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The paper presented examines the dynamics of wear of restored parts using different materials for the friction pair. The pair of crankshaft and sliding bearing largely determines the machine service life – although their overall wear index is less than 1%, it can still lead to a large number of failures and malfunctions. Vibrating arc overlaying in a shield of gas mixture of 60% argon and 40% carbon dioxide was used for restoring the surface of rollers. Subsequently, these were treated by heating with high-frequency current (HFC) and lowered to a hardness of 55±2 HRC and ground to the final size. It was found that the antifriction coating of plain bearings with electrochemical lead alloy ЕО92 showed excellent performance and insignificant wear in combination with reference material St45 and welded coating DUR500. In combination with electrochemical lead alloy ЕО92, the welded coating DUR500 showed a significantly higher wear on actuation compared to the reference material St45 at sliding friction. The relative wear resistance enhancement of crankshafts and bearings by restorative coatings represents an essential measure, as their service life can be prolonged by 20–50% in contrast to the new parts without restorative coatings.

The most common crane structural scheme used in the practice includes 4-link guiding mechanism and 4-link balancing mechanism. Some special crane construction as such designed by Kranbau – Eberswalde contains a 6-link balancing mechanism with structural scheme obtained by conjunction of 2 consecutive 4-hinged units. Similar construction is a subject of research, related to synthesis of 6-links mechanism during designing of new crane constructions. Another paperwork presents an approach for development of jib system of existing gantry crane type. Such approach relates to keep both – jib and arm without changes in their mass, shape and loading conditions. Still another paperwork revealing an approach for synthesis of existing gantry crane allowing minor structural changes by addition of small-sized links to the scheme of balance mechanism without changes in the structure of jib, arm and frame. According Assur’s classification the number of links in each mechanism would be theoretically unlimited although it would cause significant difficulties during production of such systems. Practically, not any crane constructions designed with 8-link or 10-link structural scheme exists. At other side, increasing the number of links is a precondition to more accurate dimensional movement of balance unit. Structural schemes for plain linkage mechanisms appropriate for application in a portal crane are being synthesized. At the synthesis the limitations of the links must be no more than ten and they save the configuration of the crane’s mechanism that is mostly used in practice. Potential applications of 4 different structural schemes indicated as Н1У1, Н2У1, Н1У2 and Н2У2, synthesized by a practical example, are being appraised. Results for alteration of the reduced moment to jib from weights of links of jib system depending on the range of jib with and without useful load are obtained.

A dynamic model of a lifting rope-drum mechanism, replaced by an equivalent two-mass system is created. Differential equations of rotation of the rotor under the action of constant torque and the movement of the load in the process of acceleration when starting the motor are formulated. Theoretical dependencies for studying the influence of the times in transitional processes on the dynamic load of the elements of lifting device and supporting metal structure are derived. Dependencies for establishment of the influence of the start / stop time ratio and the characteristic oscillations of the load after the completion of the transitional processes on the minimum and maximum amplitude values for the acceleration and the dynamic force are determined. It has been proven that during the process of moving downwards, the maximum dynamic load occurs after the acceleration process, which means that depending of the length of the rope or the period of damping, both - very high and very low values of the maximum dynamic load may be obtained for a given lifting mechanism and load. In the processes of starting and stopping during lifting and lowering of the load, the maximum overloads of the elements of the lifting mechanism and of the bearing elements of the metal structure are found, using the coefficient of dynamism, which is defined as the ratio of the maximum force in the flexible element to the summarized weight of the load and load handling device.

The paper presents the results of experiments related to microstructural analysis of specimens obtained from details welded by gas metal arc welding process with a vibrating wire electrode. Work pieces made of steel 45, with dimensions of 50 mm diameter, and 250 mm length, were selected as the object of this research. The working regime of overlaying process features voltage of 20V, current of 150-180, vibrating amplitude of 1,5 mm, overlaying speed of 1,26 m/min, wire feeding rate of 2,3 m/min, wire electrode outlet of 15 mm and overlaying step at 3 mm/min-1. The shielding mixture consists of 100% CO2 fed at a rate of 16 l/min. The wire electrode vibrating frequency was accepted as the main variable as its rates from 0 to 150 Hz were selected and changed during experiments at step of 25 Hz. Six work pieces were welded at the mentioned regime parameters as each of them received three deposited sections. All the specimens were prepared according to the standard procedure in order to reveal the three zones – welded zones, zone of fusion and heat-affected zone. Optix-Cam software was used for measuring the dimensions of all the zones, the average rate being obtained as a result of a large number of measures performed at different sections according to the picture presented in the main text. The influence of the increased wire electrode vibrating frequency upon the total area size and thickness of the zones is presented in the respective figures.

