Les systemes binaires AlPO4−M3PO4 (M=Li,Na, K)

The liquid-solid phase diagram of the binary systems AlPO₄?M₃PO₄(M=Li, Na, K) have been established. The additional compounds Na₃Al(PO₄)₂, Na₃Al₂(PO₄)₃ and K₃Al₂(PO₄)₃ have been found again. A new compound K₃Al(PO₄)₂ is observed. The melting point of Na₃PO₄ is 1545°C and K₃PO₄ does not melt up to 1700°C.     

Interaction of RT3 (R=Ce, Y; T=Ni, Co) intermetallic compounds with alkaline solutions of MBH4 (M=Na, K, Rb, and Cs)

The interaction of RT₃ (R=Ce, Y; T=Ni, Co) intermetallic compounds (IMC)with alkaline solutions of MBH₄ (M=Na, K, Rb, and Cs) was studied in the temperature range of 298–318 K. For all intermetallic compounds, the reaction of catalytic hydrolysis of NaBH₄ is zero order with respect to MBH₄ and first order with respect to RT₃. The reaction rate decreases and the activation energy of the catalytic hydrolysis of MBH₄ increases in the following order. NaBH₄, KBH₄, RbBH₄, and CsBH₄. The hydride phases RT₃H_x (x2.3—3.9) were synthesized by the interaction of RT₃ IMC with alkaline solutions of MBH₄. They are similar in composition to the products formed in the reaction of RT₃ with gaseous hydrogen at high pressure. The rate of hydrogenation of RT₃ in alkaline solutions of MBH₄ decreases on going from sodium to cesium. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 921–923, May, 1997.     

Octacoordination of the nitrogen atom in M4NO 4 + systems (M = Li, Na, K)

The electronic and geometric structures of M₄NO ₄ ⁺ compounds (M = Li, Na, K) in classical and nonclassical isomeric forms were studied by the ab initio (MP2(full)/6-311+G**) and density functional theory (B3LYP/6-311+G**) methods. For all M atoms, structurally stable nonclassical isomers were found with octacoordinated nitrogen atoms and tetracoordinated oxygen atoms. For Li₄NO ₄ ⁺ , the classical structure with the tetracoordinated nitrogen atom is energetically more stable, whereas nonclassical structures with the octacoordinated nitrogen center are more stable for Na₄NO ₄ ⁺ and K₄NO ₄ ⁺ .     

Reactions of Sn(NMe2)2 with MPHCy: the effects of alkali metal phosphide coupling (Cy=cyclohexyl; M=Li, Na, K, Rb)

The reactions of the SnII base Sn(NMe2)2 with CyPHM (Cy=cyclohexyl) produce a range of products, depending primarily on the alkali metal (M) involved. The 1:3 stoichiometric reaction of Sn(NMe2)2 with CyPHNa in the presence of the Lewis base donor PMDETA (PMDETA=(Me2NCH2CH2)2NMe) gives [(NaPMDETA)2{Sn(mu-PCy)}3] (3), containing the electron-deficient [{Sn(mu-PCy)}3]2- dianion. Natural bond order (NBO) and electron localisation function (ELF) calculations show that this species is described most appropriately by a two-electron, three-centre Sn3 bonding model. Evidence that 3 results from phosphide coupling is provided by the 1:1 reaction of Sn(NMe2)2 with CyPHNa in the presence of PMDETA, which gives 3 and trace amounts of (NaPMDETA)2[{Sn(mu-PCy)}2(mu-PCyPCy)] (4) (containing one PCyPCy2- dianion). Greater extents of phosphide coupling are observed as the size of the Group 1 metal is increased. Thus, the 1:3 reaction of Sn(NMe2)2 with CyPHK in THF gives the co-crystalline product {(K2 THF)2[{Sn(mu-PCyPCy)}2(mu-PCy)]}0.9{(K2 THF)2[{Sn(mu-PCy)}2(mu-PCyPCy)]}0.1 (5) (containing [{Sn(mu-PCyPCy)}2(mu-PCy)]2- and [{Sn(mu-PCy)}2(mu-PCyPCy)]2- dianions), whereas the analogous reaction of Sn(NMe2)2 with RbPHCy gives [RbPMDETA{(CyP)3SnP(H)Cy}] (6) (containing a cyclic {(CyP)3Sn} unit).     

