Nitridochromate(IV): LiSr2[CrN3].

The quaternary nitridochromate(IV) LiSr2[CrN3] crystallizes in a new structure type with the non-centrosymmetric space group P21 (no. 4) with a = 5.5685(7) Å, b = 5.3828(8) Å, c = 7.5381(1) Å, and ß = 92.291(8)°. Predominant structural features of the compound are slightly nonplanar trigonal units [CrN3]5-, which are connected by three-fold coordinated lithium to form slabs in the (001) plane. Shorter Cr-N bond lengths in comparison with reported nitridochromates(III), as well as diamagnetic behavior and vibrational spectroscopy data indicate Cr(IV), which is in a good agreement with the charge balance. According to electronic structure calculations, the compound is a semiconductor with a band gap of 1.19 eV.

Type-II Clathrate Na24-δ Ge136 from a Redox-Preparation Route.

The metastable type-II clathrate Na24-δ Ge136 was obtained from Na12 Ge17 by applying a two-step procedure. At first, Na12 Ge17 was reacted at 70 °C with a solution of benzophenone in the ionic liquid (IL) 1,3-dibutyl-2-methylimidazolium-bis(trifluoromethylsulfonyl) azanide. The IL was inert towards Na12 Ge17 , but capable of dissolving the sodium salts formed in the redox reaction. By annealing at 340 °C under an argon atmosphere, the X-ray amorphous intermediate product was transformed to crystalline Na24-δ Ge136 (δ≈2) and α-Ge in an about 1 : 1 mass ratio. The product was characterized by X-ray powder diffraction, chemical analysis, and 23 Na solid-state NMR spectroscopy. Metallic properties of Na24-δ Ge136 were revealed by a significant Knight shift of the 23 Na NMR signals and by a Pauli-paramagnetic contribution to the magnetic susceptibility. At room temperature, Na24-δ Ge136 slowly ages, with a tendency to volume decrease and sodium loss.

Cage Adaption by High-Pressure Synthesis: The Clathrate-I Borosilicide Rb8B8Si38.

Rb8B8Si38 forms under high-pressure, high-temperature conditions at p = 8 GPa and T = 1273 K. The new compound (space group Pm3̅n, a = 9.9583(1) Å) is the second example for a clathrate-I borosilicide. The phase is inert against strong acids and bases and thermally stable up to 1300 K at ambient pressure. (Rb+)8(B-)8(Si0)38 is electronically balanced, diamagnetic, and shows semiconducting behavior with moderate Seebeck coefficient below 300 K. Chemical bonding analysis by the electron localizability approach confirms the description of Rb8B8Si38 as Zintl phase.

Tricyanidoferrates(-IV) and Ruthenates(-IV) with Non-Innocent Cyanido Ligands.

Exceptionally electron-rich, nearly trigonal-planar tricyanidometalate anions [Fe(CN)3 ]7- and [Ru(CN)3 ]7- were stabilized in LiSr3 [Fe(CN)3 ] and AE3.5 [M(CN)3 ] (AE=Sr, Ba; M=Fe, Ru). They are the first examples of group 8 elements with the oxidation state of -IV. Microcrystalline powders were obtained by a solid-state route, single crystals from alkali metal flux. While LiSr3 [Fe(CN)3 ] crystallizes in P63 /m, the polar space group P63 with three-fold cell volume for AE3.5 [M(CN)3 ] is confirmed by second harmonic generation. X-ray diffraction, IR and Raman spectroscopy reveal longer C-N distances (124-128 pm) and much lower stretching frequencies (1484-1634 cm-1 ) than in classical cyanidometalates. Weak C-N bonds in combination with strong M-C π-bonding is a scheme also known for carbonylmetalates. Instead of the formal notation [Fe-IV (CN- )3 ]7- , quantum chemical calculations reveal non-innocent intermediate-valent CN1.67- ligands and a closed-shell d10 configuration for Fe, that is, Fe2- .

Structural Peculiarities and Thermoelectric Study of Iron Indium Thiospinel.