The structure, trends and perspectives in development of hot methods as such used for reconditioning of worn details during the new Millennium are presented in the article as well as trends in production of consumables in industrially developing countries. The structure of welding methods is also shown giving priority to its development until 2020. It can be concluded that in the industrially developed countries by 2020 the share of arc welding will be stabilized at levels of 10-15% of the total number of methods used for weld overlaying of worn-out components. These figures will be 45-55 % and 7-9% for gas shielded and submerged arc welding respectively. The welding methods that will be prioritized for the period until 2020 will be gas shielded arc welding, contact, laser beam and hybrid welding.

The aim of the research is related to the influence of the vibration's frequency increasing upon wear-resistance of the applied layers. Wear-resistance is one of the most important properties of the materials that is considered as criteria about durability and reliability of the details of agricultural equipment and machinery.

Lead chalcogenide materials have drawn attention in recent years because of their outstanding thermoelectric properties. Bulk n-type materials of AgPbmSbTe2+m have been reported to exhibit high figure of merit, ZT, as high as 1.7 at 700 K. Recent reports have shown p-type lead selenide-based compounds with comparable ZT. The analogous material AgPbmSbSe17 shares a similar cubic rock-salt structure with PbTe-based compounds; however, it exhibits a higher melting point, and selenium is more abundant than tellurium. Using solid solution chemistry, we have fabricated cast AgPb15SbSe17 samples that show a peak power factor of approximately 17 μW/cm K2 at 450 K. Increasing the strength of such materials is commonly achieved through powder processing, which also helps to homogenize the source materials. Pulsed electric current sintering (PECS) is a hot-pressing technique that utilizes electric current through the die and sample for direct Joule heating during pressing. The mechanisms present during PECS processing have captured significant research interest and have led to some notable improvements in sample properties compared with other densification techniques. We report the thermoelectric properties of PECS samples of AgPbmSbSe17 along with sample fabrication and processing details.

In situ nanostructuring in bulk thermoelectric materials through thermo-dynamic phase segregation has established itself as an effective paradigm for optimizing the performance of thermoelectric materials. In bulk PbTe small compositional variations create coherent and semicoherent nanometer sized precipitates embedded in a PbTe matrix, where they can impede phonon propagation at little or no expense to the electronic properties. In this paper the nanostructuring paradigm is for the first time extended to a bulk PbS based system, which despite obvious advantages of price and abundancy, so far has been largely disregarded in thermoelectric research due to inferior room temperature thermoelectric properties relative to the pristine fellow chalcogenides, PbSe and PbTe. Herein we report on the synthesis, microstructural morphology and thermoelectric properties of two phase (PbS)(1-x)(PbTe)(x)x = 0-0.16 samples. We have found that the addition of only a few percent PbTe to PbS results in a highly nanostructured material, where PbTe precipitates are coherently and semicoherently embedded in a PbS matrix. The present (PbS)(1-x)(PbTe)(x) nanostructured samples show substantial decreases in lattice thermal conductivity relative to pristine PbS, while the electronic properties are left largely unaltered. This in turn leads to a marked increase in the thermoelectric figure of merit. This study underlines the efficiency of the nanostructuring approach and strongly supports its generality and applicability to other material systems. We demonstrate that these PbS-based materials, which are made primarily from abundant Pb and S, outperform optimally n-type doped pristine PbTe above 770 K.

The characterization and understanding of the presence of nanostructuring in bulk thermoelectric materials requires real space atomic level information. We report electron diffraction and high-reso...

