Tobias Schlöder

Identification of an iridium-containing compound with a formal oxidation state of IX

One of the most important classifications in chemistry and within the periodic table is the concept of formal oxidation states. The preparation and characterization of compounds containing elements with unusual oxidation states is of great interest to chemists. The highest experimentally known formal oxidation state of any chemical element is at present VIII, although higher oxidation states have been postulated. Compounds with oxidation state VIII include several xenon compounds (for example XeO4 and XeO3F2) and the well-characterized species RuO4 and OsO4 (refs 2, 3, 4). Iridium, which has nine valence electrons, is predicted to have the greatest chance of being oxidized beyond the VIII oxidation state. In recent matrix-isolation experiments, the IrO4 molecule was characterized as an isolated molecule in rare-gas matrices. The valence electron configuration of iridium in IrO4 is 5d1, with a formal oxidation state of VIII. Removal of the remaining dxa0electron from IrO4 would lead to the iridium tetroxide cation ([IrO4]+), which was recently predicted to be stable and in which iridium is in a formal oxidation state of IX. There has been some speculation about the formation of [IrO4]+ species, but these experimental observations have not been structurally confirmed. Here we report the formation of [IrO4]+ and its identification by infrared photodissociation spectroscopy. Quantum-chemical calculations were carried out at the highest level of theory that is available today, and predict that the iridium tetroxide cation, with a Td-symmetrical structure and a d0 electron configuration, is the most stable of all possible [IrO4]+ isomers.

Synthesis of the Smallest Axially Chiral Molecule by Asymmetric Carbon–Fluorine Bond Activation

Surprisingly, thecarbon backbones of 3 and 5adeviate by 4.4(3)8 and 4.6(2)8from the linearity that would be expected based on their sp-hybridized central carbon atoms (Figure 2). Furthermore, thetwo terminal F-C-H planes in5a have a torsion angle of91.9(2)8. The previously reported structures derived frommicrowave spectroscopy do not show the same distortions(Supporting Information, Table S2), because erroneously, therefinement was based on a constrained linear geometry.

Infrared Spectroscopic and Theoretical Investigations of the OUF2 and OThF2 Molecules with Triple Oxo Bond Character

The terminal oxo species OUF(2) and OThF(2) have been prepared via the spontaneous and specific OF(2) molecule reactions with laser ablated uranium and thorium atoms in solid argon and neon. These isolated molecules are characterized by one terminal M-O and two F-M-F (M = U or Th) stretching vibrational modes observed in matrix isolation infrared spectra, which are further supported by density functional frequency calculations and CASPT2 energy and structure calculations. Both molecules have pyramidal structures with singlet (Th) and triplet (U) ground states. The molecular orbitals and metal-oxygen bond lengths for the OUF(2) and OThF(2) molecules indicate triple bond character for the terminal oxo groups, which are also substantiated by NBO analysis at the B3LYP level and by CASPT2 molecular orbital calculations. Dative bonding involving O(2p) → Th(6d) and U(df) interactions is clearly involved in these oxoactinide difluoride molecules. Finally, the weak O-F bond in OF(2) as well as the strong U-O, U-F and Th-O, Th-F bonds make reaction to form the OUF(2) and OThF(2) molecules highly exothermic.

Can Zinc Really Exist in Its Oxidation State +III?

Very recently, a thermochemically stable Zn(III) complex has been predicted by Samanta and Jena (J. Am. Chem. Soc. 2012, 134, 8400-8403). In contrast to their conclusions we show here by quantum chemical calculations that (a) Zn(AuF(6))(3) is not a thermochemically feasible compound, and (b) even if it could be made, it would not represent a Zn(III) oxidation state by any valid definition.

New evidence in an old case: the question of chromium hexafluoride reinvestigated.

The question of whether or not the chromium hexafluoride molecule has been synthesized and characterized has been widely discussed in the literature and cannot, in spite of many efforts, yet be answered beyond doubt. New matrix-isolation experiments can now show, together with state-of-the-art quantum-chemical calculations, that the compound previously isolated in inert gas matrixes, was CrF5 and not CrF6. New bands in the matrix IR spectra can be assigned to the Cr2F10 dimer, and furthermore evidence was found in the spectra for a photodissociation or reversible excitation of CrF5 under UV irradiation. However, even if CrF6 is not stable at ambient conditions, its formation under high fluorine pressures in autoclave reactions cannot be excluded completely.