The homogeneity range of ternary iron indium thiospinel at 873 K was investigated. A detailed study was focused on two distinct series (y=z): 1) a previously reported charge-balanced (In0.67+0.33y □0.33-0.33y )tetr [In2-z Fez ]oct S4 (A1-series; □ stands for vacancy; the abbreviations "tetr" and "oct" indicate atoms occupying tetrahedral 8a and octahedral 16d sites, respectively) and 2) a new charge-unbalanced (In0.67+y □0.33-y )tetr [In2-z Fez ]oct S4 (A2-series). Fe atoms were confirmed to exclusively occupy an octahedral position in both series. An unusual reduction of the unit cell parameter with increasing Fe content is explained by differences in the ionic radii between Fe and In, as well as by an additional electrostatic attraction originating from charge imbalance (latter only in A2-series). The studied compound is an n-type semiconductor, and its charge carrier concentration increases or decreases for larger Fe content within the A1- and A2-series, respectively. The thermal conductivity κtot is significantly reduced upon increasing vacancy concentration, whereas the change of power factor is insufficient to drastically improve the thermoelectric figure of merit.

In-Cage Interactions in the Clathrate Superconductor Sr8 Si46.

The clathrate I superconductor Sr8 Si46 is obtained under high-pressure high-temperature conditions, at 5 GPa and temperatures in the range of 1273 to 1373 K. At ambient pressure, the compound decomposes upon heating at T=796(5) K into Si and SrSi2 . The crystal structure of the clathrate is isotypic to that of Na8 Si46 . Chemical bonding analysis reveals conventional covalent bonding within the silicon network as well as additional multi-atomic interactions between Sr and Si within the framework cages. Physical measurements indicate a bulk BCS type II superconducting state below Tc =3.8(3) K.

Crystal Structure and Physical Properties of the Cage Compound Hf2B2-2δIr5+δ.

Hf2B2-2δIr5+δ crystallizes with a new type of structure: space group Pbam, a = 5.6300(3) Å, b = 11.2599(5) Å, and c = 3.8328(2) Å. Nearly 5% of the boron pairs are randomly replaced by single iridium atoms (Ir5+δB2-2δ). From an analysis of the chemical bonding, the crystal structure can be understood as a three-dimensional framework stabilized by covalent two-atom B-B and Ir-Ir as well as three-atom Ir-Ir-B and Ir-Ir-Ir interactions. The hafnium atoms center 14-atom cavities and transfer a significant amount of charge to the polyanionic boron-iridium framework. This refractory boride displays moderate hardness and is a Pauli paramagnet with metallic electrical resistivity, Seebeck coefficient, and thermal conductivity. The metallic character of this system is also confirmed by electronic structure calculations revealing 5.8 states eV-1 fu-1 at the Fermi level. Zr2B2-2δIr5+δ is found to be isotypic with Hf2B2-2δIr5+δ, and both form a continuous solid solution.

Cluster Formation in the Superconducting Complex Intermetallic Compound Be21Pt5.

Materials with the crystal structure of γ-brass type (Cu5Zn8 type) are typical representatives of intermetallic compounds. From the electronic point of view, they are often interpreted using the valence electron concentration approach of Hume-Rothery, developed previously for transition metals. The γ-brass-type phases of the main-group elements are rather rare. The intermetallic compound Be21Pt5, a new member of this family, was synthesized, and its crystal structure, chemical bonding, and physical properties were characterized. Be21Pt5 crystallizes in the cubic space group F4̅3m with lattice parameter a = 15.90417(3) Å and 416 atoms per unit cell. From the crystallographic point of view, the binary substance represents a special family of intermetallic compounds called complex metallic alloys (CMA). The crystal structure was solved by a combination of synchrotron and neutron powder diffraction data. Besides the large difference in the scattering power of the components, the structure solution was hampered by the systematic presence of very weak reflections mimicking wrong symmetry. The structural motif of Be21Pt5 is described as a 2 × 2 × 2 superstructure of the γ-brass structure (Cu5Zn8 type) or 6 × 6 × 6 superstructure of the simple bcc structural pattern with distinct distribution of defects. The main building elements of the crystal structure are four types of nested polyhedral units (clusters) with the compositions Be22Pt4 and Be20Pt6. Each cluster contains four shells (4 + 4 + 6 + 12 atoms). Clusters with different compositions reveal various occupation of the shells by platinum and beryllium. Polyhedral nested units with the same composition differ by the distance of the shell atoms to the cluster center. Analysis of chemical bonding was made applying the electron localizability approach, a quantum chemical technique operating in real space that is proven to be especially efficient for intermetallic compounds. Evaluations of the calculated electron density and electron localizability indicator (ELI-D) revealed multicenter bonding, being in accordance with the low valence electron count per atom in Be21Pt5. A new type of atomic interactions in intermetallic compounds, cluster bonds involving 8 or even 14 atoms, is found in the clusters with shorter distances between the shell atoms and the cluster centers. In the remaining clusters, four- and five-center bonds characterize the atomic interactions. Multicluster interactions within the polyhedral nested units and three-center polar intercluster bonds result in a three-dimensional framework resembling the structural pattern of NaCl. Be21Pt5 is a diamagnetic metal and one of rather rare CMA compounds revealing superconductivity (Tc = 2.06 K).

