Structure and bonding of Sr3In11: how size and electronic effects determine structural stability of polar intermetallic compounds

The binary compound Sr(3)In(11) (SrIn(3.667)) was synthesized and structurally characterized by X-ray diffraction experiments. It crystallizes in the orthorhombic La(3)Al(11) structure type (space group Immm, Z = 2; a = 4.9257(6), b = 14.247(2), c = 11.212(2) A). The crystal structure of Sr(3)In(11) bears features of the monoclinic EuIn(4) structure, which is adopted by SrIn(4), and the prominent tetragonal BaAl(4) structure. Sr(3)In(11) is stable until 550 degrees C. At higher temperatures it decomposes peritectically into SrIn(2) and In. Structural stability and bonding properties of Sr(3)In(11) were investigated by first principles calculations and compared to SrIn(4) in the monoclinic EuIn(4) and the tetragonal BaAl(4) structure. All three structures consist of a three-dimensional, polyanionic, network formed by In atoms and Sr cations encapsulated in cages. For the BaAl(4)-type SrIn(4), In-In network bonding is perfectly optimized. In contrast, the networks of EuIn(4)-type SrIn(4) and Sr(3)In(11) appear hypo- and hyperelectronic, respectively. The formation of Sr(3)In(11) with a composition close to 1:4 and the nonexistence of BaAl(4)-type SrIn(4) is explained by a delicate interplay of size and electronic factors governing structural stability in the In-rich part of the Sr-In system.     

ChemInform Abstract: Contrasts in Structural and Bonding Representations among Polar Intermetallic Compounds. Strongly Differentiated Hamilton Populations for Three Related Condensed Cluster Halides of the Rare-Earth Elements.

The crystal and electronic structures of three related Ln₃MX₃ (Ln: lanthanoid; M: transition metal; X: Cl, I) phases, Pr₃RuI₃ (space group P2₁/m), Gd₃MnI₃ (P2₁/m), and Pr₃RuCl₃ (Pnma) containing extended mixed-metal chains are compared and contrasted using LMTO-ASA calculations with local spin density approximation and crystal orbital Hamilton population analyses.     

Structural correlations of the lanthanide halides and related compounds. Derivatives of the anti-nickel-arsenide structure

An examination of structural data for lanthanide halides and related compounds has shown that a substantial number of different structure types are conveniently described as layered structures derived from anti-NiAs by removal or shear of cation layers and distortion of the residual layers. The structural correlations of various MX, MX_1.5, MX₂, MXY, MX₃, and MX₂Y compositions (M = cation, X and Y = anions) are described by the presentation of a subgroup-supergroup diagram relating their space groups and by comparison of their structural projections. A close relationship between the CsCl- and NiAs-type structures is observed. The occurrence of displacive and order-disorder phase transitions, the formation ternary derivatives by ion accommodation processes and the possible formation of intermediate halides, M₂X_2n+1, by coherent intergrowth of MX₂ and MX₃ structures are discussed. The effects of radius ratio and cation coordination number on the stabilities of halide structures and on the formation of complex MX₂ layers derived from hexagonal-closest-packed metal arrays are examined.     

Peculiarities of the synthesis and thermolysis of heterometallic coordination compounds used as precursors for nickelates of rare-earth elements

The influence of the solvent on the composition of solid products is investigated using the example of the interaction of rare-earth element (REE) nitrates, Ln(NO₃)₃, with square-planar complexes of nickel and Schiff bases, Ni(SB). The composition of solid products is determined by X-ray fluorescence analysis and elemental analysis. It is shown that from the labile Ln(NO₃)₃-Ni(SB) systems, individual heterometallic compounds can be obtained, moreover, if in systems there are complexes with more dentate Ni(mosalen) ligands, only binuclear heterocomplexes can be produced. In case of Ni(salen) ligand, the formation of trinuclear complexes is achieved by selecting the optimal solvent. Among the considered compounds, binuclear complexes are of special interest due to the possibility of their use as precursors of REE nickelates.     

