Heavier Alkaline Earth Research Articles

Heavy Alkaline Earth Cyclic (Alkyl)(Amino)Carbene Complexes Supported by Aryl-Silyl Amides.

A series of 8 trigonal planar, heavy alkaline earth (AE = Ca-Ba) metal complexes containing cyclic (alkyl)(amino)carbene (CAAC) ligands were prepared from AE bis(amide) species. Complexation can be achieved by first generating the free carbene in situ or by direct addition of the free carbene, with the former route giving rise to unexpected mixed-amide AE complexes. The frontier molecular orbitals of the highly equatorial, 3-coordinate AE-CAAC species were also probed computationally, revealing the lowest unoccupied molecular orbital (LUMO) consisting predominantly of the π* system located on the carbene ligand.

Low-Temperature NH3-SCR Technology for Industrial Application of Waste Incineration: An Overview of Research Progress

Selective catalytic reduction of nitrogen oxides with NH3 (NH3-SCR) was investigated deeper and deeper with poisoning factors such as H2O, SO2, heavy metals, etc. In order to remove the reheating process before the SCR reactor, the application trend of NH3-SCR technology in the non-power industry is concentrated on the condition of low temperature even ultra-low temperature. The present study summarizes the research process of SO2 and H2O resistance of NH3-SCR catalysts under low temperatures related to the working conditions of municipal solid waste incineration plants. In detail, the effects of a high content of H2O and low concentration of SO2 are reviewed. Other factors such as heavy metals, alkali, or alkaline earth metals in the reaction system, synergistic removal of NOx, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are addressed. Finally, the catalytic performance of assembled monolithic catalysts and pilot-scale experiments are also analyzed for the possibility of industrial application. Hopefully, in view of the questions outlined in this study, valuable insights could be taken into consideration for the development of NH3-SCR in waste incineration.

Large 2π aromatic six-membered Al/In rings stabilized by transition-metal-like heavy alkaline earth metals

Density functional theory calculations revealed that four half-sandwich Ae(MH)6 (Ae = Sr or Ba; M = Al or In) complexes all feature large six-membered Al6/In6 rings with rare 2π aromaticity. Together with two Ca analogues, these six molecules all exhibit good thermodynamic and kinetic stabilities. Heavy Ca/Sr/Ba atoms can effectively stabilize the two hexagonal rings via both ionic and covalent interactions involving their ns, (n − 1)p and even (n − 1)d orbitals. Our work not only adds new members to the emerging 2π-aromatic ring family, but also demonstrates the critical role of the transition-metal-like behavior of Ca/Sr/Ba in stabilizing novel metalloaromatic ring structures.

Theoretical Study of Transition Metal Chemistry in Alkali Metal Complexes [K2M(COT)2]− (M=K, Rb, Cs)

AbstractThe transition metal properties of heavy alkaline earth metals have been extensively studied, and their neighbouring heavy alkali metals have been limited to the interactions with CO‐σ ligands. Based on this, the complexes [K2M(COT)2]− (M=K, Rb, Cs) interacting with heavy alkali metals and COT‐π ligands are theoretically designed in this paper. The electronic structure analysis showed that the three complexes had 10 occupied molecular orbitals (MOs), in which 8 of them were related to the atomic orbitals (AOs) of central alkali metals, including 4 d orbitals (dxy, dx2−y2, dxz, dyz), so they also exhibited the typical behaviors of transition metals. NBO analysis indicated that the central metals in these complexes are common valence of +1, the ligands are negative, so the electrostatic coulomb interaction between positive and negative ions makes them more stable. This can be reflected by the high binding energies of −585.8 to −594.0 kcal/mol, which are much higher than those of −6.5 to −63.3 kcal/mol for the trace amount of complexes combined by neutral metals and ligands. It would be a feasible strategy for the design of the macrosynthesis of related complexes by combining the positive ions and negative ligands, which can stabilize the complexes through the favorable Coulomb attractions.