Unconventional Metal-Framework Interaction in MgSi5.

The silicon-rich cage compound MgSi5 was obtained by high-pressure high-temperature synthesis. Initial crystal structure determination by electron diffraction tomography provided the basis for phase analyses in the process of synthesis optimization, finally facilitating the growth of single crystals suitable for X-ray diffraction experiments. The crystal structure of MgSi5 (space group Cmme, Pearson notation oS24, a=4.4868(2) Å, b=10.1066(5) Å, and c=9.0753(4) Å) constitutes a new type of framework of four-bonded silicon atoms forming Si15 cages enclosing the Mg atoms. Two types of smaller Si8 cages remain empty. The atomic interactions are characterized by two-center two-electron bonds within the silicon framework. In addition, there is evidence for multi-center Mg-Si bonding in the large cavities of the framework and for lone-pair-like interactions in the smaller empty voids.

Lutetium Trigermanide LuGe3: High-Pressure Synthesis, Superconductivity, and Chemical Bonding.

LuGe3 was obtained under high-pressure and high-temperature conditions at pressures between 8(1) and 14(2) GPa and at temperatures in the range from 1100(150) to 1500(150) K. The high-pressure phase is isotypic to DyGe3 and decomposes at ambient pressure and T = 690 K mainly into ( cF8)Ge and LuGe2- x. Chemical bonding analysis of LuGe3 reveals two-center electron-deficient Ge-Ge bonds, multicenter polar Lu-Ge interactions, and lone pairs on germanium. Magnetic susceptibility, specific heat, and electrical conductivity measurements indicate transition into a superconducting state below Tc = 3.3(3) K.

Ca12 [Mn19 N23 ] and Ca133 [Mn216 N260 ]: Structural Complexity by 2D Intergrowth.

Two new calcium nitridomanganates, Ca12 [Mn19 N23 ] (P3, a=11.81341(3) Å, c=5.58975(2) Å, Z=1) and Ca133 [Mn216 N260 ] (P3‾ , a=39.477(1) Å, c=5.5974(2) Å, Z=1), were obtained by a gas-solid reaction of Ca3 N2 and Mn with N2 at 1273 K and 1223 K, respectively. The crystal structure of Ca12 [Mn19 N23 ] was determined from high-resolution X-ray synchrotron powder diffraction data, whereas single-crystal X-ray diffraction was employed to establish the crystal structure of the Ca133 [Mn216 N260 ] phase, which classifies as a complex metallic alloy (CMA). Both crystal structures have 2D nitridomanganate layers containing similar building blocks but of different levels of structural complexity. Bonding analysis as well as magnetic susceptibility and electron spin resonance measurements revealed that only a fraction of the Mn atoms in both structures carries a localized magnetic moment, while for most Mn species the magnetism is quenched as a result of metal-metal bond formation.

Intermediate-Valence Ytterbium Compound Yb4Ga24Pt9: Synthesis, Crystal Structure, and Physical Properties.

The title compound was synthesized by a reaction of the elemental educts in a corundum crucible at 1200 °C under an Ar atmosphere. The excess of Ga used in the initial mixture served as a flux for the subsequent crystal growth at 600 °C. The crystal structure of Yb4Ga24Pt9 was determined from single-crystal X-ray diffraction data: new prototype of crystal structure, space group C2/m, Pearson symbol mS74, a = 7.4809(1) Å, b = 12.9546(2) Å, c = 13.2479(2) Å, ß = 100.879(1)°, V = 1260.82(6) Å3, RF = 0.039 for 1781 observed reflections and 107 variable parameters. The structure is described as an ABABB stacking of two slabs with trigonal symmetry and compositions Yb4Ga6 (A) and Ga12Pt6 (B). The hard X-ray photoelectron spectrum (HAXPES) of Yb4Ga24Pt9 shows both Yb2+ and Yb3+ contributions as evidence of an intermediate valence state of ytterbium. The evaluated Yb valence of ∼2.5 is in good agreement with the results obtained from the magnetic susceptibility measurements. The compound is a bad metallic conductor.

