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Updated: Sep 2, 2026
Hyperspectral Imaging as a Tool to Study Optical Anisotropy in Lanthanide-Based Molecular Single Crystals
Published on: April 14, 2020
Element-Specific Sensitivity of Lanthanoid Ions to Chiral Crystal Fields in K3[Ln2(NO3)9] Probed by 4f-4f Circular
Yusuke Inomata1, Chihiro Mochizuki1, Tetsuya Kida2,3
1Faculty of Advanced Science and Technology, Kumamoto University, Kumamoto860-8555, Japan.
Abstract:
For chiral inorganic crystals composed of achiral components, chiral crystal fields around metal ions are expected to play a key role in the emergence of chiroptical properties. Circular dichroism (CD) spectra can serve as useful probes of such chiral crystal fields. Here, we report the optical resolution of K3[Ln2(NO3)9], a family of chiral potassium lanthanoid nitrates, and systematically investigate chiral crystal fields associated with 4f electrons in the solid state. The K3[Ln2(NO3)9] series (Ln = La, Ce, Pr, Nd, Sm, Eu, and Gd) crystallizes in the chiral space groups P4132 and P4332, and both enantiomorphs are obtained by spontaneous resolution. Among the series, K3[Pr2(NO3)9], K3[Nd2(NO3)9], K3[Sm2(NO3)9], and K3[Eu2(NO3)9] show sharp CD bands arising from 4f-4f transitions, demonstrating the presence of chiral crystal fields around lanthanoid ions in a fully inorganic environment. The distorted, noncentrosymmetric coordination environment around the lanthanoid ion partially relaxes the Laporte-forbidden nature of 4f-4f transitions, leading to enhanced absorption and CD intensities. Notably, Sm3+ exhibits the largest absolute CD anisotropy factor (|gCD|), suggesting that it is particularly sensitive to the chiral crystal field among the lanthanoid ions investigated.
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