Navigating through the coordination preferences of heavy alkaline earth metals: Laying the foundations for 223Ra- and 131/135mBa-based targeted alpha therapy and theranostics of cancer

The clinical success of [223Ra]RaCl2 (Xofigo®) for the palliative treatment of bone metastases in patients with prostate cancer has highlighted the therapeutic potential of α-particle emission. Expanding the applicability of radium-223 in Targeted Alpha Therapy of non-osseous tumors is followed up with significant interest, as it holds the potential to unveil novel treatment options in the comprehensive management of cancer. Moreover, the use of barium radionuclides, like barium-131 and -135m, is still unfamiliar in nuclear medicine applications, although they can be considered as radium-223 surrogates for imaging purposes. Enabling these applications requires the establishment of chelators able to form stable complexes with radium and barium radionuclides. Until now, only a limited number of ligands have been suggested and these molecules have been primarily inspired by existing structures known for their ability to complex large metal cations. However, a systematic inspection of chelators specifically tailored to Ra2+ and Ba2+ has yet to be conducted.This work delves into a comprehensive investigation of a series of small organic ligands, aiming to unveil the coordination preferences of both radium-223 and barium-131/135m. Electronic binding energies of both metal cations to each ligand were theoretically computed via Density Functional Theory calculations (COSMO-ZORA-PBE-D3/TZ2P), while thermodynamic stability constants were experimentally determined for Ba2+-ligand complexes by potentiometry, NMR and UV–Vis spectroscopies. The outcomes revealed malonate, 2-hydroxypyridine 1-oxide and picolinate as the most favorable building blocks to design multidentate chelators. These findings serve as foundation guidelines, propelling the development of cutting-edge radium-223- and barium-131/135m-based radiopharmaceuticals for Targeted Alpha Therapy and theranostics of cancer.

Infrared Spectroscopy of [M(CO2)n]+ (M = Ca, Sr, and Ba; n = 1-4) in the Gas Phase: Solvation-Induced Electron Transfer and Activation of CO2.

Cationic complexes of heavy alkaline earth metal and carbon dioxide [M(CO2)n]+ (M = Ca, Sr, and Ba) are produced by a laser vaporization-supersonic expansion ion source in the gas phase and are studied by infrared photodissociation spectroscopy in conjunction with quantum chemistry calculations. For the n = 1 complexes, the metal-ligand binding arises primarily from the electrostatic interaction with the CO2 ligand bound to the metal (+I) center in an end-on η1-O fashion. The more highly coordinated complexes [M(CO2)n]+ with n ≥ 2 are characterized to involve a [M2+(CO2-)] core ion with the CO2- ligand bound to the metal (+II) center in a bidentate η2-O, O manner. The activation of CO2 in forming a bent CO2- moiety occurs via solvation-induced metal cation-ligand electron transfer reactions. Bonding analyses reveal that the attractive forces between M2+ and CO2- in the core cation come mainly from electrostatic attraction, but the contribution of covalent orbital interactions should not be underestimated. The atomic orbitals of metal dications that are engaged in the orbital interactions are ns and (n - 1)d orbitals.

Advances in heavy alkaline earth chemistry provide insight into complexation of weakly polarizing Ra2+, Ba2+, and Sr2+ cations.

Numerous technologies-with catalytic, therapeutic, and diagnostic applications-would benefit from improved chelation strategies for heavy alkaline earth elements: Ra2+, Ba2+, and Sr2+. Unfortunately, chelating these metals is challenging because of their large size and weak polarizing power. We found 18-crown-6-tetracarboxylic acid (H4COCO) bound Ra2+, Ba2+, and Sr2+ to form M(HxCOCO)x-2. Upon isolating radioactive 223Ra from its parent radionuclides (227Ac and 227Th), 223Ra2+ reacted with the fully deprotonated COCO4- chelator to generate Ra(COCO)2-(aq) (log KRa(COCO)2- = 5.97 ± 0.01), a rare example of a molecular radium complex. Comparative analyses with Sr2+ and Ba2+ congeners informed on what attributes engendered success in heavy alkaline earth complexation. Chelators with high negative charge [-4 for Ra(COCO)2-(aq)] and many donor atoms [≥11 in Ra(COCO)2-(aq)] provided a framework for stable complex formation. These conditions achieved steric saturation and overcame the weak polarization powers associated with these large dicationic metals.

