Dataset Information

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

ABSTRACT: The Ce3+ ion in Cs2NaCe(NO2)6 (I), which comprises the unusual Th site symmetry of the Ce(NO2)63- 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+.

SUBMITTER: Luo Y

PROVIDER: S-EPMC6224556 | biostudies-other | 2018 Nov

REPOSITORIES: biostudies-other

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

Luo Yuxia Y Hau Chun-Kit CK Yeung Yau Yuen YY Wong Ka-Leung KL Shiu Kwok Keung KK Tanner Peter A PA

Scientific reports 20181108 1

The Ce3+ ion in Cs2NaCe(NO2)6 (I), which comprises the unusual Th site symmetry of the Ce(NO2)63- 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 s ...[more]

PMID: 30409997

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Project description:This study presents Nuclear Resonance Vibrational Spectroscopy (NRVS) data on the five-coordinate (5C) ferrous heme-nitrosyl complex [Fe(OEP)(NO)] (1, OEP(2-) = octaethylporphyrinato dianion) and the corresponding (15)N(18)O labeled complex. The obtained spectra identify two isotope sensitive features at 522 and 388 cm(-1), which shift to 508 and 381 cm(-1), respectively, upon isotope labeling. These features are assigned to the Fe-NO stretch nu(Fe-NO) and the in-plane Fe-N-O bending mode delta(ip)(Fe-N-O), the latter has been unambiguously assigned for the first time for 1. The obtained NRVS data were simulated using our quantum chemistry centered normal coordinate analysis (QCC-NCA). Since complex 1 can potentially exist in 12 different conformations involving the FeNO and peripheral ethyl orientations, extended density functional theory (DFT) calculations and QCC-NCA simulations were performed to determine how these conformations affect the NRVS properties of [Fe(OEP)NO]. These results show that the properties and force constants of the FeNO unit are hardly affected by the conformational changes involving the ethyl substituents. On the other hand, the NRVS-active porphyrin-based vibrations around 340-360, 300-320, and 250-270 cm(-1) are sensitive to the conformational changes. The spectroscopic changes observed in these regions are due to selective mechanical couplings of one component of E(u)-type (in ideal D(4h) symmetry) porphyrin-based vibrations with the in-plane Fe-N-O bending mode. This leads to the observed variations in Fe(OEP) core mode energies and NRVS intensities without affecting the properties of the FeNO unit. The QCC-NCA simulated NRVS spectra of 1 show excellent agreement with experiment, and indicate that conformer F is likely present in the samples of this complex investigated here. The observed porphyrin-based vibrations in the NRVS spectra of 1 are also assigned based on the QCC-NCA results. The obtained force constants of the Fe-NO and N-O bonds are 2.83-2.94 (based on the DFT functional applied) and about 12.15 mdyn/A, respectively. The electronic structures of 5C ferrous heme-nitrosyls in different model complexes are then analyzed, and variations in their properties based on different porphyrin substituents are explained. Finally, the shortcomings of different DFT functionals in describing the axial FeNO subunit in heme-nitrosyls are elucidated.

Dataset Information

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

Publications

Massive Stokes shift in 12-coordinate Ce(NO2)<sub>6</sub><sup>3-</sup>: crystal structure, vibrational and electronic spectra.

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