Thermal stability of alkali metal bifluorides

The thermal stability and non-isothermal kinetics of the decomposition of alkali metal bifluorides were studied using a derivatograph. The removal of hydrogen fluoride from LiF · HF and NaF · HF takes place before melting and their decomposition occurs in a single stage; however, potassium, rubidium and cesium bifluorides at first undergo polymorphous transformation and melting on heating, and their decomposition proceeds stepwise. The thermal stability of alkali metal bifluorides has been found to increase with increasing ionic radius of the cation, reflecting its correlation with the hydrogen bond strength in these compounds.

---

Zusammenfassung Es wurde die thermische Stabilität und die nichtisotherme Kinetik der Zersetzung der Alkalibifluoride thermogravimetrisch untersucht. HF entweicht aus LiF · HF und NaF · HF vor dem Schmelzen in einer Stufe. Bei den entsprechenden Salzen des Kaliums, Rubidiums und Cäsiums erfolgt zuerst eine polymorphe Umwandlung, danach das Schmelzen, wobei die Zersetzung in mehreren Stufen vor sich geht. Die thermische Stabilität der Verbindungen wächst mit zunehmenden Ionenradien, was auf die entsprechende Stärke der Wasserstoffbindung zurückgeführt werden kann.

---

Résumé Etude thermogravimétrique de la stabilité thermique de fluorhydrates de métaux alcalins et de la cinétique de leur décomposition en conditions non isothermes. Dans le cas de LiF · HF et de NaF · HF, le départ de l'acide fluorhydrique se produit avant la fusion et la décomposition s'effectue en une seule étape. Par contre, les fluorhydrates de potassium, rubidium et césium subissent une transition cristalline et une fusion avant de se décomposer. On observe que la stabilité thermique des fluorhydrates de métaux alcalins augmente avec le rayon ionique du cation et l'on montre qu'elle peut être reliée à la force de la liaison hydrogène dans ces composés.

---

. LiF · HF NaF · HF , , , . , , .

     

Tetraphenylborate salts of alkali and alkaline earth metal complex cations

An introductory review summarises complex formation between poly(alkyleneoxy) adducts and inorganic salts. This is followed by preparative and IR and NMR spectroscopic features of the tetraphenylborates of complexes of polyethylene glycols, nonylphenoxy(polyethyleneoxy)ethanols and polypropylene glycols with sodium, magnesium, calcium, strontium and barium ions. Generally, an alkylene oxide:cation ratio of 8.5:1 is indicated for the complexes with sodium, and 12:1 (∼10.5:1 for the polyethylene glycols)_for the complexes with the alkaline earth metals.     

Modification of sulfonated polyphenylquinoxaline by alkali and alkaline earth metal cations

Salts of sulfonated polyphenylquinoxaline (SPPQ) containing alkaline earth metal ions—Mg²⁺, Ca²⁺, and Ba²⁺—were synthesized. The paper considers their solubilities, the properties of solutions, and thermal stability in comparison with analogous characteristics of SPPQ salts with alkali metals. The introduction of alkaline earth metal cations into SPPQ affords soluble polymeric salts having high thermal stability. Solutions of SPPQ salts in N-methylpyrrolidone (N-MP) containing Mg²⁺, Ca²⁺, and Ba²⁺ ions do not exhibit polyelectrolyte properties, unlike solutions of SPPQ salts in which the counterions are Li⁺, Na⁺, and K⁺. Solutions of SPPQ and its salts in N-MP can be converted to water-soluble form by dialysis. This opens up new prospects for using the polymeric salts.     

