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.     

Zintl-Verbindungen mit Gold: M3AuSn4 mit M = K,Rb, Cs und M3AuPb4 mit M = Rb,Cs

Zintl-Compounds with Gold: M₃AuSn₄ with M = K, Rb, Cs and M₃AuPb₄ with M = Rb, Cs Silver coloured, brittle single crystals of the compounds M₃AuSn₄ with M = K, Rb, Cs and M₃AuPb₄ with M = Rb, Cs were synthesized by reactions of alkali metal azides (MN₃) with gold sponge and tin (lead) powder at T = 923 K. The structures of the isotypic compounds (space group Pmmn, Z = 2) were determined from X-ray single-crystal diffractometry data (see ‘‘Inhaltsübersicht”︁”︁). The Zintl-compounds M₃AuE(14)₄ with E(14) = Sn, Pb contain [AuE(14)₄]-chains with P₄-analogous E(14)₄-tetrahedra which are connected by μ₂-bridging gold atoms.     

Thermodynamic Properties of the MZr2(PO4)3 (M=Na,K, Rb or Cs) Compounds

The enthalpies of the solution of MZr₂(PO₄)₃(M=Na, K, Rb or Cs) compounds have been measured by the help of a differential automatic isothermal Calvet calorimeter and the standard enthalpies of formation have been derived. The temperature dependencies of the standard heat capacity of the samples of crystalline NaZr₂(PO₄)₃ and CsZr₂(PO₄)₃ were studied between 7 and 340 K in an automatic adiabatic vacuum calorimeter. The main thermodynamic functions H ⁰(T)–H ⁰(0), S ⁰(T) andG ⁰(T)–H ⁰(0) have been determined. The Gibbs energies of formation of the NaZr₂(PO₄)₃and CsZr₂(PO₄)₃ at 298.15 K were calculated on the basis of these experimental data and the enthalpy of formation data. Qualitative explanations for the results observed were presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

碱金属硒化物MHgSbSe~3(M=K,Rb, Cs)的晶体结构及其半导体性 质的研究

用有机溶剂热生长技术(SolvothermalTechnique)制备碱金属硒化物MHgSbSe~3(M=K,Rb,Cs),用单晶X射线衍射技术对其进行晶体结构分析,热分析结果表明,在常温(<200℃)下均为稳定的化合物。光学性质测试表明它们是半导体材料,KHgSbSe~3,RbHgSbSe~3,CsHgSbSe~3的禁带宽度依次为1.85eV,1.75eV,1.65eV。     

Crystal structures and topological aspects of the high-temperature phases and decomposition products of the alkali-metal oxalates M2[C2O4] (M=K, Rb, Cs)

The high-temperature phases of the alkali-metal oxalates M2[C2O4] (M = K, Rb, Cs), and their decomposition products M2[CO3] (M = K, Rb, Cs), were investigated by fast, angle-dispersive X-ray powder diffraction with an image-plate detector, and also by simultaneous differential thermal analysis (DTA)/thermogravimetric analysis (TGA)/mass spectrometry (MS) and differential scanning calorimetry (DSC) techniques. The following phases, in order of decreasing temperature, were observed and crystallographically characterized (an asterisk denotes a previously unknown modification): *alpha-K2[C2O4], *alpha-Rb2[C2O4], *alpha-Cs2[C2O4], alpha-K2[CO3], *alpha-Rb2[CO3], and *alpha-Cs2[CO3] in space group P6(3)/mmc; *beta-Rb2[C2O4], *beta-Cs2[C2O4], *beta-Rb2[CO3], and *beta-Cs2[CO3] in Pnma; gamma-Rb2[C2O4], gamma-Cs[C2O4], gamma-Rb2[CO3], and gamma-Cs2[CO3] in P2(1)/c; and delta-K2[C2O4] and delta-Rb2[C2O4] in Pbam. With respect to the centers of gravity of the oxalate and carbonate anions, respectively, the crystal structures of all known alkali-metal oxalates and carbonates belong to the AlB2 family, and adopt either the AlB2 or the Ni2In arrangement depending on the size of the cation and the temperature. Despite the different sizes and constitutions of the carbonate and oxalate anions, the high-temperature phases of the alkali-metal carbonates M2[CO3] (M = K, Rb, Cs), exhibit the same sequence of basic structures as the corresponding alkali-metal oxalates. The topological aspects and order-disorder phenomena at elevated temperature are discussed.     

Phase Formation in the Systems MNO3-CsNO3-MoO3 (M = K or Rb)

Phase formation in the systems MNO₃-CsNO₃-MoO₃ (M = K, Rb) have been investigated by visual polythermal, differential thermal, thermogravimetric, and X-ray powder diffraction analyses. The parameters of invariant points have been revealed, and phase diagrams of the systems have been constructed.     