Heats of hydrogenation of compounds featuring main group elements and with the potential for multiply bonding

Reaction enthalpies are calculated for the hydrogenation reactions of main group hydrides with the potential for multiple bonding, and thus the unsaturated character of these species is determined. In addition to the global minimum structures, which leave in some cases no hope for even a single E-E bond (E=Group 13, 14, or 15 element), calculations are also performed for geometries with maximum potential for multiple bonding. The trends down the groups and the periods are established. Interpretations have to take several factors into account. These factors sometimes work hand in hand but also against each other. We also include in our survey the species [HGaGaH]2- as a free anion and Na2[HGaGaH] as well as their hydrogenation products [H2GaGaH2]2- and Na2[H2GaGaH2]2-. The results show that the presence of the Na+ ions has a significant impact on their chemistry, and thus suggests that they are involved to a large extent in the bonding. Our results indicate that the compounds should be described as cluster compounds.     

Modeling of self-organization processes in crystal-forming systems: Symmetry and topology code for the cluster self-assembly of crystal structures of intermetallic compounds

We performed the combinatorial and topological modeling of 1D, 2D, and 3D packs of symmetrically connected metal clusters in the form of tetrahedra А₄. Three types of 1D chains with tetrahedral connectivity of 4, 6, and 8 were used to model 2D layers L-1, L-2, and L-3 and 3D frameworks FR-1, FR-2, FR-3, and FR-4. The model structures of the identified suprapolyhedral precursor clusters were used in topological analysis of crystal structures of intermetallic compounds (program package TOPOS and data bases ICSD and CRYSTMET). A match was found between the topological models of tetrahedral 3D frameworks and all types of crystal structures formed in binary systems; in Au–Cu: FR-1 for Cu₃Au-cP4 (Auricupride), Cu₂Au₂-tP2 (Tetraauricupride), CuAu₃-cP4 (Bogdanovite), and Cu_2–x Au_{2 + x} -cF4; in Mg–Cd: FR-3 for Mg₃Cd-hP8, Mg₂Cd₂-oP4, MgCd₃-hP8, and Mg_2–x Cd_{2 + x} -hP2; in Li–Hg: FR-2 for Li₃Hg-cF16 and Li₂Hg₂-cP2 and FR-3 for LiHg₃-hP8; in ternary system Li–Ag–Al: FR-2 for LiAg₂Al-cF16 and Li₂AgAl-cF16; and in quaternary system: framework FR-2 for LiMgPdSn-cF16. Framework FR-4 was identified in ternary intermetallic compounds A(Li₂Sn₂)-tI20, where A = Cu, Ag, Au. The structures of precursor nanoclusters were identified for other most abundant types of crystal structures of intermetallic compounds. For this purpose, we used the algorithms for partitioning the structural graph into nonintersecting cluster substructures and constructed the basal 3D network of the crystal structure in the form of a graph whose nodes correspond to the positions of the centers of precursor clusters. The cluster self-assembly was modeled for the following intermetallic compounds: Mg₂Cu₄-cF24, MgSnCu₄-cF24, (ZrCu)Cu₄-cF24,Mg₂Zn₄-hP12, (CaCu)Cu₄-hP6, Cr₃Si-cP8, Lu₃Co(Fe₃C)-cP16, Ca₂Ge₂(Cr₂B₂)-oC8, Y₂Ni₂(Fe₂B₂)-oP8, AlB₂-hP3, Ca₂Ge-oP12, CaHg₂-hP3, Co₂Ge(Ni₂In)-hP6, Cs₂Hg₄-oI12, Ba₄Po₄-cF8, Mn₅Ge₃-hP16, and NaZn₁₃-cF112. The symmetry and topological code of self-assembly from precursor nanoclusters was reconstituted for all crystal structure types of intermetallic compounds as: primary chain → microlayer → microframework. An abundance frequency analysis of topological and symmetry routes for the generation and evolution of precursor clusters enabled us to elucidate the crystal-formation laws in intermetallic systems on the microscopic level.     