Single crystals of CaCr0.84Fe3.16As3, a Cr substituted analog of CaFe4As3, were grown from Sn flux and characterized with single crystal neutron diffraction. CaCr0.84Fe3.16As3 crystallizes in the orthorhombic space group Pnma with a three-dimensional framework, where Fe, Cr, and As form a covalent channel-like network with Ca2+ cations residing in the channels. CaCr0.84Fe3.16As3 has a unit cell of a = 12.057(4) A, b = 3.7374(13) A, and c = 11.694(3) A, as determined by room temperature single crystal neutron diffraction (R1 = 0.0747, wR2 = 0.1825). Structural data was also collected at 10 K. The single crystal neutron data showed that Cr selectively occupies a particular metal site, Fe(4). The antiferromagnetic transition associated with spin density wave (SDW) in the parent compound is preserved and shifts from 96 to 103 K with the selective Cr doping. Mossbauer, magnetic, and electrical resistivity measurements are reported.

We report experimental evidence that shows superconductivity in NaFeAs occurs when it is Na deficient. The oxidation of NaFeAs progresses differently in water and in air. In water the material oxidizes slowly and slightly retaining the original anti-PbFCl structure. In air NaFeAs oxidizes topotactically quickly and extensively transforming to the ThCr2Si2 structure type. Water acts as a mild oxidizing agent on the FeAs layer by extracting electrons and Na+ cations from the structure, while oxidation in air is more extensive and leads to change in structure type from NaFeAs to NaFe2As2. The superconducting transition temperature moves dramatically during the oxidation process. Exposed to water for an extended time period NaFeAs shows a substantial increase in Tc up to 25 K with contraction of unit cell volume. NaFe2As2, the air oxidized product, shows Tc of 12 K. We report detailed characterization of the redox chemistry and transformation of NaFeAs in water and air using single crystal and powder X-ray di...

Ставното ендопротезиране е сред най-разпространените съвременни операции в ортопедията и травматологията. Физиотерапията и рехабилитацията са финалната фаза на ендопротезирането и са от изключителна важност както за темповете, така и за степента на функционалното възстановяване. Дълбоките осцилации (DEEP OSCILLATION) са патентована терапевтична процедура, използваща резониращи вибрации на тъканите с минимален външен механичен ефект и доказано обезболяващо, антифибротично, противооточно и противовъзпалително действие. Целта на настоящото проучване е да се проследи ефектът от комплексното приложение на дълбоките осцилации и кинезитерапията върху редуцирането на отока, намаляване на болковата симптоматика и възстановяване обема на движение при пациенти след алопластика на колянна става. Проучването е проведено върху 50 пациенти, от които 21 мъже и 30 жени, разпределени в 2 групи по 25 човека, на случаен принцип - експериментална група (ЕГ) и контролна група (КГ), всичките след алопластика на колянна става. Получените резултати доказаха, че дълбоките осцилации са ефективен метод за отстраняване на отока, потискане на болката и възпалението и увеличаване на обема на движение при ранната рехабилитация на пациенти след алопластика на колянната става. Комбинираното приложение на дълбоки осцилации и кинезитерапия дава по-добри резултати по отношение на сроковете и степента на възстановяване на функцията на колянната става след ендопротезиране.

The title compounds were synthesized from the elements by heating the corresponding stoichiometric mixtures at high temperature. Their structures were determined from single-crystal X-ray diffraction. Na2Ba4Ga2Sb6 (Pnma, Z = 8, a = 12.3468(10) Å, b = 10.6621(10) Å, c = 13.8344(10) Å) contains chains of ∞[Ga2Sb6]10–. The repeating unit is made of an edge-sharing Ga-centered tetrahedron GaSb2(μ-Sb)2 and another Ga-centered tetrahedron but with additional antimony that is exo-bonded to one of the corners forming Sb–Sb dumbells, i.e. GaSb(Sb–Sb)(μ-Sb)2. The unit connects to neighboring units via sharing two corners of the tetrahedra, i.e. [Ga2Sb5Sb2/2]. Li13Ba8GaSb12 (C2/m, Z = 2, a = 18.0650(10) Å, b = 4.9407(10) Å, c = 13.0123(10) Å, β = 126.728(10)°) contains three different types of anions: single-atom anions of Sb3–, dumbells of Sb4–, and isolated Ga-centered tetrahedra of GaSb4 9–. The two compounds are electronically balanced, and this is confirmed by four-probe conductivity and magnetic measurements. Their very narrow band gaps, 0.014 and 0.049 eV for Na2Ba4Ga2Sb6 and Li13Ba8GaSb12, respectively, make them potential thermoelectric materials.

