Na 2 Ga 7 : A Zintl-Wade Phase Related to "α-Tetragonal Boron".

Na 2 Ga 7 crystallizes with the orthorhombic space group Pnma (no. 62; a = 14.8580(6) Å, b = 8.6766(6) Å, and c = 11.6105(5) Å; Z = 8) and constitutes a filled variant of the Li 2 B 12 Si 2 structure type. The crystal structure consists of a network of icosahedral Ga 12 units 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)Ga 12 ] 2- electron counting approach. The compound forms peritectically from Na 7 Ga 13 and 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 [(Ga 12 ) 2- ][Ga - ] 2 . Magnetic susceptibility measurements show that Na 2 Ga 7 is diamagnetic.