The alkali metal reduction of pyrene structural and preparative aspects

Reduction of pyrene with alkali metals yields the corresponding dianion salts. The solvent, counterion and temperature must be carefully selected since side reactions such as protonation (e.g. in liquid ammonia) or cleavage of the etheral solvent occur readily. Moreover, the spectroscopic characterization of the dianion is complicated by rapid electron transfer processes. There is no experimental evidence for distorted dianion structures or for further reduction of pyrene toward a tetraanion. Knowledge of the ionic π-structures is essential for an understanding of reductive alkylation processes.     

Comparative first-principles study of structural and optical properties of alkali metal azides

A comparative first-principles study of the structural and optical properties of the alkali metal azides has been performed with density functional theory within the generalized gradient approximation. The crystal structures of the alkali azides compare well with experimental data. Their ionic character is manifested by the closeness of their internitrogen distances to the calculated N-N bond length for the free azide ion. An analysis of electronic structure, charge transfer, and bond order shows that the alkali azides are all wide-gap insulators and ionic compounds. The energy band and density of states for lithium azide and alpha-sodium azide are very similar, while these for potassium azide, alpha-rubidium azide, and alpha-cesium azide are alike, but some modifications are observed with the increment of alkali metals' electropositivity. These changes are closely related to the differences of the crystal structures. The general shapes of the real and imaginary parts of the dielectric function, adsorption coefficient, and electron energy-loss spectra are quite similar. The peaks originate from the electron transitions from the alkali metal s and p states to the conduction band. Our calculated optical properties for the alkali azides are found to be in good agreement with available experimental data. The absorption spectra of the alkali azides show a number of absorption peaks, which are believed to be associated with different exciton states, in the fundamental absorption region. In general, the electron energy-loss spectra have two plasma frequencies.     

Theoretical studies of electronic structure and structural properties of anhydrous alkali metal oxalates

Nanocrystalline LiMn₂O₄ was synthesized by calcining LiMn₂(CO₃)_2.5·0.8H₂O above 600 °C in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, X-ray powder diffraction, and scanning electron microscopy. The result showed that highly crystallization LiMn₂O₄ with cubic structure [space group Fd-3m(227)] was obtained when the precursor was calcined at 600 °C in air for 1.5 h. The thermal process of the precursor in air experienced three steps which involved, at first, the dehydration of 0.8 water molecules, then decomposition of MnCO₃ into Mn₂O₃, at last, reaction of Mn₂O₃ and Li₂CO₃ into cubic LiMn₂O₄. Based on Starink equation, the values of the activation energies associated with the thermal process of LiMn₂(CO₃)_2.5·0.8H₂O were determined. Besides, most probable mechanism functions and thermodynamic functions (ΔS ^≠, ΔH ^≠, and ΔG ^≠) of thermal processes of LiMn₂(CO₃)_2.5·0.8H₂O were also determined.     

Theoretical studies of electronic structure and structural properties of anhydrous alkali metal oxalates

The theoretical analysis of electronic structure and bonding properties of anhydrous alkali metal oxalates, based on the results of DFT FP-LAPW calculations, Bader’s QTAIM topological properties of electron density, Cioslowski and Mixon’s topological bond orders [reported in the first part of this paper by Kole?yński (doi:10.1007/s10973-013-3126-z)] and Brown’s Bond Valence Model calculations, carried out in the light of thermal decomposition pathway characteristic for these compounds are presented. The obtained results shed some additional light on the origins of the complex pathway observed during thermal decomposition process (two stage process, first the formation of respective carbonate and then decomposition to metal oxide and carbon dioxide). For all structures analyzed, strong similarities in electronic structure and bonding properties were found (ionic-covalent bonds in oxalate anion with C–C bond as the weakest one in entire structure and almost purely ionic between oxalate group and alkali metal cations), allowing us to propose the most probable pathway consisting of consecutive steps, leading to carbonate anion formation with simultaneous cationic sublattice relaxations, which results in relative ease of respective metal carbonate formation.     

