Na(2)Ga(7): A Zintl–Wade Phase Related to “α-Tetragonal Boron”

[Image: see text] 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.