Weak Interactions under Pressure: hp-CuBi and Its Analogues.

The metastable binary compound hp-CuBi was obtained from the direct chemical reaction between copper and bismuth at a pressure of 5 GPa and a temperature of 720 K. The atomic arrangement comprises slabs of puckered Cu layers sandwiched between Bi planes. The QTAIM charges calculated for compounds of bismuth with transition metals reveal negligible charge transfer for hp-CuBi. Analysis of the chemical bonding with position-space techniques discloses multicenter interactions within the Bi-Cu-Bi slabs and lone-pair interactions of the van der Waals type between these entities. hp-CuBi exhibits metal-type electrical conductivity with superconductivity below Tc =1.3 K.

The Triply Deprotonated Acetonitrile Anion CCN3- Stabilized in a Solid.

The unprecedented, fully deprotonated form of acetonitrile, the acetonitriletriide anion CCN3- , is experimentally realized for the first time in the stabilizing bulk host framework of the Ba5 [TaN4 ][C2 N] nitridometalate via a one-pot synthesis from the elements under moderate conditions (920 K). The molecular structure of this long-sought acetonitrile derivative is confirmed by X-ray diffraction, as well as NMR, IR, and Raman spectroscopy. The anion is isoelectronic to the CO2 molecule, and, in contrast to acetonitrile (H3 C-C≡N), the electron pairs are shifted towards two double bonds, that is, [C=C=N]3- .

Germanium Dumbbells in a New Superconducting Modification of BaGe3.

We report the high-pressure high-temperature synthesis (P = 15 GPa, T = 1300 K) of BaGe3(tI32) adopting a CaGe3-type crystal structure. Bonding analysis reveals layers of covalently bonded germanium dumbbells being involved in multicenter Ba-Ge interactions. Physical measurements evidence metal-type electrical conductivity and a transition to a superconducting state at 6.5 K. Chemical bonding and physical properties of the new modification are discussed in comparison to the earlier described hexagonal form BaGe3(hP8) with a columnar arrangement of Ge3 triangles.

Zintl-phase Sr3LiAs2H: crystal structure and chemical bonding analysis by the electron localizability approach.

The compound Sr3 LiAs2 H was synthesized by reaction of elemental strontium, lithium, and arsenic, as well as LiH as hydrogen source. The crystal structure was determined by single-crystal X-ray diffraction: space group Pnma; Pearson symbol oP28; a = 12.0340(7), b = 4.4698(2), c = 12.5907(5) Å; V = 677.2(1) Å(3) ; RF = 0.047 for 1021 reflections and with 36 parameters refined. The positions of the hydrogen atoms were first revealed by the electron localizability indicator and subsequently confirmed by crystal structure refinement. In the crystal structure of Sr3 LiAs2 H the metal atoms are arranged in a Gd3 NiSi2 -type motif, whereas the hydrogen atoms are arranged in a distorted tetrahedral environment formed by strontium. The calculated band structure revealed that Sr3 LiAs2 H is a semiconductor, which is in agreement with its diamagnetic behavior. Thus, Sr3 LiAs2 H is considered as a (charge-balanced) Zintl phase.

Polymer-dispersed liquid crystal elastomers as moldable shape-programmable material.

The current development of soft shape-memory materials often results in materials that are typically limited to the synthesis of thin-walled specimens and usually rely on complex, low-yield manufacturing techniques to fabricate macro-sized, solid three-dimensional objects. However, such geometrical limitations and slow production rates can significantly hinder their practical implementation. In this work, we demonstrate a shape-memory composite material that can be effortlessly molded into arbitrary shapes or sizes. The composite material is made from main-chain liquid crystal elastomer (MC-LCE) microparticles dispersed in a silicone polymer matrix. Shape-programmability is achieved via low-temperature induced glassiness and hardening of MC-LCE inclusions, which effectively freezes-in any mechanically instilled deformations. Once thermally reset, the composite returns to its initial shape and can be shape-programmed again. Magnetically aligning MC-LCE microparticles prior to curing allows the shape-programmed artefacts to be additionally thermomechanically functionalized. Therefore, our material enables efficient morphing among the virgin, thermally-programmed, and thermomechanically-controlled shapes.