Synthetic and structural investigations of alkali metal diamine bis(phenolate) complexes

Two lithium and one sodium diamine bis(phenolate) complexes have been prepared and characterised by X-ray crystallography and NMR spectroscopy. Two parent diamine bis(phenol) ligands were utilised in the study (1-H2 and 2-H2). Dimeric (1-Li2)(2) was prepared by treating 1-H2 with two molar equivalents of n-butyllithium in hydrocarbon solvent. It adopts a ladder-like structure in the solid state, which appears to deaggregate in C6D6 solution. The monomeric (hence, dinuclear) TMEDA-solvated species [2-Li(2).(TMEDA)] has two chemically unique Li atoms in the solid state and is prepared by reacting 2-H2 with two molar equivalents of n-butyllithium in hydrocarbon solvent, in the presence of N,N,N',N'-tetramethylethylenediamine (TMEDA). Finally, the dimeric sodium-based [2-Na(2) x (OEt2](2) was prepared by reacting 1-H2 with two molar equivalents of freshly prepared n-butylsodium in a hydrocarbon-diethyl ether medium. The complex adopts a Na4O4) cuboidal structure in the solid state, which appears to remain intact in C6D6 solution.     

Hydrogen storage over alkali metal hydride and alkali metal hydroxide composites

Alkali metal hydroxide and hydride composite systems contain both protic(H bonded with O) and hydridic hydrogen. The interaction of these two types of hydrides produces hydrogen. The enthalpy of dehydrogenation increased with the increase of atomic number of alkali metals,i.e.,-23 kJ/molH2 for LiOH-LiH, 55.34 kJ/molH2 for NaOH-NaH and 222 kJ/molH2 for KOH-KH. These thermodynamic calculation results were consistent with our experimental results. H2 was released from LiOH-LiH system during ball milling. The dehydrogenation temperature of NaOH-NaH system was about 150℃; whereas KOH and KH did not interact with each other during the heating process. Instead, KH decomposed by itself. In these three systems, NaOH-NaH was the only reversible hydrogen storage system, the enthalpy of dehydrogenation was about 55.65 kJ/molH2, and the corresponding entropy was ca. 101.23 J/(molH2 K), so the temperature for releasing 1.0 bar H2 was as high as 518℃, showing unfavorable thermodynamic properties. The activation energy for hydrogen desorption of NaOH-NaH was found to be57.87 kJ/mol, showing good kinetic properties.     

Hydrogen storage over alkali metal hydride and alkali metal hydroxide composites

Alkali metal hydroxide and hydride composite systems contain both protic(H bonded with O) and hydridic hydrogen. The interaction of these two types of hydrides produces hydrogen. The enthalpy of dehydrogenation increased with the increase of atomic number of alkali metals,i.e.,-23 kJ/molH2 for LiOH-LiH, 55.34 kJ/molH2 for NaOH-NaH and 222 kJ/molH2 for KOH-KH. These thermodynamic calculation results were consistent with our experimental results. H2 was released from LiOH-LiH system during ball milling. The dehydrogenation temperature of NaOH-NaH system was about 150℃; whereas KOH and KH did not interact with each other during the heating process. Instead, KH decomposed by itself. In these three systems, NaOH-NaH was the only reversible hydrogen storage system, the enthalpy of dehydrogenation was about 55.65 kJ/molH2, and the corresponding entropy was ca. 101.23 J/(molH2 K), so the temperature for releasing 1.0 bar H2 was as high as 518℃, showing unfavorable thermodynamic properties. The activation energy for hydrogen desorption of NaOH-NaH was found to be57.87 kJ/mol, showing good kinetic properties.     

