Solid electrolytes are a key feature of all-solid-state batteries, which represent advanced energy storage systems. The investigation of electrochemical properties of promising materials is essential for the development of new compounds. Herein, we report a simple and compact polyether ether ketone (PEEK)-based cell for the analysis of air and moisture sensitive solid electrolytes, including brittle microcrystalline powders or tapes. The cell exhibits low intrinsic capacitance, enabling impedance spectroscopy across the full frequency range without interfering features and applicable for a large temperature range from-70 degrees C to 80 degrees C. Controlled fabrication and measurement pressures improve the reproducibility of impedance measurements. Using polytetrafluoroethylene samples of varying thickness, this stray capacitance is measured and determined. Temperature-dependent electrochemical impedance spectroscopy of Li6PS5Cl/hydrogenated nitrile butadiene rubber (HNBR) sheets, conducted between-70 degrees C and 80 degrees C, demonstrates the cell durability and the high reproducibility of impedance measurements. Furthermore, the airtightness and experimental consistency were maintained even after 250 h of operation. Finally, we highlight the importance of low intrinsic capacitance by successfully resolving the bulk and grain contributions in Li6PS5Cl.

ABSTRACT The chemical system Li/Ti/P has previously been subject to intensive investigation. However, reliable structural data for the reported phases have remained elusive. Motivated by the growing interest in phosphorus‐based lithium‐ion conductors, we have reinvestigated the synthesis, crystal structure, and physical properties of Li 8 TiP 4 . Phase pure Li 8 TiP 4 was obtained, which crystallizes in the tetragonal space group P 4 2 mc (no. 105) with a = 8.37581(2) Å and c = 5.90489(2) Å. According to a structure determination from X‐ray diffraction powder data, Li 8 TiP 4 is closely related to known Li 8 Tt P 4 with Tt = Si, Ge, and Sn, but adapts a different structure type. Basic structural findings are confirmed by solid state 6 Li and 31 P NMR spectroscopy. DFT calculations reveal a band gap of 2.5 eV and a good correlation between theoretical and experimental Raman spectra. From potentiostatic impedance spectroscopy an ion conductivity of (4.3 ± 0.6) × 10 −6 S∙cm −1 at 298 K was found. In addition to the investigation of ternary Li 8 TiP 4 , an isotypic quaternary Ta‐containing phase is observed and studied by single crystal structure determination. Special emphasis in this study is placed on the role of Li occupancy in the voids of the cubic close‐packed (ccp) P atom arrangement and its impact on the ionic conductivity, in comparison to the known compounds Li 7+5 x Ta x P 4 and Li 8− x Ti 1− x Ta x P 4 and traced back to the difference in crystal symmetry. Possible diffusion pathways of the Li + ions were approached by BVSE calculations.

Abstract The development of high-performance solid-state electrolytes requires a fundamental understanding of composition and structure-property relationships governing lithium-ion transport. In recent years, pnictogen-based materials have increasingly been investigated as solid-state ion conductors, with compositions of the form Li3−xScxSb currently achieving the highest known ionic conductivities of up to 42 mS cm−1. Here, we report a structure-retaining solid solution series Li7+xTa1−xGexP4 (0 ≤ x ≤ 1) that allows for a systematic tuning of lithium content via aliovalent substitution. Combining synchrotron powder X-ray diffraction and electrochemical impedance spectroscopy, we demonstrate that all compositions crystallize in the cubic space group Pa3̅ while exhibiting a pronounced, composition-dependent evolution of ionic transport properties. A two-orders-of-magnitude increase in ionic conductivity is observed across the series, which correlates with a linear increase in lithium-ion density and an exponential enhancement in the apparent lithium-ion mobility. In particular, our results highlight the critical role of octahedral void occupation and lithium sublattice topology in facilitating fast ion conduction in lithium-rich phosphides. More broadly, this work provides general design principles for the development of next-generation lithium-ion conductors for solid-state battery applications.

