Homocatenation of Aluminum: Alkane‐like Structures of Li2Al2H6 and Li3Al3H8

A new class of aluminum homocatenated compounds (Li_nAl_nH_2n+2) is proposed based on quantum chemical calculations. In these compounds, Al abstracts an electron from Li, becoming valence isoelectronic with C, Si, and Ge, thus mimicking respective structural features of Group 14 hydrides. Using the Coalescence Kick search program coupled with density functional theory calculations, we investigated the potential energy surfaces of Li₂Al₂H₆ and Li₃Al₃H₆. Then single‐point‐energy coupled‐cluster calculations were performed for the lowest energy structures found. Indeed, the global minima established for Li₂Al₂H₆ and Li₃Al₃H₆ contain the Al₂H₆^2? and Al₃H₆^3? kernels, which are isostructural with ethane (C₂H₆), disilane (Si₂H₆), digermane (Ge₂H₆) and propane (C₃H₈), trisilane (Si₃H₈), trigermane (Ge₃H₈) molecules, respectively. Structural, energetic, and electronic characteristics of the Li₂Al₂H₆ and Li₃Al₃H₈ compounds are presented and the viability of their synthesis is discussed.     

Proton‐stabilized three‐dimensional anionic framework in H[Zn6O2(BO3)3]

A three‐dimensional anionic framework built up from [ZnO₄] tetra­hedra and planar [BO₃] groups, stabilized by H atoms, has been found for hydrogen zinc oxide borate, H[Zn₆O₂(BO₃)₃]. Boron and one of the borate O atoms are on 18e (2) positions. Triple units of [ZnO₄] tetra­hedra sharing a common oxygen vertex on a 12c (3) site and strong asymmetrical linear hydrogen bonds with the H atom [on a 12c (3) position] disordered over a twofold axis are specific structural features of this zincoborate. There is evidence that the reported Zn₄O(BO₃)₂ [Harrison, Gier & Stuky (1993). Angew. Chem. Int. Ed. Engl. 32 , 724–726] corresponds to this structure.     

An organic–inorganic hybrid compound containing imidazolium cations and a one‐dimensional lithium hexacyanidocobaltate‐based anionic framework

An organic–inorganic hybrid compound, catena‐poly[bis(3H‐imidazol‐1‐ium) [[tetracyanido‐κ⁴C‐cobalt(III)]‐μ‐cyanido‐κ²C:N‐[diaqualithium(I)]‐μ‐cyanido‐κ²N:C]], {(C₃H₅N₂)₂[CoLi(CN)₆(H₂O)₂]}_n, was synthesized by the reaction of Li₃[Co(CN)₆] with imidazolium chloride in aqueous solution. The compound crystallizes in the monoclinic space group C2/c (data collected at 273 K). In the crystal structure, neighbouring [Co(CN)₆]³⁻ anionic units are linked by Li⁺ cations through the cyanide groups in a trans mode, forming a one‐dimensional zigzag chain structure extending along the c axis. A three‐dimensional supramolecular network is formed through hydrogen‐bonding interactions and is further stabilized by weak CN...π interactions between the cyanide groups and the imidazolium cations.     

Strukturbestimmung an einigen Phasen in den Systemen: Zr-Al-Si und Hf-Al-Si{ZrAl3(Si); ZrSi(Al), Hf(Si,Al); Zr3Si2; Hf3Si2}

Zusammenfassung Die ZrAl₃-Struktur wird bestätigt; man findet jedoch in deren Nachbarschaft bei Si-haltigen Legierungen eine weitere Kristallart Zr(Al, Si)₃, welcher der TiAl₃-Typ zukommt. Die Gitterkonstanten dieser Phase sind:a=5,509,c=8,990 kX·E. undc/a=1,632.Die früher als U II bezeichnete Kristallart im System: Zr–Si wird als ein Monosilicid mit CrB-Typ erkannt und durch Aluminium stabilisiert. Die Abmessungen der Elementarzelle liegen zwischen:a=3,754 und 3,780;b=9,89₂ und 10,05₀ bzw.c=3,746 und 3,78 kX·E., wobei die hohen Werte einer Zusammensetzung Zr(Al_0,3Si_0,7) entsprechen. Ähnlich wie bei Ti(Al, Si)₂ führt die Al/Si-Substitution zu einer pseudotetragonalen Symmetrie. Eine analoge, jedoch ternäre Kristallart Hf(Al_0,5Si_0,5) kristallisiert ebenfalls im CrB-Typ mit den Parametern:a=3,707;b=9,87₀;c=3,746 kX·E. Im Mittelgebiet: Hf–Si tritt eine sehr stabile Kristallart Hf₃Si₂ mit U₃Si₂-Struktur auf:a=6,986;c=3,664 kX·E. undc/a=0,5245. Mit Hilfe dieser Kristallart gelingt nunmehr auch der Nachweis der Existenz von Zr₃Si₂ mit U₃Si₂-Typ, was die Angaben vonL. Brewer undO. Krikorian bzw.C.H. Dauben bestätigt. Als Gitterkonstanten werden:a=7,068;c=3,707 kX·E. undc/a=0,5245 ermittelt.     