Non-innocent cyanido ligands: tetracyanidoferrate(-II) as carbonyl copycat.

While a negative oxidation state occurs rarely for metals in general, this is commonly known for metal carbonyl anions, i.e. carbonyl metalates. Although CO and CN- are isoelectronic, cyanidometalates usually do not exhibit metal centers with negative oxidation states. However, we report on the electron-rich tetrahedral tetracyanidoferrate(-II) anion [Fe(CN)4]6-, which was stabilized in (Sr3N)2[Fe(CN)4] (space group R3c, a = 702.12(2) pm, c = 4155.5(2) pm). Microcrystalline powders were synthesized by a solid-state route, single crystals were obtained from Na metal flux. In comparison to classical cyanidometalates, C-N distances are longer and stretching frequencies are lower as indicated by X-ray diffraction, IR and Raman spectroscopy. Weak C-N, strong Fe-C bonds as well as the anion geometry resemble the isoelectronic tetrahedral carbonyl ferrate [Fe(CO)4]2-. 57Fe Mössbauer spectroscopic measurements reveal a negative isomer shift in agreement with substantially delocalized d electrons due to strong π back-bonding. These results point to a very similar bonding situation of both 18e tetracyanido and tetracarbonyl ferrates including non-innocent redox-active ligands and a d10 closed shell configuration on iron. Hereby, new tetracyanidoferrate(-II) provides a missing link for a more in-depth understanding of the chemical bonding trends of highly-reduced cyanidometalates in the quest for even higher reduced transition metals in this exceptional class of compounds.

Composition dependent polymorphism and superconductivity in Y3+x{Rh,Ir}4Ge13-x.

Polymorphism is observed in the Y3+xRh4Ge13-x series. The decrease of Y-content leads to the transformation of the primitive cubic Y3.6Rh4Ge12.4 [x = 0.6, space group Pm3̄n, a = 8.96095(9) Å], revealing a strongly disordered structure of the Yb3Rh4Sn13 Remeika prototype, into a body-centred cubic structure [La3Rh4Sn13 structure type, space group I4132, a = 17.90876(6) Å] for x = 0.4 and further into a tetragonal arrangement (Lu3Ir4Ge13 structure type, space group I41/amd, a = 17.86453(4) Å, a = 17.91076(6) Å) for the stoichiometric (i.e. x = 0) Y3Rh4Ge13. Analogous symmetry lowering is found within the Y3+xIr4Ge13-x series, where the compound with Y-content x = 0.6 is crystallizing with La3Rh4Sn13 structure type [a = 17.90833(8) Å] and the stoichiometric Y3Ir4Ge13 is isostructural with the Rh-analogue [a = 17.89411(9) Å, a = 17.9353(1) Å]. The structural relationships of these derivatives of the Remeika prototype are discussed. Compounds from the Y3+xRh4Ge13-x series are found to be weakly-coupled BCS-like superconductors with Tc = 1.25, 0.43 and 0.6, for x = 0.6, 0.4 and 0, respectively. They also reveal low thermal conductivity (<1.5 W K-1 m-1 in the temperature range 1.8-350 K) and small Seebeck coefficients. The latter are common for metallic systems. Y3Rh4Ge13 undergoes a first-order phase transition at Tf = 177 K, with signatures compatible to a charge density wave scenario. The electronic structure calculations confirm the instability of the idealized Yb3Rh4Sn13-like structural arrangements for Y3Rh4Ge13 and Y3Ir4Ge13.

The Intermetallic Semiconductor ht-IrGa3: a Material in the in-Transformation State.

The compound IrGa3 was synthesized by direct reaction of the elements. It is formed as a high-temperature phase in the Ir-Ga system. Single-crystal X-ray diffraction analysis confirms the tetragonal symmetry (space group P42 /mnm, No. 136) with a = 6.4623(1) Å and c = 6.5688(2) Å and reveals strong disorder in the crystal structure, reflected in the huge values and anisotropy of the atomic displacement parameters. A model for the real crystal structure of ht-IrGa3 is derived by the split-position approach from the single-crystal X-ray diffraction data and confirmed by an atomic-resolution transmission electron microscopy study. Temperature-dependent electrical resistivity measurements evidence semiconductor behavior with a band gap of 30 meV. A thermoelectric characterization was performed for ht-IrGa3 and for the solid solution IrGa3-x Zn x .