The Valence Orbitals of the Alkaline-Earth Atoms

Quantum chemical calculations of the alkaline-earth oxides, imides and dihydrides of the alkaline-earth atoms (Ae=Be, Mg, Ca, Sr, Ba) and the calcium cluster Ca₆H₉[N(SiMe₃)₂]₃(pmdta)₃ (pmdta=N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) have been carried out by using density functional theory. Analysis of the electronic structures by charge and energy partitioning methods suggests that the valence orbitals of the lighter atoms Be and Mg are the (n)s and (n)p orbitals. In contrast, the valence orbitals of the heavier atoms Ca, Sr and Ba comprise the (n)s and (n−1)d orbitals. The alkaline-earth metals Be and Mg build covalent bonds like typical main-group elements, whereas Ca, Sr and Ba covalently bind like transition metals. The results not only shed new light on the covalent bonds of the heavier alkaline-earth metals, but are also very important for understanding and designing experimental studies.     

Extraction liquide-liquide par des esters alkylphosphoriques. II. Extraction des nitrates de béryllium et des autres alcalino-terreux par le tri-n-butylphosphate

The solvent extraction systems Be(NO₃)₂? HNO₃? H₂O? TBP/kerosene and M(NO₃)₂? H₂O? TBP/kerosene (TBP = tri-n-butylphosphate, M = Be, Mg, Ca and Sr) have been studied. The alkaline earths elements are poorly extracted. Only very high acidities allow better extraction of beryllium. The sequence of extraction of the alkaline earths elements by the TBP depends on the concentration of the cations and is Ca > Be > Sr > Mg if the metal concentration is lower than 2 M.     

Hierarchical Modulation of Optical Anisotropy Driven by Metal Cation Polyhedra in Fluorooxoborates MIIB4O6F2 (MII=Be,Mg, Pb,Zn, Cd)

The enhancement mechanism of birefringence is very important to modulate optical anisotropy and materials design. Herein, the different cations extending from alkaline-earth to alkaline-earth, d¹⁰ electron configuration, and 6s² lone pair cations are highlighted to explore the influence on the birefringence. A flexible fluorooxoborate framework from AEB₄O₆F₂ (AE=Ca, Sr) is adopted for UV/deep-UV birefringent structures, namely, M^IIB₄O₆F₂ (M^II=Be, Mg, Pb, Zn, Cd). The maximal enhancement on birefringence can reach 46.6 % with the cation substitution from Ca, Sr to Be, Mg (route-I), Pb (route-II), and Zn, Cd (route-III). The influence of the cation size, the stereochemically active lone pair, and the binding capability of metal cation polyhedra is investigated for the hierarchical improvement on birefringence. Significantly, the BeB₄O₆F₂ structure features the shortest UV cutoff edge 146 nm among the available anhydrous beryllium borates with birefringence over 0.1 at 1064 nm, and the PbB₄O₆F₂ structure has the shortest UV cutoff edge 194 nm within the reported anhydrous lead borates that hold birefringence larger than 0.1 at 1064 nm. This work sheds light on how metal cation polyhedra modulate birefringence, which suggests a credible design strategy to obtain desirable birefringent structures by cation control.     

The Recently Synthesized Dimagnesiabutadiene and the Analogous Dimetalla‐Beryllium, ‐Calcium, ‐Strontium,and ‐Barium Compounds

The 2014 synthesis of the remarkable dimagnesium compound Mg₂[C₄(CH₃)₂(Si(CH₃)₃)₂](C₃H₇)₂(C₄H₈O)₂ may point the way to a new chapter in alkaline earth organometallic chemistry. Accordingly, we have studied the known Mg compound and the analogous Be, Ca, Sr, and Ba structures. Although most of our theoretical predictions come from density functional methods, the latter have been benchmarked using coupled cluster theory including single, double, and perturbative triplet excitations, CCSD(T) using cc‐pVTZ basis sets. Among our most important predictions are the energies for dissociation to the butadiene plus the RM?MR [R=(C₃H₇)₂(C₄H₈O)₂; M=Be, Mg, Ca, Si, and Ba] entities. The most reliable predictions for the dissociation energies are 99–104 (Be), 85–93 (Mg), 90–99 (Ca), 83–92 (Sr), and 83–94 (Ba) kcal mol^?1. Thus, there is reason to anticipate that the four unknown compounds should be achievable synthetically. The predicted metal–metal distances (not single bonds) are 2.89 Å (Mg???Mg), 3.46 Å (Ca???Ca), 3.75 Å (Sr???Sr), and 4.04 Å (Ba???Ba). The separated RM?MR compounds have longer M?M distances but genuine metal–metal single bonds. This perhaps counter intuitive result is due to the presence of the bridging carbons in the alkaline earth butadiene compounds. All five compounds incorporate metal–carbon ionic interactions.     

