Volume 71, Issue 5 - Special issue: Dedicated to Professor Wolfgang Jeitschko on the occasion of his 80th birthday

The design of future materials for biotechnological applications via deposition of molecules on surfaces will require not only exquisite control of the deposition procedure, but of equal importance will be our ability to predict the shapes and stability of individual molecules on various surfaces. Furthermore, one will need to be able to predict the structure patterns generated during the self-organization of whole layers of (bio)molecules on the surface. In this review, we present an overview over the current state of the art regarding the prediction and clarification of structures of biomolecules on surfaces using theoretical and computational methods.

NaGe 6 As 6 is a ternary arsenide prepared by reaction of the elements at 650 °C. It crystallizes in a new monoclinic structure type [space group C 2/ m , Z = 2, a = 22.063(2), b = 3.8032(4), c = 7.2020(8) Å, β = 92.7437(15)°] that can be considered to be derived by inserting guest Na atoms between [Ge 6 As 6 ] layers identical to those found in the layered binary arsenide GeAs. An unusual feature in both structures is the presence of ethane-like Ge 2 As 6 units in staggered conformation, with Ge–Ge dumbbells oriented either parallel or perpendicular to the layers. Electronic band structure calculations have shown that the electron excess in NaGe 6 As 6 is accommodated by raising the Fermi level across a 0.6 eV band gap in semiconducting GeAs so that it cuts the bottom of the conduction band, resulting in an n -doped semiconductor.

Reaction of manganese (II) thiocyanate with 2,5-dimethylpyrazine leads to the formation of three new coordination compounds of compositions Mn(NCS) 2 (2,5-dimethylpyrazine) 2 (H 2 O) 2 ( 1 ), Mn(NCS) 2 (H 2 O) 2 (MeOH) 2 -tris(2,5-dimethylpyrazine) solvate ( 2 ), and Mn(NCS) 2 (H 2 O) 4 -tetrakis(2,5-dimethylpyrazine) solvate ( 3 ) that were characterized by single crystal X-ray diffraction. In their crystal structures, the Mn(II) cations are sixfold coordinated by two terminally N-bonded thiocyanato anions and two water molecules as well as by two 2,5-dimethylpyrazine ligands ( 1 ), two ethanol ( 2 ), or two water molecules ( 3 ), within slightly distorted octahedra. In compounds 2 and 3 , additional 2,5-dimethylpyrazine ligands are located in the cavities of the structures as solvate molecules. X-ray powder diffraction has shown that compounds 1 and 2 cannot be prepared as pure phases and that batches of compound 3 contain only minor traces of a contamination. Differential thermoanalysis and thermogravimetry have revealed that upon heating of compound 3 , an intermediate of composition Mn(NCS) 2 (2,5-dimethylpyrazine) ( 4 ) is formed, which cannot be obtained from solution. To mimic the structure of 4 , single crystals of a Cd compound of the same composition ( 5 ) were prepared from the liquid phase, and single crystal X-ray analysis has shown that it is isotypic to 4 .

[Rh 6 Te 8 (PPh 3 ) 6 ]·4C 6 H 6 , the first compound with a molecular Chevrel-type [Rh 6 Te 8 ] cluster core has been synthesized and structurally characterized. By means of quantum chemical calculation, the close relationship of its electronic configuration to that of the lighter homologue has been demonstrated. The different crystal solvent content prevents an isostructural crystallization.

The new compound [Mn 2 (bipy) 4 SbS 4 ](ClO 4 ) was prepared by a new synthetic route for the preparation of thioantimonates(V) that can be used even at room temperature. Mixing aqueous solutions of [Mn(bipy) 3 ](ClO 4 ) 2 and Na 3 SbS 4 · 9H 2 O leads to immediate crystallization of the pure compound. In the structure an SbS 4 3– anion acts as a tetradentate bridge connecting two Mn 2+ cations of [Mn(bipy) 3 ] 2+ complexes (bipy = 2,2′-bipyridine). The compound features a hitherto unknown [Mn 2 (bipy) 4 SbS 4 ] + cation. Bipy ligands of adjacent cations are arranged parallel to each other leading to weak off-center parallel π - π interactions stabilizing the crystals. Magnetic measurements indicate weak antiferromagnetic exchange interactions between the Mn 2+ centers.