An alternative way of characterising the bonding in compounds featuring main-group elements and with the potential for multiple bonding: on the dissociation of binary main-group hydrides

Herein the bonding in compounds featuring main-group elements and with the potential for multiple bonding is studied theoretically by examination of their fragmentation into two fragments that still exhibit the same structure as they had in the molecule prior to dissociation. The fragments were calculated both in their electronic ground state and in an excited electronic state, in which the number of unpaired electrons is equal to the maximal number of bonds in the compounds before dissociation. The energies of the fragmentation processes (DeltaE(frag)) can be more directly linked to the bond strengths than the dissociation energies (DeltaE(diss)), because of the absence of any secondary effects like relaxation of the electronic state or of the geometry of the fragments. These relaxation energies of the fragments (DeltaE(frag)) are also studied herein. The energies derived in this work allow for an accurate comparison of the bonding properties in main-group-element hydrides. The trends of the fragmentation and relaxation energies are discussed in detail. It will be shown that the relaxation energies allow for a classification of the bonds ("classical" sigma and pi bonds or donor-acceptor interactions), while the fragmentation energies are good quantitative measures for the total bond strength. Similar calculations are on the way to explore the bonding in systems in which the hydrogen atoms are replaced by organic groups or halogen atoms.     

Spiers Memorial Lecture. Comparative studies of cluster dynamics in the gas and condensed phases

Although an overview of the field of cluster dynamics is impossible to give in this Introductory Lecture, several important themes have emerged that can provide a backdrop for this Faraday Discussion. As a result, the first part of this paper introduces some of these themes, using results from the literature to illustrate some of the important issues. Although much of the work on clusters is being carried out in the gas phase (usually in free jet expansions and molecular beams), new approaches have recently been developed that permit the study of the same complexes in or on nanoscale clusters. In particular, recent developments in the field of superfluid helium droplet spectroscopy (SHEDS) permit high-resolution studies of atoms, molecules and clusters in this exotic quantum fluid. After introducing this new field, the author will discuss experiments from his own laboratory to illustrate some of the capabilities of the technique.     

Application of thermospray liquid chromatography-mass spectrometry for the analysis of chloramphenicol and three related compounds

The thermospray (TS) liquid chromatographic-mass spectrometric analysis of the antibiotic chloramphenicol and three related compounds is presented. The three additional compounds are dehydrochloramphenicol, aminodehydrochloramphenicol, and nitrophenylaminopropanediol. Baseline separation of the four compounds is achieved. The TS mass spectrum of each of the four compounds includes a prominent [MH]+ ion plus some fragment ion peaks.     

Unusual electronic and bonding properties of the Zintl phase Ca5Ge3 and related compounds. A theoretical analysis

Theoretical reasons for metallic behavior among diverse Zintl phases have generally not been pursued at an advanced level. Here, the electronic structure of Ca5Ge3 (Cr5B3 type), which can be formulated (Ca+2)5(Ge2-6)Ge-4 in oxidation states, has been explored comparatively by means of semiempirical and first-principles density functional methods. The FP-APW calculations show that alkaline-earth-metal and germanium orbitals, particularly the d orbitals on the cations and the p-pi orbitals of the halogen-like dimeric Ge2-6, mix considerably to form a conduction band. This covalency perfectly explains the unusual metallic properties of the nominally electron-precise Zintl phase Ca5Ge3 and its numerous relatives. Similar calculational results are obtained for Sr5Ge3, Ba5Ge3, and Ca5Sn3. Cation d orbitals appear to be a common theme among Zintl phases that are also metallic.     

Synthesis and structural characterisation of novel nickelaindenyl and nickelafluorenyl compounds: Differences in the bonding modes of nickelacyclic rings

New binuclear nickelacyclic compounds 1 (η⁵-pentamethylcyclopentadienyl)(η³-(1-(η⁵-pentamethylcyclopentadienyl))-1-nickelafluorenyl)nickel and 2 (η⁵-pentamethylcyclopentadienyl)(η³-(1-(η⁵-pentamethylcyclopentadienyl))-2-phenyl-3-ethyl-1-nickelaindenyl)nickel were synthesised in reactions of dilithioorganic compounds with Cp^∗Ni(acac) and characterised by high resolution mass spectrometry, magnetic moment determination and X-ray single crystal analysis. The bonding mode of the central nickel atom to the nickelaindenyl and nickelafluorenyl ligands was not η⁵ like in the previously described analogues of nickelocene but half way between η³ and η⁵.     

