Gas-phase structure of the monomeric alkylgallium(I) compound Ga[C(SiMe(3))(3)] and the electrochemical behavior of Ga-4[C(SiMe(3))(3)](4) and In-4[C(SiMe(3))(3)](4) with EPR evidence for a Ga(4)R(4) radical anion

The gallium(I) compound Ga-4[C(SiMe(3))(3)](4) (1) with a tetrahedral Ga-4 core in the solid state gives on evaporation the monomeric Ga(I) alkyl Ga[C(SiMe(3))(3)] with the unique structural situation of a Ga atom solely coordinated by one singly bonded carbon ligand. Its molecular structure was determined now by gas-phase electron diffraction yielding a Ga-C bond length of 206.4(17) pm, similar to that found in the solid state for the tetramer and much longer than in compounds with gallium in the normal oxidation state of +3. As shown by cyclic voltammetry, 1 and the analogous cluster In-4[C(SiMe(3))(3)](4) (2) could both be reversibly reduced at about -2 V vs Fc(+/0). Whereas the reduced organoindium tetramer did not exhibit any detectable EPR signals between 4 and 300 K, the gallium analogue showed an EPR spectrum compatible with the formulation [(RGa(0.75))(4)](.-); i.e. the unpaired electron was found to be delocalized over all four metal centers (a(Ga-69)=1.93 mT, a(Ga-71)=2.45 mT, 4 Ga).