The diarsenates MM ′As 2 O 7 ( M = Sr, Ba; M ′ = Cd, Hg) were prepared under hydrothermal conditions (~200 °C, autogenous pressure), starting from As 2 O 5 and the corresponding metal oxides or precursor compounds thereof in aqueous solutions. Structure analyses on the basis of single crystal X-ray data revealed the four structures to be isotypic. They are the first diarsenates to crystallize in the triclinic BaZnP 2 O 7 structure type (space group P 1̅, Z = 2, a ≈ 5.8 Å, b ≈ 7.3 Å, c ≈ 7.6 Å, α ≈ 101°, β ≈ 91°, γ ≈ 98°). All related MM ′As 2 O 7 diarsenates reported so far ( M = Sr, Ba, Pb; M ′ = Mg, Co, Cu, Zn) crystallize in the monoclinic α -Ca 2 P 2 O 7 structure type ( P 2 1 / n , Z = 4). Hence, the size of the divalent M ′ cation determines which of the two structure types is adopted.

RE 3 Au 5 Zn ( RE = Y, Sm, Gd–Ho) intermetallic compounds were synthesized by melting the elements in sealed tantalum tubes. They exhibit a new structure type which was studied by X-ray diffraction on powders and refined from single crystal diffraction data: Cmcm , a = 736.9(2), b = 1489.4(2), c = 1330.4(3) pm, w R2 = 0.0371, 1184 F 2 values and 55 variables for Y 3 Au 4.92 Zn 1.08 and a = 739.0(1), b = 1495.8(2), c = 1339.2(2) pm, w R2 = 0.0325, 1410 F 2 values and 54 variables for Tb 3 Au 5 Zn. The network consists of five- and six-membered gold rings in puckered conformations. Atoms of the rare earth elements are placed within the cavities of this network where every third cavity is filled by a Zn 2 dumbbell. The structure is discussed in detail and compared with the gold substructure of Hf 7 Au 10 .

Hydrogen insertion into GdFeSi induces (i) a structural transition from a tetragonal CeFeSi-type to a tetragonal ZrCuSiAs-type, (ii) an anisotropic expansion of the unit cell parameters because the a parameter decreases, whereas the c parameter increases, and (iii) a decrease in Curie temperature from 121 to 20 K. On the contrary, an amorphous ferromagnet ( T C = 65 K) is obtained by mechanical grinding of GdFeSi. The three compounds (GdFeSi, GdFeSiH, and amorphous GdFeSi) were investigated by 57 Fe Mössbauer spectroscopy. At 4.2 K, this study has revealed that the magnetically ordered Gd substructure produces a small transferred hyperfine magnetic field at the 57 Fe nucleus.

Single crystals of Ba 2 Zn Q 3 ( Q = Se, Te) were obtained by solid-state reactions at 1173 K. These isostructural compounds crystallize in the K 2 AgI 3 structure type. The Zn atoms in this structure are coordinated to four Q atoms (2 Q 1, 1 Q 2, 1 Q 3) and these form a distorted tetrahedron around each Zn atom. Each Zn Q 4 tetrahedron shares two corners with neighboring Zn Q 4 tetrahedra resulting in the formation of infinite chains of [Zn Q 4 4− ] units. The absorption spectrum of a single crystal of Ba 2 ZnTe 3 shows an absorption edge at 2.10(2) eV, consistent with the dark-red color of the crystals. From DFT calculations Ba 2 ZnSe 3 and Ba 2 ZnTe 3 are found to be semiconductors with electronic band gaps of 2.6 and 1.9 eV, respectively.

Urea (CN 2 H 4 O) is a fundamental biomolecule whose derivatives are abundant throughout chemistry. Among the latter, rubidium ureate (RbCN 2 H 3 O) and its cesium analog (CsCN 2 H 3 O) have been described only very recently and form the first structurally characterized salts of deprotonated urea. Here, we report on a neutron diffraction study on the aforementioned alkaline-metal ureates, which affords the positions for all hydrogen atoms (including full anisotropic displacement tensors) and thus allows us to gain fundamental insights into the hydrogen-bonding networks in the title compounds. The structure refinements of the experimental neutron data proceeded successfully using starting parameters from ab initio simulations of atomic positions and anisotropic displacement parameters. Such joint experimental-theoretical refinement procedures promise significant practical potential in cases where complex solids (organic, organometallic, framework materials) are studied by powder diffraction.