Assessment of Humic and Fulvic Acid Sorbing Potential for Heavy Metals in Water

Pollution of water sources with heavy metals is a pressing environmental issue. To this end, various procedures are being used to remediate water, including sorption. The aim of this study was to investigate the effectiveness of humic acids (HAs) and fulvic acids (FAs) for the removal of metals from water. Specifically, HA and FA were examined for their potential to be used as sorbent materials for 26 heavy metals, alkali metals, and alkaline earth metals. HA and FA were isolated from lignite samples from two mines (Mavropigi mine and South Field mine, Kozani, West Macedonia, Greece). Experiments were carried out using natural mineral water without pH adjustment, so as to gain a better overview of the sorption efficiency in real-life samples. The results showed that FAs were able to sorb most of the examined metals compared to HAs. Several metals such as Ba (34.22–37.77%), Ca (99.12–99.58%), and Sr (97.89–98.12%) were efficiently sorbed when 900 ppm of FAs from both sources were used but were not sorbed by HAs from any source (≤0.1%). Due to the functional groups on the surface of FA, it is plausible to conclude that it can remove more metals than HA. Meanwhile, lignite from the South Field mine was found to be more efficient for the sorption efficiency in lower concentrations (300–600 ppm), whereas lignite from the Mavropigi mine was more effective in higher concentrations (900 ppm). For instance, higher removal rates were observed in Mo (62.84%), Pb (56.81%), and U (49.22%) when 300 ppm of HAs of South Field mine were used, whilst the employment of 900 ppm of HAs from Mavropigi mine led to high removal rates of As (49.90%), Se (64.47%), and Tl (85.96%). The above results were also reflected in a principal component analysis, which showed the dispersion of the metal parameters near to or far from the HA and FA parameters depending on their sorption capacity. Overall, both HA and FA could be effectively utilized as sorbent materials for metal removal from water samples. The results of the research indicate a potential application to the remediation of water from metals under dynamic conditions in order to protect public health.

Effect of heavy metal and alkaline earth oxides on the optical and electrical mechanism of vanadium-phosphate amorphous glassy systems

In the current work, the collective effects of the doping of heavy metal oxide (Bi2O3) and alkaline metal oxide (BaO) into the host glassy network having chemical formula xBi2O3-(0.4-x)BaO-0.3V2O5–0.3P2O5 (x = 0.05, 0.15, 025, and 0.35) are studied systematically. The X-ray diffraction reveals the amorphous nature of the composites under study. Physical properties like density and molar volume have been investigated and correlated with structural modifications. The findings of Tauc's plot have confirmed the increment in optical band gap energies from 2.81 eV to 3.51 eV and correlated with the decrement of Urbach energy values. Some spectroscopic parameters like refractive index, reflectivity, reflection factor, and non-linear refractive index have been examined and interpreted accordingly. The mechanism is accountable for AC conductivity has been inspected using Almond–West formalism and Jonscher's universal power law, revealing semiconducting features. The small polaron hopping route with various activation energies at numerous temperature ranges causes non-linearity in DC conductivity in all of the studied samples.

Accumulation of Microelements and Mineral Formation in Microbial Mats of Thermal Springs of Kamchatka (Far East, Russia)

The chemical composition, distribution, and abundance of physiological groups of bacteria in thermal waters and microbial mats formed in the Nachikinsky, Malkinsky, and Verkhne-Paratunsky springs were studied. The degree of accumulation of microelements and formation of minerals by microbial mats of Kamchatka’s thermal springs was also analyzed. The study shows that the waters are characterized by different chemical composition, temperature, and pH content. The thermal waters under study show a low composition and numbers of functional groups of bacteria with the predominance of thionic bacteria. Prevalence of saprophytic, thionic, sulfate-reducing, manganese-oxidizing, ammonifying and nitrifying microorganisms in microbial mats was registered. The relevance of formed microbial mats in the concentration of many heavy metals, alkaline and alkaline earth elements was shown. Thus, cobalt, vanadium, arsenic (Nachikinsky), beryllium, cobalt (Malkinsky), cobalt and scandium (Verkhne-Paratunsky) were most concentrated in microbial mats of Kamchatka’s hydrotherms. All studied microbial communities show the lowest accumulation of Li (1.17-2.22), Sr (2.11-2.79), Rb (2.61-3.12), Cs (2.88-2.98) and As (1.98-2.58). The formation of minerals was found in algo-bacterial mats: quartz, plagioclase, anorthite, calcite, and magnetite.

