Premium
Electron Transfer in Dinuclear Cobalt Complexes with “Non‐innocent” Bridging Ligands
Author(s) -
Heinze Katja,
Huttner Gottfried,
Zsolnai Laszlo,
Jacobi Albrecht,
Schober Peter
Publication year - 1997
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19970030513
Subject(s) - chemistry , tripod (photography) , moiety , cobalt , crystallography , stereochemistry , metal , electrochemistry , bridging ligand , electron transfer , valence (chemistry) , alkyl , photochemistry , crystal structure , inorganic chemistry , organic chemistry , electrode , optics , physics
Reaction of tripod cobalt(II) templates [{CH 3 C(CH 2 PAr 2 ) 3 }Co II ] with potentially bridging ligands L generates the dinuclear compounds [(tripod)‐Co‐L‐Co(tripod)] 2+ . With L = oxalate (C 2 O 2‐ 4 ) a biscobalt(II) complex ( 1 ) is formed, while with L = C 6 H 2 O 2‐ 4 , the dianion derived from 2,5‐dihydroxy‐1,4=benzoquinone (anilic acid), two‐electron transfer within the dimetallic unit occurs and a biscobalt(III) charge distribution results ( 2a ), as shown by X‐ray structural analyses of 1 and 2a , NMR spectroscopy, and theoretical investigations by the INDO method. Complex 2a exhibits an unusually intense, low‐energy absorption in its electronic spectrum; this is explained with a simple MO model. One‐electron reduction of 2a generates the corresponding mixed‐valence complex, which is highly stabilised through extensive electron delocalisation. Substituents at the 3,6 positions of the bridging ligand (Cl, Br, I, NO 2 , Me, i Pr, Ph; 2b‐h ) as well as alkyl substitution at the aromatic rings of the tripod ligands ( 3, 4 ) influence the optical and electrochemical properties consistent with the proposed model of charge distribution. Formal replacement of one [(tripod)Co III ] 3+ moiety by [CH 2 ] 2+ leads to the mononuclear complex 6 , which is shown to be a typical [(tripod)Co III =(catecholato)] + complex. Therefore the substantially different optical and electrochemical properties of the dinuclear complexes with respect to those of 6 result from strong metal‐metal interactions mediated by the bridging ligand.