Molecular Spectroscopy of Uranium(IV) Bis(ketimido) Complexes. Rare Observation of Resonance-Enhanced Raman Scattering from Organoactinide Complexes and Evidence for Broken-Symmetry Excited States
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- 作者：Ryan E. Da Re ; Kimberly C. Jantunen ; Jeffrey T. Golden ; Jaqueline L. Kiplinger ; and David E. Morris
- 刊名：Journal of the American Chemical Society
- 出版年：2005
- 出版时间：January 19, 2005
- 年：2005
- 卷：127
- 期：2
- 页码：682 - 689
- 全文大小：147K
- 年卷期：v.127,no.2(January 19, 2005)
- ISSN：1520-5126
文摘
Electronic absorption and resonance-enhanced Raman spectra for ketimido (azavinylidene)complexes of tetravalent uranium, (C5Me5)2U[-N=C(Ph)(R)]2 (R = Ph, Me, and CH2Ph), have beenrecorded. The absorption spectra exhibit four broad bands between 13 000 and 24 000 cm-1. The highest-energy band is assigned to the ketimido-localized p
(N)
*(N=C) transition based on comparison to thespectra of (C5H5)2Zr[-N=CPh2]2 and (C5Me5)2Th[-N=CPh2]2. Upon excitation into any of these fourabsorption bands, the (C5Me5)2U[-N=C(Ph)(R)]2 complexes exhibit resonance enhancement for severalRaman bands attributable to vibrations of the ketimido ligands. Raman bands for both the symmetric andnominally asymmetric N=C stretching bands are resonantly enhanced upon excitation into the p(N)*(N=C) absorption bands, indicating that the excited state is localized on a single ketimido ligand. Ramanexcitation profiles for (C5Me5)2U[-N=CPh2]2 confirm that at least one of the lower-energy electronicabsorption bands (Emax ~ 16300 cm-1) is a charge-transfer transition between the U(IV) center and theketimido ligand(s). The observations of both charge-transfer transitions and resonance enhancement ofRaman vibrational bands are exceedingly rare for tetravalent actinide complexes and reflect the strongbonding interactions between the uranium 5f/6d orbitals and those on the ketimido ligands.
(N)*(N=C) transition based on comparison to thespectra of (C5H5)2Zr[-N=CPh2]2 and (C5Me5)2Th[-N=CPh2]2. Upon excitation into any of these fourabsorption bands, the (C5Me5)2U[-N=C(Ph)(R)]2 complexes exhibit resonance enhancement for severalRaman bands attributable to vibrations of the ketimido ligands. Raman bands for both the symmetric andnominally asymmetric N=C stretching bands are resonantly enhanced upon excitation into the p(N)*(N=C) absorption bands, indicating that the excited state is localized on a single ketimido ligand. Ramanexcitation profiles for (C5Me5)2U[-N=CPh2]2 confirm that at least one of the lower-energy electronicabsorption bands (Emax ~ 16300 cm-1) is a charge-transfer transition between the U(IV) center and theketimido ligand(s). The observations of both charge-transfer transitions and resonance enhancement ofRaman vibrational bands are exceedingly rare for tetravalent actinide complexes and reflect the strongbonding interactions between the uranium 5f/6d orbitals and those on the ketimido ligands.