Imaging benzene on nickel and copper {110} surfaces with low temperature STM:: the adsorption site

Single benzene molecules have been imaged on the {110} surfaces of both copper and nickel with an Eigler-type low temperature scanning tunnelling microscope. Conditions were chosen such that the molecule and the lattice atoms could be resolved at the same time within one image frame. On Ni{110} benzene was found to adsorb in the hollow site between the close-packed rows. For the more weakly bound molecule on Cu{110} the imaging conditions had to be changed since, for the tunnelling conditions under which the lattice atoms are resolved, a strong interaction between the tip and the benzene takes place. This results in the molecule being “dragged” along the surface. By changing the tunnelling conditions within one image frame, however, it is possible via extrapolation of the substrate lattice to show that the molecule adsorbs in the long-bridge site. The shapes of the images of individual molecules are discussed.     

Bis[(dialkylamino)cyclopropenimine]‐Stabilized PIII‐ and PV‐Centered Dications

The treatment of bis[(dialkylamino)cyclopropenimines] with dihalophosphines in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) to form diimine‐stabilized P^III‐centered dications is reported. The structures of the new compounds were determined by using X‐ray diffraction analysis and their donor abilities as ligands evaluated through electrochemical methods. Despite the two positive charges that they bear, these compounds depict intermediate behavior between that of phosphines and phosphites. The coordination of the [L₂PR]²⁺ moiety to Au^I and Ag^I is also reported. Even more surprisingly, these phosphorus centers can be oxidized to the corresponding P^V dications in the presence of strong oxidants such as peroxides or XeF₂.     

Parallel Bayesian Additive Regression Trees

Bayesian additive regression trees (BART) is a Bayesian approach to flexible nonlinear regression which has been shown to be competitive with the best modern predictive methods such as those based on bagging and boosting. BART offers some advantages. For example, the stochastic search Markov chain Monte Carlo (MCMC) algorithm can provide a more complete search of the model space and variation across MCMC draws can capture the level of uncertainty in the usual Bayesian way. The BART prior is robust in that reasonable results are typically obtained with a default prior specification. However, the publicly available implementation of the BART algorithm in the R package BayesTree is not fast enough to be considered interactive with over a thousand observations, and is unlikely to even run with 50,000 to 100,000 observations. In this article we show how the BART algorithm may be modified and then computed using single program, multiple data (SPMD) parallel computation implemented using the Message Passing Interface (MPI) library. The approach scales nearly linearly in the number of processor cores, enabling the practitioner to perform statistical inference on massive datasets. Our approach can also handle datasets too massive to fit on any single data repository.     

New reaction of ethenetetracarbonitrile with N-arylisoindolines

N-Arylisoindolines 1a-i react with ethenetetracarbonitrile 2 in aerated benzene by formation of [3-(2-aryl-3-dicyanomethylene-2,3-dihydro-1H-isoindol-1-ylidene)-2-aryl-2,3-dihydro-1H-isoindol-1-ylidene]propanedinitriles 8a-i (20-36%), N-aryl-3-dicyanomethylene-isoindol-2-ones 9a-i (15-21%) and N-arylphthalimides 10a-i (4-9%) as well as 1,1,2,2-tetracyanoethane 11 (35-55%). The structure of 8d has been unambiguously confirmed by a single crystal X-ray structure analysis. A rationale for the formation of products 8-11 is presented.