Time-Resolved Absorption, Infrared, and Resonance Raman Spectra of the Complexes [Ru(X)(R)(CO)2(α-Diimine)] (X = Halide; R = Alkyl): Influence of X on the Charge Transfer Character of the Lowest Excited State

Heleen A. Nieuwenhuis, Derk J. Stufkens, Ruth Anne McNicholl, Ala H.R. Al-Obaidi, Colin G. Coates, Steven E.J. Bell, John J. McGarvey, Jeremy Westwell, Michael W. George, James J. Turner

Research output: Journal PublicationArticlepeer-review

55 Citations (Scopus)

Abstract

Nanosecond time-resolved absorption (TA), resonance Raman (TR3), and infrared (TRIR) spectra are reported for several complexes [Ru(X)(R)(CO)2(α-diimine)] (X = Cl, Br, I; R = Me, Et; α-diimine = N, N'-diisopropyl-1, 4-diaza-1, 3-butadiene (iPr-DAB), pyridine-2-carbaldehyde-N-isopropylimine (iPr-PyCa), 2, 2'-bipyridine (bpy)). This is the first instance in which the TA, TR3, and TRIR techniques have been used to probe excited states in the same series of complexes. The TA spectra of the iodide complexes show a transient absorption between 550 and 700 nm, which does not depend on the solvent but shifts to lower energy in the order iPr-DAB > bpy > iPr-PyCa. This band is assigned to an intraligand transition. For the corresponding chloride and bromide complexes this band occurs at higher energy, most probably because of a change of character of the lowest excited state from XLCT to MLCT. The TRIR spectra show an increase in ν(CO) (and k(CO)) on promotion to the excited state; however, the shifts Δν(CO) show a decrease in the order Cl- > Br-> I-. The TR3 spectra of the excited complexes [Ru(X)-(R)(CO)2(iPr-DAB)] show νs(CN) of the iPr-DAB ligand 50-80 cm-1 lower in frequency than for the complexes in their ground state. This frequency shift decreases in the order Cl-> Br-> I-, indicating a decrease of CT character of the lowest excited state in this order. However, going from X = Br to I, the effect on Δν(CO) is much larger than the decrease of Δνs(CN). This different effect on the CO- and CN-stretching frequencies is assigned to a gradual change in character of the lowest excited state from MLCT to XLCT when Cl- is replaced by Br- and I-. This result confirms a similar conclusion derived from previous resonance Raman and emission experiments on these complexes.

Original languageEnglish
Pages (from-to)5579-5585
Number of pages7
JournalJournal of the American Chemical Society
Volume117
Issue number20
DOIs
Publication statusPublished - May 1995
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry

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