Photodegradation of [FeIIIEDTA

As discussed in Section 6.3 some EDTA complexes are light-sensitive; for instance, [Fe(III)EDTA] can undergo total photolysis in a sunny day within several hours. Others are only slightly affected (e.g., [Mn(II)EDTA], [Co(III)EDTA]), while others are not affected by light at all. The ability of [Fe(III)EDTA] to undergo a photoredox reaction is very fortunate because—as stated above—EDTA is a refractory compound and thus the natural pho-tolytic pathway provides a means for its destruction.

A simplified photoreduction reaction using a car-boxylic anion as the ligand (e.g., oxalate) is the following:

[Fe(III)(C204)3]3-+/*v -»• Fe(II) + 2C2042~ + C02" + C02 (1)

Note that in the C2O42 ligand, C has an oxidation state of 3+ whereas in C02 it is 4+. Then, C underwent oxidation in order to reduce Fe(III) to Fe(II), which is then released from the complex.

In the following qualitative experiment, an [Fe(III)EDTA] complex will be exposed to light (either natural or artificial) and decomposed to produce Fe(II), which then reacts with iron hexacyanate (III) yielding a highly colored solution of another complex (see Ibanez, 2000).

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