The title compound was synthesized in an attempt to produce stacked benzene-like Sn6 6- rings separated by alkaline-earth cations in analogy with the recently reported stacks of aromatic cyclopentadienyl-like Sn 5 6- in Na8BaSn 6 (in addition to isolated Sn 4- anions). The resulting compound, synthesized from a stoichiometric mixture of the elements at high temperature, has the “correct” stoichiometry with six tin atoms and six positive charges. However, the rings of Sn 6 6- are puckered into chair-type cyclohexanes that are interconnected into isolated cylindrical tubes stuffed with Ca2+ between the rings. Such tubes, if fused to each other, form the hexagonal diamond structure. The new compound is electronically balanced according to magnetic and four-probe resistivity measurements. Reported are also the synthesis and properties of Na 10EuSn12 and Na10YbSn12 which are isostructural with the known Na 10CaSn12.

The synthesis, structural characterization and magnetic property of two new coordination polymers [Cu(pyz)(μ-CH3CO2)4]n (1) and [Cu(pyz)(μ-CCl3CO2)4]n (2) (pyz = pyrazine) are reported. Here, the carboxylato bridged two dinuclear copper(II) complexes are linked through pyrazine giving a 1-D alternating chain. The magnetic property of the complexes indicates a significant difference originated from the introduction of electron withdrawing substituent on the bridging dicarboxylate. Complex 1 exhibits strong antiferromagnetic interactions with J = −344.61 cm−1, whereas 2 exhibits comparatively less strong antiferromagnetic coupling with J = −238.53 cm−1.

The title compounds were synthesized from the elements by heating the corresponding mixtures at high temperature. Their structures were determined from single-crystal X-ray diffraction. Li9-xEuSn6+x, Li9-xCaSn6+x, Li5Ca7Sn11, and Li6Eu5Sn9 contain columns of stacked aromatic pentagons of Sn56- that are analogous to the cyclopentadienyl anion C5H5-. The pentagons are separated with Ca2+ or Eu2+ in the columns and resemble a polymeric metallocene. In addition to the columns, the isostructural Li9-xEuSn6+x and Li9-xCaSn6+x contain isolated tin atoms and bent tin trimers while Li5Ca7Sn11 and Li6Eu5Sn9 contain flat zigzag hexamers and flat zigzag infinite chains of tin, respectively. The isostructural LiMgEu2Sn3 and LiMgSr2Sn3 do not contain columns of pentagons but only flat zigzag infinite chains of tin. The aromaticity of the pentagons and the conjugation of the π-systems of the hexamers and the infinite chains are discussed. The title compounds are also characterized by magnetic and conductivity measurements.

The X-ray analysis of 1-oxo-3-thiophen-2-yl-isochroman-4-carboxylic acid methyl ester 1 confirmed its trans-configura- tion and a conformation with diaxial H-3 and H-4 atoms in solid state. NMR experiments indicated that trans-1 exists in solution in both expected conformers. In CDCl3 and especially in CD3OD or DMSO, the conformational equilibrium is shifted towards the conformer with diequatorial H-3 and H-4, which was also determined by 2D NOESY experiments. The shift is due to the greater polarity of that conformer deduced by ab initio calculations. � 2004 Elsevier Ltd. All rights reserved.

The title compounds were prepared by direct reactions of the corresponding elements at high temperature. They are isostructural with each other (monoclinic, P2(1)/m, Z = 2; Na(8)BaPb(6), a = 13.116(4), b = 5.351(1), and c = 16.166(5) A, beta = 108.07(2) degrees; Na(8)BaSn(6), a = 12.897(4), b = 5.362(1), and c = 16.826(5) A, beta = 108.19(2) degrees; Na(8)EuSn(6), a = 12.912(2), b = 5.220(1), and c = 15.721(2) A, beta = 108.09(1) degrees ) and contain isolated, flat, and aromatic pentagonal rings of Sn(5)(6)(-) and Pb(5)(6)(-) as well as isolated anions of Sn(4)(-) and Pb(4)(-). According to four-probe conductivity measurements, the tin compounds, Na(8)BaSn(6) and Na(8)EuSn(6), are semiconducting with band gaps of 0.11 and 0.09 eV, respectively, and are therefore electronically balanced. Magnetic measurements show that Na(8)BaSn(6) is diamagnetic while Na(8)EuSn(6) is paramagnetic and undergoes two transitions at low temperatures.

