Electron Transfer in Dinuclear Cobalt Complexes with “Non‐innocent” Bridging Ligands

Abstract

Reaction of tripod cobalt(r1) templates [{CH,C(CH,PAr,),}Co"] with potentially bridging ligands L generates the dinuclear compounds (1) is formed. while with L = C,H,O:-, the dianion derived from 2,5-dihydroxy-I ,4-benzoquinone (anilic acid), two-electron transfer within the dimetallic unit occurs and a biscobalt(i1i) charge distribution results (2a), as shown by X-ray structural analyses of 1 and 2 a, N M R spectroscopy, and theoretical investigations by the INDO method. Complex 2 a exhibits an

Radical ligand-containing single-molecule magnets

“…Efforts to generate benzosemiquinonoid-containing transition metal complexes with a nuclearity of greater than one have resulted in numerous dinuclear compounds, including those containing metal centers bridged by derivatives of 2,5-dihydroxy-1,4-benzoquinonoids [172][173][174][175][176][177][178][179][180][181][182][183][184][185][186][187][188][189], bis(pyrazolyl)benzoquinonoids [190][191][192][193], bis(phosphine)benzoquinonoids [194,195], bis(amino) benzoquinonoids [196][197][198][199][200][201][202], and bis(amino)diiminobenzoquinonoids [86,[203][204][205][206]. Indeed, the radical form of these ligands has shown enhanced magnetic coupling compared to their non-radical redox isomers [174,180,182].…”

Metal–Metal Interactions in Dinuclear (triphos)Cobalt Complexes Exhibiting Mixed Valency

“…[3] Their CV data have already been reexchange coupling is observed between the unpaired elecported but are repeated here for completeness (Table 1). trons of two [(triphos)Co II ] entities in the complexes The exceptionally large separation of the two reversible re-[(triphos)Co(L)Co(triphos)] 2ϩ with L ϭ di-µ-X (X ϭ duction steps shows that the mixed-valence species are Cl, [7] [8] Br, [7] OH, [7] NH 2 , [9] SMe [10] ), 1,4,5,8-tetraoxonaphthermodynamically stable towards disproportionation into thalene, 1,4,9,10-tetraoxoanthracene, [1] fumarate and the neutral and dicationic complexes.…”

“…Reoxidation is possible by reaction with energy LMCT absorption bands. [3] In all cases the π system ferrocenium tetrafluoroborate (70Ϫ80% recovery). of the bridge proved to be essential for the interaction.…”

“…As the length of the bridging ligand has a remarkable influence on the communication between metal In the frame of a general study of magnetic [1] [2] and eleccentres, analogous complexes with the extended bridging tronic [3] interactions between two cobalt centres connected ligand 1,2,6,7-tetraoxy-9,10-dimethylanthracene are also rethrough a bridging ligand we have been interested in the ported. figurations (d 6 -Co III ; d 7 -Co II ) with zero or one unpaired (X ϭ H, Cl, Br, I, Me), 1a؊e 2ϩ , were prepared according electron, respectively, are obtained.…”

“…These solutions are somewhat more stable than solutions of FULL PAPER also observed for the parent compounds 1a؊e 2ϩ . [3] The low-energy shoulder λ 6 has a half width at full height of only ca. 1630 cm Ϫ1 which is more than three times smaller than expected for a partly localized class-II system according to the Hush theory (5150Ϫ5260 cm Ϫ1 [14] [15] ).…”