The chemical system Li/Ti/P has previously been subject to intensive investigation. However, reliable structural data for the reported phases have remained elusive. Motivated by the growing interest in phosphorus-based lithium-ion conductors, we have reinvestigated the synthesis, crystal structure, and physical properties of Li8TiP4. Phase pure Li8TiP4 was obtained, which crystallizes in the tetragonal space group P42mc (no. 105) with a = 8.37581(2) Å and c = 5.90489(2) Å. According to a structure determination from X-ray diffraction powder data, Li8TiP4 is closely related to known Li8TtP4 with Tt = Si, Ge, and Sn, but adapts a different structure type. Basic structural findings are confirmed by solid state 6Li and 31P NMR spectroscopy. DFT calculations reveal a band gap of 2.5 eV and a good correlation between theoretical and experimental Raman spectra. From potentiostatic impedance spectroscopy an ion conductivity of (4.3 ± 0.6) × 10-6 S∙cm-1 at 298 K was found. In addition to the investigation of ternary Li8TiP4, an isotypic quaternary Ta-containing phase is observed and studied by single crystal structure determination. Special emphasis in this study is placed on the role of Li occupancy in the voids of the cubic close-packed (ccp) P atom arrangement and its impact on the ionic conductivity, in comparison to the known compounds Li7+5 xTaxP4 and Li8- xTi1- xTaxP4 and traced back to the difference in crystal symmetry. Possible diffusion pathways of the Li+ ions were approached by BVSE calculations.

From a reaction of K 4 Ge 9 , GaCp*, and [18]crown‐6 in ethylenediamine, the new compound [K([18]crown‐6)] 4 [Ga 2 Ge 18 ]·4en has been obtained, containing the novel [Ge 9 Ga–GaGe 9 ] 4− cluster anion. The compound crystallizes in space group P (no. 2) with a = 12.103(3) Å, b = 12.863(3) Å, c = 17.369(3) Å, α = 82.48(2)°, β = 81.51(2)°, γ = 76.35(2)°, V = 2585.7(11) Ǻ 3 , and Z = 1. From electrospray ionization mass spectrometry, the main peak indicates a [GaGe 9 ] − group, that is, one half of the cluster anion. Quantum chemical calculations corroborate the experimental observations, confirming the location of the Ga atoms as bridging units within the dimeric 20‐atom cluster. Alternative structural arrangements with Ga atoms in different positions are significantly less favorable in energy. The paramagnetic monomer [GaGe 9 ] 2− is energetically disfavored relative to dimer formation. The [Ge 9 Ga–GaGe 9 ] 4− is only the second example of a germanium cluster dimer featuring a homoatomic bond between two Ga atoms with oxidation state +2, following the previously reported [Ge 9 Zn–ZnGe 9 ] 4− comprising Zn with formal oxidation state +1.

The incorporation of transition metal atoms into [Ge9] clusters is a widely studied area of Zintl-cluster chemistry. Recently, it was shown that clusters comprising single transition metal atoms in the cluster surface show catalytic properties. Here, we present a synthetic approach to four new compounds comprising silylated Ge9 clusters with organometallic ruthenium complexes. [η5-Ge9Hyp3]RuCp* (1), [η1-Ge9(SitBu2H)3]RuCp(PPh3)2 (2), and [Hyp3Ge9][RuCp(PPh3)2(MeCN)] (3b) (Cp = cyclopentadienyl, Cp* = pentamethylcyclopentadienyl, Hyp = Si(SiMe3)3, Ph = C6H5, tBu = tert-butyl) were characterized by means of NMR spectroscopy and single-crystal structure determination. In the case of 2, a new isomer with an approximated C4v symmetric monocapped square antiprism of nine Ge atoms with an unexpected ligand arrangement comprising three ditertbutylsilane ligands attached to the open square was obtained. [Hyp3Ge9][RuCp(PPh3)2] (3a) was characterized via NMR spectroscopy and LIFDI mass spectrometry. Overall, we were able to show that the steric demand of the ligands Cp vs. Cp* and hypersilylchloride vs. ditertbutylsilane strongly influence the arrangement of the atoms and ligands on the cluster. In addition, the solvent also affects the cluster, as it appears that the ruthenium atom in 3a dissociates from the cluster surface upon acetonitrile coordination to form 3b. These results show that choosing the right synthetic tools and ligands makes a big difference in the outcome of the metalation reaction.

