Die Akzeptoreigenschaften der Metall—Metall-Einheit in den zweikernigen Komplexen cis-M2(O2CCH3)2Cl4L2, M = Tc,Re; L = neutrale Base

The Acceptor Properties of the Metal—Metal Unit in the Dinuclear Complexes cis-M₂(O₂CCH₃)₂Cl₄L₂, M = Tc, Re; L = neutrale Base The weakly bound H₂O molecules in axial positions of the dimetalates cis-M₂(O₂CCH₃)₂Cl₄L₂, M = Tc, Re, are easily substituted on reaction with stronger donor bases. With increasing donor number D_N or donor strength D_S of the axial ligands, the metal—metal stretching frequency v₁ is lowered. The linearity between v₁ and the hard D_N scale shows, that the M₂ unit acts as a hard Lewis acid in the axial direction, according to the observation that no coordination of soft donor bases takes place. The trans influence of the metal—metal multiple bond is estimated from the ratio of the shifts observed for v₁ and the equatorial metal-ligand stretching modes after formation of adducts. The ratio is about 5: 1 in the ditechnetates and thus considerable higher than in the dirhenates with about 2: 1.