Transparent single crystals of the scheelite-type Ln [AsO 4 ] phases with Ln = La–Nd are obtained by the pressure-induced monazite - to-scheelite type phase transition in a Walker-type module under high-pressure and high-temperature conditions of 11 GPa at 1100–1300 °C. Coinciding with this transition, there is an increase in density and a reduction in molar volume of about 4.5 % for the scheelite-type phases (tetragonal, I 4 1 / a ) for La[AsO 4 ] ( a = 516.92(4), c = 1186.1(9) pm), Ce[AsO 4 ] ( a = 514.60(1), c = 1175.44(2) pm), Pr[AsO 4 ] ( a = 512.63(4), c = 1168.25(9) pm), and Nd[AsO 4 ] ( a = 510.46(4), c = 1160.32(11) pm) as compared to the well-known monazite-type phases (monoclinic, P 2 1 / n ). Surprisingly enough, the scheelite-type oxoarsenates(V) exhibit a lower coordination number for the Ln 3+ cations ( CN = 8 versus CN = 8 + 1), whereas the isolated tetrahedral [AsO 4 ] 3– anions ( d (As–O) = 168.9–169.3 pm for the scheelites as compared to d (As–O) = 167.1–169.9 pm for the monazites) remain almost unchanged. So the densification must occur because of the loss of two edge-connections of the involved [ Ln O 8+1 ] 15– polyhedra with the [AsO 4 ] 3– tetrahedra in the monazite- resulting in exclusively vertex connected [ Ln O 8 ] 13– and [AsO 4 ] 3– units in the scheelite-type structure.

Bi 2 Fe 4 O 9 was synthesized using a polyol-mediated method. X-ray powder diffraction (XRPD) revealed that the as-synthesized sample is nano-crystalline. During heating, the X-ray amorphous powder transformed into a rhombohedral perovskite-type bismuth ferrate followed by a second transformation into mullite-type Bi 2 Fe 4 O 9 at higher temperatures. This transformation was studied at in-situ conditions by temperature-dependent XRPD and 57 Fe Mössbauer spectroscopy. The 57 Fe Mössbauer spectra indicate the existence of two Fe 3+ species at two different octahedrally coordinated sites leading to the conclusion that the as-synthesized powder of the polyol synthesis possesses a disordered (Bi 1– x Fe x )FeO 3 perovskite structure. Rietveld refinements have unambiguously supported this observation and this results suggest that one third of the Bi 3+ sites are substituted by Fe 3+ representing the initial chemical composition. This study has shown that as-synthesized nano-materials are not always similar to the respective micro-crystalline ones.

The new niobium oxide fluorides M NbO 2 F 4 [ M = (Cr, Fe)], CrNb 2 O 4 F 5 , and Fe 2 Nb 3 O 6 F 9 were prepared by treatment of chromium or iron nitrate with Nb-containing hydrofluoric acid solutions. Crystal structures were investigated by means of X-ray powder diffraction. All new compounds can be structurally refined in the cubic ReO 3 -type. The iron niobium oxide fluorides are reddish orange, and chromium containing phases exhibit a light green color. The niobium atoms are in the highest formal oxidation state.

Herein we show that cyclometalated, square planar Pt(II) complexes can be tuned to achieve deep-blue phosphorescent emitters. For this purpose, the introduction of an electron-donating moiety on two different bidentate NˆN and NˆO fluorine-free luminophores, namely 2-(1 H -tetrazol-5-yl)pyridine and picolinic acid, was carried out. The remaining two coordination sites of the Pt(II) metal center were filled by a sterically demanding cyclometallating unit, namely a tertiary phosphite CˆP ligand. This ancillary ligand avoids aggregation and provides high solubility in organic solvents. Based on this approach, we were able to blue-shift the emission of the complexes down to 411 nm, and to achieve a maximal photoluminescence quantum yield of 56% in the solid state.

