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

Abstract

The crystal structure and the luminescence of the complex Na[Eu(DCTA)·H₂O]·4H₂O (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 ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions. The energy-level scheme of the ⁷F_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 ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions. The behavior of the maximum splitting of the ⁷F₁ manifold is also discussed in terms of a scalar crystal-field strength parameter.