Alkaline earth metal doped nickel ferrites as a potential material for heavy metal removal from waste water

Water pollutants especially heavy metals are very harmful to the ecosystem even at low concentrations. For the effective removal of heavy metals (lead and cadmium), nickel ferrite, and alkaline earth metals doped nickel ferrite were synthesized using the co-precipitation method. The synthesized adsorbents were characterized using XRD, BET, FESEM-EDX, FTIR, VSM, UV–Vis, and XPS analytical techniques. Batch adsorption studies were performed with different parameters of adsorption such as pH, contact time, dosage of adsorbent, and concentration of heavy metal ions solution for a period of 60 min at room temperature. Removal percentage of Pb(II) and Cd(II) ions is 83% and 45% in case of nickel ferrite and reached to 97% and 80% for doped nickel ferrites. Isothermal studies were conducted using linear and non-linear equations of Langmuir and Freundlich isotherm models. The adsorption isotherm data was better fitted in linear Langmuir model (correlation coefficient, R2 = 0.99446 for Pb(II) and 0.96682 for Cd(II) ions) than Freundlich model (R2 = 0.85171 for Pb(II) and 0.73917 for Cd(II) ions). The kinetics studies for Pb(II) and Cd(II) ions adsorption were conducted using nonlinear pseudo-first-order, second-order, and intraparticle diffusion models. The process of adsorption of heavy metals can be adequately described by a pseudo-second order model with correlation coefficient (R2) of 0.98823 and 0.98248 for Pb(II) and Cd(II) ions. The findings revealed that prepared mesoporous ferrites (as per BET analysis) act as an efficient adsorbents to remove heavy metals from wastewater along with good recyclability and easy separation under the influence of an external magnetic field.

Heavy Alkaline–Earth Metal Formazanate Complexes and Their Catalytic Applications

Heavy Alkaline–Earth Metal Formazanate Complexes and Their Catalytic Applications

Accessing the main-group metal formyl scaffold through CO-activation in beryllium hydride complexes

Carbon monoxide (CO) is an indispensable C1 building block. For decades this abundant gas has been employed in hydroformylation and Pausen-Khand catalysis, amongst many related chemistries, where a single, non-coupled CO fragment is delivered to an organic molecule. Despite this, organometallic species which react with CO to yield C1 products remain rare, and are elusive for main group metal complexes. Here, we describe a range of amido-beryllium hydride complexes, and demonstrate their reactivity towards CO, in its mono-insertion into the Be-H bonds of these species. The small radius of the Be2+ ion in conjunction with the non-innocent pendant phosphine moiety of the developed ligands leads to a unique beryllium formyl complex with an ylidic P-COC fragment, whereby the carbon centre, remarkably, datively binds Be. This, alongside reactivity toward carbon dioxide, sheds light on the insertion chemistry of the Be-H bond, complimenting the long-known chemistry of the heavier Alkaline Earth hydrides.