Various oxides with the hibonite structure were synthesized and structurally analyzed using powder neutron diffraction. The structure of CaAl 12 O 19 at 298 and 11 K shows dipoles that are apparently too dilute to order unless subjected to a suitable electric field. Magnetoplumbites, such as BaFe 12 O 19 , are isostructural with hibonite. These compounds possess ferromagnetic properties, which combined with the electric dipoles may influence multiferroic behavior. Our SrAl 12 O 19 sample showed two distinct hexagonal phases, a major phase with the normal hibonite structure and a minor phase having a closely related structure. Our sample of the defect hibonite phase La 2/3+δ Al 12–δ O 19 shows a distinctly higher δ value (0.25) vs. that reported (~0.15) for samples made from the melt. Finally, we used to advantage the negative scattering length of Ti to determine the site occupancies of Ni and Ti in CaAl 10 NiTiO 19 .

In the course of a systematic study of alkali iron chalcogenido salts containing clusters [Fe 4 Q 8 ] a series of new mixed-valent potassium and rubidium selenido and tellurido ferrates(II/III) was synthesized by carefully heating the pure elements enclosed in sample tubes under an argon atmosphere up to maximum temperatures of 800–900 °C. Their crystal structures have been determined by means of single crystal X-ray diffraction. The mixed-valent Fe II/III tellurido ferrates A 7 [Fe 4 Te 8 ] form three different structure types. All structures contain tetramers of four edge sharing [FeTe 4 ] tetrahedra, which are connected by common edges to form only slightly distorted tetrahedral [Fe 4 Te 8 ] 7− anions (‘stella quadrangula’) with a [Fe 4 Te 4 ] cubane core. In all cases, these anions are surrounded by 26 alkali cations, which are located at the eight corners and the midpoints of the six faces and 12 edges of a cube. The three crystal structures can thus be described by three different packings of cuboid moieties: The monoclinic rubidium compound Rb 7 [Fe 4 Te 8 ] (space group C 2/ c , a = 2000.16(7), b = 897.79(3), c = 1768.12(6) pm, β = 117.4995(10)°, Z = 4, R 1 = 0.0296) is isotypic to the known cesium tellurido and sulfido ferrates Cs 7 [Fe 4 (S/Te) 8 ]. Depending on the temperature, K 7 [Fe 4 Te 8 ] forms two different but closely related new structure types: The tetragonal r.t. modification (space group P 4 2 / nmc , a = 1222.25(14), c = 872.1(2) pm, Z = 2, R 1 = 0.0583) crystallizes in a supergroup of the orthorhombic l.t. (100 K) form (space group Pbcn , a = 1715.5, b = 866.76(3), c = 1715.50(7) pm, Z = 4, R 1 = 0.0160). In all structures, the cluster centered cubes are stacked to form columns along the short (≈870 pm) axis. These columns are themselves densely packed with 4 (both K compounds) and 6 ( A = Rb) adjacent face-sharing columns. According to these arrangements of cluster-centered cubes, a relation of the packing of K/Rb cations and cluster anions with the simple cubic packing can be established applying the crystallographic group-subgroup formalism. Attempts to synthesize the corresponding selenium compound K 7 [Fe 4 Se 8 ] resulted in the formation of the likewise mixed-valent compound K 6 [Fe 4 Se 8 ]. Despite the modified composition, the new orthorhombic structure (space group Pbcn , a = 1632.62(6), b = 821.10(3), c = 1592.75(6) pm, Z = 4, R 1 = 0.0540) is almost isotypic to the l.t. form of K 7 [Fe 4 Te 8 ], the only difference being a missing K site. K 5 Fe 2 Te 5 crystallizes in a new structure type (cubic, space group Pa 3̅, a = 1709.02(5) pm, Z = 4, R 1 = 0.0594). According to K 5 Fe 2 Te 5 =K 15 [Fe 3 Te 7 ] 2 (Te), its structure contains mixed-valent cuboidal trimers [Fe 3 Te 7 ] (6/7)− and isolated telluride ions, which are coordinated by cubes of K + cations.

