Sebastian Riedel

Matrix Infrared Spectroscopy and Quantum-Chemical Calculations for the Coinage-Metal Fluorides: Comparisons of ArAuF, NeAuF, and Molecules MF2 and MF3

The reactions of laser-ablated Au, Ag, and Cu atoms with F(2) in excess argon and neon gave new absorptions in the M-F stretching region of their IR spectra, which were assigned to metal-fluoride species. For gold, a Ng-AuF bond was identified in mixed neon/argon samples. However, this bonding was much weaker with AgF and CuF. Molecules MF(2) and MF(3) (M=Au, Ag, Cu) were identified from the isotopic distribution of the Cu and Ag atoms, comparison of the frequencies for three metal fluorides, and theoretical frequency calculations. The AuF(5) molecule was characterized by its strongest stretching mode and theoretical frequency calculations. Additional evidence was observed for the formation of the Au(2) F(6) molecule.

Investigation of Gold Fluorides and Noble Gas Complexes by Matrix‐Isolation Spectroscopy and Quantum‐Chemical Calculations

Noble with a difference: Matrix-isolation experiments and quantum-chemical calculations have led to the characterization of two new compounds, namely first open-shell binary gold fluoride, AuF(2), and a NeAuF complex. Moreover, ArAuF, AuF(3), Au(2)F(6), and monomeric AuF(5) have been produced and identified under cryogenic conditions in neon and argon matrices.

On the Oxidation of the Three‐Dimensional Aromatics [B12X12]2− (X=F, Cl, Br, I)

The perhalogenated closo-dodecaborate dianions [B12 X12 ](2-) (X=H, F, Cl, Br, I) are three-dimensional counterparts to the two-dimensional aromatics C6 X6 (X=H, F, Cl, Br, I). Whereas oxidation of the parent compounds [B12 H12 ](2-) and benzene does not lead to isolable radicals, the perhalogenated analogues can be oxidized by chemical or electrochemical methods to give stable radicals. The chemical oxidation of the closo-dodecaborate dianions [B12 X12 ](2-) with the strong oxidizer AsF5 in liquid sulfur dioxide (lSO2 ) yielded the corresponding radical anions [B12 X12 ](⋅-) (X=F, Cl, Br). The presence of radical ions was proven by EPR and UV/Vis spectroscopy and supported by quantum chemical calculations. Use of an excess amount of the oxidizing agent allowed the synthesis of the neutral perhalogenated hypercloso-boranes B12 X12 (X=Cl, Br). These compounds were characterized by single-crystal X-ray diffraction of dark blue B12 Cl12 and [Na(SO2 )6 ][B12 Br12 ]⋅B12 Br12 . Sublimation of the crude reaction products that contained B12 X12 (X=Cl, Br) resulted in pure dark blue B12 Cl12 or decomposition to red B9 Br9 , respectively. The energetics of the oxidation processes in the gas phase were calculated by DFT methods at the PBE0/def2-TZVPP level of theory. They revealed the trend of increasing ionization potentials of the [B12 X12 ](2-) dianions by going from fluorine to bromine as halogen substituent. The oxidation of all [B12 X12 ](2-) dianions was also studied in the gas phase by mass spectrometry in an ion trap. The electrochemical oxidation of the closo-dodecaborate dianions [B12 X12 ](2-) (X=F, Cl, Br, I) by cyclic and Osteryoung square-wave voltammetry in liquid sulfur dioxide or acetonitrile showed very good agreement with quantum chemical calculations in the gas phase. For [B12 X12 ](2-) (X=F, Cl, Br) the first and second oxidation processes are detected. Whereas the first process is quasi-reversible (with oxidation potentials in the range between +1.68 and +2.29 V (lSO2 , versus ferrocene/ferrocenium (Fc(0/+) ))), the second process is irreversible (with oxidation potentials ranging from +2.63 to +2.71 V (lSO2 , versus Fc(0/+) )). [B12 I12 ](2-) showed a complex oxidation behavior in cyclic voltammetry experiments, presumably owing to decomposition of the cluster anion under release of iodide, which also explains the failure to isolate the respective radical by chemical oxidation.

