)2]^- b. [Ti(NH3)6]^3+ c. [V(gly)2(OH)2(NH3)2]^+ d. [Fe(en)(bpy)(NH3)2]^2+

1 Answer
Mar 11, 2018

I found ["Co"("ox")_2("OH")_2]^(-)[Co(ox)2(OH)2] to have four unpaired electrons. That would make it the most paramagnetic.


I would first reference your text to check the charge of the ligands, but you would have to memorize these in an exam. I have a naming guide here.

  • "ox"ox is oxalato, a -22 bidentate ligand.
  • "gly"gly is glycine, a neutral ligand at "pH"pH 77. Since it has a carboxyl group, it is possible that it binds eta^2η2. It is also possible that it binds bidentate at basic "pH"pH.
  • "OH"OH is hydroxide, a -11 monodentate ligand.
  • "en"en and "bipy"bipy are both neutral bidentate ligands.

From that, we can then determine the oxidation states on each metal and thus their number of unpaired electrons.

  • ["Co"("ox")_2("OH")_2]^(-)[Co(ox)2(OH)2] has two -22 bidentate and two -11 monodentate ligands, giving a +3+3 oxidation state on cobalt, making it a d^6d6 metal in the octahedral ligand field.

Since "ox"^(2-)ox2 and "OH"^(-)OH are both fairly weak-field ligands (weaker sigma donors than water), this is likely a high spin d^6d6 complex, with four unpaired electrons.

https://chem.libretexts.org/

  • ["Ti"("NH"_3)_6]^(3+)[Ti(NH3)6]3+ has three neutral ammine ligands, each strong-field, making this a low-spin complex involving a d^1d1 metal. Only one unpaired electron.

  • ["V"("gly")_2("OH")_2("NH"_3)_2]^(+)[V(gly)2(OH)2(NH3)2]+ has two -11 hydroxo ligands, two neutral ammine ligands, and two neutral monodentate eta^2η2 glycine ligands (at "pH"pH 77), making this "V"^(+3)V+3, a d^2d2 metal with two unpaired electrons in the octahedral ligand field splitting diagram.

https://chem.libretexts.org/

I did not need to think about strong- or weak-field for either of the previous two complexes. Why is that?

  • ["Fe"("en")("bpy")("NH"_3)_2]^(2+)[Fe(en)(bpy)(NH3)2]2+ has two neutral bidentate ligands (ethylenediamine and 2,2'-bipyridine), and two neutral monodentate ammine ligands, making iron a +2+2 oxidation state. We therefore have a d^6d6 metal in an octahedral ligand field consisting of three species of strong-field ligands, giving a low-spin d^6d6 configuration, having diamagnetism.

https://chem.libretexts.org/