Lithium-ion conductors are one of the key features of all-solid-state lithium-ion batteries. To modify their properties and enable their implementation in high-performance devices, an understanding of the relationship between the crystal structure and the transport properties of the mobile species is important. Lithium phosphidotetrelates and -trielates are classes of lithium-ion conductors reaching ionic conductivities of up to 4.5 × 10-3 cm-1 at room temperature for ω-Li9GaP4. Here, we present the new lithium phosphidotantalate Li7TaP4, and the aliovalent substitution of Ta by Li atoms, which leads to a partial filling of octahedral voids in the structure of Li7TaP4. As a result, the lithium-ion conductivity of Li7TaP4 (1.3 × 10-7 S cm-1) increases by 3 orders of magnitude to 3.7 × 10-4 S cm-1 in Li9.5Ta0.5P4. Li7TaP4 and Li9.5Ta0.5P4 crystallizing in the cubic space groups Pa3̅ and Fm3̅m, respectively, show a close structural relationship. The structure-property relationship is highlighted and compared with the isotypic tetrel element analogues.

From a reaction of K4Ge9, GaCp*, and [18]crown-6 in ethylenediamine, the new compound [K([18]crown-6)](4)[Ga2Ge18]center dot 4en has been obtained, containing the novel [Ge9Ga-GaGe9](4-) cluster anion. The compound crystallizes in space group P 1(-) (no. 2) with a = 12.103(3) angstrom, b = 12.863(3) angstrom, c = 17.369(3) angstrom, alpha = 82.48(2)degrees, beta = 81.51(2)degrees, gamma = 76.35(2)degrees, V = 2585.7(11) angstrom(3), and Z = 1. From electrospray ionization mass spectrometry, the main peak indicates a [GaGe9](-) group, that is, one half of the cluster anion. Quantum chemical calculations corroborate the experimental observations, confirming the location of the Ga atoms as bridging units within the dimeric 20-atom cluster. Alternative structural arrangements with Ga atoms in different positions are significantly less favorable in energy. The paramagnetic monomer [GaGe9](2-) is energetically disfavored relative to dimer formation. The [Ge9Ga-GaGe9](4-) is only the second example of a germanium cluster dimer featuring a homoatomic bond between two Ga atoms with oxidation state +2, following the previously reported [Ge9Zn-ZnGe9](4-) comprising Zn with formal oxidation state +1.

Homogeneous catalytic reactions performed without or with highly abundant transition metals is an increasing field of research due to cost-effectiveness and sustainability. Therefore, using main group element Zintl cluster as support material for transition metals via synthesizing single site homogeneous catalysts (SSHoC) could be a way to make such metals feasible for catalysis, without the risk of metal loss or agglomeration like in classical single site catalysts. A synthetic protocol for four cluster compounds K[Hyp3Ge9Ni(PR3)] (Hyp = Si{SiMe3}3; R = Ph, ptolyl, iPr, Me, 1-4) is presented, in which the nickel atom is embedded into the cluster core. The products were characterized by NMR spectroscopy, ESI/MS as well as for 1 and 3 by single crystal X-ray structure determination comprising a closo-[Ge9Ni] core. The cleavage of the triphenylphosphine ligand in 1 in THF, with and without 2.2.2-crypt, and acetonitrile as well as the isomerization of 1-hexene in the same solvents have been investigated via NMR spectroscopy.