MAlH4(M=Li,Na)储氢材料*

氢能是一种新型的清洁能源,有望替代碳经济,而氢的储存是氢能应用的关键。近年来,研究集中在具有储氢容量高和可逆性好等优点的固态储氢材料上。许多新型储氢材料不断出现,其中以MAlH₄(M=Li, Na)为代表的金属复合氢化物体系被认为是最有前景的储氢材料之一。本文综述了MAlH₄(M=Li, Na)作为可逆储氢材料的研究现状,主要从吸放氢反应、储氢性能、反应机理、理论计算和存在的问题等方面进行了讨论,并指出其相关发展趋势。     

Die Systeme des Typs MCl/AlCl3/SO2 (M = Li,Na, K,NH4)

The MCl/AlCl₃/SO₂ Systems (M = Li, Na, K, NH₄) Phase diagrams of the ternary systems of the type MCl/AlCl₃/SO₂ were determined by measurement of SO₂ pressure, solubilities, and by thermal analysis. The complete phase diagram in the range from ?30 to +50°C is given for the case M = Na, partial diagrams for M = Li, K, NH₄. There exist solid compounds of the type MAlCl₄ · nSO₂ (M = Li, Na; n = 1.5 and 3) (M = K; n = 1.5 and 5) (M = NH₄; n = 5). Liquid phases can be obtained at room temperature and atmospheric pressure in the NaCl or LiCl containing systems.     

Calorimetric investigations of the MBr−NdBr3 melts (M=Li,Na, K,Cs)

Present work is a part of thermodynamic research program on the MX?LnX₃ system (M=alkali metal,X=Cl, Br andLn=lanthanide). Molar enthalpies of mixing in the LiBr?NdBr₃, NaBr?NdBr₃ and KBr?NdBr₃ liquid binary systems have been determined at temperature 1063 K by direct calorimetry in the whole range of composition. Investigated systems are generally characterized by negative enthalpies of mixing with minimum atX _NdBr3≈0.3–0.4. These enthalpies decrease with decrease of ionic radii of alkali metals. Molar enthalpies of solid-solid and solid-liquid phase transitions of K₃NdBr₆ and Cs₃NdBr₆ have been also determined by differential scanning calorimetry (DSC). K₃NdBr₆ is formed at 689 K from KBr and K₂NdBr₅ with enthalpy of 44.0 kJ·mol^?1 whereas Cs₃NdBr₆ is stable at ambient temperature and undergoes phase transition in the solid state at 731 K with enthalpy of 8.8 kJ·mol^?1. Enthalpies of melting have been also determined.     

Insights from impedance spectroscopy into the mechanism of thermal decomposition of M(NH2BH3), M = H, Li, Na, Li(0.5)Na(0.5), hydrogen stores

We report the first solid-state impedance study of hydrogen-rich ammonia borane, AB, and its three alkali metal amidoborane derivatives. Temperature-dependent impedance spectra of solid M(NH(2)BH(3)) salts are predominated by ionic conductivity, which at room temperature ranges from 5.5 μS cm(-1) (M = Li) to 2.2-3.0 mS cm(-1) (Na, Na(0.5)Li(0.5)), while the activation energy for conductivity is rather high (140-158 kJ mol(-1)). Variation of conductivity with time can be used to extract information about the evolution of the system during thermal decomposition. By using a combination of impedance spectroscopy, thermogravimetric analysis, scanning calorimetry, evolved gas analysis, infrared absorption spectroscopy as well as (11)B and (1)H MAS NMR, we were able to reconfirm the complex pathway of thermal decomposition of amidoboranes postulated by two of us earlier (J. Mater. Chem. 2009, 19, 2043).     

