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

Depending on the reaction conditions, different products are obtained from the reaction of CoCl2 with CH3C(CH2PPh2)3 (triphos), including the low-spin complexes [(triphos)Co(μ-Cl)2Co(triphos)]2+ (1 2+) and [(triphos)CoCl2] (3), their solid-state structures being determined by X-ray methods. In solution, additionally, a four-coordinate high-spin complex [(η2-triphos)CoCl2] (2) is present, its concentration relative to that of 3 depending on the solvent and the temperature. The reactivity of these species toward Lewis acids is investigated leading to the novel heterodinuclear complexes [(triphos)Co(μ-Cl)2MCl2] (M = Fe (5), Co (6)). Reactions with Lewis bases L yield complexes of the rare type [(triphos)CoCl(L)]+ (L = CO (7 +), PMe3 (8 +), NH3 (9 +), CH3CN (10 +)). One-electron reduction of 3 leads to the previously prepared pseudotetrahedral [(triphos)CoICl] complex 11, and one-electron oxidation to the novel trigonal-bipyramidal low-spin complex [(triphos)CoIIICl2]+ (12 +).

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Weak antiferromagnetic exchange interactions are observed in two CoII dimers of the general formula [{(triphos)Co}2(μ‐dicarboxylato)](BF4)2 where the dicarboxylate is the dianion of fumaric acid [3 ·(BF4)2] or terephthalic acid [4 ·(BF4)2] and triphos is the tridentate phosphorus ligand 1,1,1‐tris(diphenylphosphanomethyl)ethane. In these complexes the metal ions are separated by 8 and 10 Å, as determined by X‐ray crystallography. Insight into the interaction pathway is gained through molecular orbital calculations performed on model compounds. The influence of bridging‐ligand distortions and the stereochemistry around the two cobalt centres is discussed.

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