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.     

Endohedral and Exohedral Metalloborospherenes: M@B40 (M=Ca,Sr) and M&B40 (M=Be,Mg)

The recent discovery of the all‐boron fullerenes or borospherenes, D_2d B₄₀^?/0, paves the way for borospherene chemistry. Here we report a density functional theory study on the viability of metalloborospherenes: endohedral M@B₄₀ (M=Ca, Sr) and exohedral M&B₄₀ (M=Be, Mg). Extensive global structural searches indicate that Ca@B₄₀ ( 1 , C_2v, ¹A₁) and Sr@B₄₀ ( 3 , D_2d, ¹A₁) possess almost perfect endohedral borospherene structures with a metal atom at the center, while Be&B₄₀ ( 5 , C_s, ¹A′) and Mg&B₄₀ ( 7 , C_s, ¹A′) favor exohedral borospherene geometries with a η⁷‐M atom face‐capping a heptagon on the waist. Metalloborospherenes provide indirect evidence for the robustness of the borospherene structural motif. The metalloborospherenes are characterized as charge‐transfer complexes (M²⁺B₄₀^2?), where an alkaline earth metal atom donates two electrons to the B₄₀ cage. The high stability of endohedral Ca@B₄₀ ( 1 ) and Sr@B₄₀ ( 3 ) is due to the match in size between the host cage and the dopant. Bonding analyses indicate that all 122 valence electrons in the systems are delocalized as σ or π bonds, being distributed evenly on the cage surface, akin to the D_2d B₄₀ borospherene.     

Endohedral and Exohedral Metalloborospherenes: M@B40 (M=Ca,Sr) and M&B40 (M=Be,Mg)

The recent discovery of the all‐boron fullerenes or borospherenes, D_2d B₄₀^−/0, paves the way for borospherene chemistry. Here we report a density functional theory study on the viability of metalloborospherenes: endohedral M@B₄₀ (M=Ca, Sr) and exohedral M&B₄₀ (M=Be, Mg). Extensive global structural searches indicate that Ca@B₄₀ ( 1 , C_2v, ¹A₁) and Sr@B₄₀ ( 3 , D_2d, ¹A₁) possess almost perfect endohedral borospherene structures with a metal atom at the center, while Be&B₄₀ ( 5 , C_s, ¹A′) and Mg&B₄₀ ( 7 , C_s, ¹A′) favor exohedral borospherene geometries with a η⁷‐M atom face‐capping a heptagon on the waist. Metalloborospherenes provide indirect evidence for the robustness of the borospherene structural motif. The metalloborospherenes are characterized as charge‐transfer complexes (M²⁺B₄₀²⁻), where an alkaline earth metal atom donates two electrons to the B₄₀ cage. The high stability of endohedral Ca@B₄₀ ( 1 ) and Sr@B₄₀ ( 3 ) is due to the match in size between the host cage and the dopant. Bonding analyses indicate that all 122 valence electrons in the systems are delocalized as σ or π bonds, being distributed evenly on the cage surface, akin to the D_2d B₄₀ borospherene.     

ChemInform Abstract: Endohedral and Exohedral Metalloborospherenes: M@B40 (M: Ca,Sr) and M&B40 (M: Be,Mg).

A DFT study on the viability of the metalloborospherenes: endohedral M@B₄₀ (M: Ca, Sr) and exohedral M&B₄₀ (M: Be, Mg) is presented.     

Separation of alkaline earth elements by cation-exchange chromatography in ammonium malonate media

Be(II), Mg(II), Ca(II), Sr(II) and Ba(II) can be separated by elution from a cation-exchange column in the ammonium form with increasing concentrations of ammonium malonate. A typical elution sequence for a 60-ml column (volume in H⁺-form) of AG₅₀-X8 resin is: 200 ml of 0.20 N ammonium malonate plus 0.10 N malonic acid for Be(II); 300 ml of 0.50 N, 450 ml of 0.70 N, 350 ml of 1.10 N ammonium malonate for Mg(II), Ca(II) and Sr(II), respectively, and 200 ml of 3.0 N nitric acid for Ba(II). Separations are sharp and quantitative for element pairs in weight ratios from 1:1000 to 1000:1. Distribution coefficients, elution curves and quantitative separations are presented.     

