Lanthanide Contraction Associated Coordination Regimes and Photocatalytic Performance of Polyoxometalate-Based
Lin-Lin Wang1,2, Hong-Li Jia3, Jian-Jie Xu2
1College of Resource Environment and Tourism, Capital Normal University, Beijing100048, P.R. China.
Abstract:
Lanthanide contraction provides a continuous scale for tuning coordination structures, yet its systematic use in photoactive materials remains underexplored. Herein, 14 POM-phosphonate-lanthanide hybrids from La to Lu (excluding Pm) were synthesized under mild conditions. Single-crystal XRD identifies three coordination regimes: La3+ at the eight/nine-coordination boundary, Ce3+-Yb3+ adopting stable eight-coordination, and Lu3+ undergoing a ligand-deficient transition due to steric congestion. The Sm3+ complex 5b, obtained under diffusion conditions, exhibits the same motif as Lu3+ complex, indicating that crystal growth conditions can influence coordination-mode selection. Combined with band-structure analysis, EIS, radical trapping, EPR, and HPLC-MS, the photocatalytic mechanism was investigated. This work converts lanthanide contraction from a descriptive concept into an experimental framework for constructing structure-performance correlations.
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When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.

