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+

I found `["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"` is oxalato, a `-2` bidentate ligand.
• `"gly"` is glycine, a neutral ligand at `"pH"` `7`. Since it has a carboxyl group, it is possible that it binds `eta^2`. It is also possible that it binds bidentate at basic `"pH"`.
• `"OH"` is hydroxide, a `-1` monodentate ligand.
• `"en"` and `"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]^(-)` has two `-2` bidentate and two `-1` monodentate ligands, giving a `+3` oxidation state on cobalt, making it a `d^6` metal in the octahedral ligand field.

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

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

• `["V"("gly")_2("OH")_2("NH"_3)_2]^(+)` has two `-1` hydroxo ligands, two neutral ammine ligands, and two neutral monodentate `eta^2` glycine ligands (at `"pH"` `7`), making this `"V"^(+3)`, a `d^2` metal with two unpaired electrons in the octahedral ligand field splitting diagram.

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+)` has two neutral bidentate ligands (ethylenediamine and 2,2'-bipyridine), and two neutral monodentate ammine ligands, making iron a `+2` oxidation state. We therefore have a `d^6` metal in an octahedral ligand field consisting of three species of strong-field ligands, giving a low-spin `d^6` configuration, having diamagnetism.