Na30.5AgxGa60—x: A Three‐Dimensional Network Composed of Ga3, Ga12, and Ga18 Clusters

Single crystal X‐ray structural determinations for Na_30.5Ag_2.6(2)Ga_57.4(2) and Na_30.5Ag_6.4(2)Ga_53.6(2) (P6/mmm, Z = 1) reveal Ga₃ triangles, Ga₁₂ icosahedra, and Ga₁₈ hexacapped hexa gonal prisms that are interconnected into a three‐dimensional network. Silver substitutes on the outer gallium sites of the Ga₁₈ unit and presumably stabilizes the structure by reduction of the overall electron count. The two compositions are close to the limits of a nonstoichiometry region in Ga—Ag content, whereas the sodium content does not vary significantly. Stacking of the (Ga, Ag)₁₈ “drums” along creates a channel in which some typically less well localized sodium atoms reside; other sodium cations lie between the clusters and bond to gallium atoms in typical roles. Apparently isotypic analogues of this structure that are more or less well ordered are also known for other combinations of elements. Extended Hückel MO and band calculations were performed in order to gain a better understanding of the silver compound. The variable electron count observed falls in a region of relatively nonbonding states with only a small dependence on energy.