Hi!
Does anyone have ideas to separate Fe(II) complexes from Fe(III) complexes?
Context about the complexes:
1) Coordination of the ligand causes some type of Fe(III) to Fe(II) reduction (Always starting with Fe(III) sources)
2) They are neutral complexes that are coordinated by a macrocycle with three carboxylic acid groups and a fourth group that may or may not be coordinating
3) The only difference between the two complexes is one carboxylic acid is assumed to be uncoordinated in one
4) Most contain at least one CF3 group but the reduction behavior is seen in all of them
5) Less hydrophobic complexes can be separated reverse phase chromatography but the more hydrophobic they get the harder it is to separate
6) Complexes don't seem very stable on silica or alumina oxide gels
Edit to add that the Fe(II) complex is air-stable and I'm actually trying to isolate pure Fe(III)
Hi Raphael T Ryan
If it's true that there is one carboxylic group that is coordinated in the Fe(III) complex but not in the Fe(II) complex, you may be able to use it as your "handle" for separation.
Specifically, you can probably titrate this group with NaOH or KOH to form an alkali metal salt of the complex that will have markedly different solubility properties compared with the Fe(III) complex. Then you may be able to extract the Fe(III) complex selectively into a low-polarity, water-immiscible solvent (you'll have to figure out which solvents to try).
I realize this complex is a tough customer. Not clear whether the redox activity is intrinsic or at least partially driven by access to oxygen, but to be on the safe side I would use only thoroughly de-aired solutions in Schlenk tubes (or in a nitrogen-filled glove box). It may also help to work below room temperature (0-5 degC). Proton transfer will not be affected (so the titration will work fine), while redox reactions will be markedly slower.
Also make sure your macrocycles are peroxide-free before starting.
Good luck!
Emanuel Cooper
Raphael T Ryan Recrystallization or chromatography will help. Can everything be oxidized and synthesized into one complex?
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