Electronic Structure of a Neodymium(III) tris(oxydiacetate) Complex from Luminescence data and ab initio Calculations

Neodymium(III) is a NIR emissive and magnetic ion, which has found use in various high-technology applications. Yet, accurate predictions of the luminescent and magnetic properties of neodymium(III) based on the coordination environment remain to be done. Guideline exists, but to build structure-property relationships for this element, more data are needed. Herein, we present a high-symmetry starting point. The tris(oxydiacetate) complex of neodymium(III) was prepared and crystallised, and access to the experimentally determined structure allows us to quantify the symmetry of the compound and to perform calculations directly on the same structure that is investigated experimentally. The luminescent properties were determined and the electronic structure was computed using state-of-the-art ab initio methods. All electronic transitions in the range from 490 to 1400 nm were mapped experimentally. Using a Boltzmann population analysis, the combination of the excitation and emission spectra revealed the crystal field splitting of the 18 lowest energy Kramers levels that experimentally could be unambiguously resolved. This assignment was supported by ab initio calculations and the crystal field splitting was well reproduced. The electronic structure reported for the tris(oxydiacetate) complex is used to deduce the coordination structure in aqueous solution. Finally, the results are compared to empirical trends in the literature for the electronic structure of neodymium(III).