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σ−π* Electronic Transition of the Di- and Trinuclear Complexes Ru(E)(E‘)(CO) 2 (iPr-DAB): Resonance Raman, Electronic Absorption, Emission, and Density Functional Study (E = Me, SnPh 3 , M(CO) 5 ; E‘ = M(CO) 5 ; M = Mn, Re; iPr-DAB = N , N‘ -Diisopropyl-1,4-diaza-1,3-butadiene)

1997; American Chemical Society; Volume: 16; Issue: 10 Linguagem: Inglês

10.1021/om9608667

1520-6041

Maxim P. Aarnts, Maikel P. Wilms, Derk J. Stufkens, Evert Jan Baerends, Antonı́n Vlček,

Metal complexes synthesis and properties

Di- and trinuclear complexes Ru(E)(E')(CO)2(iPr-DAB) (E = Me, SnPh3, Mn(CO)5, E' = Mn(CO)5; E = Me, SnPh3, Re(CO)5, E' = Re(CO)5; iPr-DAB = N,N'-diisopropyl-1,4-diazabutadiene), which contain Ru−Mn or Ru−Re σ bonds, absorb strongly in the visible spectral region. A combined spectroscopic (absorption and resonance Raman) and theoretical (DFT-MO) study shows that the lowest allowed electronic transition has a σ(Ru-E) → π*(DAB) or σn(E-Ru-E') → π*(DAB) character. The latter transition originates in a σ orbital, which is only weakly bonding or even nonbonding (σn) with respect to the axial E−Ru−E' bonds. The second visible absorption band that occurs at higher energies for Ru(M(CO)5)2(CO)2(iPr-DAB) (M = Mn, Re) is attributed to a σb → π* transition, the electron being excited from a strongly E−Ru−E' σ-bonding orbital. Both σ→π* transitions of the trinuclear complexes have surprisingly high oscillator strengths (0.1−0.2). An emission study of Ru(E)(E')(CO)2(iPr-DAB) shows that their lowest excited state has a 3σπ* character. The emission is rather long lived (4−100 μs at 80 K, depending on the complex composition) because of slow nonradiative decay to the ground state.