Substitution of Lithium for Magnesium,Zinc, and Aluminum in Li15Si4: Crystal Structures,Thermodynamic Properties,as well as 6Li and 7Li NMR Spectroscopy of Li15Si4 and Li15−xMxSi4 (M=Mg,Zn, and Al)

An investigation into the substitution effects in Li₁₅Si₄, which is discussed as metastable phase that forms during electrochemical charging and discharging cycles in silicon anode materials, is presented. The novel partial substitution of lithium by magnesium and zinc is reported and the results are compared to those obtained for aluminum substitution. The new lithium silicides Li₁₄MgSi₄ ( 1 ) and Li_14.05Zn_0.95Si₄ ( 2 ) were synthesized by high‐temperature reactions and their crystal structures were determined from single‐crystal data. The magnetic properties and thermodynamic stabilities were investigated and compared with those of Li_14.25Al_0.75Si₄ ( 3 ). The substitution of a small amount of Li in metastable Li₁₅Si₄ for more electron‐rich metals, such as Mg, Zn, or Al, leads to a vast increase in the thermodynamic stability of the resulting ternary compounds_. The ^6,7Li NMR chemical shift and spin relaxation time T₁‐NMR spectroscopy behavior at low temperatures indicate an increasing contribution of the conduction electrons to these NMR spectroscopy parameters in the series for 1 – 3 . However, the increasing thermal stability of the new ternary phases is accompanied by a decrease in Li diffusivity, with 2 exhibiting the lowest activation energy for Li mobility with values of 56, 60, and 62 kJ mol^?1 for 2 , Li_14.25Al_0.75Si₁₄, and 1 , respectively. The influence of the metastable property of Li₁₅Si₄ on NMR spectroscopy experiments is highlighted.     

Li4Ca3Si2N6 and Li4Sr3Si2N6 – Quaternary Lithium Nitridosilicates with Isolated [Si2N6]10– Ions

The isotypic nitridosilicates Li₄Ca₃Si₂N₆ and Li₄Sr₃Si₂N₆ were synthesized by reaction of strontium or calcium with Si(NH)₂ and additional excess of Li₃N in weld shut tantalum ampoules. The crystal structure, which has been solved by single‐crystal X‐ray diffraction (Li₄Sr₃Si₂N₆: C2/m, Z = 2, a = 6.1268(12), b = 9.6866(19), c = 6.2200(12) Å, β = 90.24(3)°, wR₂ = 0.0903) is made up from isolated [Si₂N₆]^10– ions and is isotypic to Li₄Sr₃Ge₂N₆. The bonding angels and distances within the edge‐sharing [Si₂N₆]^10– double‐tetrahedra are strongly dependent on the lewis acidity of the counterions. This finding is discussed in relation to the compounds Ca₅Si₂N₆ and Ba₅Si₂N₆, which also exhibit isolated [Si₂N₆]^10– ions.     

DFT study of 1‐D Li6Gd(BO3)3

Solid‐state calculations were performed with the program CASTEP to analyze some electronic structure features of the crystal compound Li₆Gd(BO₃)₃ (LIGDBO), which is known to be an efficient gamma radiation detector, in particular when doped with rare‐earth ions. The structure of this material displays a clear 1‐D preference, where chains of atoms are formed along one of the crystalline axes. These quasilinear chains are responsible for the energy transfer occurring in the system prior to the actual detection. To elucidate on some aspects of the former process, calculations based on a few cluster models were also carried out by means of the molecular program JAGUAR. One of our results corresponds to a theoretical absorption energy value close to that experimentally obtained. In our calculation, the absorption process seems to be associated with the formation of an excitonic magnon state. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Li3Al(MoO4)3, a lyonsite molybdate

Trilithium aluminium trimolybdate(VI), Li₃Al(MoO₄)₃, has been grown as single crystals from α‐Al₂O₃ and MoO₃ in an Li₂MoO₄ flux at 998 K. This compound is an example of the well known lyonsite structure type, the general formula of which can be written as A₁₆B₁₂O₄₈. Because this structure can accomodate cationic mixing as well as cationic vacancies, a wide range of chemical compositions can adopt this structure type. This has led to instances in the literature where membership in the lyonsite family has been overlooked when assigning the structure type to novel compounds. In the title compound, there are two octahedral sites with substitutional disorder between Li⁺ and Al³⁺, as well as a trigonal prismatic site fully occupied by Li⁺. The (Li,Al)O₆ octahedra and LiO₆ trigonal prisms are linked to form hexagonal tunnels along the [100] axis. These polyhedra are connected by isolated MoO₄ tetrahedra. Infinite chains of face‐sharing (Li,Al)O₆ octahedra extend through the centers of the tunnels. A mixed Li/Al site, an Li, an Mo, and two O atoms are located on mirror planes.     

Oleana‐12(13),15(16)‐diene‐3α,28‐diyl di­acetate

The title compound, C₃₄H₅₂O₄, consists of five six‐membered rings. Barring the two rings, with double bonds, all other rings are in chair conformations. Mean‐plane and ring‐puckering calculations indicate these two rings to be in distorted‐chair conformations, with distortion towards the boat conformation. There are no strong hydrogen bonds and the structure is stabilized by van der Waals interactions only. The structure is compared with those reported for other triterpenes.     

