Complexes symmetrical bridged mixed-valence

In recent years several complexes have been prepared that contain oxidant and reductant ions of the same element, with the same inner-sphere ligand environment and a symmetrical bridging group (Table VI). In the most-studied cases, analogous compounds with one more and one less electron are known, forming a redox series A + XA+(env), A+ X A(env), A X A(env), and the electronic spectrum of the mixed-valence species contains a unique band in addition to the bands characteristic of the separate A+ X and A X chromophores. 

Mixed-valence mthenium(II)-ruthenium(III) complexes have been prepared. Controlled-potential oxidation of the ruthenium(II) dimer [Ru(CO)(S2CNEt2)(p-S2CNEt2)]2, in which each ruthenium carries one carbonyl, yields [Ru(CO)(S2CNEt2)(p-S2CNEt2)]2 (Eq. 128), whereby both carbonyls are bound in a cis fashion to a single metal center (288). The molecule contains a long ruthenium-ruthenium interaction [Ru-Ru 3.614(1) A] and the sulfurs bridge approximately symmetrically. The authors were not able to determine if the molecule contained separate ruthenium(II) and ruthenium(lll) centers or a delocalized state. 

The complex SmCp adds on CsHs forming a trivalent and mixed valent product CpjSmCp, and Cp SmCpSmCp, respectively. In the mixed valent product there is a deficiency of C5H6. In the complex Cp Sm"1(/4-Cp)Sm"Cp2 the two valence states have been assigned on the basis of spectroscopy [141] which has been confirmed by X-ray analysis. The Sm(III) coordination geometry is trigonal. The bridging Cp is symmetrically bound to Sm(III) and two atoms are closer to Sm(II) at distances of 2.986(8) and 3.180(9) A, respectively. 

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