Recently the crystal chemistry of ternary and quaternary lithium phosphide-trielates and phosphide-tetrelates has been investigated due to the remarkable lithium ion conductivity of some representatives. Herein, the extension of the quarternary Zintl phase Li4Sr2SiP4 to a member comprising transition metals is reported. Li4Sr2Mn2P4 crystallizes as a disordered variant of the trigonal Li3LaSb2 structure type (space group Pm1, no. 164) with lattice parameters a = 4.2367(6) & Aring; and c = 7.110(1) & Aring;. It exhibits the Li:M ratio (M = Mn, Al) in tetrahedral voids known from Li2Sr2Al2P4 but crystallizes isotypically to Li5Sr2AlP4. In addition, magnetic properties and Raman spectra are reported and discussed. While Li4Sr2Mn2P4 can formally be described in analogy to the mentioned quarternary Zintl phases, magnetic measurements indicate that it is not a Zintl phase itself.

Lithium-rich ternary lithium phosphides have proven to be good model systems for ionic conductivity, achieving lithium-ion conductivities up to 4.5 mS/cm (ω-Li9GaP4). Compounds in which lithium is partially substituted by alkaline-earth metals bear the possibility of vacancy generation and thus the possibility to reach better ion conductivity and also to gain further insight into structure-property relationships. Based on the recent report on the quaternary compound Li4Sr2SiP4, we investigated the substitution of Si by Al and found the new compounds Li5Sr2AlP4 and Li2Sr2Al2P4. The examination of the solid solution Li5- xSr2Al1- x SixP4 for x = 0.0, 0.125, 0.25, 0.5, 0.75, 0.875, and 1.0 resulted in a series of crystalline materials that adopt two different structure types in dependency of x. Compounds crystallize either in space group P 3 ¯ $\bar{3}$ ;m1 (No. 164) (Li5Sr2AlP4, Li5- xSr2Al1- xSixP4 with x < 0.5) or in space group P21/m (No. 11) (Li2Sr2Al2P4, Li5- xSr2Al1- xSixP4 with x ≥ 0.5). Li5Sr2AlP4 is structurally related to Li4Sr2SiP4 but exhibits an additional statistical disorder of Al and Li atoms, which is also found in Li2Sr2Al2P4.

Catalytic reactions with metalated Zintl clusters as catalysts represent a growing research field, whereby the concept of heterogeneous single-site catalysis is transferred towards homogeneous reactions, leading to so-called single-site homogeneous catalysts (SSHoCs). A synthetic protocol for three cluster compounds [Hyp3Ge9Ir(CO)PR3] (Hyp = Si{SiMe3}3; R = Ph, ptolyl, Me; 1-3) is presented, in which the iridium atom is embedded in the polyhedral cluster surface. The products are characterized by NMR, IR and LIFDI/MS and also structurally characterized for R = Ph by single crystal X-ray structure determination, revealing a closo-[Ge9Ir] cluster. The exchange of the phosphine ligand of 1 in solution, which is regarded as an important step to create the active site, is investigated for various phosphines. In subsequent reactions, oxidative addition of Si-H bonds of primary and secondary silanes SiHR2R' (R/R' = H/Ph, H/pMePh, H/p{OMe}Ph, H/p{NMe2}Ph, and Ph/H) to the Ir atom is investigated. The addition reaction is directly monitored by NMR spectroscopy. Additionally, LIFDI/MS, IR spectroscopy, and single crystal structure determination of the addition products confirm the reaction. X-ray photoelectron spectroscopy (XPS) reveals that the transition metal atom and the Ge atoms of the supporting cluster have a low oxidation state.

