Premium
Ru II (α‐diimine) or Ru III (α‐diimine ·– )? Structural, Spectroscopic, and Theoretical Evidence for the Stabilization of a Prominent Metal‐to‐Ligand Charge‐Transfer Excited‐State Configuration in the Ground State
Author(s) -
Grupp Anita,
Bubrin Martina,
Ehret Fabian,
Zeng Qiang,
Hartl František,
Kvapilová Hana,
Záliš Stanislav,
Kaim Wolfgang
Publication year - 2014
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201301206
Subject(s) - diimine , chemistry , ruthenium , ligand (biochemistry) , excited state , electron paramagnetic resonance , metal , photochemistry , resonance (particle physics) , bond length , oxidation state , crystallography , crystal structure , nuclear magnetic resonance , atomic physics , catalysis , organic chemistry , biochemistry , physics , receptor
The new compounds [Ru(R‐DAB)(acac) 2 ] (R‐DAB = 1,4‐diorganyl‐1,4‐diazabuta‐1,3‐diene; R = tert ‐butyl, 4‐methoxyphenyl, 2,6‐dimethylphenyl; acac – = 2,4‐pentanedionate) exhibit intrachelate ring bond lengths 1.297 < d (CN) < 1.344 Å and 1.382 < d (CC) < 1.425 Å, which suggest a Ru III (R‐DAB · – ) oxidation state formulation. This notion is confirmed by the negligible solvatochromism of the intense ( ϵ ≈ 10 4 M –1 cm –1 ) charge‐transfer absorption band in the visible region and by DFT calculations. Oxidation of the compounds occurs mainly at the R‐DAB · – radical ligand to produce UV/Vis/NIR and electron paramagnetic resonance (EPR) spectroelectrochemically detectable Ru III species, whereas the reduction proceeds less reversibly and yields predominantly (R‐DAB)‐ligand‐based spin for the 4‐methoxyphenyl derivative, measured at low temperature. The results are discussed with respect to metal‐to‐ligand charge‐transfer (MLCT) excited states of conventional (α‐diimine)ruthenium(II) complexes and in view of other (α‐diimine)metal complexes with ambiguous oxidation‐state assignments.