Massive Stokes shift in 12-coordinate Ce(NO2)63-: crystal structure, vibrational and electronic spectra

Yuxia Luo; Chun-Kit Hau; Yau Yuen Yeung; Ka-Leung Wong; Kwok Keung Shiu; Peter A Tanner

doi:10.1038/s41598-018-34889-4

Massive Stokes shift in 12-coordinate Ce(NO2)₆^3-: crystal structure, vibrational and electronic spectra

Sci Rep. 2018 Nov 8;8(1):16557. doi: 10.1038/s41598-018-34889-4.

Authors

Yuxia Luo¹, Chun-Kit Hau¹, Yau Yuen Yeung², Ka-Leung Wong³, Kwok Keung Shiu¹, Peter A Tanner⁴

Affiliations

¹ Department of Chemistry, Hong Kong Baptist University, 224 Waterloo Road, Kowloon, Hong Kong, S.A.R., P. R. China.
² Department of Science and Environmental Studies, The Education University of Hong Kong, 10 Lo Ping Road, Tai Po, New Territories, Hong Kong, S.A.R., P. R. China.
³ Department of Chemistry, Hong Kong Baptist University, 224 Waterloo Road, Kowloon, Hong Kong, S.A.R., P. R. China. klwong@hkbu.edu.hk.
⁴ Department of Chemistry, Hong Kong Baptist University, 224 Waterloo Road, Kowloon, Hong Kong, S.A.R., P. R. China. peter.a.tanner@gmail.com.

Abstract

The Ce³⁺ ion in Cs₂NaCe(NO₂)₆ (I), which comprises the unusual T_h site symmetry of the Ce(NO₂)₆^3- ion, demonstrates the largest Ce-O Stokes shift of 8715 cm^-1 and the low emission quenching temperature of 53 K. The activation energy for quenching changes with temperature, attributed to relative shifts of the two potential energy curves involved. The splitting of the Ce³⁺ 5d¹ state into two levels separated by 4925 cm^-1 is accounted for by a first principles calculation using the crystal structure data of I. The NO₂^- energy levels and spectra were investigated also in Cs₂NaLa(NO₂)₆ and modelled by hybrid DFT. The vibrational and electronic spectral properties have been thoroughly investigated and rationalized at temperatures down to 10 K. A comparison of Stokes shifts with other Ce-O systems emphasizes the dependence upon the coordination number of Ce³⁺.