Achieving high ionic conductivities in solid state electrolytes is crucial for the development of efficient all‐solid‐state‐batteries. Considering future availability and sustainability, sodium materials hold promises for an alternative for lithium materials in all‐solid‐state batteries, due to the higher abundance. Here, we report on a sodium phosphide ion conductor Na 8 SnP 4 with a conductivity of 0.53 mS cm −1 at room temperature as a pristine material. Due to the simple tetrahedral SnP 4 structure units, Na 8 SnP 4 has potential for optimization through aliovalent substitution as successfully applied in sulfide‐based materials. Na 8 SnP 4 is easily accessible from exclusively abundant elements and forms a high‐ and low‐temperature polymorph, which further allows for a fundamental understanding of the structure‐property relationship. Both polymorphs are structurally characterized by synchrotron X‐ray powder diffraction and MAS–NMR spectroscopy. Ion conductivity and activation energy for ion mobility is determined by temperature dependent impedance spectroscopy and static 23 Na‐NMR measurements. Both MEM analysis of scattering densities as well as structure determination by Rietveld methods hint for ionic motion between special Na positions in the structure and that ion migration proceeds along pathways passing triangular faces of neighboring tetrahedral and octahedral voids. The specific voids filling in the disordered HT‐phase are found to be a crucial parameter for ion migration.

Zintl phases are excellent precursors for nine atom [E9]4- clusters, which are readily accessible by dissolution of A4E9 phases (A = Na-Rb; E = Ge-Pb) in ethylenediamine (en). In contrast, the binary alkali-metal tetrel phases of composition A4E4 are insoluble in en. Furthermore, Li+ cations are rarely investigated as counterions for tetrel element Zintl clusters. We report here that K4E4, comprising [E4]4- polyanions (E = Ge, Sn, and Pb), which are insoluble in en, readily dissolves in en in the presence of lithium ions and the four atomic polyanions [E4]4- are oxidized to nine-atom [E9]4- clusters during dissolution. We isolated crystals of [Li(en)2.5]4[Ge9] and [Li(en)2]4[E9] (E = Sn and Pb) with exclusively Li counterions. Furthermore, the alkali-metal ion exchange of K4Ge9 with LiCl in en results also in the oxidation of [Ge9]4- to [Ge9-Ge9]6- dimers which were isolated as partially and fully ion-exchanged salts such as K2[Li(en)2]4[Ge9-Ge9] and [Li(en)2]6.5[Ge9-Ge9], respectively. NMR spectroscopic investigations of solutions of [Sn9]4- that contain variable Li:K ratio reveal contact K+/[Sn9]4- ion pairs, while Li+ ions form solvent-separated ion pairs. The role of Li+ ions on the solubility of Zintl phases and Li+ assisted oxidation of Zintl ions is highlighted.

Recently the crystal chemistry of ternary and quaternary lithium phosphide‐trielates and phosphide‐tetrelates has been investigated due to the remarkable lithium ion conductivity of some representatives. Herein, the extension of the quarternary Zintl phase Li 4 Sr 2 SiP 4 to a member comprising transition metals is reported. Li 4 Sr 2 Mn 2 P 4 crystallizes as a disordered variant of the trigonal Li 3 LaSb 2 structure type (space group P m 1, no. 164) with lattice parameters a = 4.2367(6) Å and c = 7.110(1) Å. It exhibits the Li: M ratio ( M = Mn, Al) in tetrahedral voids known from Li 2 Sr 2 Al 2 P 4 but crystallizes isotypically to Li 5 Sr 2 AlP 4 . In addition, magnetic properties and Raman spectra are reported and discussed. While Li 4 Sr 2 Mn 2 P 4 can formally be described in analogy to the mentioned quarternary Zintl phases, magnetic measurements indicate that it is not a Zintl phase itself.