We report on crystal structure data and hydrogenation properties of 24 palladium-rich intermetallic compounds with elements from groups 12–16 of the Periodic Table. Refined crystal structures based on X-ray powder diffraction data are presented for Pd 3 As (Fe 3 P type structure) and several members of the Pd 5 TlAs type structure family. Hydrogenation was studied in situ by differential scanning calorimetry (DSC) under 5.0 MPa hydrogen pressure up to 430 °C. Pd 0.75 Zn 0.25 , PdCd, PdHg, Pd 2 Sn, Pd5Pb3, Pd 13 Pb 9 , Pd 3 As, Pd 20 Sb 7 , Pd 8 Sb 3 , Pd 5 Sb 2 , PdSb, Pd 5 Bi 2 , Pd 17 Se 15 , Pd 4 Se, Pd 5 TlAs, Pd 5 CdSe, Pd 5 CdAs, Pd 5 HgSe, Pd 5 InAs, Pd 8 In 2 Se and Pd 3 Bi 2 Se 2 do not show any sign of hydrogen uptake according to DSC and X-ray diffraction. For Pd 3 Sn and Pd 3 Pb a significant hydrogen uptake with unit cell volume increases of 0.4 and 0.6 %, respectively, with a retained structure type of the parent intermetallic was observed. Hydrogenation of Pd 5 InSe yields Pd 3 InH ≈0.9 and a mixture of palladium selenides. Thermal analysis experiments in helium and in hydrogen atmosphere show that this is a multistep reaction with a decomposition of Pd 5 InSe to Pd 3 In and a liquid phase and subsequent hydrogenation of Pd 3 In.

The chlorine functionalized dialkynylsilane (4- t Bu-C 6 H 4 )(Cl)Si(C≡C- t Bu) 2 ( 3 ) reacted with equimolar quantities of H–Al t Bu 2 or H–Ga t Bu 2 by hydrometallation of a C≡C triple bond and formation of mixed alkenyl-alkynylsilanes ( 4 and 5 ) in which the Si and Lewis acidic metal atoms adopt geminal positions at the α -C atoms of the alkenyl groups. Intramolecular M···Cl interactions (M=Al, Ga) afforded four-membered SiCMCl heterocycles which in comparison with 3 had significantly lengthened Si–Cl bonds. Dual hydrometallation of 3 was only observed for H–Ga t Bu 2 . One Ga atom of the product ( 6 ) was coordinated by the silicon-bound Cl atom, while the second one showed an interaction with the aromatic ring of the tert -butyl-phenyl group. Treatment of the aluminium compound 4 with two equivalents of H–Ga t Bu 2 afforded a Si–H bond by Cl-H exchange and release of Cl–Al t Bu 2 . The resulting silane ( 7 ) has the Si atom and two Ga atoms bridged by the α -C atoms of two vinyl groups. The specific functionality of 4 caused a remarkable reactivity. Phenyl isocyanate reacted by the formal insertion into the Al–C(vinyl) and the activated Si–Cl bonds and resulted in the formation of a C–C bond. The product ( 8 ) has a SiC 2 N heterocycle with an Si–N bond and exocyclic C=C and C=O double bonds. The keto group is coordinated to a Cl–Al t Bu 2 molecule, which was formed by the shift of the Cl atom from silicon to aluminium.

V 18 P 9 C 2 crystallizes in the orthorhombic space group Pmma with the lattice parameters a = 17.044(3), b = 3.2219(7), and c = 13.030(2) Å, Z = 2. The crystal structure is composed of 19 symmetry-independent atoms. The crystal structure is considered as a network formed by the transition metal atoms exhibiting cubic, trigonal prismatic, and octahedral voids centered by V, P, and C atoms, respectively. Vice versa , the V and P atoms form a three-dimensional network. The two CV 6 octahedra are edge- and corner-connected to chains running parallel to [010]. The five unique P atoms are trigonal prismatically coordinated by V atoms with one to three faces capped again by a V atom. The V atoms have mainly cubic environments formed solely by V or by V and P atoms. V 18 P 9 C 2 exhibits some structural relations to other compounds of the ternary system V–P–C as well as to other intermetallic phases. Despite the low carbon content, V 18 P 9 C 2 is considered as a ternary compound rather than an interstitially stabilized (binary) phosphide in view of its special structural features.

