EVALUATION OF SOLUTION STRUCTURES OF HIGHLY LUMINESCENT EUROPIUM(III)CHELATES BY USING LASER-INDUCED EXCITATION OF THE F-7(0)-]D-5(0) TRANSITION

Solution structures of 13 Eu(III) chelates were examined by using lase r induced excitation of the F-7(0) --> O-5(0) transition. Remarkable v ariations in the F-7(0) --> D-5(0) excitation spectra of ,2'''-{[aryl] bis(methylenenitrilo)}tetrakis(acetic acid) complexes of Eu(III) are o bserved depending on the denticity of the ligand and the number and ch aracter of the coordinated nitrogen atoms. The evaluation of the struc tures is made on the basis of the energy of the F-7(0) --> D-5(0) exci tation transition of Eu(III) because the F-7(0) --> D-5(0) transition energy is dependent on the number and type of coordinating atoms in th e first coordination sphere of Eu(lII). Additional information about t he structures is obtained by measuring the excited-state lifetimes of the Eu(III) chelates. The F-7(0) --> D-5(0) transition energy shifts a lways an equal amount to lower energies due to the coordinaton of a ce rtain group or atom. The energies of the F-7(0) --> D-5(0) excitation transitions are also used to calculate these 'nephelauxetic' shift par ameters for coordinated nitrogen heteroatoms in the ne-2,6-diyl]bis-(m ethylenenitrilo)}tetrakis(acetic acid) (3), 2,2',2 e-6,6'-diyl)bis-(me thylenenitrilo)]tetrakis(acetic acid) (4), 2,2',2 '',2'''-[(2,2':6'2 ' '-terpyridine-6,6 ''-diyl)bis(methylenenitrilo)]tetrakis(acetic acid) (5), 2,2',2 [6,6'-(pyrazole-1,3-diyl)-bis(pyridine)-2,2'-diyl] bis(met hylenenitrilo)}tetrakis(acetic acid) (7), 2,2',2 '',2'''-([6,6'-(thiaz ole-2,4-diyl)bis(pyridine) bis(methylenenitrilo)}tetrakis(acetic acid) (8) and 2,2',2 -4,4'-diyl]bis-(methylenenitrilo)]-tetrakis(acetic aci d) (9) complexes. The variation in the shift parameters of the nitroge n heteroatoms is suggested to be due to the different distances betwee n the nitrogen heteroatoms and Eu(III) ions. (C) 1998 Elsevier Science S.A.