X-ray photoelectron spectroscopy of alkaline earth metal uranate complexes

Summary X-ray photoelectron spectra for MgUO_4–x, MgU₃O_8.9, CaUO_4–x, Ca₂UO₅, Ca₃UO₆, Ca₂U₃O₁₁, CaU₂O₇, CaU₄O₁₂, SrUO₄, SrUO_3.67, Sr₂U₃O₁₁, SrU₄O_12.8, Sr₂UO₅, Sr₃UO₆, BaUO₄, Ba₃UO₆, BaU₂O₇, Ba₂U₂O₇ and Ba₂U₃O₁₁ have been recorded.Recorded O(1s) peak positions range from 529.5 to 533.4 eV and certain trends can be related to data obtained from other studies. By contrast, the range of U(4f) peak positions is much smaller totalling 0.7 eV. All compounds show satellite structure to the high binding energy side of the U(4f) peaks. Satellites separated byca. 10 eV from the main peaks are assigned to a transition from the uranium-oxygen bonding band to the U(6d) conduction band.     

Heavy Grignard reagents: challenges and possibilities of aryl alkaline earth metal compounds

Compounds of the type aryl--M--X, with M=Ca, Sr, Ba and X as any kind of ligand (such as halide, phosphanide, amide, aryl), are presented. The low reactivity of the heavy alkaline earth metals calcium, strontium, and barium enforces an activation prior to use for the direct synthesis. The insertion of these metals into C--I bonds of aryl iodides (direct synthesis) yields aryl metal iodides and has to be performed at low temperatures and in THF. Aryl alkaline-earth-metal compounds show some characteristics: 1) the ease of ether cleavage enforces low reaction temperatures, 2) for Sr and Ba the Schlenk equilibrium is shifted towards homoleptic MI2 and MPh2, 3) high solubility of diaryl alkaline-earth-metal derivatives in THF even at low temperatures initiated quantum chemical investigations on the aggregation behavior, and 4) a strong low field shift of the 13C resonances of the ipso carbon atoms in NMR spectra was observed. First results from quantum chemical calculations on diaryl dicalcium(I) suggest a long Ca--Ca bond with a considerable Ca--Ca bond dissociation energy. Initial results on a selection of applications such as metallation, metathesis, and addition reactions of aryl calcium compounds are presented as well.     

Basicities of alumina-supported alkaline earth metal oxides

A series of alumina-supported alkaline earth metal oxide catalysts were prepared by incipient-wetness impregnation. These catalysts were characterized by nitrogen-sorption to determine their surface areas and pore size distributions. The basicities of these catalysts were characterized by temperature-programmed desorption of carbon dioxide. The TPD results demonstrate that all of the catalysts have one-peak profiles. The basicity increases with increasing atomic number of the alkaline earth metal. The alumina-supported alkaline earth oxides exhibit the same basic properties as bulk metal oxides. However, the presence of alumina can increase the mechanical strength of the catalyst, since the alkaline earth oxides have a weak mechanical strength. The basic properties of the catalysts are strongly influenced by the calcination temperature.     

Electronic polarization spectroscopy of metal phthalocyanine chloride compounds in superfluid helium droplets

We report the electronic polarization spectroscopy of two metal phthalocyanine chloride compounds (MPcCl, M=Al,Ga) embedded in superfluid helium droplets and oriented in a dc electric field. For both compounds, the laser induced fluorescence spectra show preference for perpendicular excitation relative to the orientation field. This result indicates that the permanent dipoles of both compounds are predominantly perpendicular to the transition dipole. Since the permanent dipole derives from the metal chloride, while the transition dipole derives from the phthalocyanine chromophore, in the plane of phthalocyanine, this qualitative result is not surprising. However, quantitative modeling reveals that this intuitive model is inadequate and that the transition dipole might have tilted away from the molecular plane of phthalocyanine. The out of plane component of the transition dipole amounts to approximately 10% if the permanent dipole is assumed to be approximately 4 debye. The origin for this tilt is puzzling, and we tentatively attribute it to the transition of nonbonding orbitals, either from the chlorine atom or from the bridge nitrogen atom, to the pi* orbitals of the phthalocyanine chromophore. On the other hand, although unlikely, we cannot completely exclude the possibility that both our high level density functional theory calculation and ab initio results severely deviate from reality. The droplet matrix induces redshifts in the origin of the electronic transition and produces discrete phonon wings. Nevertheless, in dc electric fields, all phonon wings and the zero phonon line demonstrate the same dependence on the polarization direction of the excitation laser. Although electronic excitation does couple to the superfluid helium matrix and the resulting phonon wings add complications to the electronic spectrum, this coupling does not affect the direction of the electronic transition dipole. Electronic polarization spectroscopy in superfluid helium droplets is thus still informative in revealing the permanent dipole and its relation relative to the transition dipole.     

Fission of multiply charged alkaline earth metal clusters

We have studied the fission of multiply photoionized alkaline earth metal clusters having charges up to Z = +5 by means of high-resolution time-of-flight mass spectrometry. The determined appearance sizes can be compared to results of simple model calculations assuming that both fragments can still be treated as metallic liquid droplets. In this case the measured appearance sizes for the alkaline earth metals are found to be smaller than the ones predicted by the calculations. However, if one fixes the small fragment to be an atomic ion, good agreement between measurement and theory is acheived.     

