Bonding, structure, and stability of solid A2MH2 with A = Li, Na; M = Pd, Pt were investigated with a relativistically corrected density-functional approach, which reliably describes the trends among these four compounds. In order to examine the influence of the ligands (A) and of the crystalline environment, calculations were also made for free A2MH2 molecules and MH22– ions. The free MH22– complex is held together by strong bonds between formally closed shell atomic units because of strong M-d,s hybridization. The M–H bonds are further stabilized by the alkali metal ion ligands and by the crystal surrounding. The crystal field expands the H–A distance and enhances the H–A polarity. Relativistic effects contribute to M–H bonding in the solid state. The experimentally determined bond lengths and their trends are in accordance with theory. Due to relativistic and lanthanide effects, the Pt–H bond length becomes nearly as short as the Pd–H one. The small Li ion causes a distortion of the Li2PtH2 crystal resulting in an even shorter Pt–H bond length. In the gas-phase, A2PtH2 is more stable against dissociation than A2PdH2. The stability of the solid compounds is strongly influenced by the cohesive energy of the metal M, and also by the nature of the alkali metal. The evaluated enthalpies of formation favor increasing stability of solid A2MH2 against disproportionation into M and AH from Pt to Pd and from Li to Na. This is in agreement with experimental findings. The assignment of the experimental vibrational excitations should be reconsidered. 相似文献
Solid‐state hydrogen storage using various materials is expected to provide the ultimate solution for safe and efficient on‐board storage. Complex hydrides have attracted increasing attention over the past two decades due to their high gravimetric and volumetric hydrogen densities. In this account, we review studies from our lab on tailoring the thermodynamics and kinetics for hydrogen storage in complex hydrides, including metal alanates, borohydrides and amides. By changing the material composition and structure, developing feasible preparation methods, doping high‐performance catalysts, optimizing multifunctional additives, creating nanostructures and understanding the interaction mechanisms with hydrogen, the operating temperatures for hydrogen storage in metal amides, alanates and borohydrides are remarkably reduced. This temperature reduction is associated with enhanced reaction kinetics and improved reversibility. The examples discussed in this review are expected to provide new inspiration for the development of complex hydrides with high hydrogen capacity and appropriate thermodynamics and kinetics for hydrogen storage.
A procedure for the direct synthesis of dialkoxyaluminum hydrides (RO)2AlH (R=Pri, But, and Et) from aluminum metal and corresponding alcohols in organic solvents (hydrocarbons, ethers) in the presence of catalytic
amounts of tertiary amines (NMe3, NEt3) at a pressure of H2 of 80 to 350 atm and at a temperature of 100 to 160°C has been developed. A possible mechanism for the reaction was proposed.
Thermal decomposition of (RO)2AlH was studied by differential thermogravimetric analysis (DTGA),27Al NMR spectroscopy, IR spectroscopy, and GLC.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2052–2055, November, 1997. 相似文献
[(η5-C5R5)Fe(PMe3)2H] (R = H, Me) can be made in good yields in a simple one-pot reaction between FeCl2, PMe3, C5R5H (R = H, Me) and Na/Hg in thf. Reaction of [(η5-C5H5)Fe(PMe3)2H] with pentaborane(9) gives the known metallaborane [(η5-C5H5)-nido-2-FeB5H10] (1) in improved yield as well as the new metallaboranes [(η-C5H5)-nido-2-FeB5H8{μ-5,6-Fe(η5-C5H5)(PMe3)(μ-6,7-H)}] (2), [(η-C5H5)(PMe3)-arachno-2-FeB3H8] (3), [(η5-C5H5)2-capped-nido-2,3-Fe2B4H8] (4), [(η5-C5H5)-nido-2-FeB4H7(PMe3)] (5) and [(η5-C5H5)-nido-2-FeB5H8(PMe3)] (6). Reaction of [(η5-C5Me5)Fe(PMe3)2H] with pentaborane(9) gives predominantly [(η5-C5Me5)-nido-2-FeB5H10] (7) and [(η5-C5Me5)(PMe3)-arachno-2-FeB3H8] (8). Reaction of [(η5-C5H5)Fe(PMe3)2H] with 2 equiv. of BH3 · thf gives low yields of ferrocene and compound 3. Compound 7 thermally isomerises to the apical isomer [(η5-C5H5)-nido-2-FeB5H10] (9) in low yield. Compounds 1 and 7 deprotonate cleanly in the presence of KH at the unique B-H-B bridge to give [(η5-C5H5)-nido-2-FeB5H9−][K+] (10) and [(η5-C5Me5)-nido-2-FeB5H9−][K+] (11) respectively, whilst 6 deprotonates more slowly at one of two equivalent B-H-B bridges to give the fluxional anion [(η5-C5H5)-nido-2-FeB5H7(PMe3)−] (12). 相似文献
A simple method for one-step preparation of the organoaluminum compounds R3Al, R2AlH, R2R"Al, and RR"AlH by the reaction of MAlH4 (M = Li, Na) with R2AlHal (Hal = Cl, Br) and -olefins (3-methylbut-1-ene, hex-1-ene, oct-1-ene, dec-1-ene) was proposed. 相似文献
A series of novel arylgermanium hydrides ArnGeH4–n (n = 1–3) and diaryl(chloro)germanium hydrides Ar2Ge(Cl)H were synthesized and characterized. Systematic preparation and purification were achieved via the lithium chloride–triflic acid and the optimized Grignard route. Arylgermanium hydrides ArnGeH4–n (Ar = 2,5-Me2C6H3, n = 1–3) were characterized by 1H and 73Ge NMR spectroscopy and single crystal X-ray diffractometry. 相似文献