The title compound, C21H24N2O3, crystallizes as a racemic mixture of R,R and S,S enanti­omers. The three-dimensional packing is stabilized by a system of hydrogen bonds and weak C—H⋯O inter­actions.

In the title compound, C23H16O4S, the dibenzo[c,h]chromene ring system is almost planar. The trans-substituted thio­phenyl and methoxy­carbonyl groups are in an anti­periplanar conformation. The mol­ecules are linked into dimers through weak inter­molecular C—H⋯O hydrogen bonds [H⋯O = 2.53 A]. The mol­ecule has a thienyl-ring flip disorder.

The article reveals the development of spa therapy through the years and centuries and its revival by receiving renewed attention from many medical specialties and health tourists. According to their character spas nowadays reflect the progress of science and culture of mankind. The accent is on the contemporary understanding of spa which is based on health promotion and prevention of illnesses. The idea for health prophylaxis has reached a higher level which serves as a base for thefoundations of wellness conception. The idea of this conception is aspiration for achieving complete prosperity of the human personality by synergy of all aspects of health - physical, mental, intellectual, emotional and social.

We report promising thermoelectric properties of the rock salt PbSe-PbS system which consists of chemical elements with high natural abundance. Doping with PbCl(2), excess Pb, and Bi gives n-type behavior without significantly perturbing the cation sublattice. Thus, despite the great extent of dissolution of PbS in PbSe, the transport properties in this system, such as carrier mobilities and power factors, are remarkably similar to those of pristine n-type PbSe in fractions as high as 16%. The unexpected finding is the presence of precipitates ~2-5 nm in size, revealed by transmission electron microscopy, that increase in density with increasing PbS concentration, in contrast to previous reports of the occurrence of a complete solid solution in this system. We report a marked impact of the observed nanostructuring on the lattice thermal conductivity, as highlighted by contrasting the experimental values (~1.3 W/mK) to those predicted by Klemens-Drabble theory at room temperature (~1.6 W/mK). Our thermal conductivity results show that, unlike in PbTe, optical phonon excitations in PbSe-PbS systems contribute to heat transport at all temperatures. We show that figures of merit reaching as high as ~1.2-1.3 at 900 K can be obtained, suggesting that large-scale applications with good conversion efficiencies are possible from systems based on abundant, inexpensive chemical elements.

We report a systematic study of the thermoelectric properties of PbSe doped with Ga, In, and excess Pb as a function of carrier density and temperature. All metal dopants efficiently generate electron carriers in the crystal lattice with densities as high as ∼1020 cm−3 measured by the Hall effect. The Seebeck coefficient as a function of carrier density at room temperature was found to be similar for all dopants, while at 700 K substantial differences were observed with PbSe-In exhibiting a larger response. Infrared spectral reflectivity measurements at room temperature showed that both Ga and In substitution in PbSe weakens the curvature of the dispersion relation of the conduction band compared to Pb. This electronic effect contributes a larger density of states in transport processes at high temperatures. We have obtained thermoelectric figures of merit of ∼0.9 at 900 K, exceeding that of PbTe for T > 800 K.

Single crystals of CaCr0.84Fe3.16As3 are prepared from the elements using Sn as a flux (1000 °C, 6 h) and characterized by single crystal neutron diffraction, Moessbauer spectroscopy, electrical resistivity, and magnetic measurements.

The redox chemistry and transformations of NaFeAs in water and air are characterized by single crystal and powder XRD, magnetization measurements, TEM, and Moessbauer spectroscopy.

The synthesis and properties characterization of several PbS1-xTexx = 0-0.16 samples are presented. Notably it is shown how a local minimum occurs in the thermal diffusivity for the PbS1-xTex samples at x ≈ 0.03. The thermoelectric properties of doped PbS1-xTex with x = 0.03 are reported and the properties are compared to the pure PbS and PbTe end members. The electronic contribution to the total thermal conductivity is analyzed for PbS1-xTexx = 0.03 and it is shown how the lattice thermal conductivity is significantly lowered compared to single crystalline PbS.

