The effects of experimentally obtained electron correlation and polarization on electron densities and exchange-correlation potentials.

In X-ray constrained wavefunction (XCW) fitting, external information, such as electron correlation and polarization, is included into a single-determinantal isolated-molecule wavefunction. In a first step, we show that the extraction of these two physical effects by XCW fitting is complete and accurate by comparing to theoretical reference calculations. In a second step, we show that fitting to data from single-crystal x-ray diffraction measurements provides the same results qualitatively and how the physical effects can be separated, although always inherently convolved in the experiment. We further demonstrate that exchange-correlation potentials are systematically affected by XCW fitting in a physically meaningful way, which could be exploited for method development in quantum chemistry, subject to some remaining challenges that we also outline.

Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B12 Cl11 ].

It is common and chemically intuitive to assign cations electrophilic and anions nucleophilic reactivity, respectively. Herein, we demonstrate a striking violation of this concept: The anion [B12 Cl11 ]- spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of "superelectrophilic" dications. [B12 Cl11 Ng]- adducts, with Ng binding energies of 80 to 100 kJ mol-1 , contain B-Ng bonds with a substantial degree of covalent interaction. The electrophilic nature of the [B12 Cl11 ]- anion is confirmed spectroscopically by the observation of a blue shift of the CO stretching mode in the IR spectrum of [B12 Cl11 CO]- and theoretically by investigation of its electronic structure. The orientation of the electric field at the reactive site of [B12 Cl11 ]- results in an energy barrier for the approach of polar molecules and facilitates the formation of Ng adducts that are not detected with reactive cations such as [C6 H5 ]+ . This introduces the new chemical concept of "dipole-discriminating electrophilic anions."

Acetone and the precursor ligand acetylacetone: distinctly different electron beam induced decomposition?

In focused electron beam induced deposition (FEBID) acetylacetone plays a role as a ligand in metal acetylacetonate complexes. As part of a larger effort to understand the chemical processes in FEBID, the electron-induced reactions of acetylacetone were studied both in condensed layers and in the gas phase and compared to those of acetone. X-ray photoelectron spectroscopy (XPS) shows that the electron-induced decomposition of condensed acetone layers yields a non-volatile hydrocarbon residue while electron irradiation of acetylacetone films produces a non-volatile residue that contains not only much larger amounts of carbon but also significant amounts of oxygen. Electron-stimulated desorption (ESD) and thermal desorption spectrometry (TDS) measurements reveal striking differences in the decay kinetics of the layers. In particular, intact acetylacetone suppresses the desorption of volatile products. Gas-phase studies of dissociative electron attachment and electron impact ionization suggest that this effect cannot be traced back to differences in the initial fragmentation reactions of the isolated molecules but is due to subsequent dissociation processes and to an efficient reaction of released methyl radicals with adjacent acetylacetone molecules. These results could explain the incorporation of large amounts of ligand material in deposits fabricated by FEBID processes using acetylacetonate complexes.

Synthesis of a peptide-linked chlorin dyad as a model compound for the photosynthetic reaction centre.

The enantiomerically pure chlorins 19 and 21 were synthesised from tripyrrolic nickel complex rac-17 and pyrrole building blocks 12 and 16. The pyrroles are annelated with norbornane moieties which contain the chiral information as well as two different functionalities. The functional groups, namely a carboxylic acid ester and a carbonitrile group, of chlorin 21 finally allowed the formation of an amino acid functionality at the periphery of the macrotetracycle. By using principles of peptide chemistry, the two chlorin subunits were joined to form the peptide-linked chlorin-chlorin dyad 24, which mimics the molecular parts of the natural photosynthetic reaction centre.

[1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazolidyl: a long-lived radical anion and its stable salts.

[1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazole (1) is synthesized in 62% yield by fluoride ion-induced condensation of 3,4-difluoro-1,2,5-thiadiazole with (Me(3)SiN=)(2)S. The reversible electrochemical reduction of 1 leads to the long-lived [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazolidyl radical anion (2) and further to the dianion (3). The radical anion 2 is also obtained by the chemical reduction of the precursor 1 with t-BuOK in MeCN. The radical anion 2 is characterized by ESR spectroscopy in solution and in the crystalline state. The stable salts [K(18-crown-6)][2] and [K(18-crown-6)][2].MeCN (8 and 9, respectively) are isolated from the spontaneous decomposition of the [K(18-crown-6)][PhXNSN] (6, X = S; 7, X = Se) salts in MeCN solution followed by XRD characterization. The radical anion 2 acts as a bridging ligand in 8 and as chelating ligand in 9. The structural changes observed by XRD in going from 1 to 2 are explained by means of DFT/(U)B3LYP/6-311+G calculations.

Tris(dimethylamino)oxosulfonium difluorotrimethylsilicate, (Me(2)N)(3)SO(+)Me(3)SiF(2)(-) (TAOS Fluoride).

In the OSF(4)/Me(2)NSiMe(3) system besides the long known Me(2)NS(O)F(3) only the trisubstituted derivative is isolated as (Me(2)N)(3)SO(+)Me(3)SiF(2)(-) (3). Similar to (Me(2)N)(3)S(+)Me(3)SiF(2)(-) compound 3 is an excellent fluoride ion donor. With AsF(5) and HF the corresponding hexafluoroarsenate (Me(2)N)(3)SO(+)AsF(6)(-) (4) and the hydrogen bifluoride (Me(2)N)(3)SO(+)HF(2)(-) (5) are formed in almost quantitative yield. X-ray structure determinations of 3-5 surprisingly showed two different types of structures for the cation. In 3 and 5 this cation has C(3) symmetry, while in the hexafluoroarsenate 4 a (Me(2)N)(3)S(+)-like structure with C(s)() symmetry is determined. The experimental results for (Me(2)N)(3)SO(+) and (Me(2)N)(3)S(+) are compared with theoretical calculations for these cations and their isoelectronic neutral counterparts, the phosphorus amides (Me(2)N)(3)PO and (Me(2)N)(3)P, respectively.