The Au(III)-mediated oxidative cyclization of a series of 2-hydrazinylquinolines is reported. This intramolecular reaction represents a reliable way towards obtaining various 3 H -1,2,4-triazolo[4,3- a ]quinolin-10-ium cations. The molecular structures of three of the starting compounds (2-(1-methyl-2-(pyridin-2-ylmethylene)hydrazinyl)quinoline, 2-(1-methyl-2-(thiophen-2-ylmethylene)hydrazinyl)quinoline, 2-((2-methyl-2-(quinolin-2-yl)hydrazono)methyl)aniline) as well as of one cyclized system (3-methyl-1-(pyridin-2-yl)-3 H -1,2,4-triazolo[4,3- a ]quinolin-10-ium dichloridoaurate(I)) were determined by means of single-crystal X-ray diffraction.

The rare earth borates RE 2 B 8 O 15 ( RE = La, Pr, Nd) were synthesized in a Walker-type multianvil apparatus under conditions of 5.5 GPa and 1100 °C. Starting from the corresponding rare earth oxides and boron oxide, the syntheses yielded crystalline products of all new compounds that allowed crystal structure analyses based on single-crystal X-ray diffraction data for La 2 B 8 O 15 and Nd 2 B 8 O 15 . The compound Pr 2 B 8 O 15 could be characterized via X-ray powder diffractometry. The results show that the new compounds crystallize isotypically to Ce 2 B 8 O 15 in the monoclinic space group P 2/ c . The infrared spectra of RE 2 B 8 O 15 ( RE = La, Pr, Nd) have also been studied.

A series of hitherto unknown mixed-metal phosphates of the monophosphate tungsten bronze structure family [MPTB; (WO 3 ) 2 m (PO 2 ) 4 ] have been obtained by solution combustion synthesis followed by annealing ( ϑ = 850°C) at appropriate oxygen pressures. These new phosphates show substitution of W 5+ by either M 3+ 1/3 W 6+ 2/3 ( M : V, Cr, Fe, Mo) or Ti 4+ 1/2 W 6+ 1/2 . Members of the MPTB structural series with m = 2 [e.g. Cr III 4/3 W VI 8/3 O 12 (PO 2 ) 4 ; Ti IV 6/3 W VI 6/3 O 12 (PO 2 ) 4 ] and m = 4 [e.g. Cr 4/3 W 20/3 O 24 (PO 2 ) 4 ] have been obtained. In the course of our investigation the crystal structure of WOPO 4 (MPTB with m = 2: W 4 O 12 (PO 2 ) 4 ) has been re-determined from X-ray single-crystal data, showing monoclinic instead of the orthorhombic symmetry reported in literature ( P 2 1 /m , Z = 1, 80 parameters, 1832 independent reflections R 1 = 0.027, wR 2 = 0.063). The crystal structures of Mo III 4/3 W VI 8/3 O 12 (PO 2 ) 4 and Cr III 4/3 W VI 8/3 O 12 (PO 2 ) 4 (MPTBs with m = 2) were also refined from single-crystal data {(Mo/W (Cr/W): P 2 1 /m , Z = 1, 80(86) parameters, 1782(1769) independent reflections, R 1 = 0.035(0.059), wR 2 = 0.081(0.146)}. These refinements indicate statistical distribution of M III and W VI over the metal sites. By selected area electron diffraction the unit cell dimensions of Cr III 4/3 W VI 8/3 O 12 (PO 2 ) 4 and Cr III 4/3 W VI 20/3 O 24 (PO 2 ) 4 derived from XRPD and SXRD are confirmed. HRTEM images of Cr 4/3 W 20/3 O 24 (PO 2 ) 4 are in agreement with its assumed close structural relation to W 8 O 24 (PO 2 ) 4 and show an highly ordered atomic arrangement.