The effect of K and K-Na substitution for Pb atoms in the rock salt lattice of PbTe was investigated to test a hypothesis for development of resonant states in the valence band that may enhance the thermoelectric power. We combined high temperature Hall-effect, electrical conductivity and thermal conductivity measurements to show that K-Na co-doping do not form resonance states but2 can control the energy difference of the maxima of the two primary valence sub-bands in PbTe. This leads to an enhanced interband interaction with rising temperature and a significant rise in the thermoelectric figure of merit of p-type PbTe. The experimental data can be explained by a combination of a single and two-band model for the valence band of PbTe depending on hole density that varies in the range of 1-15 x 10^19 cm^-3., Comment: 8 figures

We report the synthesis, structure, spectroscopic properties, charge and thermal transport, and electronic structure of a new member of the Zintl family, Yb5Al2Sb6. The compound crystallizes in the Ba5Al2Bi6 structure type and requires the addition of Ge or Si in the synthesis, which appears to act as a catalyst. Yb5Al2Sb6 has an anisotropic structure with infinite anionic double chains cross-linked by Yb2+ ions. Polycrystalline ingots of Yb5Al2Sb6 prepared in the presence of 0.5 mol equiv of Ge showed room-temperature conductivity, thermopower, and thermal conductivity of ∼1100 S/cm, ∼20 μV/K, and ∼3.8 W/m·K, respectively. Investigations of other solid solutions of Yb5Al2Sb6, doping effects, and chemical modifications are discussed. Sr only partially replaces Yb in the structure leading to Sr0.85Yb4.15Al2Sb6. Electronic structure calculations performed using a highly precise full-potential linearized augmented plane wave method within the density functional theory scheme show the presence of a negative b...

We report the synthesis, structure, spectroscopic properties, charge and thermal transport, and electronic structure of a new member of the Zintl family, Yb(5)Al(2)Sb(6). The compound crystallizes in the Ba(5)Al(2)Bi(6) structure type and requires the addition of Ge or Si in the synthesis, which appears to act as a catalyst. Yb(5)Al(2)Sb(6) has an anisotropic structure with infinite anionic double chains cross-linked by Yb(2+) ions. Polycrystalline ingots of Yb(5)Al(2)Sb(6) prepared in the presence of 0.5 mol equiv of Ge showed room-temperature conductivity, thermopower, and thermal conductivity of approximately 1100 S/cm, approximately 20 microV/K, and approximately 3.8 W/m.K, respectively. Investigations of other solid solutions of Yb(5)Al(2)Sb(6), doping effects, and chemical modifications are discussed. Sr only partially replaces Yb in the structure leading to Sr(0.85)Yb(4.15)Al(2)Sb(6). Electronic structure calculations performed using a highly precise full-potential linearized augmented plane wave method within the density functional theory scheme show the presence of a negative band gap and suggest incomplete electron transfer and a metallic character to the compound.

The iron arsenide CaFe(4)As(3) features a three-dimensional network derived from intergrown Fe(2)As(2) layers and Ca ions in channels. Complex magnetic interactions between Fe atoms give rise to unexpected transitions and novel direction-dependent magnetic behavior.

The title compounds were prepared by direct reactions of the corresponding elements at high temperature. They are isostructural and crystallize in the chiral orthorhombic space group P212121 (Li2Ce5Sn7: a = 6.273(1), b = 13.839(2), and c = 17.467(2) A; Li2Pr5Sn7: a = 6.241(1), b = 13.762(2), and c = 17.367(1) A; Li2Sm5Sn7: a = 6.262 (1), b = 13.809(1), and c = 17.432(1) A; Li2Eu5Sn7: a = 6.165(1), b = 13.562(2), and c = 17.128(1) A). The structure contains isolated Sn7 oligomers that resemble the carbon core of an open-chain heptane molecule C7H16. Although these heptamers are stacked along the a axis at a distance that is comparable to the distances within the heptamer, electronic structure calculations show that this intermolecular contact is nonbonding for a formal charge of 16− or higher per heptamer. A hypothetical lower charge of 14−, on the other hand, leads to positive and substantial bond-overlap population that would result in branched infinite chains of ∞[Sn714-]. Magnetic measurements of t...

