Includes bibliographical references and index.

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The nature of the Ga−Ga bond in the naked dianion PhGaGaPh2- and its Na+-coordinated counterpart is discussed using the recently proposed formalism based on the analysis of domain-averaged Fermi holes. The analysis shows clearly that three electron pairs, i.e., two σ and one π, contribute to the Ga−Ga bonding interactions in the free dianion PhGaGaPh2- and in the sodium-complexed species (PhGaGaPh)Na2. The eigenvalues and the eigenvectors of the Fermi hole indicate, however, that the Ga−Ga bonding situation does not correspond to classical triple bonds and should not be interpreted using classical bonding models. The reason is that only one of the three electron pairs involved in Ga−Ga bonding, namely that contributing to the Ga−Ga π bond, corresponds to an “ordinary” shared electron pair bond in the sense of Lewis. The bonding interactions of the other two pairs are much more complex and have no classical counterparts. The eigenvalues and the eigenvectors of the latter Fermi holes cannot be considered as fully bonding, but they have partial lone-pair character. This is why the calculated bond orders yield values which are close to a weak double bond. Essentially the same bonding picture holds also for the Na+-coordinated species, but the coordination of sodium causes further weakening of the contributions of all three electron pairs to the Ga−Ga bonding. This weakening yields an effective reduction of the multiplicity of the Ga−Ga bond. The calculated bond order therefore has a value which is otherwise typical for single bonds.