ic0c00056_si_001.pdf (2.83 MB)
Solution Structure, Electronic Energy Levels, and Photophysical Properties of [Eu(MeOH)n−2m(NO3)m]3–m+ Complexes
journal contribution
posted on 2020-02-28, 16:42 authored by Nicolaj Kofod, Patrick Nawrocki, Mikkel Juelsholt, Troels Lindahl Christiansen, Kirsten M. Ø. Jensen, Thomas Just SørensenThe structure of lanthanide(III)
ions in solutions high in nitrate
has been debated since the early days of lanthanide coordination chemistry.
The structure and properties of lanthanides in these solutions are
essential in industrial rare-earth separation, as well as in the fundamental
solution chemistry of these elements. Pending decades of debate, it
was established that nitrate is bidentate and coordinates in the inner
sphere, and complexes have been observed with as many as four nitrates
coordinated to a single lanthanide(III) center in nonaqueous solutions.
We revisit the interactions between nitrate and europium(III) in methanol
using optical spectroscopy, X-ray total scattering, and the current
understanding of europium(III) photophysics. By a combination of direct
and indirect methods to probe the structure, it was found that four
distinct species from Eu(MeOH)93+ to [Eu(MeOH)3(NO3)3] are present in solutions containing
from 0 to 2 M NO3– ions. It was shown
that the changes in transition probabilities together with high-resolution
spectra can provide information on speciation and how the minute changes
in ligand field affect the microstates. By a comparison to total X-ray
scattering, it was concluded that the optical spectra alone allow
the constitution and symmetry of the europium(III) species to be determined.
Most notably, the minute changes in the all oxygen atom coordination
imply significant changes in the optical properties of the europium(III)
center.