Ca5Cl3(C2)(CBC): A Compound with a Layer Structure and an Unusual Anion Combination

Allene homologous cumulenes are not always linear! The title compound, which has now been synthesized and structurally characterized, contains a BC₂ unit that is isoelectronic with CO₂ and that deviates by 16° from linearity without losing the double-bond character of the B–C bonds. The BC₂ unit is located in the center of a bicapped trigonal prism of calcium ions (see picture).     

First Step Towards Planning of Syntheses in Solid-State Chemistry: Determination of Promising Structure Candidates by Global Optimization

A method is presented here that allows, in principle, the prediction of the existence and structure of (meta)stable solid compounds. It is based on a set of adjustable modules that are applied to the study of the energy function of the chemical system of interest. The main elements are a set of routines for global optimization and local minimization, as well as algorithms for the investigation of the phase space structure near local minima of the potential energy, and the analysis and characterization of the structure candidates. The current implementation focuses on ionic compounds, for which empirical potentials are used for the evaluation of the energy function in the first stage, and a Hartree–Fock algorithm for refinements. The global optimization is performed with a stochastic simulated annealing algorithm, and the local minimization employs stochastic quenches and gradient methods. The neighborhoods of the local minima are studied with the threshold algorithm. The results of this approach are illustrated with a number of examples: compounds of binary noble gases, and binary and ternary ionic compounds. These include several substances that have not been synthesized yet, but should stand a fair chance of being kinetically stable, for example further alkali metal nitrides besides Li₃N, as well as Ca₃SiBr₂ or SrTi₂O₅.     

Time dependent wave packet treatment of 2ΠgN2− and 3Σ−NO− shape resonances using two‐dimensional surfaces for electron‐N2 and NO interactions

The ²Π_gN and ³Σ^?NO^? resonances in electron‐N₂ and NO collisions have been treated using both nuclear and electronic degrees of freedom and a two‐dimensional (2D) time dependent wave packet approach to ascertain the importance of nonlocality in electron–nuclear interaction. The results so obtained are compared with vibrational excitation cross‐sections obtained experimentally and those from other theoretical/numerical approaches using 1D local complex potential, 2D model with a combination of the exterior complex scaling method and a finite‐element implementation of the discrete‐variable representation. The results obtained provide detailed insight into the nuclear dynamics induced by electron–molecule collision and reveal that while for resonant excitation of lower vibrational modes, the nonlocal effect may not be as critical but importance of nonlocal effects may increase with increase in quanta of resonant vibrational excitation. © 2012 Wiley Periodicals, Inc.