Structural Proof for a Higher Polybromide Monoanion: Investigation of [N(C3H7)4][Br9]

The chemistry of polyhalides, especially of polyiodides, has long been known. 2] The first systematic investigation of these anions goes back to Jçrgensen in 1870. Since these pioneering years, a great variety, mainly of polyiodides, have been investigated. The lighter and more reactive halogens, bromine, chlorine, and fluorine, have been less explored which is probably due to the relative ease of handling iodine. However, in the past year, the investigation of lighter polyhalides has once again come into the focus of the scientific community. Feldmann et al. have reported the preparation of a 3D polybromide network [C4MPyr]2[Br20] [7] in ionic liquids. A series of tetraethylammonium polybromides was also investigated by Raman spectroscopy. Moreover, the first free trifluoride monoanion was characterized by matrix-isolation spectroscopy under cryogenic conditions in argon and neon matrices. All these recent reports indicate that our knowledge of polyhalides is still relatively limited and provides room for new discoveries. The chemistry of polybromides is especially limited compared to the extensive chemistry of polyiodides. Among the polybromide monoanions, only the [Br3] anion was fully characterized, including single-crystal X-ray diffraction. All other known polybromide monoanions (penta, hepta, and nona) were only characterized by IR and/or Raman spectroscopy. Based on these data, their structures were only tentatively assigned. High level quantum-chemical calculations, which could support the structure assignment based on vibrational data for the nonabromide have not been performed. Only calculations at the HF level have been carried out but these do not provide definitive information because of the lack of electron correlation. By far the most prominent polybromides are dianions, such as [Br8] 2 , [Br10] 2 , and [Br20] 2 [7] or polybromide networks 14–16] [{Br3} ·=2 Br2], and [(Br )2·3 Br2]. These compounds are not only of academic interest, they can be used for many practical applications such as zinc–bromine batteries, 18] water treatment, or selective bromination reactions. Furthermore, an application as redox couple in dyesensitized solar cells (DSSC) is promising, a field which is a more and more important in energy generation. Herein, we report the first synthesis of the nonabromide salt [NPr4][Br9]. The reaction of tetrapropylammonium bromide and excess bromine leads to the formation of brownish red crystals. These crystals are relatively stable and can even be handled briefly in air. The single-crystal X-ray structure determination shows that the salt [NPr4][Br9], crystallizes in the tetragonal space group I 4, Figure 1. Similar to other known polyhalides, the [Br9] structure is based on a central bromide anion Br ,

The Reaction of White Phosphorus with NO+/NO2+[Al(ORF)4]−: The [P4NO]+ Cluster Formed by an Unexpected Nitrosonium Insertion†

Despite decades of intense research into polyphosphorus chemistry, our knowledge of homoleptic polyphosphorus cations is still limited to the results of mass spectrometry and quantum chemical calculations. In general, the diamagnetic cage cations with an odd number of phosphorus atoms are more stable, with P9 , composed of two C2v symmetric P5 cages joined by a common phosphonium atom having special stability. This cage was found in one of the few types of simple inorganic phosphorus cluster cations that are known, that is, [P5R2] + (R = Cl, Br, I, Ph, DippN(Cl)NDipp (Dipp = 2,6-diisopropylphenyl)). Those P5 cages are formed by the formal insertion of carbene-analogous PR2 + fragments into the P P bond of P4 (see Ref. [9, 10] for Reviews on P4 activation). Stable carbenes also interact with P4, leading to compounds including P1 up to P12 moieties, depending on the electronic nature of the carbene. Larger cationic P7 cages were recently prepared, but all preparative approaches to true Pn + ions remained futile. However, we expected that an appropriate one-electron oxidant should be able to oxidize P4 (ionization energy (IE) 9.34 eV) and lead to phosphorus cluster cations Pn . Herein we give an account of the reaction of P4 with the salts [NO] [Al(OC(CF3)3)4] [13] (1; IE NO = 9.26 eV) and [NO2] [Al(OC(CF3)3)4] (2 ; IE NO2 = 9.59 eV. At least 2 was expected to be a strong enough oxidant to yield Pn + cations. The novel salt 2 was synthesized in 94 % yield from NO2[BF4] and Li[Al(OC(CF3)3)4] in SO2 solution with precipitation of insoluble Li[BF4]; it was fully characterized by X-ray diffraction and vibrational and NMR spectroscopy (for details, see the Supporting Information). Unexpectedly, the reactions of 1 and 2 with P4 in CH2Cl2 show an analogous process, regardless of the ratios of phosphorus to oxidant employed (between 3P:1 NOx + and 9P:1 NOx ). They form a red intermediate and yield the same yellow final product ([P4NO] [Al(OC(CF3)3)4] (3 ; Scheme 1). Compound 3 may be viewed as the insertion

Fluorine-Rich Fluorides: New Insights into the Chemistry of Polyfluoride Anions.