Formation and Unimolecular Dehydrogenation of Gaseous Alkaline‐earth Metal Amidoboranes M(NH2BH3)2 (M = Be – Ba): Comparative Computational Study

Formation of alkaline‐earth metal amidoboranes M(NH₂BH₃)₂ (M = Be, Mg, Ca, Sr, Ba) and unimolecular dehydrogenation reactions were computationally studied at the B3LYP/def2‐TZVPPD level of theory. Formation of M(NH₂BH₃)₂ from ammonia borane and MH₂ is exergonic, but subsequent unimolecular dehydrogenation reactions are endergonic at room temperature. In contrast to alkali metal amidoboranes, for M(NH₂BH₃)₂ the nature of M significantly affects their reactivity. Activation energies for the dehydrogenation of first and second hydrogen molecules decrease from Be to Ba. In case of Be compounds, intramolecular M ··· H–B contacts play an important role, whereas for heavier analogs such contacts are much less pronounced.     

Medium-size Gaussian basis sets for hydrogen through argon

Summary Medium-sized Gaussian basis sets are reoptimized for the ground states of the atoms from hydrogen through argon. The composition of these basis sets is (4s), (5s), and (6s) for H and He, (9s5p) and (12s7p) for the atoms Li to Ne, and (12s8p) and (12s9p) for the atoms Na to Ar. Basis sets for the² P states of Li and Na, and the³ P states of Be and Mg are also constructed since they are useful in molecular calculations. In all cases, our energies are lower than those obtained previously with Gaussian basis sets of the same size.     

The behavior of xenon dynamic adsorption on granular activated carbon packed bed adsorber

In order to retard radioxenon release into the atmosphere from nuclear power station or to sensitively monitor its concentration to ensure environmental and human safety, it is necessary to know the behavior of xenon dynamic adsorption on granular activated carbon pack bed adsorber. The quantities, including the dynamic adsorption coefficient (k _d), the amount of xenon adsorbed (q), the length of mass transfer zone (L _MTZ) and the length of the unused bed (LUB), used to describe the adsorption behavior, were sorted out and calculated. The factors, including xenon concentrations, pressures and temperatures, to affect these quantities were investigated. The results show that: (1) The values of k _d and q decrease with increasing temperatures, but increase with increasing pressures, (2) The values of L _MTZ and LUB increase with increasing temperatures or pressures, but are independent of concentrations. Knowledge of these quantities is very helpful for packed bed adsorber operation.     

Alkaline earth metal salts of 1‐naphthoic acid

The structures of the Mg, Ca, Sr and Ba salts of 1‐naphthoic acid are examined and compared with analogous structures of salts of benzoate derivatives. It is shown that catena‐poly[[[diaquabis(1‐naphthoato‐κO)magnesium(II)]‐μ‐aqua] dihydrate], {[Mg(C₁₁H₇O₂)₂(H₂O)₃]·2H₂O}_n, exists as a one‐dimensional coordination polymer that propagates only through Mg—OH₂—Mg interactions along the crystallographic b direction. In contrast with related benzoate salts, the naphthalene systems are large enough to prevent inorganic chain‐to‐chain interactions, and thus species with inorganic channels rather than layers are formed. The Ca, Sr and Ba salts all have metal centres that lie on a twofold axis (Z′ = ) and all have the common name catena‐poly[[diaquametal(II)]‐bis(μ‐1‐naphthoato)‐κ³O,O′:O;κ³O:O,O′], [M(C₁₁H₇O₂)₂(H₂O)₂]_n, where M = Ca, Sr or Ba. The Ca and Sr salts are essentially isostructural, and all three species form one‐dimensional coordination polymers through a carboxylate group that forms three M—O bonds. The polymeric chains propagate via c‐glide planes and through MOMO four‐membered rings. Again, inorganic channel structures are formed rather than layered structures, and the three structures are similar to those found for Ca and Sr salicylates and other substituted benzoates.     

Theoretical insights into the properties of the XY≡YX...M<Superscript><Emphasis Type="Italic">n</Emphasis>+</Superscript> complexes (X = H,F, Cl; Y = C,Si; M = alkaline and alkaline earth metals)

The character of alkaline (M⁺= Li, Na, K) and alkaline earth metal ions (M²⁺= Be, Mg, Ca) interactions with disilyne and acetylene has been studied by using high-level ab initio computations. The interaction energies were calculated at MP2/6-311++G(2d,2p) level. These calculations show that the size and charge of cation are two significant factors that affect the character of interaction. AIM and NBO analyses of M ⁿ⁺...X₂Y₂ interactions specify that the variation of densities and the extent of charge transfers upon complexation correlate well with the obtained interaction energies.     