Tuning aromaticity in trigonal alkaline earth metal clusters and their alkali metal salts

In this work, we analyze the geometry and electronic structure of the [X_nM₃]^n?2 species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo‐[M₃]^2? unit. The cyclo‐[M₃]^2? ring is held together through a three‐center two‐electron bond of σ‐character. Interestingly, the interaction of these small clusters with alkali metals stabilizes the cyclo‐[M₃]^2? ring and leads to a change from σ‐aromaticity in the bound state of the cyclo‐[M₃]^2? to π‐aromaticity in the XM₃^? and X₂M₃ metallic clusters. Our results also show that the aromaticity of the cyclo‐[M₃]^2? unit in the X₂M₃ metallic clusters depends on the nature of X and M. Moreover, we explored the possibility for tuning the aromaticity by simply moving X perpendicularly to the center of the M₃ ring. The Na₂Mg₃, Li₂Mg₃, and X₂Ca₃ clusters undergo drastic aromaticity alterations when changing the distance from X to the center of the M₃ ring, whereas X₂Be₃ and K₂Mg₃ keep its aromaticity relatively constant along this process. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Automatic ion-exchange chromatograph for analysis of alkali and alkaline earth metal mixtures

A new automatic chromatograph for ultramicro determination of alkali and alkaline earth metals has been developed. It combines a high-sensitivity hydrogen flame-ionization detector with ion-exchange chromatography. Zirconium phosphate was chosen as ion-exchanger.     

Thermal studies and decomposition kinetics of alkaline earth metal trichloroacetates

Alkaline earth metal trichloroacetates M(O₂CCCl₃)₂·nH₂O, where M = Be (1), n = 4; M = Mg (2), n = 6; M = Ca (3) or Sr (4) or Ba (5), n = 4, were synthesized and their thermal behavior analyzed using thermogravimetric analysis (TG/DTG/DSC). A critical examination was made for the apparent activation energy by means of non-isothermal kinetic methods employing multiple heating rates. A systematic and comparative study of thermal decomposition was carried out at different heating rates i.e., 5, 10, 15, and 20 °C min^?1 for various trichloroacetates synthesized. It was observed that the Ca, Sr, and Ba trichloroacetates decompose preferentially to respective metal halides while Be and Mg compounds decompose to metal and metal oxide, respectively. The composition of the final residues was also confirmed using FT-IR spectroscopy. The activation energy follows the order: Mg > Ca > Sr > Ba, Be being the exception. Results reveal that each metal trichloroacetate decomposes through its unique thermolysis mechanism.     

Calorimetric study of vitreous and crystalline alkali metal borates

The enthalpies of solution in 2 N nitric acid at 298 K were measured for alkali metal borate glasses and crystals. From the data obtained, their enthalpies of formation from the oxides and the heats of crystallization of the glasses were calculated.The negative deviation from ideality observed in alkali metal borate systems is interpreted in terms of the acid-base interaction of their components. The heats of crystallization of the glasses appeared to be mainly determined by the ordering effect of the boron-oxygen network. The contents of different borate groupings in the glasses studied were estimated. The structures of the borate glasses are discussed.

---

Zusammenfassung Für Alkaliborat-Gläser und Kristalle wurden die Lösungsenthalpien in 2N Salpetersäure bei 298 K gemessen. Daraus wurden die Enthalpien der Bildung aus den Oxiden sowie die Kristallisationswärmen der Gläser berechnet. Die negativen Abweichungen der Bildungsenthalpien vom idealen Verhalten werden als Resultat der Säure-Base-Umsetzung der Oxide gedeutet. Die Kristallisationswärmen der Gläser scheinen im wesentlichen von ordnungsvorgängen des Bor-Sauerstoff-Netzwerks bestimmt zu scin. Der Gehalt der Gläser an den verschiedenen Boratgruppen wird abgeschätzt und die Struktur der Boratgläser diskutiert.

---

298 2 . . , - . . .

     

Dissociation of alkali metal borates and acid-base interactions in oxide systems

The stability relative to decomposition to oxides has been estimated for alkali metal borates M₂O·_nB₂O₃(M=Li, Na, K, Rb and Cs), wheren=1,2,3 and 4. The correlation between the degrees of dissociation and the enthalpies of formation is discussed.

---

Zusammenfassung Es wurde die relative Stabilität von Alkalimetallboraten der Formel M₂O·nB₂O₃ mitM=Li, K, Rb, Cs undn= 1, 2, 3, 4 gegenüber der der Oxide ermittelt. Der Zusammenhang von Dissoziationsgrad und Bildungsenthalpie wird besprochen.

