Polynuclear cations bridging ligands

The dihydroxo-bridged binuclear complexes are among the most common, structurally well-characterized polynuclear complexes. For symmetrical bidentate nonbridging ligands, LL, the cation (LL)2M(OH)2M(LL)2"+ may exist in three isomeric forms a meso isomer (A,A) with configuration A and A, respectively, at the two metal centers, and a racemic pair of isomers (A,A and A, A) with configuration A or A at each of the two metal centers (cf. Fig. 2). If the bidentate... 

Mg[CpFe(CO)2]2, Mg[Co(CO)3L]2, and Tl[Co(CO)4] in THF and similar solvents 13). Similarly, the anion [Cr2(CO)10]2-, which contains only terminal carbonyls, forms contact ion pairs with Na+ in THF (17,18). In strong donor solvents such as dimethyl sulfoxide or hexamethylphosphor-amide, the contact ion pair is broken up. As will be described in Section II,B,2, contact ion pairs are seen also in polynuclear carbonyls containing bridging carbonyls, in which case the cation has an affinity for the bridging CO ligand. 

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