Theoretical studies of structures and stabilities of endohedral fullerenes X0/n+ @C32 (X = H,Li, Na,K, Be,Mg, Ca,B, Al,C, Si,N, P,n = 1–3)

Based on the D₃ C₃₂ fullerene, the equilibrium geometries, electronic structures, and binding energies of the endohedral fullerenes X^0/n+@C₃₂ (X = H, Li, Na, K, Be, Mg, Ca, B, Al, C, Si, N, P, n = 1–3) have been calculated using the DFT/B3LYP/6‐31G(d) method. The results show that the C₃₂ cages are slightly enlarged due to encapsulation, and the sizes of non‐neutral molecules are smaller than the corresponding neutral ones. Cages containing Li, Na, and Ca and most of the cations, except Na⁺ and K⁺, are energetically favorable. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Valence p functions for alkali and alkaline-earth atoms

Contracted Gaussian-type function (CGTF) basis sets are reported for valence p orbitals of the six alkali and alkaline-earth atoms Li, Be, Na, Mg, K, and Ca for molecular applications. These sets are constructed by Roothaan–Hartree–Fock calculations for the ns → np excited states of atoms, in which both linear and nonlinear parameters of CGTFs are variationally optimized. The present CGTF sets reproduce well the numerical Hartree–Fock ns → np excitation energies: the largest error is 0.0009 hartrees for Li. New CGTFs are tested with diatomic Li₂, Na₂, K₂, and MH molecules, where M = Li, Be, Na, Mg, K, and Ca, by self-consistent-field (SCF) and multiconfiguration SCF calculations. The resultant spectroscopic constants compare well with those of more elaborate calculations and are sufficiently close to experimental values, supporting the efficiency of the present set for the valence p orbitals. Received: 9 July 1998 / Accepted: 17 September 1998 / Published online: 1 February 1999     

A screened hybrid density functional study on energetic complexes: Alkaline-earth metal carbohydrazide perchlorates

The molecular geometries, electronic structures and stabilities of a series of alkaline-earth metal carbohydrazide perchlorates were investigated using the Heyd–Scuseria–Ernzerhof (HSE) screened hybrid density functional. The results show that Be and Mg complexes have six-coordinated octahedron features, as previously reported for the transition metal complexes. However, Ca, Sr and Ba complexes have additional coordinated oxygen atoms from the perchlorate ion. Detailed NBO analyses indicate that the metal–ligand interactions are essentially ionic and play an important role in the stabilities of these energetic complexes. The donor–acceptor interactions result in a reduction of occupancies of σ_C=O and σ_N–H bond orbitals, and also their subsequent impact on bond length and bond order.     

<Emphasis Type="Italic">Ab initio</Emphasis> structural study of M(mda)<Subscript>2</Subscript> complexes (M = Be,Mg, Ca; mda = C<Subscript>3</Subscript>O<Subscript>2</Subscript>H<Subscript>3</Subscript>)

The structure of M(mda)₂ (M = Be, Mg, Ca; mda = C₃O₂H₃) bis-complexes was investigated by the ab initio Hartree-Fock method and by including electron correlation in terms of second order Möller-Plesset perturbation theory; for calculations we used triple-zeta valence basis sets complemented with polarization functions. Two most probable geometrical nuclear configurations (D _2h and D _2d ) are considered for each molecule. The structure with two mutually orthogonal chelate ligands (D _2d symmetry) corresponds to the potential energy surface (PES) minimum. The planar D _2h configuration corresponds to the first order saddle point on PES; consequently, its relative energy determines the height of the barrier to the D _2d D _2h D _2d intramolecular rearrangement. Correlation equations that relate the calculated values of equilibrium internuclear distances, force constants, and rearrangement barrier heights to the value of the ionic radius of the metal atom have been obtained. These correlations were employed to evaluate the molecular constants for Sr(mda)₂ and Ba(mda)₂. The theoretical data are compared with the available experimental literature data.Original Russian Text Copyright © 2004 by V. V. Sliznev, S. B. Lapshina, and G. V. GirichevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 611–623, July–August, 2004This revised version was published online in April 2005 with a corrected cover date.     

Dispersion and polar contributions to surface tension of poly(methylene oxide) and Na-treated polytetrafluoroethylene

Average values for dispersion γ_s^d and polar γ_s^d contributions of the solid surface tension γ_s γ_s^d + γ_s^p for poly(methylene oxide) (PMO) and Na-treated polytetrafluoroethylene (PTFE) are determined by a new computational analysis of wettability data. PMO displays γ_s^d equals; 21.8 ± 0.9 and γ_s^p = 11.5 ± 1.5 dyn/cm while Na-treated PTFE displays γ_s^d = 36.1 ± 3.0 and γ_s^p = 14.5 ± 2.9 dyne/cm. These surfaces present the highest fractional surface polarity p_s = γ_s^p/γ_s = 0.29-0.35 yet encountered for organic polymers or oriented monolayers. These unusual surface tension properties are correlated with surface chemistry and adhesion phenomena.