---

M₂O·nB₂O₃, M=, , , , =1–4, . .

     

Electrospray ionization of alkali and alkaline earth metal species. Electrochemical oxidation and pH effects

The utility of electrospray ionization mass spectrometry (ESI-MS) for characterizing dissolved metal species has generated considerable interest in the use of this technique for metal speciation. However, the development of accurate speciation methods based on ESI-MS requires a detailed understanding of the mechanisms by which dissolved metal species are ionized during electrospray. We report how the analysis of alkali and alkaline earth metal species provides new information about some of the processes that affect electrospray ion yield. Selected metal ions and organic ligands were combined in 50 : 50 water-acetonitrile buffered with acetic acid or ammonium acetate and analyzed by flow injection ESI-MS using mild electrospray conditions. Species formed by alkali metal ions with thiol and oxygen-donating ligands were detected in acidic and neutral pH solutions. Electrochemical oxidation of N, N-diethyldithiocarbamate and glutathione during electrospray was indicated by detection of the corresponding disulfides as protonated or alkali metal species. The extent of ligand oxidation depended on solution pH and the dissociation constant of the thiol group. Tandem mass spectrometric experiments suggested that radical cations such as [NaL](+.) (where L=N,N-diethyldithiocarbamate) can be generated by in-source fragmentation of disulfide species. Greater complexation of alkali metals at neutral pH was indicated by a corresponding decrease in the relative abundance of the free metal ion. The number of alkali metal ions bound by glutathione and phthalic acid also increased with increasing pH, in accordance with thermodynamic equilibrium theory. Alkaline earth metal species were detected only in acidic solutions, the absence of 8-hydroxyquinoline complexes being attributed to their relative instability and subsequent dissociation during electrospray. Hence, accurate speciation by ESI-MS depends on experimental conditions and the intrinsic properties of each analyte. Copyright 2000 John Wiley & Sons, Ltd.     

Ion solvation of aqueous solutions of alkali, alkaline earth, and transition metal halides

The published data on the density and velocity of ultrasound are used to determine the ion solvation parameters of sodium, magnesium, and cobalt chlorides. It is shown that the solvation of typical coordination compounds, such as cobalt chloride, is determined by the same underlying systems and interactions as that of electrolytes with ions of alkali and alkaline earth metals.     

Selectivity of potassium cobalt hexacyanoferrate (II) for alkali and alkaline earth metal ions

The distribution coefficients for alkali and alkaline earth metal ions on potassium cobalt hexacyanoferrate (II), K₂CoFe(CN)₆×1.4H₂O, show high selectivity for cesium. The uptake values of the ions vary widely. The uptake is most probably an ion exchange process.     

Weak alkali and alkaline earth metal complexes of low molecular weight ligands in aqueous solution

This work is aimed at reviewing the chemical literature dealing with thermodynamic aspects of the weak complex formation (species with log K values less than about 3) between alkali and alkaline earth metal ions with low molecular weight inorganic and organic ligands in aqueous solution. The following ligands (up to hexavalent anions) were examined in detail: (i) hydroxide, chloride, sulfate, carbonate and phosphate as inorganic, and (ii) carboxylates, amines, amino acids, complexones and nucleotides as organic ligands. The paper also identifies the main reasons responsible for the dispersion of the stability data on ion pairs in the literature. When possible, the trend of stability for the different metal ions interacting with the same ligand will be considered to find predictive interaction relationships. Since the stability of weak alkali and alkaline earth metal complexes are mainly due to electrostatic interaction, simple empirical relationships were obtained between log K and the charge of the anionic ligand. The interest for alkali and alkaline earth cations rises since they are used in study of basic science as components of the supporting electrolyte and are widely diffused in natural fluids. Some examples of application of this science were presented too, to show the role of weak complex formation in the modelling process of natural systems.     

