Na₂Ga₇: A Zintl–Wade Phase Related to “α-Tetragonal Boron”

Abstract

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.

Synthesis and characterization of ternary trielides Na7KTr4 [Tr=In or Tl] including [Tr4]8− Tetrahedra

“…The oxidation of a small [In 4 ] 8À Zintl anion precasted in solid state in the compounds Na 2 In or Na 7 KIn 4 in liquid ammonia solution can be interpreted as first evidence for a reactivity of trielides according to the well-established chemistry of salt-like tetrelides in this solvent. [92][93][94][95] Future experiments will show, if the isolation of intermediates support this idea.…”

Ordering by cation replacement in the system Na2−xLixGa7

“…This behaviour notably differs from the preparation of Na 2 Ga 7 , which does not form directly from the melt. 5 However, the presence of foreign phases indicates that NaLiGa 7 forms incongruently as well. Subsequent annealing at 300 °C for one week led to the formation of single-phase products for all compositions Na 2− x Li x Ga 7 , with x = 0.2, 0.5, 0.8 and 1 as confirmed by PXRD analysis (Fig.…”

“…The binary phase Na 2 Ga 7 forms peritectically at 501(2) °C from Na 7 Ga 13 17 and the melt. 5 Regarding the ternary system Na 2− x Li x Ga 7 , the thermal stability decreases with increasing Li content. A single-phase sample of Na 1.8 Li 0.2 Ga 7 revealed a slightly lower decomposition temperature of T = 498(2) °C.…”

“…The crystal structure of samples with compositions Na 2− x Li x Ga 7 ( x = 0.2, 0.5, 0.8) was determined by the Rietveld method (Tables S7–S9†). In the initial structure model, the Ga positions were adopted from Na 2 Ga 7 5 and refined with isotropic ADPs. Subsequently, the positions of cations were determined.…”

“…2 They typically adopt polyhedral Wade clusters, such as closo [B 6 ] 2− in CaB 6 , 3 or form multiatomic bonds, like in BaAl 4 , 4 which may be considered as a framework of 2D edge-condensed nido clusters. An example of the first type is the recently discovered Na 2 Ga 7 , 5 which exhibits a framework of 12-bonded [Ga 12 ] 2− closo clusters and 4-bonded [Ga] – Zintl anions. The electronic balance is achieved by the Na cations according to [Na + ] 4 [(Ga 12 ) 2− ][Ga – ] 2 .…”