Preparative methods and electrochemical and spectral properties are reported for binuclear Mo(V) complexes containing di-µ-(Mo2042+), µ--µ-sulfido (Mo203S2+), and di^-sulfido (Mo202S22+) centers coordinated to EDTA, cysteine, and ethyl cysteinate ligands. The µ--µ-sulfido complexes are prepared here for the first time, and improved synthetic procedures are reported for the di^-sulfido complexes. Infrared and electronic absorption spectra of these compounds are sensitive to substitution of sulfur atoms into the bridge system. The systematic changes upon bridge modification are useful in characterizing the compounds and in clarifying assignments of Mo-O and Mo-S bridge stretching frequencies.The EDTA and cysteine complexes undergo electrochemical reduction in a single four-electron step to Mo(III) dimers in aqueous buffers. Although the ease of reduction and electrochemical reversibility of the Mov2/Mom2 couple increase with insertion of S into the bridge system, the Mo(III) dimers become increasingly unstable upon bridge sulfur substitution.The corresponding ethyl cysteinate complexes are reduced by successive one-electron transfers in dimethyl sulfoxide to Mov-Molv and Mo,v2 species. The chemical stability of these reduced products increases in the sequence Mo204 < Mo203S < Mo202S2. The different behavior of sulfido bridging is attributed to greater lability of Mom-S bonds in the former case and to greater electron delocalization by sulfur atoms over the binuclear framework in the latter.
Die Komplexe (Ia) bis (IIIa) wurden nach bekannten Methoden′ (Ib) bis (IIIb) erstmalig durch Reaktion von MoCl5 in HCl mit H2S und L‐Cysteinhydrochlorid, L‐Cysteinethylester bzw. Dinatriumethylendiamintetraacetat und (Ic) bis (IIIc) nach einem verbesserten Verfahren aus Molybdat‐Ionen und HZS in ungepufferter saurer Lösung nach Zugabe der Liganden erhalten und durch IR‐ und elektronenspektroskopische Daten charakterisiert.
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