The new equiatomic scandium transition metal aluminides Sc T Al for T = Cr, Ru, Ag, Re, Pt, and Au were obtained by arc-melting of the elements followed by subsequent annealing for crystal growth. The samples were studied by powder and single crystal X-ray diffraction. The structures of three compounds were refined from single crystal X-ray diffractometer data: ScCrAl, MgZn 2 type, P 6 3 / mmc , a = 525.77(3), c = 858.68(5) pm, R 1 = 0.0188, wR 2 = 0.0485, 204 F 2 values, 13 variables, ScPtAl, TiNiSi type, Pnma , a = 642.83(4), b = 428.96(2), c = 754.54(5) pm, R 1 = 0.0326, wR 2 = 0.0458, 448 F 2 values, 20 variables and ScAuAl, HfRhSn type, P 6̅2 c , a = 722.88(4), c = 724.15(4) pm, R 1 = 0.0316, wR 2 = 0.0653, 512 F 2 values, 18 variables. Phase pure samples of all compounds were furthermore investigated by magnetic susceptibility measurements, and Pauli-paramagnetism but no superconductivity was observed down to 2.1 K for all of them. The local structural features and disordering phenomena have been characterized by 27 Al and 45 Sc magic angle spinning (MAS) and static NMR spectroscopic investigations.

The gold-rich intermetallic compounds Sr 2 Au 6 Zn 3 , Eu 2 Au 6 Zn 3 , Sr 2 Au 6 Ga 3 , and Eu 2 Au 6 Ga 3 were synthesized from the elements in sealed tantalum ampoules in induction or muffle furnaces. The europium compounds are reported for the first time and their structures were refined from single crystal X-ray diffractometer data: Sr 2 Au 6 Zn 3 type, R 3̅ c , a = 837.7(1), c = 2184.5(4) pm, wR 2 = 0.0293, 572 F 2 values for Eu 2 Au 6.04 Zn 2.96 and a = 838.1(2), c = 2191.7(5) pm, wR 2 = 0.0443, 513 F 2 values for Eu 2 Au 6.07 Ga 2.93 with 20 variables per refinement. The structures consist of a three-dimensional gold network with a 6R stacking sequence, similar to the respective diamond polytype. The cavities of the network are filled in a ratio of 2:1 by strontium (europium) atoms and Ga 3 (Zn 3 ) triangles in an ordered manner. Sr 2 Au 6 Zn 3 and Sr 2 Au 6 Ga 3 are diamagnetic with room temperature susceptibilities of –3.5 × 10 −4 emu mol –1 . Temperature dependent susceptibility and 151 Eu Mössbauer spectroscopic measurements show a stable divalent ground state for both europium compounds. Eu 2 Au 6 Zn 3 and Eu 2 Au 6 Ga 3 order antiferromagnetically below Néel temperatures of 16.3 and 12.1 K, respectively. Anisotropic electrical conductivity of Sr 2 Au 6 Ga 3 is proven by an alignment of the crystallites in the magnetic field. Orientation-dependent 69;71 Ga NMR experiments combined with quantum mechanical calculations (QM) give evidence for a highly anisotropic charge distribution of the Ga atoms.

A reinvestigation of the alkali metal thiosulfates has led to the new phase Cs 2 S 2 O 3 ·H 2 O. At first cesium thiosulfate monohydrate was obtained as a byproduct of the synthesis of Cs 4 In 2 S 5 . Further investigations were carried out using the traditional synthesis reported by J. Meyer and H. Eggeling. Cs 2 S 2 O 3 ·H 2 O crystallizes in transparent, colorless needles. The crystal structure of the title compound was determined by single crystal X-ray diffraction at room temperature: space group C 2/ m (No. 12), unit cell dimensions: a = 11.229(4), b = 5.851(2), c = 11.260(5) Å, β = 95.89(2)°, with Z = 4 and a cell volume of V = 735.9(5) Å 3 . The positions of all atoms including the hydrogen atoms were located in the structure refinement. Cs 2 S 2 O 3 ·H 2 O is isotypic with Rb 2 S 2 O 3 ·H 2 O. Isolated tetrahedra [S 2 O 3 ] 2− are coordinated by the alkali metal cations, and in addition they serve as acceptors for hydrogen bonding. For both Cs atoms the shortest distances are observed to oxygen atoms of the S 2 O 3 2− anions whereas the terminating sulfur atom has its shortest contacts to the water hydrogen atoms. Thus, an extended hydrogen bonding network is formed. The title compound has also been characterized by IR spectroscopy. IR spectroscopy reveals the vibrational bands of the water molecules at 3385 cm −1 . They show a red shift in the OH stretching and bending modes as compared to free water. This is due both to the S···H hydrogen bonding and to the coordination of H 2 O molecules to the cesium atoms.