Phase formation in the Re-Se-Br-MBr systems (M = Li, Na, K, Rb, Cs)

Phase formation in the Re-Se-Br-MBr systems (M = K, Rb, Cs) was studied by NMR spectroscopy and powder X-ray diffraction. The reactions taking place in alkali metal halide melts were found to give, among the series of cluster anions [{Re₆Se_{8 − n} Br _n }Br₆]^{(4 − n)}− (0 ≤ n≤ 4), polymeric complexes Re₆Se₈Br ₂ and M₂Re₆Se₈Br₄ (M = Cs, Rb) and salts containing cluster anions [Re₆Se₆Br₈]²⁻ and [Re₆Se₇Br₇]³⁻ as the major products. The effect of the alkali metal cation on the product composition and ratio was established. Original Russian Text ? S.S. Yarovoi, Yu.V. Mironov, S.V. Tkachev, V.E. Fyodorov, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 2, pp. 344–349.     

Ion Mobility,Phase Transitions,and Ion Conductivity in Alkali Metal Tetrafluoroantimonates(III) MSbF4 (M = Na,K, Rb,Cs)

The internal mobility of fluoride ions and electrophysical characteristics of alkali metal tetrafluoroantimonates(III) (M = Na, K, Rb, and Cs) are studied by ¹⁹F NMR and impedance spectroscopies. The types of ion motions in the anionic sublattice of these compounds are determined in the 180-510 K temperature range. The superionic conductivity of the MSbF₄ compounds is established above 480 K ( 2.9 × 10^-2 to 1.3 × 10^-4 S/cm).     

Thermodynamic Study of the Solid-Liquid Equilibria in the Systems MIPO3-Pr(PO3)3 (MI=Na,Rb, Cs OR Ag)

A previously established equation of a stoichiometric phase liquidus curve was applied to determination of the phase diagrams of the systems M^IPO₃-Pr(PO₃)₃ (with M^I=Na, Rb, Cs or Ag). The temperature, enthalpy and entropy of fusion were calculated for each solid phase with the exception of silver polyphosphate, the crystallization field of which was very limited. The enthalpy of fusion of the polyphosphate Pr(PO₃)₃ was determined from the DTA curve. The melting enthalpy of Pr(PO₃)₃ calculated from the different binary systems was approximately equal to the measured value. The calculated temperatures and compositions were in good agreement with those determined experimentally. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fluxional bonds in quasi-planar and half-sandwich (M = K,Rb, and Cs)

Detailed molecular orbital and bonding analyses reveal the existence of both fluxional σ- and π-bonds in the global minima C_s ( 1 ) and C_s MB₁₈ ( 3 ) and transition states C_s ( 2 ) and C_s ( 4 ) of dianion and monoanions (M = K, Rb, and Cs). It is the fluxional bonds that facilitate the fluxional behaviors of the quasi-planar and half-sandwich which possess energy barriers smaller than the difference of the corresponding zero-point corrections. © 2019 Wiley Periodicals, Inc.     

A close look at short C-CH3...potassium contacts: synthetic and theoretical investigations of [M2Co2(mu3-OtBu)2(mu2-OtBu)4(thf)n] (M = Na, K, Rb, thf = tetrahydrofuran)

Agostic interactions of the type Si-CH3M+ (M = alkali metal) are frequently mentioned in discussions of solid-state structures of trimethylsilyl compounds and the purpose of this work was to elucidate if they also exist in the related tert-butyl species by using density functional theory. The compounds [M2Co2(mu3-OtBu)2(mu2-OtBu)4(thf)n] (M = Na, n = 2; M = K, n = 0; M = Rb, n = 1) have been synthesised and their crystal structures determined. Close contacts of methyl groups with K atoms are observed in the solid-state structure of [K2Co2(mu3-OtBu)2(mu2-OtBu)4], and calculations of the rotational barrier of a tert-butoxy group about the axis through the C-O bond were performed. It was shown that apparent short C-CH3K distances are in this case a consequence of the packing in the extended solid-state structure.     

烟酸的低温热容和标准摩尔生成焓

利用精密自动绝热热量计测量了分析纯烟酸在78～400 K温区的低温热容. 用最小二乘法将实验摩尔热容对温度进行拟合, 得到了热容随温度变化的多项式方程. 用此方程进行数值积分, 得到在此温区每隔5 K的舒平热容值和相对于298.15 K时的热力学函数值. 利用精密静止氧弹燃烧热量计测定了烟酸在298.15 K时的恒体积燃烧能为 Δ_cU＝ －(24528.3±16.1) J•g^－1. 依据物质燃烧焓定义计算出烟酸的标准摩尔燃烧焓为: Δ_cH_m^o＝－(3019.05±1.98) kJ•mol^－1. 最后, 依据Hess定律计算出烟酸的标准摩尔生成焓为: Δ_fH_m^o＝－(56.76±2.13) kJ•mol^－1.     