Polyfluoride anions have been investigated by matrix-isolation spectroscopy and quantum-chemical methods. For the first time the higher polyfluoride anion [F5 ](-) has been observed under cryogenic conditions in neon matrices at 850 cm(-1) . In addition, a new band for the Cs(+) [F3 ](-) complex in neon is reported.

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.

Polychloride monoanions from [Cl3]- to [Cl9]- : a Raman spectroscopic and quantum chemical investigation.

Polychloride monoanions stabilized by quaternary ammonium salts are investigated using Raman spectroscopy and state-of-the-art quantum-chemical calculations. A regular V-shaped pentachloride is characterized for the [N(Me)(4)][Cl(5)] salt, whereas a hockey-stick-like structure is tentatively assigned for [N(Et)(4)][Cl(2)⋅⋅⋅Cl(3)(-)]. Increasing the size of the cation to the quaternary ammonium salts [NPr(4)](+) and [NBu(4)](+) leads to the formation of the [Cl(3)](-) anion. The latter is found to be a pale yellow liquid at about 40 °C, whereas all the other compounds exist as powders. Further to these observations, the novel [Cl(9)](-) anion is characterized by low-temperature Raman spectroscopy in conjunction with quantum-chemical calculations.

In‐Between Complex and Cluster: A 14‐Vertex Cage in [Ag2Se12]2+

Numerous cyclic sulfur and selenium allotropes En (E = S: n = 6–15, 18, 20 etc.; E = Se: n = 6, 7, 8) are known, while hexagonal Te1 remains the only accessible allotrope of tellurium. For Se, the stability of the allotropes increases from Se7< Se6< Se8< Se1. Although being structurally related to crown ethers, only a few examples of chalcogen rings coordinated to a metal ion exist, including [Agn(Se6)] n+ (n = 1, 2), 3] [M(S8)n] + (M = Cu; Ag), [Cu(S12)] , [Cu(S8)(S12)] . All of these cations are partnered with weakly coordinating anions (WCA). Related salts containing almost non-interacting cationic stacks are [Rb(Se8) ]1 [8] and [Rb(Se6)2 ]1. [9] The neutral selenium complexes [PdX2(Se6)] [10] (X = Cl, Br), [(AgI)2Se6], [11] [Re2I2(CO)6(Se7)], [12]

Exploring new 129Xe chemical shift ranges in HXeY compounds: hydrogen more relativistic than xenon.

Among rare gases, xenon features an unusually broad nuclear magnetic resonance (NMR) chemical shift range in its compounds and as a non-bonded Xe atom introduced into different environments. In this work we show that (129)Xe NMR chemical shifts in the recently prepared, matrix-isolated xenon compounds appear in new, so far unexplored (129)Xe chemical shift ranges. State-of-the-art theoretical predictions of NMR chemical shifts in compounds of general formula HXeY (Y = H, F, Cl, Br, I, -CN, -NC, -CCH, -CCCCH, -CCCN, -CCXeH, -OXeH, -OH, -SH) as well as in the recently prepared ClXeCN and ClXeNC species are reported. The bonding situation of Xe in the studied compounds is rather different from the previously characterized cases as Xe appears in the electronic state corresponding to a situation with a low formal oxidation state, between I and II in these compounds. Accordingly, the predicted (129)Xe chemical shifts occur in new NMR ranges for this nucleus: ca. 500-1000 ppm (wrt Xe gas) for HXeY species and ca. 1100-1600 ppm for ClXeCN and ClXeNC. These new ranges fall between those corresponding to the weakly-bonded Xe(0) atom in guest-host systems (δ < 300 ppm) and in the hitherto characterized Xe molecules (δ > 2000 ppm). The importance of relativistic effects is discussed. Relativistic effects only slightly modulate the (129)Xe chemical shift that is obtained already at the nonrelativistic CCSD(T) level. In contrast, spin-orbit-induced shielding effects on the (1)H chemical shifts of the H1 atom directly bonded to the Xe center largely overwhelm the nonrelativistic deshielding effects. This leads to an overall negative (1)H chemical shift in the range between -5 and -25 ppm (wrt CH(4)). Thus, the relativistic effects induced by the heavy Xe atom appear considerably more important for the chemical shift of the neighbouring, light hydrogen atom than that of the Xe nucleus itself. The predicted NMR parameters facilitate an unambiguous experimental identification of these novel compounds.