Electronic Structure and Excited States of Rhenium(I) Amido and Phosphido Carbonyl-Bipyridine Complexes Studied by Picosecond Time-Resolved IR Spectroscopy and DFT Calculations
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- 作者：Anders Gabrielsson ; Michael Busby ; Pavel Matousek ; Michael Towrie ; Eva Hevia ; Luciano Cuesta ; Julio Perez ; Stanislav Zá ; li
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- 刊名：Inorganic Chemistry
- 出版年：2006
- 出版时间：November 27, 2006
- 年：2006
- 卷：45
- 期：24
- 页码：9789 - 9797
- 全文大小：328K
- 年卷期：v.45,no.24(November 27, 2006)
- ISSN：1520-510X
文摘
UV-vis absorption and picosecond time-resolved IR (TRIR) spectra of amido and phosphido complexes fac-[Re(ER2)(CO)3(bpy)] (ER2 = NHPh, NTol2, PPh2, bpy = 2,2'-bipyridine, Tol = 4-methylphenyl) were investigated inconjunction with DFT and TD-DFT calculations in order to understand their ground-state electronic structure, low-lying electronic transitions and excited-state character and dynamics. The HOMO is localized at the amido/phosphidoligand. Amide and phosphide ligands are 
-bonded to Re, the 
interaction being negligible. Absorption spectrashow a weak band at low energies (1.7-2.1 eV) that arises from essentially pure ER2 
bpy ligand-to-ligandcharge transfer (LLCT). The lowest excited state is the corresponding triplet, 3LLCT. Low triplet energies and largedistortions diminish the excited-state lifetimes to 85 and 270 ps for NHPh and NTol2, respectively, and to ca. 30ps for PPh2. 
(CO) vibrations undergo only very small (
10 cm-1) shifts upon excitation, attesting to its LLCTcharacter, which hardly affects the electron-density distribution on the Re(CO)3 moiety. Relaxation of the 3LLCTstate occurs with complex dynamics ranging from units to tens of picoseconds. The "pure" LLCT excitation, whichdoes not mix with the Re bpy MLCT character, is a unique feature of the amido/phoshido complexes, whoselowest excited state can be viewed as containing a highly unusual aminyl/phosphinyl radical-cationic ligand. Forcomparison, the amino and phosphino complexes fac-[Re(NHPh2)(CO)3(bpy)]+ and fac-[Re(PPh3)(CO)3(bpy)]+ areshown to have the usual Re bpy 3MLCT lowest excited states, characterized by upshifted (CO) bands.
-bonded to Re, the interaction being negligible. Absorption spectrashow a weak band at low energies (1.7-2.1 eV) that arises from essentially pure ER2 bpy ligand-to-ligandcharge transfer (LLCT). The lowest excited state is the corresponding triplet, 3LLCT. Low triplet energies and largedistortions diminish the excited-state lifetimes to 85 and 270 ps for NHPh and NTol2, respectively, and to ca. 30ps for PPh2. (CO) vibrations undergo only very small (10 cm-1) shifts upon excitation, attesting to its LLCTcharacter, which hardly affects the electron-density distribution on the Re(CO)3 moiety. Relaxation of the 3LLCTstate occurs with complex dynamics ranging from units to tens of picoseconds. The "pure" LLCT excitation, whichdoes not mix with the Re bpy MLCT character, is a unique feature of the amido/phoshido complexes, whoselowest excited state can be viewed as containing a highly unusual aminyl/phosphinyl radical-cationic ligand. Forcomparison, the amino and phosphino complexes fac-[Re(NHPh2)(CO)3(bpy)]+ and fac-[Re(PPh3)(CO)3(bpy)]+ areshown to have the usual Re bpy 3MLCT lowest excited states, characterized by upshifted (CO) bands.