Thermal effects of solvation processes on alkali metal alcoxide formation and stability

The formation of alkali metal alcoxides by an alcohol reacting on the elemental metal itself cannot be completed under stoichiometric conditions. As a consequence of solvation, the chemical activity of the reacting alcohol is drastically reduced. Thus, the reaction cannot undergo completion without a large excess of alcohol with respect to the alkali metal. Moreover, solvation processes can drop the reaction kinetics down to nearly zero. When an excess of alkali metal is reacted with alcohol, the heat accumulated by solvation can be suddenly released by an addition of pure alcohol. Extremely dangerous thermal runaways can be started this way. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fluorometric sensing of alkali metal and alkaline earth metal cations by novel photosensitive monoazacryptand derivatives in aqueous micellar solutions

Novel monoazacryptand-type fluorescent chemosensors, (derived from an 18-crown-6) and (derived from a 15-crown-5) both with a pyrene ring as their photoresponsive moiety, were synthesized. Their fluorescence properties for alkali metal and alkaline earth metal cations in water were then examined. The detection of metal cations was accomplished by a change in the fluorescence intensity of the host compounds, based on a photoinduced electron transfer (PET) mechanism. In aqueous solution, showed little fluorescence upon the addition of Ba2+ because of the very weak complexation with Ba2+, but the presence of micelles of polyoxyethylene(10) isooctylphenyl ether (Triton X-100) enabled to show highly sensitive and selective Ba2+ detection among alkali metal and alkaline earth metal cations. With respect to the selective fluorescent detection of important metal cations (Na+, K+, Mg2+, Ca2+) relevant to living organisms, was found to detect K+ with high selectivity in aqueous micellar solutions of polyoxyethylene(20) sorbitan monostearate (Tween-60). The selectivity for metal cations was mainly dependent on the goodness of fit of the host cavity and the metal cation size. In the presence of anionic surfactants, detected alkaline earth metal cations more effectively than alkali metal cations.     

Thermochemistry of 18C6 complexation with alkali,alkaline earth metal cations and ammonium ion

The object of the present study is to examine the factors governing the process of 18C6 complexation in aqueous solution by interpreting of thermodynamic parameters of the reaction in terms of observed selectivity and solvation characteristics under various temperature conditions.     

Solvent‐free alkali and alkaline earth metal complexes of di‐imine ligands

Compound [(dph‐BIAN)Mg(THF)]₂ ( 2 ) was prepared by reacting magnesium metal with 1,2‐bis[(2‐biphenyl)imino]acenaphthene (dph‐BIAN) in THF, followed by crystallization from toluene. Reaction of CaI₂ with (dpp‐BIAN)Li₂ in toluene afforded [(dpp‐BIAN)Li]₂Ca ( 3 ) (dpp‐BIAN = 1,2‐bis[(2,6‐diisopropylphenyl)imino]acenaphthene). Both complexes 2 and 3 were characterized by single crystal X‐ray diffraction. The ¹H NMR spectroscopic data obtained for complex 3 in toluene solution indicated an agostic interaction between the methyl groups of the ligand and lithium atoms. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:663–670, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20168     

Ultrafine Na-4-mica: uptake of alkali and alkaline earth metal cations by ion exchange

The cation exchange properties of alkali and alkaline earth metal cations at room temperature were investigated on an ultrafine, highly charged Na-4-mica (with the ideal mica composition Na4Mg6Al4Si4O20F4.xH2O). Ultrafine mica crystallites of 200 nm in size led to faster Sr2+ uptake kinetics in comparison to larger mica crystallites. The alkali metal ion (K+, Cs+, and Li+) exchange uptake was rapid, and complete exchange occurred within 30 min. For the alkaline earth metal ions Ba2+, Ca2+, and Mg2+, however, the exchange uptake required lengthy periods from 3 days to 4 weeks to be completed, similar to its Sr uptake, as previously reported. Kinetic models of the modified Freundlich and parabolic diffusion were examined for the experimental data on the Ba2+, Ca2+, and Mg2+ uptakes. The modified Freundlich model described well the Ba2+ ion uptake kinetics as well as that for the Sr2+ ion, while for the Ca2+ and Mg2+ ions the parabolic diffusion model showed better fitting. The alkali and alkaline earth ion exchange isotherms were also determined in comparison to the Sr2+ exchange isotherm. The thermodynamic equilibria for these cations were compared by using Kielland plots evaluated from the isotherms.