Characterisation of edge-sharing decahalogenodiosmate complexes in multiple oxidation states; synthesis, magnetochemistry, voltammetry and associated spectroelectrochemistry of [PPh4]2[Os2(µ-X)2X8] (X = Br or Cl)†

Organo-soluble salts of the edge-sharing bioctahedral [Os2(µ-X)2X8]2– complexes (X = Br or Cl) have been prepared by an improved procedure and investigated electrochemically. Their solution redox behaviour spans five levels, [Os2(µ-X)2X8]z– (z = 1–5), complementing pentavalent [Os2(µ-Cl)2Cl8] known only in the solid phase. Chilled solutions of electrogenerated [Os2(µ-X)2X8]3– and [Os2(µ-X)2X8]4– have been characterised by UV/VIS/NIR spectroscopy (213 K; 45 000 to 5000 cm–1). In contrast, [Os2(µ-X)2X8]– and [Os2(µ-X)2X8]5– rearrange rapidly to the face-sharing nonahalides, [Os2(µ-X)3X6]– and [Os2(µ-X)3X6]4–, losing ½ X2 or X– as appropriate. The redetermined magnetic moments of the [Os2(µ-X)2X8]2– dimers (as their [PPh4]+ salts) are convergent at 1.52 and 1.48 µB per Os (296 K) for X = Br and Cl respectively. Cleavage reactions of [Os2(µ-X)2X8]z– (X = Br or Cl) are valence-dependent, leading to [OsX5L]– (L = MeCN) for z = 2, [OsX6]2– and trans-[OsX4L2]– for z = 3, and exclusively trans-[OsX4L2]– for z = 4.

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