Non-cyclopentadienyl organometallic compounds of calcium, strontium and barium

The use of sterically demanding ligands has allowed the organometallic compounds of the heavy alkaline-earth metals calcium, strontium and barium to emerge from the shadow cast by the far better studied organomagnesium Grignard reagents. Metallocenes and other cyclopentadienyl-based complexes have been the most intensively investigated, but in the past decade a wealth of new non-cyclopentadienyl compounds have been characterized. A broad range of structure types are known, encompassing σ- and π-bound anionic ligands, and Lewis base adducts with neutral donors. In this review, crystallographically characterized complexes are discussed, and current interpretations of the bonding in heavier Group 2 element compounds are examined. Recent applications of non-cyclopentadienyl compounds in organic synthesis are surveyed.     

A new generation of visible-light-active photocatalysts—The alkaline earth metal bismuthates: Syntheses,compositions, structures,and properties

Semiconductor materials containing bismuth have attracted the attention of researchers over the past several decades, as a result of their high photocatalytic activity in various reactions and/or high efficiency in their photoelectric conversion of solar energy. This interest originated from the observations that bismuth-containing semiconductors have a sufficiently small bandgap, which makes them sensitive to radiation in the visible spectral range; thus, visible-light-active materials. Among the various bismuth-containing semiconductor materials, the bismuthates of alkaline earth metals are distinguished and describe into separate groups. This article reviews research on the known methods of obtaining bismuthates of various alkaline earth metals (magnesium, calcium, strontium, and barium), and further analyzes their composition, structure, and visible-light-active photocatalytic activity.     

[Cp3Ba]−: The First Structurally Characterized Barate Complex

A [Cp ₃ Ba] _∞ coordination polymer with a chain structure is present in the compound [Cp₃Ba]⁻[Bu₄P]⁺. The barium center is tetrahedrally coordinated by four η⁵-Cp rings (a section of the chain is shown on the right). The Bu₄P cations bridge neighboring [Cp₃Ba]_∞ chains through short hydrogen bonds, and the cocrystallized THF molecules do not coordinate to the barium centers but are instead involved in short CH⋅⋅⋅O hydrogen bonds with the Bu₄P cations.     

BaClSCN und Na4Mg(SCN)6: Zwei neue wasserfreie Thiocyanate der Erdalkalimetalle

BaClSCN and Na₄Mg(SCN)₆: Two New Thiocyanates of the Alkaline Earth Metals The reaction of BaCl₂ and NaSCN yielded single crystals of BaClSCN (P 2₁/m, Z = 2, a = 588.6(1) pm, b = 465.8(1) pm, c = 864.4(2) pm, β = 100.20(3)°, R_all = 0.0214). According to X‐ray single crystal investigations, the structure consists of anionic SCN^– and Cl^– layers, respectively, alternating in [001] direction. The SCN^–‐ions are connected via the N and the S atoms to the cations. Na₄Mg(SCN)₆ (P 3 1c, Z = 2, a = 863.8(1) pm, c = 1399.3(2) pm, R_all = 0.0870), which was obtained from a melt of NaSCN and MgCl₂, consists of anionic layers with the cations between the sheets. The holes are filled altenatingly by Na⁺ or Na⁺ and Mg²⁺. Regarding only the C‐atoms of the SCN^– group, the structure can be described as a hexagonal closest packing whith the cations occupying 5/6 of the octahedral voids.     

Response of polyacrylamide—acyclic poly(oxyethylene)-coated ion-selective electrodes to alkali and alkaline earth metal ions in propylene carbonate and its thermodynamic application

The response of ion-selective electrodes with a membrane of polyacrylamide (PAA) coupled to acyclic poly(oxyethylene) neutral carriers to lithium, sodium, potassium, magnesium and barium ions in propylene carbonate (PC) was investigated. Tetraethylene glycol monododecyl ether (POE4) and hexaethylene glycol monododecyl ether (POE6) were used as the acyclic poly(oxyethylene). Both the PAA-POE4 and the PAA-POE6 electrodes showed a more rapid dynamic response in PC than that in acetonitrile. Nernstian responses to lithium, magnesium and barium ions were obtained with the PAA-POE4 electrode. The selectivity coefficients, logk_Ba²⁺,M^x+, for lithium, sodium, potassium and magnesium ions vs. barium ion obtained in PC with the PAA-POE4 electrode were 3.6, 0.23, 0.02 and 1.1, respectively. The PAA-POE4 electrode was applied to obtain the successive formation constants of the barium ion in PC with N, N-dimethylacetamide (DMA). From the successive formation constants obtained in PC-rich solutions, the Gibbs free energies of transfer of the barium ion from PC to DMA and to PC-DMA mixtures were calculated. The electrode was also used to obtain directly the Gibbs free energies of transfer of the barium ion from PC to PC-DMA mixtures. The calculated values of the free energies were in good agreement with the values obtained experimentally, suggesting that the electrode responded to variations in solvation energy for the barium ion.     

M(SCN)2 (M = Eu,Sr, Ba): Kristallstruktur,thermisches Verhalten,Schwingungsspektroskopie

M(SCN)₂ (M = Eu, Sr, Ba): Crystal Structure, Thermal Behaviour, Vibrational Spectroscopy Single crystals of M(SCN)₂ (M = Eu, Sr, Ba) have been obtained via metathesis of NaSCN and MCl₂ (M = Eu, Sr, Ba) at 340 °C. The isotypic crystal structures of the thiocyanates M(SCN)₂ (C2/c, Z = 4, Eu: a = 979.3(2), b = 660.8(1), c = 815.7(2) pm, β = 91.58(3)°, R_all = 0.0245, Sr: a = 985.5(2), b = 662.9(2), c = 819.6(2) pm, β = 91.29(3)°, R_all = 0.0435, Ba: a = 1018.8(2), b = 687.2(1), c = 852.2(1) pm, β = 92.43(2)°, R_all = 0.0392) contain alternating layers of M²⁺ and SCN^–. According to M(SCN)_4/4(NCS)_4/4 M²⁺ is eight‐coordinated by four sulfur and four nitrogen atoms forming a square antiprism. Thermal investigations show that the compounds melt without decomposition. Vibrational spectroscopic investigations are presented and discussed.     

A new method to estimate the atomic volume of ternary intermetallic compounds

The atomic volume of an A_xB_yC_z ternary intermetallic compound can be calculated starting from volumes of some proper A-B, A-C and B-C binary phases. The three methods by Colinet, Muggianu and Kohler, originally used to estimate thermodynamic quantities, and a new method here proposed, were tested to derive volume data in eight systems containing 91 ternary phases with the known structure. The comparison between experimental and calculated volume values shows the best agreement both for the Kohler method and for the new proposed procedure.