The adsorption of diethyl ether (Et 2 O) on Si(001) was studied by means of scanning tunneling microscopy (STM) and photoelectron spectroscopy. Et 2 O reacts on Si(001) via a datively bonded intermediate, which was isolated at surface temperatures below 100 K. At higher surface temperature, Et 2 O converts dissociatively into the final state by cleaving one O−C bond; the resulting −O−C 2 H 5 and −C 2 H 5 fragments are found to attach on two Si dimers of neighboring dimer rows. Tipinduced hopping of the −C 2 H 5 fragment on one dimer was observed at positive sample bias. The results are discussed in the context of recent experiments on the reaction of tetrahydrofuran (THF) on Si(001) (Mette et al. ChemPhysChem 2014, 15, 3725) and allow a more general description of the reaction of ethers on Si(001).
The reaction of tetrahydrofuran (THF), an otherwise inert solvent molecule, on Si(001) was experimentally studied in ultra-high vacuum. Using scanning tunneling microscopy (STM) and photoelectron spectroscopy at variable temperature, we could both isolate a datively bound intermediate state of THF on Si(001), as well as the final configuration that bridges two dimer rows of the Si(001) surface after ether cleavage. The latter configuration implies splitting of the OC bond, which is typically kinetically suppressed. THF thus exhibits a hitherto unknown reactivity on Si(001).
The molecular ligand pyrphyrin, a tetradentate bipyridine based macrocycle, represents an interesting but widely unexplored class of molecules. It resembles the well-known porphyrin, but consists of pyridyl subunits instead of pyrroles. Metal complexes based on pyrphyrin ligands have recently shown promise as water reduction catalysts in homogeneous photochemical water splitting reactions. In this study, the adsorption and metalation of pyrphyrin on a single crystalline Au(111) surface is investigated in an ultrahigh vacuum by means of scanning tunneling microscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy and density functional theory. Pyrphyrin coverages of approximately one monolayer and less are obtained by sublimation of the molecules on the substrate kept at room temperature. The molecules self-assemble in two distinct phases of long-range molecular ordering depending on the surface coverage. The deposition of cobalt metal and subsequent annealing lead to the formation of Co-ligated pyrphyrin molecules accompanied by a pronounced change of the molecular self-assembly. Electronic structure calculations taking the herringbone reconstruction of Au(111) into account show that the molecules are physisorbed, but preferred adsorption sites are identified where Co and the N atoms of the two terminal cyano groups are optimally coordinated to the surface Au atoms. An intermediate state of the metalation reaction is observed and the reaction steps for the Co metalation of pyrphyrin molecules on Au(111) are established in a joint experimental and computational effort.
The introduction of chirality in lead halide perovskites and related metal halide materials allows for an expansion of their unique and useful properties toward nonlinear optics. However, when synthesizing materials based on less toxic metals antimony and bismuth, the large variability in the crystal structures of their metalates and their tendency to form molecular or chainlike anion motifs can be a challenge when creating tunable materials. Here, we show that using a chiral amine template, we can synthesize an isomorphous family of compoundsand Bi; X = Cl, Br, and I) that combines multiple aspects: the compounds are not only chiral but also feature a trilayered arrangement of cations and anions that allows for facile cleavage and exfoliation. The different combinations of E and X allow for a variation of the onset of absorption between 3.35 and 2.09 eV. Using femtosecond laser spectroscopy, we show that our materials allow for efficient second-harmonic generation. Together with a simple synthesis and good stability, this makes these materials promising candidates for linear and nonlinear optical devices.
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