Imidazolidene carboxylate bound MBPh4 complexes (M = Li, Na) and their relevance in transcarboxylation reactions

Combination of 1,3-bis(2,6-diisopropylphenyl)imidazolum-2-carboxylate (IPrCO(2)) with the Lewis acids MBPh(4), where M = Li or Na, provided two separate complexes. The crystal structures of these complexes revealed that coordination to NaBPh(4) yielded a dimeric species, yet coordination of IPrCO(2) with LiBPh(4) yielded a monomeric species. Combination of 1,3-bis(2,4,6-trimethylphenyl)imidazolum-2-carboxylate (IMesCO(2)) with LiBPh(4) also afforded a dimeric species that was similar in global structure to that of the IPrCO(2)+NaBPh(4) dimer. In all three cases, the cation of the organic salt was coordinated to the oxyanion of the zwitterionic carboxylate. Thermogravimetric analysis of the crystals demonstrated that decarboxylation occurred at lower temperatures than the decarboxylation temperature of the parent NHC·CO(2) (NHC = N-heterocyclic carbene). Kinetic analysis of the transcarboxylation of IPrCO(2) to acetophenone with NaBPh(4) to yield sodium benzoylacetate was performed. First-order dependences were observed for IPrCO(2) and acetophenone, whereas zero -order dependence was observed for NaBPh(4). Direct dicarboxylation was observed when I(t)BuCO(2) was added to MeCN in the absence of added MBPh(4).     

Study of the reduction of tungsten trioxide doped with MCl (M=Li,Na, K)

Thermodynamic calculations predict the formation of hydrochloric acid gas and alkali tungstates during hydrogen reduction of WO₃ doped with alkali chlorides MCl (M=Li, Na, K). The formation of HCl was proved experimentally by simultaneously coupled TG-MS measurements from RT to 1200°C. The formation of HCl is the result of the reaction between MCl, WO₃ and water. Ubiquitous traces of moisture in the gas are sufficient for reaction according to WO₃+(2+2n)MCl +(1+n)H₂O→M_2+2nWO_4+n+(2+2n)HCl (n=0, 1, 2). Laboratory reduction tests showed that the formed tungstates differ. NaCl and KCl form monotungstates (n=0), while LiCl produces more lithium-rich compounds (n=1, 2). Temperature and humidity, among other process factors, control subsequent reduction of the tungstates to metals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Les systèmes MFTlF3 (M = Li,Na, K)

A large number of new phases have been prepared and characterized in the MFTlF₃ system: Na₃TlF₆ isostructural with cryolite, Na₃Tl₂F₉, Na_xTl_1−xF_3−2x (0.425 ? x ? 0.565 at 500°C) and Na₅Tl₉F₃₂ related to the fluorite type, K₃TlF₆ with a structure similar to that of (NH₄)₃FeF₆, K₅Tl₃F₁₄ with the chiolite structure, Na_yTl_1−yF_3−2y (0.12 ? y ? 0.14 at 500°C) and K₂Tl₇F₂₃ affiliated to α-UO₃, KTlF₄, and KTl₂F₇.     

121Sb Mössbauer spectra of alkali metal antimonides M3Sb (M3 = Na3, K3, Na2K, Rb3)

¹²¹Sb Mössbauer spectra for M₃Sb (M₃ = Na₃, K₃, Na₂K, Rb₃) were measured at 12 K. The values of isomer shift (d) and quadrupole coupling constant suggest that the valence state of antimony in M₃Sb is –3. The d values increase in the order Rb₃Sb<K₃Sb<Na₃Sb<Na₂KSb. The differences in d values are discussed by examining M–Sb distances and bond valence for M–Sb interactions. Some covalent interactions between alkali metal atoms and antimony atom are suggested.     

