Time-Resolved Spectroscopy of the Metal-to-Metal Charge Transfer Excited State in Dinuclear Cyano-Bridged Mixed-Valence Complexes

• Published in: Inorganic chemistry Vol. 44; no. 15; pp. 5530 - 5536
• Main Authors: Macpherson, Brendan P, Bernhardt, Paul V, Hauser, Andreas, Pagès, Stéphane, Vauthey, Eric
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 25-07-2005
• Subjects: Metals, Heavy - chemistry; Molecular Conformation; Nitriles - chemistry; Organometallic Compounds - chemistry; Spectroscopy, Fourier Transform Infrared - methods; Thermodynamics; Time Factors
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic0506512

Visible pump−probe spectroscopy has been used to identify and characterize short-lived metal-to-metal charge transfer (MMCT) excited states in a group of cyano-bridged mixed-valence complexes of the formula [LCoIIINCMII(CN)5]-, where L is a pentadentate macrocyclic pentaamine (L14) or triamine-dithiaether (L14S) and M is Fe or Ru. Nanosecond pump−probe spectroscopy on frozen solutions of [L14CoIIINCFeII(CN)5]- and [L14SCoIIINCFeII(CN)5]- at 11 K enabled the construction of difference transient absorption spectra that featured a rise in absorbance in the region of 350−400 nm consistent with the generation of the ferricyanide chromophore of the photoexcited complex. The MMCT excited state of the Ru analogue [L14CoIIINCRuII(CN)5]- was too short-lived to allow its detection. Femtosecond pump−probe spectroscopy on aqueous solutions of [L14CoIIINCFeII(CN)5]- and [L14SCoIIINCFeII(CN)5]- at room temperature enabled the lifetimes of their CoII−FeIII MMCT excited states to be determined as 0.8 and 1.3 ps, respectively.