The thermal decomposition of alkaline earth metal salicylates

The thermal decompositions of the salicylates of magnesium, calcium, strontium and barium were investigated using thermogravimetry and differential thermal analysis, together with the analysis of intermediate products formed during the decomposition processes. One intermediate product was isolated and identified during the decomposition of the magnesium salt, and two for each of the remaining metal salts.

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Zusammenfassung Die thermische Zersetzung der Salicylate von Magnesium, Calcium, Strontium und Barium sowie die Analyse der während des Vorganges gebildeten Zwischenprodukte wurden durch die thermogravimetrische und Differential-Thermal-Analyse untersucht. Im Verlaufe der Zersetzung des Magnesiumsalzes wurde ein Zwischenprodukt isoliert und identifiziert, bei den übrigen Metallsalzen je zwei.

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Résumé On a étudié par thermogravimétrie et analyse thermique différentielle la décomposition thermique des salicylates de magnésium, calcium, strontium et baryum et l'on a analysé les produits intermédiaires qui se forment pendant la décomposition. C'est ainsi que l'on a isolé et identifié un produit intermédiaire au cours de la décomposition du sel de magnésium et deux pour chacun des autres sels.

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Conductivity of alkaline earth metal soaps in methanol

The conductance of the solution of calcium, strontium and barium butyrates in methanol has been measured at 35–50 °C (± 0.05 °C) in order to determine the CMC, dissociation constant, molecular conductance at infinite dilution, and thermodynamic parameters viz. enthalpy, free energy, entropy changes for both dissociation and association processes. The results show that these soaps behave as a weak electrolyte in methanol and Debye-Huckel-Onsager's equation is not applicable to the solutions of these soaps.     

Thermal stability of alkali metal borates and alkaline earth metal borates

The correlation between the enthalpies of formation of alkali metal and alkaline earth metal borates and the composition of the vapor in equilibrium with their melts is considered. The thermal stabilities of the studied borates have been estimated. A method is suggested for determination of the relative composition of the vapor over borate melts on the basis of their enthalpies of formation.

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Zusammenfassung Es wurde die Beziehung zwischen den Bildungsenthalpien von Alkali- (Erdalkali-)metallboraten und der Zusammensetzung der sich mit der Schmelze im Gleichgewicht befindlichen Gasphase betrachtet. Die thermische Stabilität der untersuchten Borate wurde geschätzt. Es wurde ein Verfahren entwickelt, die relative Zusammensetzung der Gasphase über Boratschmelzen auf Grund ihrer Bildungsenthalpien zu bestimmen.

     

X-ray absorption spectroscopy of rare earth intermediate oxides

The M_IV–V and L_III absorption spectra (between 850 and 7500 eV) of intermediate rare earth oxides (Pr₇O₁₂ and Pr₉O₁₆) were studied. These oxides required careful preparation and handling in order to assure their composition.The spectra are characterized by multiplet features that are interpreted as having contributions from both trivalent and tetravalent sites. In the M_IV–V spectra the appearance of distinct multiplet lines and additional weaker features demonstrate clearly the increasing ratio of the tetravalent sites as the oxygen content increases from Pr₇O₁₂ to PrO₂. Similar behavior has been observed for the CeO_x and TbO_x systems. These observations show that in these oxides, the trivalent and tetravalent sites are inequivalent and that the evidence of valence transition is seen in the appearance of the complex spectral features originating from the tetravalent sites.     

Homoleptic alkaline earth metal bis(trifluoromethanesulfonyl)imide complex compounds obtained from an ionic liquid

The first homoleptic alkaline earth bis(trifluoromethanesulfonyl)imide (Tf2N) complexes [mppyr]2[Ca(Tf2N)4], [mppyr]2[Sr(Tf2N)4], and [mppyr][Ba(Tf2N)3] were crystallized from a solution of the respective alkaline earth bis(trifluoromethanesulfonyl)imide and the ionic liquid [mppyr][Tf2N] (mppyr = 1,1-N-methyl-N-propylpyrrolidinium). In the calcium and strontium compounds, the alkaline earth metal (AE) is coordinated by four bidentately chelating Tf2N ligands to form isolated (distorted) square antiprismatic [AE(Tf2N)4]2- complexes which are separated by N-methyl-N-propylpyrrolidinium cations. In contrast, the barium compound, [mppyr][Ba(Tf2N)3], forms an extended structure. Here the alkaline earth cation is surrounded by six oxygen atoms belonging to three Tf2N- anions which coordinate in a bidentate chelating fashion. Three further oxygen atoms of the same ligands are linking the Ba2+ cations to infinite (infinity)(1)[Ba(Tf2N)3] chains.     

