Aerogels are fine inorganic superstructures with enormously high porosity and are known to be exceptional materials with a variety of applications, for example in the area of catalysis. [1] The chemistry of the aerogel synthesis originated from the pioneering work [2] from the early 1930s and was further developed starting from the 1960s. [1,3] Attractive catalytic, thermoresistant, piezoelectric, antiseptic, and many other properties of the aerogels originate from the unique combination of the specific properties of nanomaterials magnified by macroscale self-assembly. Currently, the most investigated materials that form fine aerogel superstructures are silica and other metal oxides together with their mixtures. Recently, the possibility of creating aerogels and even light-emitting monoliths with densities 500 times less than their bulk counterparts from colloidal quantum dots and clusters of metal chalcogenides has attracted attention. These developments may open opportunities in areas such as semiconductor technology, photocatalysis, optoelectronics, and photonics. [4][5][6][7][8][9][10][11][12][13] Quite a number of different approaches have focused on modifying oxide-based aerogels (silica, titania, alumina, etc.) with metal nanoparticles (such as of platinum) to carry the catalytic properties from the metal [14,15] into the porous structures of the aerogels. [1,16,17] Fine mesoporous assemblies of catalytically active metal nanoparticles were also created by using artificial opals [18] and fungi [19] as templates. Other superstructural materials derived from metal nanoparticles include mesoporous platinum-carbon composites, [20] gold nanoparticles interlinked with dithiols, [21] necklace nanochains of hybrid palladium-lipid nanospheres, [22] electrocatalytically active nanoporous platinum aggregates, [23] foams, [24] and highly ordered two-and three-dimensional supercrystals. [25][26][27][28][29] The creation of non-supported metal aerogels has however not been reported to date. Recently, the formation of highly porous spherical aggregates ("supraspheres") of several hundred nanometers in diameter, where nanoparticles from one or two different metals were cross-linked with dithiols, was reported. [30,31] The metal aerogels presented herein exhibit an average density two orders of magnitude lower than that of the reported foams.[32] Their primary structural units match the size range of single nanoparticles (5-20 nm), which is an order of magnitude smaller than that of the self-assembled supraspheres.[31] Moreover, in the present case, no chemical cross-linkers are involved in the self-assembly process. The formation of such noble-metal nanoparticle-based mesoporous monometallic and bimetallic aerogels is an important step towards self-supported monoliths with enormously high catalytically active surfaces. Considering that metal nanoparticles possess very specific optical properties owing to their pronounced surface plasmon resonance, aerogels from metal nanoparticles may also find future applications in nano...

Eu 8 Ga 16 Ge 30 is the only clathrate known so far where the guest positions are fully occupied by a rare-earth element. Our investigations show that, in addition to the previously synthesized Eu 8 Ga 16 Ge 30 modification with clathrate-I structure, there exists a second modification with clathrate-VIII structure. Polycrystalline samples of both phases behave as local-moment ferromagnets with relatively low Curie temperatures ͑10.5 and 36 K͒. The charge-carrier concentrations are rather small ͑3.8 and 12.5ϫ10 20 cm Ϫ3 at 2 K͒ and, together with the low Curie temperatures, point to a semimetallic behavior. Both the specific heat and the thermal conductivity are consistent with the concept of guest atoms ''rattling'' in oversized host cages, leading to low thermal conductivities ͑''phonon glasses''͒. However, the electron mobilities are quite low, which, if intrinsic, would question the properties of an ''electron crystal'', commonly presumed in ''filled-cage'' materials. The dimensionless thermoelectric figure of merit reaches values of 0.01 at 100 K.

The relatively small and sole micropores in zeolite catalysts strongly influence the mass transfer and catalytic conversion of bulky molecules. We report here aluminosilicate zeolite ZSM-5 single crystals with b-axis-aligned mesopores, synthesized using a designed cationicamphiphilic copolymer as a mesoscale template. This sample exhibits excellent hydrothermal stability. The orientation of the mesopores was confirmed by scanning and transmission electron microscopy. More importantly, the b-axis-aligned mesoporous ZSM-5 shows much higher catalytic activities for bulky substrate conversion than conventional ZSM-5 and ZSM-5 with randomly oriented mesopores. The combination of good hydrothermal stability with high activities is important for design of novel zeolite catalysts. The b-axis-aligned mesoporous ZSM-5 reported here shows great potential for industrial applications.

The reinvestigation of the crystal structure of Ba8Ge43□3 (space group $Ia{\bar 3}d$, no. 230; a = 21.3123(5) Å; Z = 8; Pearson symbol cI408) shows a full ordering of the vacancies (□) in the germanium framework. This ordered crystal structure can be considered as a derivative of an ideal “Ba8Ge46” clathrate‐I type structure ($Pm{\bar 3}n$, a′ = a/2) in which three Ge vacancies (per formula unit) are allowed to order in a cubic superstructure with a doubled unit cell parameter (□ at the 24c site, space group $Ia{\bar 3}d$). In the resulting Ge framework, each vacancy □ is surrounded by four three‐bonded (3b)Ge‐ species. The ordering in crystals of as‐cast samples (cooled in argon atmosphere, non‐annealed) is partially disrupted. For the “as‐cast” crystals, a short‐range model is proposed based on the partial distribution of Ge on the 24c and 24d sites. From the electron balance, Ba8Ge43 can be considered as a metallic Zintl phase with four excess electrons per formula unit. The Ba8Ge43 phase is stable in the temperature range 770 ‐ 810 °C and exists in equilibrium with Ba6Ge25 and Ge. By decomposition of undercooled (metastable) Ba8Ge43, a new metastable binary BaGe˜5 phase is formed.