Due to the high impact of semiconductors with respect to many applications for electronics and energy transformation, the search for new compounds and a deep understanding of the structure–property relationship in such materials has a high priority. Electron-precise Zintl compounds of the composition A3TrPn2 (A = Li − Cs, Tr = Al − In, Pn = P, As) have been reported for 22 possible element combinations and show a large variety of different crystal structures comprising zero-, one-, two- and three-dimensional polyanionic substructures. From Li to Cs, the compounds systematically lower the complexity of the anionic structure. For an insight into possible crystal–structure band–structure relations for all compounds (experimentally known or predicted), their band structures, density of states and crystal orbital Hamilton populations were calculated on a basis of DFT/PBE0 and SVP/TZVP basis sets. All but three (Na3AlP2, Na3GaP2 and Na3AlAs2) compounds show direct or pseudo-direct band gaps. Indirect band gaps seem to be linked to one specific structure type, but only for Al and Ga compounds. Arsenides show smaller band gaps than phosphides due to weaker Tr-As bonds. The bonding situation was confirmed by a Mullikan analysis, and most states close to the Fermi level were assigned to non-bonding orbitals.

Eduard Zintl was a pioneer in this regard in introducing the concept of localized chemical bonds for intermetallic compounds, and he did so with the caution and restraint customary at that time. In the 1930s, he deduced from the radius increments that specific intermetallic phases composed of two or more metal components might exhibit stronger interactions between only one type of metal. Zintl raised this idea in his paper on the determination of the NaTl structure.1 The existence of NaTl had been deduced before from melt diagrams,2 and was finally synthesized by Zintl from liquid ammonia solutions of sodium and thallium iodide.3 Laves’ contribution published after Zintl's early death in 1942 put the idea to front by comparing the two AB compounds CsCl and NaTl (Figure 1). In CsCl, cations are located in the center of a cube of eight anions, thus allowing a maximum of heteroatomic attractive (Coulomb) interactions. In NaTl, the Tl atoms are in the center of a cube with alternating Na and Tl atoms: “So it seems that bonding forces between atoms of the same type are involved here.”4 Today, however, we are not hesitating at all to draw localized covalent two-center-two-electron bonds according to the pseudo-element concept (8-N rule) between the Tl atoms (Figure 1). Comparison between the CsCl and NaTl structure, as well as a comparison of the description of the Pb94− unit in Zintl's polyanionic salt and as a Wade-type nido-cluster. Zintl's idea was disseminated later by Klemm, Schäfer, Eisenmann, Corbett, von Schnering, Nesper and many others, and there are several terrific review articles on the Zintl concept and its history as well as Zintl phases and Zintl ions.5 The wonderful and useful Zintl concept describes solid state compounds AnBm, in which the constituting metals strongly differ in their electronegativity - such as A being more electropositive relative to a more electronegative main-group p-block (semi)metal element B. Then, the A atoms formally transfer their electrons to the B atoms, which allows them to form either monoatomic anions or an appropriate number of covalent bonds between B atoms; in both cases the atoms reach their noble gas electron configuration. This amazingly simple idea forms the most important bridge between solid-state chemistry of so-called Zintl phases and molecular main-group or organic chemistry. Eduard Zintl was also a pioneer in creating ideas on polyanions: by analytical methods, he demonstrated the existence of a Pb94− polyanion in solution and in solids of compositions such as Na4Pb9. These intermetallic compounds are known as Zintl's polyanionic salts that in contrast to “salt-like” Zintl phases form soluble species. Since at that time the structure of such a complex polyanion of nine Pb atoms was unknown, he again used the idea to assign the Pb4− anion with a noble-gas electron configuration inside a cube of eight Pb atoms. His description resembles but also decidedly differs from the polyhedral nido-structure as found many years later.6 Thus, Zintl also was a forerunner in the formulation of non-classical bonds between metal atoms nowadays known as Zintl polyanions or Zintl clusters (Figure 1). Zintl's revolutionary ideas are certainly connected to his academic carrier. Born on January 21, 1898, in Bavaria, Germany, he studied Chemistry at the Bavarian Academy of Sciences in Munich and performed his PhD thesis work in the laboratory of Otto Hönigschmid, head of the German Atomic Weight Laboratory. He worked on a most challenging project, namely on the determination of atomic weights by analytical methods, which afforded wet-chemical analytical skills at the highest level. Three years after his habilitation in Munich in 1925, he accepted a position as an associate professor at the University of Freiburg in Breisgau. In 1933, he was appointed a full professor of chemistry and head of the Institute for Inorganic Chemistry at the Technical University of Darmstadt. In Darmstadt Zintl put forward the idea of combining inorganic and physical