Thermochemical and structural investigations on alkali metal chlorides-iron(III)-chloride systems

The pseudobinary systems ACl?FeCl₃ (A=Na, K, Rb, Cs) were reinvestigated by means of differential thermal analysis and X-ray powder diffraction. The existence of the compounds AFeCl₄ (A=Na?Cs) and Cs₃Fe₂Cl₉ could be confirmed; Cs₃Fe₂Cl₉ is a stable compound which decomposes to CsCl and CsFeCl₄ above 270°C. Additionally, two Rb-compounds—Rb₃FeCl₆ and Rb₃Fe₂Cl₉—were found, which decompose, when heated, in the solid state. Rb₃Fe₂Cl₉ is isotypic with the analogous Cs-compound; Rb₃FeCl₆ has the Cs₃BiCl₆ structure. Cs₃FeCl₆ is isotypic with Cs₃CrCl₆, a recently found orthorhombic variant of the elpasolite type.     

Adduct formation between alkali metal ions and divalent metal salicylaldimine complexes having methoxy substituents. A structural investigation

Sodium, potassium, and cesium salts (iodides, nitrates, acetates, and tetraphenylborates) form 1/1, 1/2 and 2/3 adducts with MLn [M = Co, Ni, Cu, and Zn; n = 1-4; H2L1 = N,N'-(3-methoxysalicyliden)ethane-1,2-diamine; H2L2, H2L3, and H2L4 are the -propane-1,2-diamine, -o-phenylenediamine, and -propane-1,3-diamine analogues of H2L1). Metal salicyladimine, alkali metal, and anion all exert influence on stoichiometry and reactivity. Sodium ions tend to reside within the planes of the salicylaldimine oxygens, as in Na(NO3)(MeOH).NiL4 (1), Na(NO3)(MeOH).CuL1 (2; both with unusual seven-coordinated sodium), and Na.(NiL4)2I.EtOH.H2O (3; with dodecahedral sodium coordination geometry). Potassium and cesium tend to locate between salicylaldimine ligands as in KI.NiL4 (4) and [Cs(NO3).NiL4]3.MeOH (5; structures with infinite sandwich assemblies), CsI.(NiL2)2.H2O (6), CsI3.(NiL4)2 (7; simple sandwich structures), and [K(MeCN)]2.(NiL4)3 (8; a triple-decker sandwich structure). Crystal data for 1 are the following: triclinic, P1, a = 7.3554(6) A, b = 11.2778(10) A, c = 13.562(2) A, alpha = 96.364(10) degrees, beta = 101.924(9) degrees, gamma = 96.809(10) degrees, Z = 2. For 2, triclinic, P1, a = 7.2247(7) A, b = 11.0427(6) A, c = 13.5610(12) A, alpha = 94.804(5) degrees, beta = 98.669(7) degrees, gamma = 99.26(6) Z = 2. For 3, orthorhombic, Pbca, a = 14.4648(19) A, b = 20.968(3) A, c = 28.404(3) A, Z = 8. For 4, triclinic, P1, a = 12.4904(17) A, b = 13.9363(13) A, c = 14.1060(12) A, alpha = 61.033(7) degrees, beta = 89.567(9) degrees, gamma = 71.579(10) degrees, Z = 2. For 5, monoclinic. P2(1)/n, a = 12.5910(2) A, b = 23.4880(2) A, c = 22.6660(2) A, beta = 99.3500(1) degree, Z = 4. For 6, orthorhombic, Pbca, a = 15.752(3) A, b = 23.276(8) A, c = 25.206(6) A, Z = 8. For 7, triclinic, P1, a = 9.6809(11) A, b = 10.0015(13) A, c = 11.2686(13) A, alpha = 101.03 degrees, beta = 90.97 degrees, gamma = 100.55 degrees, Z = 2. For 8, monoclinic, C2/c, a = 29.573(5) A, b = 18.047(3) A, c = 23.184(3) A, beta = 122.860(10) degrees, Z = 8.     