Models for unimolecular reactions in the solid phase and stability prediction of energetic compounds in the condensed state

Russian Chemical Bulletin - The results of analysis and refinement of phenomenological models for unimolecular reactions proceeding homogeneously in the bulk of undistorted crystal lattice or...     

Concentration levels of rare-earth elements and thorium in plants from the Morro do Ferro environment as an indicator for the biological availability of transuranium elements

Plants and soils from a natural thorium and rare-earth element occurrence (Morro do Ferro, Brazil) were analyzed by alpha spectrometry (Th) and ICP-AES (REE), after pre-concentration of the elements by solvent extraction, co-precipitation and ion exchange procedures. Leaching experiments with humic acid solutions and different soils were performed to estimate the fraction of elements biologically available. High concentrations of the light rare-earth elements (LREE) and of Th, reaching some hundreds of g/g-ash, were measured in plant leaves from the areas of the highest concentration of these elements in soil and in near-surface waters. Chondrite normalized REE plots of plant leaves and corresponding soils are very similar, suggesting that there is no significant fractionation between the REE during uptake from the soil solution and incorporation into the leaves. However, Ce-depletion was observed for some plant species, increasing forSolanum ciliatum in the sequence: leaves<fruits<seeds. Soil to plant concentration ratios (CR's) for Th and the REE, based on the total concentration of these elements in soils, are in the range of 10^–3 to 10^–2. Leaching experiments confirmed the importance of humic acid complexation for the bio-uptake of Th and REE and further showed that only a very small fraction of these elements in soil is leachable. The implications of these results on the calculated CR's will be discussed.     

Some new methods for the determination of rare-earth elements in geological materials using thermal and epithermal neutron activation

Three procedures are outlined for the determination of rare-earth elements in geological materials. The irradiation of the samples is carried out by either thermal or epithermal neutrons. Two of the methods, one of which is especially suitable for ultramafic rocks are based on radiochemical separations, while in the third method non-destructive analysis is applied to apatites. The γ-ray activity measurements are performed by means of coaxial Ge(Li)-detectors.     

Synthesis, structure, and bonding of BaTl(3): an unusual competition between cluster and classical bonding in the thallium layers.

The new BaTl(3) compound has been synthesized and characterized by physical property measurements and electronic structure calculations. Its structure (Cmcm) is a new intermediate in the Ni(3)Sn family (P6(3)/mmc), and consists of thallium layers formed from two-center bond formation between the parallel chains of face-sharing octahedral clusters. The valence electron concentration (VEC) of the thallium layers is consistent with their two-dimensional nature, in comparison with those in other AX(3)-type compounds with one- or three-dimensional anionic networks with the same building blocks and different VECs. The unique geometric features of the anionic thallium layers bring on an unusual competition between inter- and intracluster bonds. Detailed studies of the energetics of BaTl(3) reveal for the first time the important role of cation-anion interactions in the bonding competition in such an anionic substructure.     

Collision‐induced dissociation of 3‐keto anabolic steroids and related compounds after electrospray ionization. Considerations for structural elucidation

The collision‐induced dissociation of forty‐one 3‐keto anabolic steroids and related compounds has been studied using both triple quadrupole (QqQ) and hybrid quadrupole‐time of flight (QTOF) instruments. Due to the complexity of the product ion spectra of these analytes, which generate a large number of ions, only two specific regions were studied in depth: the product ions near the precursor ion (m/z ≥M–100) and the most abundant product ions at a collision energy of 30 eV. Accurate mass measurements were used in order to obtain an unequivocal assignment of the empirical formula and the origin of each selected product ion. Analytes have been divided into eight groups according to the number and position of double bonds and the presence of functional groups such as hydroxyl‐ or nitrogen‐containing rings. A correlation between the steroid structure and the product ions obtained has been postulated. The application of these correlations can be useful in the elucidation of feasible structures for unknown steroids and/or their metabolites. Copyright © 2008 John Wiley & Sons, Ltd.