chemistry by planning an institute which was supported by a new building hosting both disciplines. The foundation stone was set on October 1st, 1937, but Eduard Zintl already died on January 17, 1941, and thus did not move into the nearly finished new institute located at the Herrengarten in the city center of Darmstadt. The building was posthumously named in his honor: Eduard-Zintl-Institut für Anorganische und Physikalische Chemie (Eduard-Zintl Institute for Inorganic and Physical Chemistry). On the occasion of a memorial event of the German Chemical Society and the Bunsen Society one year later, the Boehringer-Ingelheim company donated a bronze bust of Eduard Zintl, which was suitably placed in the main staircase of the institute. Eduard Zintl's broad interest in natural sciences reaching from physics and physical chemistry to inorganic molecular and solid-state chemistry is reflected in the design of the institute, which was not only equipped according to the highest technical standards, but also displayed a total of twelve busts in gray basalt tuff on the red sandstone façade, which show famous scientists in the fields of chemistry and physis of various nationalities.7 After the building had housed research groups of the chemistry department for many years, it was renovated in 2000 to host computer sciences, and it was renamed 2003 to Robert-Piloty building. Until then all chemistry groups had completely moved from the Eduard-Zintl Institute to the Campus Lichtwiese in Darmstadt. On the occasion of the 5th Eduard-Zintl-Kolloquium at TU Darmstadt in 2002 (Figure 2), the Eduard-Zintl-Institut für Anorganische und Physikalische Chemie was re-opened, and the Zintl bust was relocated in front of the new building of Inorganic Chemistry on the Campus Lichtwiese (Figure 3). 5th Eduard-Zintl Colloquium, 2002. From left to right: R. Nesper (ETH Zürich), Thomas F. Fässler (TU Darmstadt), Hansjörg Schnöckel (TU Karlsruhe), Stan Vepřek (TU Munich), and Peter Claus (TU Darmstadt). Re-opening of the Eduard-Zintl Institute and relocation of the bust at Campus Lichtwiese, Darmstadt. From left to the right (all TU Darmstadt): Thomas F. Fässler, Karl Heinrich Lieser, Brigitte Eisenmann, Jürgen Brickmann, Herbert Plenio, Klaus-Peter Dinse. There is no doubt that an understanding of the bonding properties allows for the prediction of structures and physical properties, and ultimately is also a prerequisite for synthesis planning. The contributions of R. Hoffman together with Albright, Burdett, and Whangbo, who succeeded in translating the complex physical relationships into a language understandable to chemists, represent a further milestone to the understanding of chemical bonding in solids. “To make sense of the marvelous electronic properties of the solid state, chemists must learn the language of solid-state physics, of band structures. An attempt is made here to demystify that language, drawing explicit parallels to well-known concepts in theoretical chemistry.”8 For almost 40 years now, the teaching of electronic bands, band structures and density of states has been part of students’ chemistry education.9 And based on this, methods have been developed to graphically depict localized bonds in intermetallic compounds using a quantum chemistry approach in order to justify the application of molecular concepts in intermetallics.10 Based on Zintl's ideas, the chemists′ intuitive understanding of the covalent chemical bond has unambiguously be transferred to the solid state. From 1939 to January 1942 Eduard Zintl was together with Wilhelm Biltz and Wilhelm Klemm the managing editor of the Zeitschrift für Anorganische und Allgemeine Chemie. In 1940, the year before he passed away after the outburst of an incurable disease, he published six articles in this journal on silicon monoxide, boron monoxide, sodium silicophosphate, sodium monothioorthophosphate, sodium orthoperjodate, double oxides, and sodium bismutate, all submitted on October 3rd, showing a last time also his broad interest in the chemistry of oxides.11 This special issue of Zeitschrift für Anorganische und Allgemeine Chemie is dedicatd to Eduard Zintl to honor his scientific work by many extraordinary contributions of experts in the field, covering all facets of Zintl phases and Zintl ions from the synthesis and structures of classical Zintl phases, to theoretical descriptions, showing also possible extensions of the concept, and to the important impact of his ideas to material science. Modern materials chemistry is inconceivable without an understanding of structure-property relationships, and closing with Eduard Zintl's words: “Fundamental research is applied research on a long term!”12 Eduard Zintl realized his ideas at a time when the German society was dominated by National Socialism. The focus at this point is on his important contributions in science. His political influence is controversially discussed and surveyed elsewhere.13 The reliefs, which were placed on the outside of the institute building on Zintl's initiative, represent scientists of different nationalities and - despite the many controversies - bear witness to an openness to the world that could not be taken for granted in those years. T.F.F thanks Prof. R. Kniep for helpful information as well as A. Schier and the editors of ZAAC for a revision of the manuscript.