Investigation of heterodimeric and homodimeric radical cations of the series: [F2O2]+, [F2Cl2]+, [Cl2O2]+, [F4]+, and [Cl4]+

In this state-of-the-art quantum-chemical investigation we report structures, thermochemical stabilities, Born-Fajans-Haber cycles as well as vibrational data of heterodimeric and homodimeric radical cations of the series [F2O2]+, [F2Cl2]+, [Cl2O2]+, [F4]+, and [Cl4]+. The so far experimentally unknown species [F4]+, [F2O2]+ and [F2Cl2]+ are predicted to be thermochemically stable and could be possible targets for gas-phase or matrix-isolation experiments. Furthermore, their stabilities as homodimeric [X4]+ or heterodimeric [X2Y2]+ radical cation salts in the solid state have been estimated by Born-Fajans-Haber cycles.

Synthesis, structure, bonding, and properties of Sc(3)Al(3)O(5)C(2) and ScAl(2)ONC-unique compounds with ordered distribution of anions and cations.

Single crystals of the new compounds Sc(3)Al(3)O(5)C(2) and ScAl(2)ONC were obtained by reacting Sc(2)O(3) and C in an Al-melt at 1550 degrees C. Their crystal structures continue the row of transition metal oxide carbides with an ordered distribution of anions and cations with ScAlOC as the first representative. In the structure of Sc(3)Al(3)O(5)C(2) (P6(3)/mmc, Z = 2, a = 3.2399(8) A, c = 31.501(11) A, 193 refl., 23 param., R(1)(F) = 0.024, wR(2)(I) = 0.058) the anions form a closest packing with five layers of oxygen separated by two layers of carbon atoms. Sc is placed in octahedral voids and Al in tetrahedral voids thus forming layers of AlOC(3) tetrahedra and ScC(6)- and ScO(6)-octahedra, respectively. Surprisingly the layers of ScO(6) octahedra are connected by an additional layer of undistorted trigonal bipyramids AlO(5). The structure of ScAl(2)ONC (space group R3m, Z = 3, a = 3.2135(8) A, c = 44.636(1) A, 187 refl., 21 param., R(1)(F) = 0.023, wR(2)(F(2)) = 0.043) can directly be derived from the binary nitrides AlN (wurtzite-type) and ScN (rocksalt-type). The anions form a closest packing with alternating double layers of C and O separated by an additional layer of N. Again, Al and Sc occupy tetrahedral and octahedral voids, respectively. All compositions were confirmed by energy dispersive X-ray spectroscopy (EDXS) measurements on single crystals. According to band structure calculations Sc(3)Al(3)O(5)C(2) is electron precise with a band gap of 0.3 eV. Calculations of charges and charge densities reveal that the mainly ionic bonding contains significant covalent contributions, too. As expected Sc and C show higher covalent shares than Al and O. The different coordinations of O, Al, and Sc are clearly represented in the corresponding p and d states.

Oxygen radical character in group 11 oxygen fluorides

Transition metal complexes bearing terminal oxido ligands are quite common, yet group 11 terminal oxo complexes remain elusive. Here we show that excited coinage metal atoms M (Mu2009=u2009Au, Ag, Cu) react with OF2 to form hypofluorites FOMF and group 11 oxygen metal fluorides OMF2, OAuF and OAgF. These compounds have been characterized by IR matrix-isolation spectroscopy in conjunction with state-of-the-art quantum-chemical calculations. The oxygen fluorides are formed by photolysis of the initially prepared hypofluorites. The linear molecules OAgF and OAuF have a 3Σxa0− ground state with a biradical character. Two unpaired electrons are located mainly at the oxygen ligand in antibonding O−M π* orbitals. For the 2B2 ground state of the OMIIIF2 compounds only an O−M single bond arises and a significant spin-density contribution was found at the oxygen atom as well.While transition metal complexes bearing terminal oxido ligands are common, those of group 11 elements have yet to be experimentally observed. Here, Riedel and colleagues synthesise molecular oxygen fluorides of copper, silver and gold, and show that the oxo ligands possess radical character.