Na2Ga7crystallizes with the orthorhombic
space groupPnma(no. 62;a= 14.8580(6)
Å,b= 8.6766(6) Å, andc= 11.6105(5) Å;Z= 8) and constitutes a filled
variant of the Li2B12Si2structure
type. The crystal structure consists of a network of icosahedral Ga12units with 12 exohedral bonds and four-bonded Ga atoms in
which the Na atoms occupy the channels and cavities. The atomic arrangement
is consistent with the Zintl [(4b)Ga]−and Wade
[(12b)Ga12]2–electron counting approach.
The compound forms peritectically from Na7Ga13and the melt at 501 °C and does not show a homogeneity range.
The band structure calculations predict semiconducting behavior consistent
with the electron balance [Na+]4[(Ga12)2–][Ga–]2. Magnetic
susceptibility measurements show that Na2Ga7is diamagnetic.