The title compounds were prepared by direct reactions of the corresponding elements at high temperature. They are isostructural and crystallize in the chiral orthorhombic space group P212121 (Li2Ce5Sn7: a = 6.273(1), b = 13.839(2), and c = 17.467(2) A; Li2Pr5Sn7: a = 6.241(1), b = 13.762(2), and c = 17.367(1) A; Li2Sm5Sn7: a = 6.262 (1), b = 13.809(1), and c = 17.432(1) A; Li2Eu5Sn7: a = 6.165(1), b = 13.562(2), and c = 17.128(1) A). The structure contains isolated Sn7 oligomers that resemble the carbon core of an open-chain heptane molecule C7H16. Although these heptamers are stacked along the a axis at a distance that is comparable to the distances within the heptamer, electronic structure calculations show that this intermolecular contact is nonbonding for a formal charge of 16- or higher per heptamer. A hypothetical lower charge of 14-, on the other hand, leads to positive and substantial bond-overlap population that would result in branched infinite chains of infinity[Sn714-]. Magnetic measurements of the Ce and Pr compounds indicate a 3+ oxidation state for the rare-earth cations and, therefore, 17 available electrons from the cations per formula unit. According to four-probe conductivity measurements, the compounds are metallic.

The title compounds were synthesized from the elements by heating the corresponding mixtures at high temperature. Their structures were determined from single-crystal X-ray diffraction. Li9-xEuSn6+x, Li9-xCaSn6+x, Li5Ca7Sn11, and Li6Eu5Sn9 contain columns of stacked aromatic pentagons of Sn56- that are analogous to the cyclopentadienyl anion C5H5-. The pentagons are separated with Ca2+ or Eu2+ in the columns and resemble a polymeric metallocene. In addition to the columns, the isostructural Li9-xEuSn6+x and Li9-xCaSn6+x contain isolated tin atoms and bent tin trimers while Li5Ca7Sn11 and Li6Eu5Sn9 contain flat zigzag hexamers and flat zigzag infinite chains of tin, respectively. The isostructural LiMgEu2Sn3 and LiMgSr2Sn3 do not contain columns of pentagons but only flat zigzag infinite chains of tin. The aromaticity of the pentagons and the conjugation of the π-systems of the hexamers and the infinite chains are discussed. The title compounds are also characterized by magnetic and conductivity measurements.

The title compounds were synthesized from the elements by heating the corresponding mixtures at high temperature. Their structures were determined from single-crystal X-ray diffraction. Li(9)(-)(x)()EuSn(6+)(x)(), Li(9)(-)(x)()CaSn(6+)(x)(), Li(5)Ca(7)Sn(11), and Li(6)Eu(5)Sn(9) contain columns of stacked aromatic pentagons of Sn(5)(6)(-) that are analogous to the cyclopentadienyl anion C(5)H(5)(-). The pentagons are separated with Ca(2+) or Eu(2+) in the columns and resemble a polymeric metallocene. In addition to the columns, the isostructural Li(9)(-)(x)()EuSn(6+)(x)() and Li(9)(-)(x)()CaSn(6+)(x)() contain isolated tin atoms and bent tin trimers while Li(5)Ca(7)Sn(11) and Li(6)Eu(5)Sn(9) contain flat zigzag hexamers and flat zigzag infinite chains of tin, respectively. The isostructural LiMgEu(2)Sn(3) and LiMgSr(2)Sn(3) do not contain columns of pentagons but only flat zigzag infinite chains of tin. The aromaticity of the pentagons and the conjugation of the pi-systems of the hexamers and the infinite chains are discussed. The title compounds are also characterized by magnetic and conductivity measurements.

We present the synthesis, crystal structure, spectroscopic properties, and electronic structure of a new member of the Zintl family, Yb5Al2Sb6. The compound crystallizes in the Ba5Al2Bi6 structure type. A preliminary assessment of its thermoelectric properties including electrical conductivity, thermopower, and thermal conductivity are reported. Moreover, investigations of solid solutions of this phase, doping effects and chemical modifications will be presented. The room temperature conductivity, thermopower and thermal conductivity of Yb5Al2Sb6/0.5Ge were 1100 S/cm, 20 μV/K, and 3.8 W/m.K, respectively.