The crystal structures of the trigermanides AE Ge 3 ( tI 32) ( AE = Ca, Sr, Ba; space group I 4/ mmm , for SrGe 3 : a = 7.7873(1), c = 12.0622(3) Å) comprise Ge 2 dumbbells forming layered Ge substructures which enclose embedded AE atoms. The chemical bonding analysis by application of the electron localizability approach reveals a substantial charge transfer from the AE atoms to the germanium substructure. The bonding within the dumbbells is of the covalent two-center type. A detailed analysis of SrGe 3 reveals that the interaction on the bond-opposite side of the Ge 2 groups is not lone pair-like – as it would be expected from the Zintl-like interpretation of the crystal structure with anionic Ge layers separated by alkaline-earth cations – but multi-center strongly polar between the Ge 2 dumbbells and the adjacent metal atoms. Similar atomic interactions are present in CaGe 3 and BaGe 3 . The variation of the alkaline-earth metal has a merely insignificant influence on the superconducting transition temperatures in the s , p -electron compounds AE Ge 3 .

The electronic properties of the layered ternary metal boride carbide ScB 2 C 2 , the structure of which consists of B/C layers made of fused five- and seven-membered rings alternating with scandium sheets, are analyzed. In particular, the respective positions of the B and C atoms (the so-called coloring problem) are tackled using density functional theory, quantum theory of atoms in molecules, and electron localizability indicator calculations. Results reveal that (i) the most stable coloring minimizes the number of B–B and C–C contacts and maximizes the number of boron atoms in the heptagons, (ii) the compound is metallic in character, and (iii) rather important covalent bonding occurs between the metallic sheets and the boron–carbon network.

Pb 2 As x P 14– x was synthesized by reacting the pnicogens in a lead melt in sealed silica ampoules. A mixture of hydrogen peroxide and glacial acetic acid removed lead from the final product. Pb 2 As x P 14– x represents the first lead arsenide phosphide adopting a new structure type. Systematic substitution of phosphorus by arsenic leads to the formation of Pb 2 As x P 14– x with x ~ 3.7, a compound with a two-dimensional arrangement of polypnictide layers, coordinated by Pb 2+ cations. Pb 2 As x P 14– x is structurally related to PbP 7 where a three-dimensional polyphosphide network is realized instead. The structure of Pb 2 As 3.7(1) P 10.3(1) was determined from single crystal X-ray diffraction data: space group P 2 1 2 1 2 1 (no. 19), a = 10.060(1), b = 10.500(1), c = 13.711(2) Å, and V = 1448.3(4) Å 3 . The structure is discussed relative to PbP 7 focusing on the differences in the polyanionic substructures of the two polypnictides.

Combining laboratory X-ray powder diffraction with in-situ high-temperature synchrotron experiments and differential scanning calorimetry, it has been shown that Ba 21 Al 40 , Ba 3 Al 5 , Ba 7 Al 10 and Ba 4 Al 5 decompose peritectically at 914, 826, 756, and 732°C, respectively. In addition, a new binary compound with the composition Ba 4 Al 7+ x ( x = 0.17) and the formation temperature of 841°C was found. The initial structural model (space group P 6 3 / mmc , a = 6.0807(1), c = 39.2828(8) Å) with four Ba and five Al crystallographic positions was developed. It is based on the intergrowth concept involving the neighboring Ba 21 Al 40 and Ba 3 Al 5 phases and the derived atomic arrangement is subsequently refined using X-ray diffraction data. The crystal structures of all phases in the Ba–Al system, except BaAl 4 , exhibit Kagomé nets of aluminum atoms resembling those observed for the B atoms in the Laves phases AB 2 . In the crystal structure of Ba 4 Al 7+ x , single Kagomé layers alternate with double slabs (MgZn 2 motif) along [001] and are separated by Ba cations. Intergrowth features of Ba 4 Al 7+ x are discussed together with the neighboring Ba–Al compounds and Sr 5 Al 9 .