Cs2Hg27, das quecksilberreichste Amalgam – ein naher Verwandter der Bergman-Phasen

Local Atomic Configurations in Intermetallic Crystals: Beyond the First Coordination Shell

We have used a combined geometrical-topological approach to analyze 21,697 intermetallic crystal structures stored in the Inorganic Crystal Structure Database. Following a geometrical scheme of close packing of balls, we have considered the three most typical polyhedral atomic environments of the icosahedral, cuboctahedral, or twinned cuboctahedral shape as well as multi-shell (up to four shells) local atomic configurations (LACs) based on these cores in 10,657 unique crystal structure determinations. In total, half of intermetallic structures have been found to contain one of these configurations, with the icosahedral LACs being the most frequent. We have revealed that even a two-shell configuration strongly predetermines the overall connectivity (topological type) of an intermetallic crystal structure. The chemical and stoichiometric composition of the multi-shell LACs generally obeys the close-packing model: the number of atoms in the subsequent shells (N_k) varies around the value N_k = 10k² + 2, which is valid for the same size atoms, to reach the densest packing for the kth shell. Deviations from the revealed regularities often indicate inconsistencies in the crystallographic information, unusual features of the structure, or the existence of more stable phases that can be used for the validation of experimental and modeling data.

Superconductivity in Crystallographically Disordered LaHg6.4

The influence of structural disorder on superconductivity is not yet fully understood. A concurrent examination of crystallographic and physical properties of LaHg_6.4 reveals that this material enters a superconducting state below T_c = 2.4 K while showing crystallographic disorder in one dimension. Lanthanum mercuride, which crystallizes in a new structure type (space group Cmcm, a = 9.779(2) Å, b = 28.891(4) Å, c = 5.0012(8) Å, Z = 8), has remained out of reach for nearly 50 years. In this crystal structure, strong disorder is present in the channels that propagate along the [001] direction. By implementing a combination of cutting-edge synthesis and characterization techniques, we were able to circumvent the complexity associated with the low formation temperature and chemical reactivity of this substance and study the superconductivity of LaHg_6.4 in detail.

Syntheses and crystal structures of solvate complexes of alkaline earth and lanthanoid metal iodides with N,N-dimethylformamide

The solvate complexes that can be obtained by either dissolving metal iodides in N,N-dimethylformamide (DMF) or by synthesising them in DMF have the general composition [M(DMF) x ]I y . DMF shows to behave as simple monodentate ligand with low sterical impact, so that x in the composition follows the radius of M y+. We present here the crystal structures of the alkaline earth and lanthanoid metal iodide complexes [Mg(DMF)6]I2, [Ca(DMF)6]I2, [Sr(DMF)7]I2, [Ba(DMF)8]I2, [La(DMF)9]I3, [Ln(DMF)8]I3 (isotypic series for Ln = Nd, Sm, Eu, Dy, Gd, Er, Yb and Lu) and for the tris-triiodide complex salt [Sc(DMF)6](I3)3. Their different crystal structure types can be compared on the basis of the packing topologies of the nearly spherical cationic entities which show simple sphere packing motifs.

Synthesis and crystal structures of β-[Be(DMF)4]I2, [Be(Pyr)4]I2, [Be(NMP)4]I2 and [BeI2(Lut)2]

Four solvent complexes of beryllium iodide were prepared by dissolving BeI2 in N,N-dimethyl formamide (DMF), pyridine (Pyr), N-methyl pyrrolidone (NMP) and 2,6-dimethyl pyridine (2,6-lutidine, Lut). Their crystal structures were established from single crystal X-ray diffraction. For [Be(DMF)4]I2 a new modification is reported (monoclinic, space group P21/c, a = 12.491(2), b = 11.593(2), c = 15.310(3) Å, β = 94.7073(6)°). In [Be(Pyr)4]I2 (monoclinic, space group C2/c, a = 17.8799(13), b = 7.6174(5), c = 18.2611(14) Å, β = 113.508(4)°) and [Be(NMP)4]I2 (orthorhombic, space group Pbca, a = 13.941(5), b = 15.754(3), c = 24.634(7) Å) homoleptic tetrahedral complex cations are formed, while the sterically demanding solvent ligand Lut yields a neutral complex with covalently bound iodine ligands [BeI2(Lut)2] (monoclinic, space group P21/c, a = 7.8492(9), b = 24.265(3), c = 27.037(3) Å, β = 97.076(3)°). Their electrochemical stability with respect to their application as beryllium electrolytes for deposition of beryllium from solution is discussed.

Alkaline-earth tri-mercurides A IIHg3 (A II=Ca, Sr, Ba): binary intermetallic compounds with a common and a new structure type

The alkaline-earth tri-mercurides AHg3 (A=Ca, Sr, Ba) were yielded from stoichiometric melts of the elements in pure phase (in the case of Sr with Sr11Hg54 as a by-product) and their structures were determined by means of single crystal X-ray data. As reported long ago from powder data, CaHg3 and SrHg3 crystallize in the Ni3Sn-type (P63/mmc, a=662.26(2)/689.39(3), c=501.64(2)/510.38(3) pm, Z=2, R1=0.0233/0.0306 for A=Ca/Sr). The structure consists of a hexagonal close packing of ordered layers AHg3 or a dense packing of anti-cuboctahedra [AHg12] (as cation coordination polyhedra, CCP) and [Hg6] octahedra fused via opposite faces to form columns along c. BaHg3 crystallizes in a unique structure type (P4/ncc, a=1193.04(3), c=958.02(5) pm, Z=12, R1=0.0461). It contains three crystallographically different Hg atoms, which form layers of distorted flat square pyramids. In contrast to the layers of the BaAl4-type, 1 5 ${1 \over 5}$ of the pyramids are missing. Due to the 45 degree rotation of adjacent layers, the connection between the layers is not a ‘apical-to-apical’ one like in BaAl4, but is established by ‘apical-to-basal’ bonds. Compared to the Ca and Sr compound, the CCPs of the two different Ba atoms, which are embedded between the pyramid layers, are increased to 12+4 and 14+2 (for Hg+Ba). For all title compounds and the Li phase LiHg3, which is isotypic to CaHg3, the electronic band structures were calculated within the framework of the FP-LAPW DFT method. Even though the compounds are metals and exhibit only very slight minima of the tDOS at the Fermi level, the electron transfer from the alkali/alkaline-earth element towards mercury is almost complete. Thus, Coulomb interactions and the optimized size and arrangement of the A CCPs, besides the flexible Hg–Hg bonding within the polyanion, determine the structure formation.

The simplest representative of a complex series: the Hg-rich amalgam Yb11Hg54

Yb11Hg54 is a new member of a series of amalgams with composition close to MHg5. Its crystal structure was solved and refined on the basis of single crystal data. The structure model was confirmed with a Rietveld refinement. Yb11Hg54 has the first crystal structure in this family in which no disorder effects such as mixed occupation, split positions or superstructure formation is observed. It therefore can be regarded as a parent structure for all other amalgams. The crystal structure of Yb11Hg54 can be derived from the Gd14Ag51 structure type, the aristotype of this family. We give a detailed crystal structure description for Yb11Hg54 and discuss it in the context of the further known crystal structures closely related. A ranking within this structure family can be established by calculating features for the structural complexity for all structures, including the individual disorder phenomena.