Optical and Infrared Spectroelectrochemical Studies of CN-Substituted Bipyridyl Complexes of Ruthenium(II)
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- Department of Chemistry, University of Reading, Whiteknights Park, Reading RG6 6DX, United Kingdom
- J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, CZ-18223 Prague, Czech Republic, Department of Inorganic Chemistry, University of Chemistry and Technology, Prague, CZ-16628 Prague, Czech Republic
- ELI Beamlines, Institute of Physics, Czech Academy of Sciences, CZ-18200 Prague, Czech Republic
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
- J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, CZ-18223 Prague, Czech Republic
- School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, E1 4NS London, United Kingdom, J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, CZ-18223 Prague, Czech Republic
Ruthenium(II) polypyridyl complexes [Ru(CN-Me-bpy)x(bpy)3–x]2+ (CN-Me-bpy = 4,4'-dicyano-5,5'-dimethyl-2,2'-bipyridine, bpy = 2,2'-bipyridine, and x = 1–3, abbreviated as 12+, 22+, and 32+) undergo four (12+) or five (22+ and 32+) successive one-electron reduction steps between –1.3 and –2.75 V versus ferrocenium/ferrocene (Fc+/Fc) in tetrahydrofuran. The CN-Me-bpy ligands are reduced first, with successive one-electron reductions in 22+ and 32+ being separated by 150–210 mV; reduction of the unsubstituted bpy ligand in 12+ and 22+ occurs only when all CN-Me-bpy ligands have been converted to their radical anions. Absorption spectra of the first three reduction products of each complex were measured across the UV, visible, near-IR (NIR), and mid-IR regions and interpreted with the help of density functional theory calculations. Reduction of the CN-Me-bpy ligand shifts the ν(C≡N) IR band by ca. –45 cm–1, enhances its intensity ~35 times, and splits the symmetrical and antisymmetrical modes. Semireduced complexes containing two and three CN-derivatized ligands 2+, 3+, and 30 show distinct ν(C≡N) features due to the presence of both CN-Me-bpy and CN-Me-bpy•–, confirming that each reduction is localized on a single ligand. NIR spectra of 10, 1–, and 2– exhibit a prominent band attributable to the CN-Me-bpy•– moiety between 6000 and 7500 cm–1, whereas bpy•–-based absorption occurs between 4500 and 6000 cm–1; complexes 2+, 3+, and 30 also exhibit a band at ca. 3300 cm–1 due to a CN-Me-bpy•– → CN-Me-bpy interligand charge-transfer transition. In the UV–vis region, the decrease of π → π* intraligand bands of the neutral ligands and the emergence of the corresponding bands of the radical anions are most diagnostic. The first reduction product of 12+ is spectroscopically similar to the lowest triplet metal-to-ligand charge-transfer excited state, which shows pronounced NIR absorption, and its ν(C≡N) IR band is shifted by –38 cm–1 and 5–7-fold-enhanced relative to the ground state.
- Research Organization:
- Queen Mary Univ. of London (United Kingdom)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- FG02-01ER15282
- OSTI ID:
- 1768650
- Alternate ID(s):
- OSTI ID: 1770854
- Journal Information:
- Inorganic Chemistry, Journal Name: Inorganic Chemistry Vol. 60 Journal Issue: 6; ISSN 0020-1669
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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