The electronic structure of borabenzene: Combination of an aromatic π-sextet and a reactive σ-framework

The electronic structure of borabenzene (C₅H₅B, known also as borinane, borinine, borine) is studied using modern valence bond theory in its spin-coupled (SC) form. Three different types of SC wave functions—with six active π orbitals and with four and eight active σ orbitals—are used to describe the π system of the molecule and the σ-bond framework around the boron atom. It is demonstrated that the SC picture of the π space in borabenzene is very similar to that in benzene: The spins of six distorted nonorthogonal 2p_π orbitals are combined in a spin-coupling pattern involving two dominating Kekulétype and three less important Dewar-type Rumer spin functions. This indicates that it is appropriate to consider the π-electron sextet in borabenzene as aromatic and that the reason for the reactivity of this molecule should lie with its σ framework. The two SC models of the σ bonding around B show that the boron-carbon σ bonds in borabenzene involve orbitals are “bent” to the outer side of the six-membered ring. This creates an orbital “hole” at the boron, which should represent the preferred attachment site for Lewis acids. © 1997 John Wiley & Sons, Inc.     

Determination of radiostrontium in soil samples using a crown ether

A simple and rapid method has been developed for the separation and determination of total radiostrontium in soil. The method consists of three basic steps: oxalate precipitation to remove bulk potassium, chromatographic separation of strontium from most inactive and radioactive interferences utilizing a crown ether (Sr. Spec, EIChroM Industries, Il. USA) and oxalate precipitation of strontium to evaluate the chemical yield. Radiostrontium is then determined by liquid scintillation counting of the dissolved precipitate. When 10 g samples of soil are used, the sensitivity of the method is about 10 Bq/kg. The chemical yield is about 80%. The separation and determination of radiostrontium can be carried out in about 8 hours.     

Flux growth and structure of two compounds with the EuIn2P2 structure type,AIn2P2 (A = Ca and Sr), and a new structure type,BaIn2P2

Single crystals of the new Zintl phases AIn₂P₂ [A = Ca (calcium indium phosphide), Sr (strontium indium phosphide) and Ba (barium indium phosphide)] have been synthesized from a reactive indium flux. CaIn₂P₂ and SrIn₂P₂ are isostructural with EuIn₂P₂ and crystallize in the space group P6₃/mmc. The alkaline earth cations A are located at a site with m symmetry; In and P are located at sites with 3m symmetry. The structure type consists of layers of A²⁺ cations separated by [In₂P₂]²⁻ anions that contain [In₂P₆] eclipsed ethane‐like units that are further connected by shared P atoms. This yields a double layer of six‐membered rings in which the In—In bonds are parallel to the c axis and to one another. BaIn₂P₂ crystallizes in a new structure type in the space group P2₁/m with Z = 4, with all atoms residing on sites of mirror symmetry. The structure contains layers of Ba²⁺ cations separated by [In₂P₂]²⁻ layers of staggered [In₂P₆] units that form a mixture of four‐, five‐ and six‐membered rings. As a consequence of this more complicated layered structure, both the steric and electronic requirements of the large Ba²⁺ cation are met.