Synthetic, structural, and theoretical investigations of alkali metal germanium hydrides--contact molecules and separated ions

The preparation of a series of crown ether ligated alkali metal (M=K, Rb, Cs) germyl derivatives M(crown ether)_nGeH₃ through the hydrolysis of the respective tris(trimethylsilyl)germanides is reported. Depending on the alkali metal and the crown ether diameter, the hydrides display either contact molecules or separated ions in the solid state, providing a unique structural insight into the geometry of the obscure GeH₃^? ion. Germyl derivatives displaying M? Ge bonds in the solid state are of the general formula [M([18]crown‐6)(thf)GeH₃] with M=K ( 1 ) and M=Rb ( 4 ). The compounds display an unexpected geometry with two of the GeH₃ hydrogen atoms closely approaching the metal center, resulting in a partially inverted structure. Interestingly, the lone pair at germanium is not pointed towards the alkali metal, rather two of the three hydrides are approaching the alkali metal center to display M? H interactions. Separated ions display alkali metal cations bound to two crown ethers in a sandwich‐type arrangement and non‐coordinated GeH₃^? ions to afford complexes of the type [M(crown ether)₂][GeH₃] with M=K, crown ether=[15]crown‐5 ( 2 ); M=K, crown ether=[12]crown‐4 ( 3 ); and M=Cs, crown ether=[18]crown‐6 ( 5 ). The highly reactive germyl derivatives were characterized by using X‐ray crystallography, ¹H and ¹³C NMR, and IR spectroscopy. Density functional theory (DFT) and second‐order Møller–Plesset perturbation theory (MP2) calculations were performed to analyze the geometry of the GeH₃^? ion in the contact molecules 1 and 4 .     

Photoionization of alkali metal clusters

The photoionization cross section for spherical alkali metal clusters is predicted to oscillate as a function of the photon wavenumber with a frequency determined by the diameter of the cluster. The oscillations and other principal features of the photo cross section can be worked out analytically using semiclassical techniques. An accurate numerical calculation with different cluster potentials confirms these results qualitatively. Quantitative details depend sensitively on the actual potential. Hence, properties of the true cluster potential can be inferred from the experimental cross section. This might turn out to be useful for improving theoretical cluster potentials.     

Synthesis and structural chemistry of alkali metal tris(HMDS) magnesiates containing chiral diamine donor ligands

Six alkali metal tris(HMDS) magnesiate complexes (HMDS, 1,1,1,3,3,3,-hexamethyldisilazide) containing chiral diamine ligands have been prepared and characterised in both the solid- and solution-state. Four of the complexes have a solvent-separated ion pair composition of the form [{M·(chiral diamine)(2)}(+){Mg(HMDS)(3)}(-)] [M = Li for 1 and 3, Na for 2 and 4; chiral diamine = (-)-sparteine for 1 and 2, (R,R)-TMCDA for 3 and 4, (where (R,R)-TMCDA is N,N,N',N'-(1R,2R)-tetramethylcyclohexane-1,2-diamine)] and two have a contacted ion pair composition of the form [{K·chiral diamine}(+){Mg(HMDS)(3)}(-)](n) [chiral diamine = (-)-sparteine for 5 and (R,R)-TMCDA for 6]. In the solid-state, complexes 1-4 are essentially isostructural, with the lithium or sodium cation sequestered by the respective chiral diamine and the previously reported anion consisting of three HMDS ligands coordinated to a magnesium centre. As such, complexes 1-4 are the first structurally characterised complexes in which the alkali metal is sequestered by two molecules of either of the chiral diamines (-)-sparteine (1 and 2) or (R,R)-TMCDA (3 and 4). In addition, complex 4 is a rare (R,R)-TMCDA adduct of sodium. In the solid state, complexes 5 and 6 exist as polymeric arrays of dimeric [{K·chiral diamine}(+){Mg(HMDS)(3)}(-)](2) subunits, with 5 adopting a two-dimensional net arrangement and 6 a linear arrangement. As such, complexes 5 and 6 appear to be the only structurally characterised complexes in which the chiral diamines (-)-sparteine (5) or (R,R)-TMCDA (6) have been incorporated within a polymeric framework. In addition, prior to this work, no (-)-sparteine or (R,R)-TMCDA adducts of potassium had been reported.     

