2,3-Bis( p-methoxybenzoyl)cyclopentadiene was studied as iron(III)-chelating agent. Its pKa value was determined by spectrophotometry (pKa = 8.27
0.02 at 25
0.1C;  = 421 nm). 2,3-Bis( p-methoxybenzoyl) cyclopentadiene reacts with Fe3+ ions in aqueous ethanol (1 : 1, by volume) to give a 2 : 1 ligand metal complex. The effects of different factors on the complex formation were studied. The reaction of 2,3- bis( p-methoxybenzoyl)cyclopentadiene with Fe3+ ions can be used as an alternative method for spectrophotometric determination of iron(III) in a range of concentrations from 0.1 to 1 g cm3, where the Beer law is fulfilled with a correlation coefficient of 0.9992. The results of spectrophotometric determination of iron(III) in geological materials (iron rock) showed very good agreement with those obtained by the atomic absorption measurements.

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