EUROPIUM(III) COMPLEXES OF POLYFUNCTIONAL CARBOXYLIC-ACIDS - LUMINESCENCE PROBES OF POSSIBLE BINDING-SITES IN FULVIC-ACID

The F-7(0) --> D-5(0) excitation spectra of Eu(III) complexed with pol yfunctional dicarboxylic acid containing neutral O, N, and S donors we re investigated using Eu(III) luminescence spectroscopy. Three distinc t peaks are seen in the excitation spectra in the Eu(III)-diglycolic a cid (ODA) and Eu(III)-iminodiacetic acid (IMDA) systems showing the fo rmation of three species, where each tridentate ODA(2-) and IMDA(2-) d isplace approximately three coordinated water molecules; however, the central S donor of Eu(III)-thiodiglycolate and 2,5-thiophenedicarboxyl ate are shown to be poor chelators for free Eu3+ ions. The neutral O a nd N donors in combination with neighboring carboxylates may form stro ng metal chelation sites on fulvic acid. (C) 1997 Academic Press.