The infrared spectrum of Au-.CO2

The Au-.CO2 ion-molecule complex has been studied by gas phase infrared photodissociation spectroscopy. Several sharp transitions can be identified as combination bands involving the asymmetric stretch vibrational mode of the CO2 ligand. Their frequencies are redshifted by several hundred cm(-1) from the frequencies of free CO2. We discuss our findings in the framework of ab initio and density-functional theory calculations, using anharmonic corrections to predict vibrational transition energies. The infrared spectrum is consistent with the formation of an aurylcarboxylate anion with a strongly bent CO2 subunit.     

b1Σ+ Emissions from group V–VII diatomic molecules. b 0+ → X1 0+, X2 1 emissions of AsI and SbI

Chemiluminescence from the b 0⁺ → X₁ 0⁺ band system of AsI and of the b 0⁺ → X₁ 0⁺, X₂ 1 systems of SbI in the near-infrared spectral region has been observed in a discharge flow system. Analysis of the spectra led to the spectroscopic constants (in cm^?1) of AsI: ω_e(X₁, X₂) = 257 ± 2, ω_ex_e(X₁, X₂) = 0.82 ± 0.2, T_e(b 0⁺) = 11738 ± 5, ω_e(b 0⁺) = 271 ± 2, ω_ex_e(b 0⁺) = 0.66 ± 0.2, and of SbI: T_e(X₂ 1) = 965 ± 10, ω_e(X₁, X₂) = 206 ± 6, T_e(b 0⁺) = 12328 ± 10, ω_e(b 0⁺) = 211 ± 6. The intensity ratio of the two sub-systems b 0⁺ → X₂ 1 and b 0⁺→ X₁ 0⁺ was found to be ≈0.013 in the case of SbI and ? 0.01 for AsI.     

Pyrimidine acyclo-C-nucleosides by ring transformations of 2-formyl-L-arabinal

The protected 2-formyl-L-arabinal 2 reacted with thiourea and cyanamide in the presence of sodium hydride to afford via ring transformations the 5-[1R,2S-1,2- bis(benzyloxy)-3-hydroxypropyl]-1,2-dihydropyrimidines 3 and 4, respectively. Similarly, treatment of 2 with 3-amino-2H-1,2,4-triazole yielded 6-[1R,2S-1,2- bis(benzyloxy)-3-hydroxypropyl][1,2,4]-triazolo[1,5-a]pyrimidine (5).     

Self-assembled organic monolayers terminated in perfluoroalkyl pentafluoro-lambda(6)-sulfanyl (-SF5) chemistry on gold

Recently synthesized (Winter, R.; Nixon, P. G.; Gard, G. L.; Radford, D. H.; Holcomb, N. R.; Grainger, D. W. J. Fluorine Chem. 2001, 107, 23-30) SF5-terminated perfluoroalkyl thiols (SF5(CF2)nCH2CH2SH, where n = 2, 4, and 6) and a symmetric SF5-terminated dialkyl disulfide ([SF5-CH=CH-(CH2)8-S-]2) were assembled as thin films chemisorbed onto gold surfaces. The adsorbed monolayer films of these SF5-containing molecules on polycrystalline gold were compared using ellipsometry, contact angle, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and infrared spectroscopy (FTIR) surface analytical methods. The resulting SF5-dialkyl disulfide monolayer film shows moderate angle dependence in depth-dependent XPS analysis, suggesting a preferentially oriented film. The SF5-terminated perfluoroalkyl thiols exhibit angular-dependent XPS compositional variance depending on perfluoroalkyl chain length, consistent with improved film assembly (increasingly hydrophobic, fewer defects, and more vertical chain orientation increasing film thickness) with increasing chain length. Tof-SIMS measurements indicate that both full parent ions for these film-forming molecules and the unique SF5 terminal group are readily detectable from the thin films without substantial contamination from other adsorbates.     

Stability of the gold(i)-phosphine bond. A comparison with other group 11 elements

The stability of gold phosphine complexes of the form [Au(PH(3))(n)()](+) (n = 1-4) and [AuCl(PH(3))(n)()] (n = 1-3) is analyzed in detail by applying quantum theoretical methods and compared to the coordination behavior of the lighter group 11 elements copper and silver. It is shown that, once [M(PH(3))(2)](+) or [MClPH(3)] (M = Cu, Ag, and Au) is formed, further coordination by PH(3) ligands is relatively weak; i.e., the energy gain to form [M(PH(3))(3)](+) from [M(PH(3))(2)](+) is less than 60 kJ mol(-)(1), and less than 100 kJ mol(-)(1) to form [MCl(PH(3))(2)] from [MClPH(3)]. Relativistic effects in gold significantly influence these factors and reduce the tendency for phosphine coordination beyond two-coordination. This implies that the most favored coordination number for gold is two with either a linear P-Au-P or P-Au-X arrangement (X = a strongly coordinating ligand like Cl(-)). Instead, X-Au-PH(3) units prefer to interact via close Au-Au contacts (aurophilic interactions) keeping the linear structure approximately intact, while the corresponding copper and silver compounds prefer PH(3) coordination to strongly bound M(2)Cl(2) units (M = Cu or Ag) where two chlorine atoms bridge the two metal atoms thus having the formal coordination number of three for copper or silver.     

Crystal Structures of Twisted Di(2-Pyridyl)ketone and Planar Azo-di(2-Pyridine) and Their Discussion Based on PM3 Enthalpy Hypersurfaces for the Isoelectronic Molecules

Single crystal structure determinations prove the two pyridine substituents in di(2-pyridyl)ketone (H₄C₄NC)₂C=O to be twisted out of the carbonyl skeleton plane by torsion angles (OCCN) of 41° and –163°, in contrast to their planar arrangement in azo-di(2-pyridine) H₄C₄NC)-N=N-(CNC₄H₄). In order to rationalize the surprising difference between the two isoelectronic molecules, approximate PM3 enthalpy of formation hypersurfaces have been calculated for each of the two ring torsions, which are assumed to be the dominant ones among the 3N – 6 = 60 degrees of freedom. For both the ketone and the azo derivative, global minima are calculated, the torsion angles of which deviate from the crystal structure results, and, therefore, support the assumption that both the experimentally determined twisting of di(2-pyridyl)ketone as well as the flattening of azo-di(2-pyridine) might be affected by the crystal packing.     

Separation of dixanthogen and sulphur xanthates by H.P.L.C.: Disproportionation of Sulphur Dixanthates

High-performance liquid chromatography on C₁₃ reverse-phase or silica gel columns, with methanol—water (85:15) or n-hexane, respectively, as mobile phase, is used to separate dixanthogens and sulphur xanthates with different alkyl groups. Detection limits are as low as 1 ng (0.05 ppm) with u.v. detectors. When molecular emission cavity analysis is used for the detector, detection limits are reduced to ca. 0.25 ng (0.013 ppm). In aqueous methanol, alkyl sulphur dixanthates, (ROCS₂)₂S, disproportionate to yield mixtures of the corresponding dixanthogen, (ROCS₂)₂ , alkyl sulphur monoxanthates, (ROCS₂)₂S₂ , and dixanthates.