Electronic second hyperpolarizability of alkaline earth metal chains end capped with −NH2 and –CN

A comparative study of the electronic structure and second hyperpolarizability has been performed by considering alkaline earth metal-bridged chains (Be_n, Mg_n, Ca_n) end capped with NH₂ and CN groups. For the sake of comparison of the calculated second hyperpolarizability, analogous molecular species H₂N−(CC)_n−CN has also been included in the present investigation. Since the metal-metal interactions are weaker, the dispersion corrected DFT methods are employed to calculate the stability of the investigated species. Similar to the conventional donor-π-acceptor system, the longitudinal component of first- and second-hyperpolarizabilities of Mg and Ca chains increases on increasing the chain length. The highest γ_zzzz value of Mg and Ca chains (n ​= ​7) are found to be in the order 10⁷ au and 10⁸ au, respectively. Both transition moment and transition energy associated with the crucial electronic transition play a significant role in the variation of second hyperpolarizability.     

Membrane extraction of alkaline earth metal by phosphorylated azapodands

ABSTRACT

Membrane transport properties of the new lipophilic phosphorylated azapodands toward Сa(II), Ва (II), Mg(II), and Sr(II) were studied. The investigation of the processes of passive membrane ion transport showed the high values of the transfer flow of the alkaline earth metals’ ions with all carriers. It was found that N,N’-bis(di-p-tolylphosphorylmethyl)-1,8-diamino-3,6-dioxaoctane (I) is the most effective carrier among all compounds studied.     

Heterogeneity of surface colour centres on alkaline earth metal oxides as revealed through EPR/ENDOR spectroscopy

A variety of surface anion vacancies, or point defects, are created by high‐temperature activation of a series of polycrystalline alkaline earth metal oxides (MgO, CaO and SrO). Subsequent UV irradiation of the activated oxide under a hydrogen atmosphere results in the generation of surface colour centres [F_S⁺(H)], by electron trapping at these anion vacancies. The paramagnetic properties of these colour centres were studied by EPR and ENDOR spectroscopy. ¹H ENDOR spectroscopy revealed that a well defined heterogeneity of trapped electron species exists on each oxide surface, as characterized by the different superhyperfine couplings between the trapped electron and the nearby proton of the F_S⁺ (H) centre. On MgO and CaO two dominant F_S⁺ (H) centres were identified (labelled sites I and II) whereas on SrO three F_S⁺ (H) species were found (sites I, II and III). The possible surface sites responsible for electron stabilization are discussed, and include a 3C corner mono‐vacancy, a 4C mono‐vacancy and an anion–cation di‐vacancy. The results indicate that regardless of the oxide used, a common degree of morphological similarities exists on each oxide. Copyright © 2002 John Wiley & Sons, Ltd.     

Kinetics of the thermal decomposition of alkaline earth metal hydrofluorides

The thermal stability of alkaline earth metal hydrofluorides was studied by means of a Derivatograph. The values of the activation energy, reaction order and rate constant were determined. The comparison of the kinetic parameters of the decomposition process for the complete series of hydrofluorides studied led to a certain regularity in the differences in their thermal stabilities and its correlation with the strength of the hydrogen bond in their structure.

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Zusammenfassung Die thermische Stabilität von Erdalkalihydrofluoriden wurde mit Hilfe eines Derivatographen untersucht, die Werte der Aktivierungsenergien, der Reaktionsordnung und der Geschwindigkeitskonstanten bestimmt. Der Vergleich der kinetischen Parameter des Zersetzungsvorganges wies auf eine gewisse Regelmäßigkeit in ihrer verschiedenen thermischen Stabilität, die in Zusammenhang mit der Stärke ihrer strukturalen Wasserstoffbindung steht.

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Résumé On a étudié la stabilité thermique des hydrogénofluorures des métáux alcalinoterreux et déterminé les valeurs des énergies d'activation, des ordres de réaction et des constantes de vitesse de réaction à l'aide d'un Dérivatographe. Après comparaison des paramètres cinétiques on a pu établir une certaine régularité dans le changement de la stabilité thermique en corrélation avec la force de liaison de l'hydrogène dans la structure.

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Effects of alkaline earth metal ion complexation on amino acid zwitterion stability: results from infrared action spectroscopy

The structures of isolated alkaline earth metal cationized amino acids are investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and theory. These results indicate that arginine, glutamine, proline, serine, and valine all adopt zwitterionic structures when complexed with divalent barium. The IRMPD spectra for these ions exhibit bands assigned to carboxylate stretching modes, spectral signatures for zwitterionic amino acids, and lack bands attributable to the carbonyl stretch of a carboxylic acid functional group. Structural and spectral assignments are strengthened through comparisons with absorbance spectra calculated for low-energy structures and the IRMPD spectra of analogous ions containing monovalent alkali metals. Many bands are significantly red-shifted from the corresponding bands for amino acids complexed with monovalent metal ions, owing to increased charge transfer to divalent metal ions. The IRMPD spectra of arginine complexed with divalent strontium and barium are very similar and indicate that arginine adopts a zwitterionic form in both ions. Calculations indicate that nonzwitterionic forms of arginine are lowest in free energy in complexes with smaller alkaline earth metal cations and that zwitterionic forms are preferentially stabilized with increasing metal ion size. B3LYP and MP2 calculations indicate that zwitterionic forms of arginine are lowest in free energy for M = Ca, Sr, and Ba.