Ba3Ge4: Polymerization of Zintl Anions in the Solid and Bond Stretching Isomerism

Abstract

Polymerizations in single crystals have rarely been described-in the case of the title compound they are even reversible. The rebuttoning of the bonds can be regarded as bond stretching isomerism, which is currently the subject of controversial discussion in many areas of chemistry. The geometrical arrangement of the monomeric Ge ions in the crystal is shown in the picture.

La26Ge19M5O5 (M = Ag, Cu): Rare-Earth Metal Suboxide Superconductors with [La18O5] Cluster Units

“…A similar geometric unit, Ba 18 O 5 , was reported in the Zintl phase in Ba 21 Ge 2 O 5 H 24 . The [Ge] 4 units are similar to previously reported butterfly [Ge 4 ] 6– anions in Ba 3 Ge 4 , wherein Ge–Ge distances, including the common edge, are close to those of single bonds (2.59 Å), with dihedral angles of 144°. The Ge–Ge bond distance along the edges of the butterfly in the title compounds is 2.6042(2) Å, consistent with a single-bond distance.…”

Molecular Silicon Clusters

“…Despite the omnipresence of the [E 4 ] 4– and [E 9 ] 4– cluster species in solid Zintl phases of the tetrel elements, there are also few reports on phases containing polyanions of different charge and shape: In case of tin, the eight-atomic [Sn 8 ] 6– cluster with a square-antiprismatic shape was reported by Sevov . Butterfly shaped [E 4 ] 6– anions are present in Ba 3 E 4 phases (E = Si, Ge). , Furthermore, Zintl phases containing “Y-shaped” [Si 4 ] 12– stars, , five-membered [E 5 ] 6– rings (E = Si–Pb), − or even six-membered [E 6 ] 10– rings (E = Si, Ge) , are known.…”

“…176 Butterfly shaped [E 4 ] 6− anions are present in Ba 3 E 4 phases (E = Si, Ge). 177,178 Furthermore, Zintl phases containing "Y-shaped" [Si 4 ] 12− stars, 179,180 five-membered [E 5 ] 6− rings (E = Si− Pb), 179−184 or even six-membered [E 6 ] 10− rings (E = Si, Ge) 185,186 are known.…”

Thermodynamics of phase transitions in Zintl clusters from density functional theory: making and breaking of bonds in Ba3Ge4

“…Above 630 K, the Ge analogue Ba 3 Ge 4 adopts a tetragonal phase that is structurally very similar to Ba 3 Si 4 , with isolated Ge 4 6− anions and (3b)Ge–(3b)Ge and (3b)Ge–(2b)Ge bond lengths of 2.78 Å and 2.59 Å, respectively (the tetragonal phase). 22 Below this temperature, however, a first-order transition to a different, orthorhombic, phase, where precisely half of the Ge 4 units polymerise along the crystallographic a -axis (designated (Ba 2+ ) 6 [Ge 4 ] 6− 1 ∞ [Ge 4 ] 6− ), with concomitant cleavage of the intra-cluster (3b)Ge–(3b)Ge bond. Polymerisation causes contraction along the a -axis (11.799 Å vs. 12.193 Å) and a ∼ 2% reduction in cell volume.…”

“…17 A weak feature in the differential thermal analysis at ∼610 K was, however, consistent with the transition temperature identified by Zürcher and Nesper. 22…”