Dehydrogenation mechanisms and thermodynamics of MNH2BH3 (M=Li, Na) metal amidoboranes as predicted from first principles

Electronic structure calculations have been used to determine and compare the thermodynamics of H(2) release from ammonia borane (NH(3)BH(3)), lithium amidoborane (LiNH(2)BH(3)), and sodium amidoborane (NaNH(2)BH(3)). Using two types of exchange correlation functional we show that in the gas-phase the metal amidoboranes have much higher energies of complexation than ammonia borane, meaning that for the former compounds the B-N bond does not break upon dehydrogenation. Thermodynamically however, both the binding energy for H(2) release and the activation energy for dehydrogenation are much lower for NH(3)BH(3) than for the metal amidoboranes, in contrast to experimental results. We reconcile this by also investigating the effects of dimer complexation (2×NH(3)BH(3), 2×LiNH(2)BH(3)) on the dehydrogenation properties. As previously described in the literature the minimum energy pathway for H(2) release from the 2×NH(3)BH(3) complex involves the formation of a diammoniate of diborane complex ([BH(4)](-)[NH(3)BH(2)NH(3)](+)). A new mechanism is found for dehydrogenation from the 2×LiNH(2)BH(3) dimer that involves the formation of an analogous dibroane complex ([BH(4)](-)[LiNH(2)BH(2)LiNH(2)](+)), intriguingly it is lower in energy than the original dimer (by 0.13 eV at ambient temperatures). Additionally, this pathway allows almost thermoneutral release of H(2) from the lithium amidoboranes at room temperature, and has an activation barrier that is lower in energy than for ammonia borane, in contrast to other theoretical research. The transition state for single and dimer lithium amidoborane demonstrates that the light metal atom plays a significant role in acting as a carrier for hydrogen transport during the dehydrogenation process via the formation of a Li-H complex. We posit that it is this mechanism which is responsible, in condensed molecular systems, for the improved dehydrogenation thermodynamics of metal amidoboranes.     

Structure determination and relative properties of novel cubic borates MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba)

A series of novel borates, MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba), have been successfully synthesized by standard solid-state reaction. The crystal structures have been determined from powder X-ray diffraction data. They crystallize in the cubic space group Iad with large lattice parameters: a = 14.95066(5) A for LiSr4(BO3)3, a = 15.14629(6) A for NaSr4(BO3)3, and a = 15.80719(8) A for NaBa4(BO3)3. The structure was built up from 64 small cubic grids, in which the M' atoms took up the corner angle and the BO3 triangles or MO6 cubic octahedra filled in the interspaces. The isolated [BO3]3- anionic groups are perpendicular to each other, distributed along three 100 directions. The anisotropic polarizations were counteracting, forming an isotropic crystal. Sr and Ba atoms were found to be completely soluble in the solid solution NaSr(4-)xBax(BO3)3 (0 < or = x < or = 4). The photoluminescence of samples doped with the ions Eu2+ and Eu3+ was studied, and effective yellow and red emission was detected, respectively. The results are consistent with the crystallographic study. The DTA and TGA curves of them show that they are chemically stable and congruent melting compounds.     

New examples of metalloaromatic Al-clusters: (Al4M4)Fe(CO)3 (M = Li, Na and K) and (Al4M4)2Ni: rationalization for possible synthesis

Ab initio calculations reveal that all-metal antiaromatic molecules like Al4M4 (M = Li, Na and K) can be stabilized in half sandwich (Al4M4)Fe(CO)3 and full sandwich (Al4M4)2Ni complexes. The formation of the full sandwich complex [(Al4M4)2Ni] from its organometallic precursor depends on the stability of the organic-inorganic hybrid (C4H4)Ni(Al4Li4).     

Alkali metal salts of acrylamide C3H4NOM (M = Li,Na, and K): Synthesis and vibrational spectra

Alkali metal salts of acrylamide C₃H₄NOM (M = Li, Na, and K) were synthesized for the first time by metallation of acrylamide with alkali metals, their alkyl derivatives, or hydrides. The structures of the compounds synthesized were studied by Raman and IR spectroscopy. Based on the results obtained, an ionic structure was proposed for the salts. The salts were tested as initiators of the anionic polymerization of acrylamide. The catalytic activity of C₃H₄NOM in the polymerization of acrylamide is not lower than that of the well known catalyst, KOBu¹.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2316–2319, September, 1996.