Zintl Phases: From Curiosities to Impactful Materials

Abstract

The synthesis of new compounds and crystal structures remains an important research endeavor in pursuing technologically relevant materials. The Zintl concept is a guidepost for the design of new functional solid-state compounds. Zintl phases are named in recognition of Eduard Zintl, a German chemist who first studied a subgroup of intermetallics prepared with electropositive metals combined with main-group metalloids from groups 13–15 in the 1930s. Unlike intermetallic compounds, where metallic bonding is the norm, Zintl phases exhibit a combination of ionic and covalent bonding and are typically semiconductors. Zintl phases provide a palette for iso- and aliovalent substitutions that can each contribute uniquely to the properties. Zintl electron-counting rules can be employed to interrogate a structure type and develop a foundation of structure–property relationships. Employing substitutional chemistry allows for the rational design of new Zintl compounds with technological properties, such as magnetoelectronics, thermoelectricity, and other energy storage and conversion capabilities. Discovering new structure types and compositions through this approach is also possible. The background on the strength and innovation of the Zintl concept and a few highlights of Zintl phases with promising thermoelectric properties in the context of structural and electronic design will be provided.

Zintl Ions and Phases Promote the Catalytic Hydrophosphination of Alkynes, Alkenes, and Imines

“…Zintl ions and phases have been known for over a century but remained largely ignored. Their chemistry is now experiencing a renaissance, with developments as ligands in coordination chemistry, which have unlocked unique physical properties, in small molecule activations including reactivity akin to frustrated Lewis pair chemistry, , and as precursors to nanostructures and light-emitting diodes . One burgeoning area is the application of these ions and phases in organic catalysis.…”

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

“…In the so-called Zintl phases, in contrast, the cations are ‘naked’, leading to much smaller separations between the cluster anions. 7–9 Simple examples of this class would be the binary silicides and germanides such as NaSi, 10 which contains tetrahedral E 4 4− units, isoelectronic with P 4 . The relatively close proximity of the cluster anions in these phases admits the possibility of forming additional inter-cluster bonds, and indeed, in LiSi and LiGe, the very small Li + cation allows the tetrel atoms to form an extended network rather than a lattice of discrete E 4 4− tetrahedra.…”

[Ag(Sn9–Sn9)]5− and [(η4-Sn9)Ag(η1-Sn9)]7−, as aggregates of spherical aromatic building blocks. Persistence of aromaticity upon cluster gathering

“…Nine-atom deltahedral Zintl ions of group 14 have experienced a renewed interest in their chemistry during the past decade 1–7 owing to their unusual reactivity paving the way to further functionalizations reaching the formation of novel compounds. Coordination to transition metals, leads to the characterization of both endo - and exo -hedral intermetalloid clusters, 8 extending the rich structural diversity of Zintl ions displaying diverse electronic and bonding patterns.…”

“…The controlled aggregation of Zintl-ions envisages further construction of molecular materials based on superatoms, 6,25 where finite and infinite chains have been obtained via oxidative coupling. 41–44 Moreover, exo -hedral transition metals serve to coordinate to different Zintl-ions, 11,45–50 resulting in another approach in connecting several cluster units in a single molecular structure.…”