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Co II Complexes with Mixed Amino‐ N and Thiolato‐ S Donor Sets − Structural Characterization and Electronic Properties of a Stable Bis(μ‐thiolato)‐Bridged Binuclear Co II Complex
Author(s) -
Bonnet Didier,
Leduc Philippe,
Bill Eckhard,
Chottard Geneviève,
Mansuy Daniel,
Artaud Isabelle
Publication year - 2001
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 - 10.1002/1099-0682(200106)2001:6<1449::aid-ejic1449>3.0.co;2-5
Subject(s) - chemistry , crystallography , electron paramagnetic resonance , ligand (biochemistry) , cobalt , magnetic susceptibility , pyridine , valence (chemistry) , oxidation state , stereochemistry , metal , medicinal chemistry , inorganic chemistry , nuclear magnetic resonance , biochemistry , physics , receptor , organic chemistry
Two different ligands [S 2 N 3 py ] and [S 2 N 2 ], prepared from 2,6‐bis[1‐(2‐mercaptoanilino)ethyl]pyridine and 2,3‐bis(2‐mercaptoanilino)butane, respectively, have been used to investigate cobalt coordination with mixed amine nitrogen/sulfur donor sets. The pentadentate [S 2 N 3 py ] ligand gave rise to a mononuclear [Co II (S 2 N 3 py )] complex, which was found to be stable only at low temperatures under argon, and was characterized as having a high‐spin Co II state on the basis of 1 H NMR and EPR measurements. In contrast, the tetradentate [S 2 N 2 ] ligand led to a binuclear bis(μ‐thiolato) [Co II (S 2 N 2 )] 2 complex, the structure of which was solved by X‐ray crystallography. Each Co II centre was found to reside in an N 2 S 3 square‐pyramidal environment in the crystal, the two Co atoms being bridged by one of the two thiolates of an [S 2 N 2 ] ligand. On the basis of the temperature dependence of the magnetic susceptibility, the two Co II centres were found to be in a low‐spin state and slightly antiferromagnetically coupled with an absolute J value of less than 3 cm −1 . In aerated CH 2 Cl 2 in the presence of CH 3 SO 3 H, the binuclear complex proved to be stable in its mixed valence state, [Co II /Co III ], which could be converted back to [Co II /Co II ] upon addition of NBu 4 OH in MeOH. Three different stable oxidation states could be characterized by electro‐ and spectroelectrochemistry ( E [Co II /Co II ]/[Co II /Co III ] = −0.19 V, E [Co II /Co III ]/[Co III / Co III ] = 0.2 V vs. SCE). The electronic spectrum of the [Co II / Co II ] state features a broad absorption at 630 nm and a sharp band at 565 nm, while that of the [Co II /Co III ] state shows two bands at 657 and 800 nm. The Raman spectrum of the [Co II /Co II ] state was found to be dominated by a Co 2 S 2 core vibration at 223 cm −1 , which proved to be strongly resonanceenhanced within the 565 nm absorption band, thus giving a sound basis for its assignment as an S→Co II charge‐transfer band. For the [Co II /Co III ] state, a significant resonance Raman enhancement was observed within the 657 nm absorption band for a larger number of vibrations involving the Co 2 S 2 core as well as the phenyl ring.