Anionic polymerization. III. Polymerization of butadiene with alkali metal alkoxide-modified alkali metal system

A high molecular weight polybutadiene was prepared in hexane solvent by using alkali metal (Li, Na, K) and metal tert-butoxide (Li, Na, K) as a polymerization initiator. The microstructure of polybutadiene varies, depending on the type of modifiers and polymerization and temperatures. The results and mechanistic implications of this study are discussed.     

Titanium alkali metal nitrido complexes

Treatment of [(Ti(eta5-C5Me5)(mu-NH))3(mu3-N)] with alkali metal bis(trimethylsilyl)amido reagents in toluene afforded the complexes [M(mu3-N)(mu3-NH)2[Ti3(mu5-C5Me5)3(mu3-N)]]2 (M = Li (2), Na, (3), K (4)). The molecular structures of 2 and 3 have been determined by X-ray crystallographic studies and show two azaheterometallocubane cores [MTi3N4] linked by metal-nitrogen bonds. Reaction of the lithium derivative 2 with chlorotrimethylsilane or trimethyltin chloride in toluene gave the incomplete cube nitrido complexes [Ti3(eta5-C5Me5)3(mu-NH)2(mu-NMMe3)(mu3-N)] (M = Si (5), Sn (6)). A similar reaction with indium(I) or thallium(I) chlorides yielded cube-type derivatives [M(mu3-N)(mu3-NH)2[Ti(eta5-C5Me5)3(mu3-N)] (M=In (7), Tl (8)).     

Properties of molten alkali metal trifluoracetates

We have studied the thermal stabilities of the alkali metal trifluoroacetates by means of DTA and TG, and shown that they are stable in the solid form, with the exception of the lithium salt. We have determined the enthalpies of melting of these five salts. We have also studied the kinetics of decomposition of CF₃COONa, of CF₃COOK and of their mixture. This decomposition is in all cases of the first order. The mixture decomposes in two steps, the first one corresponding to the decomposition of the sodium salt.

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Zusammenfassung Die ThermostabilitÄt der Alkalitrifluoracetate wurde durch DTA und TG untersucht und festgestellt, da\ diese in der festen Form mit Ausnahme des Lithiumsalzes stabil sind. Die Schmelzenthalpie dieser fünf Salze wurde bestimmt. Die Kinetik der Zersetzung von CF₃COONa, CF₃COOK und ihrer Gemische wurde ebenfalls untersucht. Diese Zersetzung ist in allen FÄllen ein Vorgang erster Ordnung. Die Gemische werden in zwei Stufen zersetzt, wobei die erste Stufe der Thermolyse des Natriumsalzes entspricht.

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Résumé Nous avons étudié la stabilité thermique des trifluoroacétates alcalins par ATD et TG, et montré que seul le sel de lithium se décompose avant la fusion. Nous avons déterminé les enthalpies de fusion de ces cinq sels. Nous avons également étudié la cinétique de décomposition de CF₃COONa, CF₃COOK et de leurs mélanges. Cette décomposition est dans tous les cas d'ordre 1. Les mélanges se décomposent en deux étapes, la première correspondant à la thermolyse complète du sel de sodium.

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. , . , . CF₃COOK, CF₃COONa . . , .

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We are grateful to Miss H. Lartigue for technical assistance. Thanks are due to Prof. A. Buchs, Director of the Mass-spectrometry Laboratory.     

Incomplete decomposition of alkali metal azides

The thermal decomposition of sodium azide has been studied in the temperature range 240–360°C in vacuum and under pressure of an inert gas, argon. The results show that the decomposition is partial 360°C. From the observations made in the present work, namely: (i) the decomposition is incomplete both under vacuum and inert gas; (ii) mass spectrometric studies do not reveal any decrease in the intensity of the background species, CO⁺₂, CO⁺, H₂O⁺, and (iii) sodium metal remains in the ‘free state’ as seen by the formation of a metallic mirror at temperatures above 300°C, it has been argued that the partial nature of decompostion is due to the confinement of the decomposition to intermosaic regions within the lattice.