Crystal structure and luminescence of Na[Eu(DCTA)•H2O]•4H2O (DCTA = trans-cyclohexane-1,2-diyldinitrilotetraacetate)

The crystal structure and the luminescence of the complex Na[Eu(DCTA). H2O]. 4H(2)O (DCTA = trans-cyclohexane-1,2-diyldinitrilotetraacetate) have been determined. In the structure the: Eu-III is co-ordinated by two nitrogen atoms and four terminal oxygen atoms of two iminodiacetate groups, and two water oxygen atoms which bridge two adjacent Eu-III. When the crystals are excited by UV light they produce a very characteristic luminescence responsible for the D-5(0) --> F-7(J) (J = 0, 1, 2, 3, 4) transitions. The energy-level scheme of the F-7(J) states and detailed assignments for the observed luminescence lines have been proposed by phenomenological simulation in the framework of the free-ion and crystal-field Hamiltonians. Although an additional correction to the free-ion model is needed for the barycenter shifting due to the complexation, the set of refined crystal-field parameters under C-2v site symmetry satisfactorily reproduces the fine splitting of the luminescence lines in the D-5(0) --> F-7(J) (J = 0, 1, 2, 3, 4) transitions. The behavior of the maximum splitting of the F-7(1) manifold is also discussed in terms of a scalar crystal-field strength parameter.