Signature of half-metallicity in [formula omitted]: A DFT study

BiFeO3 has drawn great attention over the last several decades due to its promising multiferroic character. In the ground state, the bulk BiFeO3 is found to be in the rhombohedral phase. However, it has been possible to stabilize BiFeO3 with a tetragonal structure. The importance of the tetragonal phase is due to its much larger value of the electric polarization and the possible stabilization of ferromagnetism as in the rhombohedral phase. Furthermore, the tetragonal structure of BiFeO3 has been reported with different c/a ratios, opening up the possibility of a much richer set of electronic phases. In this work, we have used the density functional theory based first-principle method to study the ferromagnetic phase of the tetragonal BiFeO3 structure as a function of the c/a ratio. We have found that, as the c/a ratio decreases from 1.264 to 1.016, the tetragonal phase evolves from a ferromagnetic semiconductor to a ferromagnetic metal, passing through a half-metallic phase. This evolution of the electronic properties becomes even more interesting when viewed with respect to the volume of each structure. The most stable half-metallic phase initially counter-intuitively evolve to the magnetic-semiconducting phase with a reduction in the volume, and after further reduction in the volume, it finally becomes a metal. So far, this type of metal to insulator transition on compression was known to exist only in alkali metals, especially in lithium, in heavy alkaline earth metals, and in some binary compounds.

Generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their synthetic applications.

Organomagnesium compounds, represented by the Grignard reagents, are one of the most classical yet versatile carbanion species which have widely been utilized in synthetic chemistry. These reagents are typically prepared via oxidative addition of organic halides to magnesium metals, via halogen–magnesium exchange between halo(hetero)arenes and organomagnesium reagents or via deprotonative magnesiation of prefunctionalized (hetero)arenes. On the other hand, recent studies have demonstrated that the organo-alkaline earth metal complexes including those based on heavier alkaline earth metals such as calcium, strontium and barium could be generated from readily available non-polar unsaturated molecules such as alkenes, alkynes, 1,3-enynes and arenes through unique metallation processes. Nonetheless, the resulting organo-alkaline earth metal complexes could be further functionalized with a variety of electrophiles in various reaction modes. In particular, organocalcium, strontium and barium species have shown unprecedented reactivity in the downstream functionalization, which could not be observed in the reactivity of organomagnesium complexes. This perspective will focus on the newly emerging protocols for the generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their applications in chemical synthesis and catalysis.

Trace element fractionation between biotite, allanite, and granitic melt

The partitioning of a large suite of trace elements between biotite and water-saturated granitic melt was measured at 2 kbar and 700—800 ˚C. To reach equilibrium and to grow biotite crystals large enough for analysis, runs usually lasted from 30 to 45 days. In every charge, a few trace elements were initially doped at the 0.1—0.5 wt. % level and analyzed by electron microprobe after the run. First-row transition metal ions are highly compatible in biotite with Dbiotite/melt of 17 for Ti, 35 for V, 47 for Co, 174 for Ni, and 5.8 for Zn. A very notable exception is Cu with Dbiotite/melt < 0.9. This is likely one of the reasons why Cu is enriched together with Mo (Dbiotite/melt = 0.29) in porphyry deposits associated with intermediate to felsic plutons, while the other transition metals are not. Both Nb and Ta are mildly compatible in biotite with Dbiotite/melt being larger for Nb (3.69) than for Ta (1.89). Moderate (15—30%) biotite fractionation would be sufficient to reduce the Nb/Ta ratio from the chondritic value to the range observed in the continental crust. Moreover, the strong partitioning of Ti into biotite implies that already modest biotite fractionation suppresses the saturation of Ti-oxide phases and thereby indirectly facilitates the enrichment of Ta over Nb in the residual melt. The heavy alkalis, alkaline earths, and Pb are only mildly fractionated between biotite and melt (Dbiotite/melt = 3.8 for Rb, 0.6 for Cs, 0.6 for Sr, 1.8 for Ba, 0.7 for Pb). The rare earth elements are generally incompatible in biotite, with a minimum for Dbiotite/melt of 0.03–0.06 at Gd, Tb, and Dy, while both the light and heavy rare earths are less incompatible (e.g. Dbiotite/melt = 0.6 for La and 0.3 for Yb). This behavior probably reflects a partitioning into two sites, the K site for the light rare earths and the octahedral Mg site for the heavy rare earths. There is no obvious dependence of the rare earth partition coefficients on tetrahedral Al in the biotite, presumably because charge balancing by cation vacancies is possible. Allanite was found as run product in some experiments. For the light rare earths, Dallanite/melt is very high (e.g. 385 to 963 for Ce and Nd) and appears to increase with decreasing temperatures. However, the rather high solubility of allanite in the melts implies that it likely only crystallizes during the last stages of cooling of most magmas, except if the source magma is unusually enriched in rare earths.