苏糖酸钾的低温热溶及标准摩尔生成焓测定

以苏糖酸与碳酸氢钾反应制得苏糖酸钾K(C₄H₇O₅)·H₂O，通过红外光谱、热重、化学分析及元素分析等对其进行了表征。用精密自动绝热热量计测量了该化合物在78K-395K温区的摩尔热容。实验结果表明，该化合物存在明显的脱水转变，其脱水浓度、摩尔脱水焓以及摩尔脱水熵分别为：(380.524 ± 0.093) K，(19.655 ± 0.012) kJ/mol 和 (51.618 ± 0.051) J/（K·mol）。将78K-362K和382K-395K两个温区的实验热容值用最小二乘法拟合，得到了两个表示热容随温度变化的多项式方程。以RBC-II型恒容转动弹热量计测定目标化合物的恒容燃烧能为(-1749.71 ± 0.91) kJ/mol，计算得到其标准摩尔生成焓为(-1292.56 ± 1.06) kJ/mol。     

三聚氰胺的生成焓、热容和熵

通过多种热化学方法研究了三聚氰胺的热力学性质. 首先用氧弹式燃烧热量计测定了三聚氰胺在298.15 K 时的燃烧热, 根据燃烧热结果, 计算出三聚氰胺的标准摩尔燃烧焓和标准摩尔生成焓, 分别为: △cHΘm=(-2455.17±4.65) kJ·mol-1; △fHΘm =(-763.38±5.16) kJ·mol-1. 然后根据键焓与燃烧焓之间的关系, 估算出三聚氰胺中的C≈N(此键介于单键与双键之间)键能为458.30 kJ·mol-1, 此值介于碳氮单键键能和双键键能之间. 通过绝热热量计测定了三聚氰胺从80到385 K的低温热容. 根据热容值, 计算了此温度区间的标准摩尔生成焓, 其与温度呈线性关系. 另外, 三聚氰胺的热稳定性也用热重-差示扫描量热(TG-DSC)法进行了分析, 确定其分解的DSC曲线的峰顶温度为603.37 K.     

Zintl‐Verbindungen mit Gold und Germanium: M3AuGe4 mit M = K,Rb und Cs

Zintl‐Compounds with Gold and Germanium: M₃AuGe₄ with M = K, Rb, Cs Black, brittle single crystals of M₃AuGe₄ with M = K, Rb, Cs were synthesized by reactions of alkali metal azides (MN₃) with gold sponge and germanium powder at T = 1120 K. The structures of the compounds (space group Pmmn, Z = 2, K₃AuGe₄: a = 6.655(1)Å, b = 11.911(2)Å, c = 6.081(1)Å; Rb₃AuGe₄: a = 6.894(1)Å, b = 12.421(1)Å, c = 6.107(1)Å; Cs₃AuGe₄: a = 7.179(1)Å, b = 12.993(2)Å, c = 6.112(2)Å) were determined from X‐ray single‐crystal diffractometry data. The semiconducting compounds contain equation/tex2gif-stack-2.gif[AuGe₄]‐chains with P₄‐analogous Ge₄‐tetrahedra which are connected by μ₂‐bridging gold atoms in a distorted tetrahedral Ge‐coordination.     

Thermo‐analytical Investigations on the Superoxides AO2 (A = K,Rb, Cs), Revealing Facile Access to Sesquioxides A4O6

Rb₄O₆ and Cs₄O₆ represent open shell p electron systems, featuring charge, spin, orbital and structural degrees of freedom, which makes them unique candidates for studying the ordering processes related, otherwise exclusively encountered in transition metal based materials. Probing the physical responses has been restrained by the intricacy of synthesizing appropriate amounts of phase pure samples. Tracing the thermal decomposition of respective superoxides has revealed that at least the rubidium and cesium sesquioxides exist in thermodynamic equilibrium, appropriate p‐T conditions given. These insights have paved the way to highly efficient and convenient access to Rb₄O₆ and Cs₄O₆.     

Evidence of Multiple Phase Transitions in Single-crystalline CuO by DSC Heat Capacity Measurement

Heat capacity measurements were carried out on single-crystalline CuO in the temperature range 130–300 K. Sharp peaks corresponding to the antiferromagnetic transitions were clearly observed at 211 and 227 K. At the low-temperature end, near 160 K, a wide peak in the heat capacity signal was also demonstrated. An electric anomaly was observed in the temperature range 150–160 K, which strongly suggests the possibility of a new low-temperature phase transition in CuO. This study also indicates that DSC measurement is an effective tool to detect magnetic transitions and probe subtle phase transitions in solids.This revised version was published online in November 2005 with corrections to the Cover Date.