Recently, ternary lithium phosphidotetrelates have attracted interest particularly due to their high ionic conductivities, while corresponding sodium and heavier alkali metal compounds have been less investigated. Hence, we report the synthesis and characterization of the novel ternary sodium phosphidogermanate Na3Ge2P3, which is readily accessible via ball milling of the elements and subsequent annealing. According to single crystal X-ray structure determination, Na3Ge2P3 crystallizes in the monoclinic space group P2(1)/c (no. 14.) with unit cell parameters of a = 7.2894(6) & Aring;, b = 14.7725(8) & Aring;, c = 7.0528(6) & Aring;, beta = 106.331(6)degrees and forms an unprecedented two-dimensional polyanionic network in the b/c plane of interconnected [P3Ge-GeP3] building units. The system can also be interpreted as differently sized ring structures that interconnect and form a two-dimensional network. A comparison with related ternary compounds from the corresponding phase system as well as with the binary compound GeP shows that the polyanionic network of Na3Ge2P3 resembles an intermediate step between highly condensed cages and discrete polyanions, which highlights the structural variety of phosphidogermanates. The structure is confirmed by Na-23- and P-31-MAS NMR measurements and Raman spectroscopy. Computational investigation of the electronic structure reveals that Na3Ge2P3 is an indirect band gap semiconductor with a band gap of 2.9 eV.

Dendritic copper offers a highly effective method for synthesizing porous copper anodes due to its intricate branching structure. This morphology results in an elevated surface area-to-volume ratio, facilitating shortened electron pathways during aqueous and electrolyte permeation. Here, we demonstrate a procedure for a time- and cost-efficient synthesis routine of fern-like copper microstructures as a host for polymer-templated Si/Ge/C thin films. Dissolvable Zintl clusters and sol-gel chemistry are used to synthesize nanoporous coating as the anode. Cyclic voltammetry (CV) with KOH as the electrolyte is used to estimate the surface area increase in the dendritic copper current collectors (CCs). Half cells are assembled and tested with battery-related techniques such as CV, galvanostatic cycling, and electrochemical impedance spectroscopy, showing a capacity increase in the dendritic copper cells. Energy-dispersive X-ray spectroscopy is used to estimate the removal of K in the bulk after oxidizing the Zintl phase K12Si8Ge9 in the polymer/precursor blend with SiCl4. Furthermore, scanning electron microscopy images are provided to depict the thin films after synthesis and track the degradation of the half cells after cycling, revealing that the morphological degradation through alloying/dealloying is reduced for the dendritic Cu CC anodes as compared with the bare reference. Finally, we highlight this time- and cost-efficient routine for synthesizing this capacity-boosting material for low-mobility and high-capacity anode coatings.