Abstract
Nine nona-coordinated Eu(III) complexes (1–9) studied here have three unsymmetric β-diketonate ligands and one chiral Ph-Pybox ligand, which can produce eight possible coordination isomers, depending on the position of the three unsymmetric β-diketonate ligands. Substituents on the β-diketonate ligands cause a rational structural rearrangement upon crystallization. Substituents with higher polarity, including −CN, −F, −Cl, −Br, −OMe, and −OEt, employ intercomplex hydrogen bonding to generate an association complex through structural rearrangement upon crystallization. Substituents with lower polarity, including −CF3, −SMe, and −Me, cause the most energetically favorable isomer to crystallize directly from solution. These two crystal structures exhibit well-resolved f–f emission lines with characteristic Stark splitting structures. This work revealed that the configuration of the Eu(III) complexes in solution can be determined by systematic comparison of their Stark splitting structures to those obtained from the solid phase using density functional theory (DFT)-based predictions combined with circular dichroism data.
Highlights
Nine nona-coordinated Eu(III) complexes (1−9) studied here have three unsymmetric β-diketonate ligands and one chiral Ph-Pybox ligand, which can produce eight possible coordination isomers, depending on the position of the three unsymmetric β-diketonate ligands
The determination of the configuration of coordination complexes has a major impact on various fields of chemistry
Structure determination of kinetically labile species using this technique is always challenging because such species undergo structural rearrangements upon crystallization, and the configurations of the solid-state crystal structures are often different from those that exist in solution.1−5 In particular, lanthanide ions are extremely labile and have versatile coordination numbers (n ≥ 8),3−7 giving rise to dynamic ensembles of coordination isomers that coexist in solution.8−10 most lanthanide ions are paramagnetic, making NMR-based structure determination of their complexes challenging.3−5,11
Summary
We thank Alicia Glatfelter, Ph.D., from the Edanz Group (https://en-author-services.edanz.com/ac), for editing a draft of this manuscript
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