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The ability to prepare nanostructured and/or nanocomposite materials on a large scale by simple and controllable routes still remains a challenge in chemistry and material science. By employing well-established synthetic strategies, nanoparticles with different sizes, shapes and compositions can be readily produced. The high tendency for self-aggregation and selforganization of these nanosized building blocks, which are surface-stabilized by organic molecules, into superstructures has been used to create 2D and 3D assemblies. [1][2][3][4][5][6][7][8][9] In the last decade, a series of 3D colloidal superlattices composed of different nanoparticles (Ag, Au, PbS, PbSe, CeO 2 , FePt, CoPt 3 , Fe 3 O 4 , PbSe/Au, Fe 2 O 3 /PbSe, PbSe/Pd, CdSe/PbSe, etc.) has been reported. [10][11][12][13][14][15][16][17][18][19][20] Particularly, PbS-organic nanoparticles of different shapes (including cubes, octahedra, truncated octahedra, rhombicuboctahedra, etc.) can be easily synthesized on a large scale, and attracted much attention [15,16,21,22] because of a variety of possible applications. [23][24][25][26][27] Therefore, this kind of system provides a chance to study diverse packing arrangements (e.g., fcc, bcc, etc.) and specific orientational ordering of nanoparticles. [11,13,15,16,28,29] Experimental observations [16,[29][30][31][32][33][34] suggest that nanoparticles within a colloidal crystal tend to arrange in such a way that the optimal packing efficiency is achieved (principle of maximum space filling [35] ). In a relatively common case of truncated octahedrally shaped nanoparticles, the available experimental data [4,5,16,[29][30][31][32][33]36] allow to rationalize the formation of a particular type of the superlattice array (depending on the degree of coverage of nanocrystals by organic molecules) by considering four phenomenological models: A) Rigid, anisotropically shaped space-filling nanoparticles (inorganic part) without or with a tiny shell of organic molecules; B) Hard spheres with a comparatively large anisotropic core (inorganic part) covered by a relatively thin shell of organic molecules; C) Hard spheres with a comparatively small anisotropic core (inorganic part) and a thick shell of organic molecules; D) Soft and easily deformable spheres with a small anisotropic core (inorganic part) and an even thicker shell of organic molecules.For each case (A-D) the type of superlattice packing (translational order [37] ) and orientational ordering of nanoparticles within the superlattice array is significantly different. In the simplest case (A), the more or less pure, inorganic, truncated octahedrally shaped nanoparticles assemble into a bcc superlattice [33] with 100 % packing efficiency and strong orientational relationship (crystallographic directions of nanocrystals are coaxial with those of the superlattice). [35,37] In case of models B and C, by increasing the degree of coverage of anisotropic (inorganic) nanoparticles by organic molecules, their faces are continuously smoothed, thereby introducing a certa...

The binary germanides M12Ge17 and M4Ge9 (M  Na, K, Rb, Cs) and the stannides M12Sn17 and M4Sn9 (M  K, Rb, Cs) were identified by a combination of direct synthesis, thermogravimetric analysis, vibrational spectroscopy, X‐ray powder data and single crystal structure analysis. The M12E17 phases contain the cluster anions [E9]4− and [E4]4− in the ratio 1:2, forming a hierarchical structure with the cluster anions at the atomic positions of the hexagonal Laves phase MgZn2. Like the M4E4 phases, the M4Ge9 compounds are hierarchical derivatives of the cubic Cr3Si structure but with [Ge9]4− anions. The thermogravimetric analyses give strong evidence for the existence of at least one more phase with [E9]4− and [E4]4− clusters and of the clathrate phases M6E136 in addition to the well‐known M8E44□2 chlathrates.

The single phase clathrate-I Ba(8)Ge(43)square(3) (space group Ia3d (no. 230), a = 21.307(1) A) was synthesized by quenching the melt between cold steel plates. Specimens for physical property measurements were characterized by microstructure analysis and X-ray diffraction on polycrystalline samples as well as single crystals. Transport properties including thermopower, electrical resistivity, thermal conductivity and specific heat were investigated in a temperature range of 2-673 K. The electrical resistivity exhibits a metal-like temperature dependence below 300 K turning into a semiconductor-like behaviour above 300 K. The analysis of the specific heat at low temperature indicates a finite density of states at the Fermi level, thus corroborating the metallic character below 300 K. The temperature dependence of the specific heat was modelled assuming Einstein-like localized vibrations of Ba atoms inside the cages of the Ge framework. A conventional crystal-like behaviour of the thermal conductivity with a low lattice contribution (kappa(l)(300 K) = 2.7 W m(-1) K(-1)) has been evidenced.