Ca10(CrVO4)6(CrVIO4), a disordered mixed‐valence chromium compound exhibiting inversion twinning

The structure analysis of so‐called 9CaO·4CrO₃·Cr₂O₃ proved it to be the title compound, decacalcium hexakis[chromate(V)] chromate(VI), with the simultaneous presence of unusual chromium oxidation states. The structure determination was carried out on a crystal that had inversion twinning. The Cr^VIO₄ tetrahedron is situated on a threefold axis and is disordered over two possible orientations that share three O atoms, while the Cr^VO₄ tetrahedra are in general positions and are ordered. The charge is balanced by Ca²⁺ cations, one of which is located on a threefold axis. The Ca²⁺ ions are coordinated by six, seven or eight O atoms. The compound is a significant phase in the CaO–CrO_x system and its formation reduces the refractoriness of calcium‐rich compositions in an oxidizing atmosphere.     

Na1.50Mn2.48Al0.85(PO4)3, a new synthetic alluaudite‐type compound

The first hydro­thermal synthesis of an Al‐rich alluaudite‐type compound, namely disodium dimanganese aluminium tris­(phosphate), which has been obtained at 1073 K and 0.1 GPa starting from the composition Na₂Mn₂Al(PO₄)₃, is reported. The crystal structure, which has been refined in the monoclinic C2/c space group, is identical to that of natural alluaudite. The structure consists of kinked chains of edge‐sharing M1 and M2 octa­hedra, which contain Mn²⁺ and Al³⁺ ions. The chains are stacked parallel to {101} and are connected in the b direction by the P1 and P2 tetra­hedra. These inter­connected chains produce channels parallel to c, which contain the large A1 and A2′ sites occupied by Na⁺ and Mn²⁺ ions.     

A 1‐Aza‐2‐silacyclobut‐3‐ene and an Alkyne from [Li{Si(SiMe3)3}(thf)3] and the Isocyanide 2,6‐Me2C6H3NC

The novel zwitterionic heterocycle 1 was unexpectedly obtained from the reaction between [Li(SiR₃)(thf)₃] and ArNC. Upon heating 1 underwent an interesting ring opening to give the alkyne 2 . Hence the C≡C bond effectively arises from the C−C coupling of two ArNC moieties. R=SiMe₃, Ar=2,6‐Me₂C₆H₃, tmeda=N,N,N′,N′‐tetramethylethylenediamine.     

From a Si3‐Cyclopropene to a Si3S‐Bicyclo[1.1.0]butane to a Si3S‐Cyclopropene to a Si3S2‐Bicyclo[1.1.0]butane: Back‐and‐Forth,and In‐Between

Compact and highly reactive bicyclo[1.1.0]butanes constitute one of the most fascinating classes of organic compounds. Furthermore, interplay of bicyclo[1.1.0]butanes with their valence isomers, such as buta‐1,3‐dienes and cyclobutenes, is among the fundamental pericyclic transformations in organic chemistry. Herein we report the back‐and‐forth interconversion between the cyclotrisilenes and thiatrisilabicyclo[1.1.0]butanes, allowing for the synthesis of novel representatives of such classes of highly reactive organometallics. The peculiar structural and bonding features of the newly synthesized compounds, as well as the mechanism of their isomerization, were verified both experimentally and computationally.     

From a Si3‐Cyclopropene to a Si3S‐Bicyclo[1.1.0]butane to a Si3S‐Cyclopropene to a Si3S2‐Bicyclo[1.1.0]butane: Back‐and‐Forth,and In‐Between

Compact and highly reactive bicyclo[1.1.0]butanes constitute one of the most fascinating classes of organic compounds. Furthermore, interplay of bicyclo[1.1.0]butanes with their valence isomers, such as buta‐1,3‐dienes and cyclobutenes, is among the fundamental pericyclic transformations in organic chemistry. Herein we report the back‐and‐forth interconversion between the cyclotrisilenes and thiatrisilabicyclo[1.1.0]butanes, allowing for the synthesis of novel representatives of such classes of highly reactive organometallics. The peculiar structural and bonding features of the newly synthesized compounds, as well as the mechanism of their isomerization, were verified both experimentally and computationally.     

Li6B18(Li2O)x – A boride with a porous framework of B6 octahedra

The synthesis and crystal structure of the red transparent lithium boride Li₆B₁₈(Li₂O)_x (0 < x ≤ 1) is reported. The lattice constants are a = 8.21708(17) Å and c = 4.15893(16) Å for x = 0.26 (powder data), a = 8.223(4) Å and c = 4.160(2) Å for x = 0.7 (single crystal data), a = 8.21179(16) Å and c = 4.14485(13) Å for x = 0.9 (powder data). The compound crystallizes in the space group P6/mmm (no. 191). The crystal structure consists of B₆ octahedra forming a 3-dimensional network with large open channels. This compound has remarkable topological similarities with hexagonal tungsten bronzes and zeolites and is only formed, when a template is present during the synthesis.