Small Amount Makes a Big Difference: Critical (n - 1)d Valence Orbitals of Heavy Alkaline Earth Metals inside Cage Clusters.

Heavy alkaline earth metals (Aes) are usually considered to engage in chemical bonding by donating the two electrons on ns atomic orbitals (AOs). In this work, a series of typical endohedrally doped cage clusters Ae@cage (Ae = Ca, Sr, Ba; cage = C32, C74, C94, B40, Si20, Sn12, Au16) were thoroughly investigated by means of density functional theory calculations. We found that their occupied molecular orbitals have ∼1 to 14% contributions from Ae-(n - 1)d AOs due to electron back-donation from the cage. Though the amount is small, it is hard to ignore: with the d orbitals, all these endohedral clusters exhibit obviously shortened Ae-cage distances, greatly enhanced encapsulation stabilities, changed highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, and much lowered Ae valences far from ideal +2. Evidently, the valence orbitals of Ca/Sr/Ba in these systems should include both ns and (n - 1)d. By disclosing the critical role of unnoticed metal orbitals, our work provides completely new insights into the cluster field.

Variations in local heavy metal concentrations over the last 16,000 years in the central Atacama Desert (22°S) measured in rodent middens

Mining is a major industry in the Atacama Desert, one of the world's leading regions for copper and other minerals. Intense industrialization of copper mining in the mid-twentieth century has likely led to significant environmental pollution through the deposition of heavy metals in the hyperarid Atacama, but how heavy metal pollution has changed over time in arid regions have rarely been assessed. Here, we analyzed both modern and ancient fecal pellets from paleomiddens collected in the central Atacama for heavy metals and by comparing current heavy metal concentrations with pre-industrial ones, we establish ecological baselines for such pollution. Sixteen paleomiddens spanning the last 1000 years from multiple localities in the eastern Calama Basin (22°S) show elevated concentrations of Cu and As in modern compared to older middens, and that heavy metal, alkali metals and alkaline earth metals show positive correlations with each other. Heavy metals also tend to be higher in paleomiddens collected along perennial rivers in comparison to those collected from surrounding ranges, irrespective of sample age. Twenty paleomiddens spanning the last c. 16,000 years from a single locality (El Hotel) between the Calama and San Pedro de Atacama basins were used to establish long term variations in plant communities and associated heavy metals since the last glacial termination. Results show that heavy metal concentrations including Cr, Mo and B vary over time and tend to be higher in paleomiddens for which Cactaceae are more abundant whereas those dominated by annuals show less of an effect from trace metals. Our results imply that climate change-driven plant community composition plays a key role in explaining how contamination varies in these desert ecosystems and show that paleomiddens are a unique and unexplored source for understanding how heavy metals vary over time. Given their ubiquity in many of the world's arid regions, they can be used to establish long-term ecological baselines to compare against human alterations.

Transition metal chemistry in synthetically viable alkaline earth complexes M(Cp)3- (M = Ca, Sr, Ba).

We predicted the stable alkaline earth complexes M(Cp)3- (M = Ca, Sr, Ba; Cp = cyclopentadienyl), where the M centers were in their stable +2 oxidation state and mimicked the bonding behaviour of transition metals by participating in bonding with the π orbitals of Cp ligands using their d orbitals.

Alkyl complexes of divalent lanthanides and heavy alkaline earth metals

The review presents data on the synthesis, structure, reactivity, and catalytic activity of alkyl derivatives of rare earth metals in the oxidation state +2 (Sm, Eu, Yb) and their analogues containing heavy alkaline earth metals (Ca, Sr, Ba). The synthetic aspects and structural features of this unique class of organometallic compounds, which contain highly reactive M–C bonds, including alkyl, α-silylmethyl, and also benzyl, diphenylmethyl, and triphenylmethyl derivatives are considered.The bibliography includes 157 references.