An X-ray study of some 2,3-diphenyltetrazolium salts

An X-ray diffraction study is reported for three molecules of salts containing a cation with a positive charged 2,3-diphenyltetrazolium ring. The results confirm aromatic structure of the tetrazole ring and the delocalization of charge on the whole molecules of the cations. The molecular geometry obtained is compared with that for free mesoionic 2,3-diphenyltetrazoles which have already been studied and the ring parameters do not reveal significant differences. But is shows that the geometry of the (NNO)^– exocyclic group is changed as a result of alkylation. Compound I C₁₃H₁₂N₅Cl, P2₁/a,a=16.934(4),b=6.575(1),c=26.121(4) Å, =108.15(2)°, II C₁₄H₁₃N₆OI, P3₁2,a=10.774(3),c=12.821(4) Å, IV C₂₆H₂₀N₈Cl₂, C2/c,a=22.316(4),b=6.6903(7),c=20.437(3) Å, =92.51(1)°.     

New measurements and global analysis of rotational spectra of Cl-, Br-, and I-benzene: Spectroscopic constants and electric dipole moments

The data available from rotational spectroscopy for chlorobenzene, bromobenzene, and iodobenzene have been extended by new measurements in the mm-wave region and in supersonic expansion in the cm-wave region. All available ground state measurements have been combined in global fits to derive precise rotational, centrifugal, and nuclear quadrupole coupling constants for the molecules. Rotational transitions in first excited states of the lowest frequency normal modes in bromobenzene and iodobenzene have been assigned and fitted. The values of electric dipole moments for ³⁵Cl-, ⁷⁹Br-, ⁸¹Br-, and I-benzene have been determined from Stark effect measurements on selected hyperfine components in the supersonic expansion spectrum, and are compared with values for several other series of monohalogen molecules.     

Experimental and quantum‐chemical studies of 1H, 13C and 15N NMR coordination shifts in Au(III), Pd(II) and Pt(II) chloride complexes with picolines

¹H, ¹³C and ¹⁵N NMR studies of gold(III), palladium(II) and platinum(II) chloride complexes with picolines, [Au(PIC)Cl₃], trans‐[Pd(PIC)₂Cl₂], trans/cis‐[Pt(PIC)₂Cl₂] and [Pt(PIC)₄]Cl₂, were performed. After complexation, the ¹H and ¹³C signals were shifted to higher frequency, whereas the ¹⁵N ones to lower (by ca 80–110 ppm), with respect to the free ligands. The ¹⁵N shielding phenomenon was enhanced in the series [Au(PIC)Cl₃] < trans‐[Pd(PIC)₂Cl₂] < cis‐[Pt(PIC)₂Cl₂] < trans‐[Pt(PIC)₂Cl₂]; it increased following the Pd(II) → Pt(II) replacement, but decreased upon the trans → cis‐transition. Experimental ¹H, ¹³C and ¹⁵N NMR chemical shifts were compared to those quantum‐chemically calculated by B3LYP/LanL2DZ + 6‐31G**//B3LYP/LanL2DZ + 6‐31G*. Copyright © 2008 John Wiley & Sons, Ltd.     

Tantalum irradiation by high power pulsed laser at 1315 and 438 nm wavelengths

The high power pulsed laser Prague asterix laser system (PALS), operating at the fundamental (1ω) and third (3ω) harmonics (1315 and 438 nm wavelengths, respectively), is employed in a single-shot mode to irradiate tantalum targets in vacuum. The laser pulse width is 400 ps and the laser pulse energy ranges between 43 and 736 J at 1ω and between 12 and 230 J at 3ω. High ablation yields (0.1–0.6 mg per pulse) are measured as a function of the laser pulse energy at both wavelengths; at 438 nm higher etching rates are observed. The produced craters are analysed by the scanning electron microscope (SEM) and by the high sensitivity surface profiler system. They are investigated in dimension, shape and angle aperture as a function of the incident laser energy. Different possible mechanisms responsible for the different crater shapes are presented and discussed.     

Structural studies by 1H and 13C dynamic n.m.r.: Part III alternative protonation sites in carbonyl conjugated enamines of the type R1?C(O)?CH?CH?NR2R3

¹³C magnetic resonance spectra of several enamino ketones with secondary and tertiary amino groups were obtained for trifluoroacetic acid solutions. In both series O-protonation is predominant and the chemical shifts are related to the electron density changes with respect to the parent base. The spectra of the tertiary compounds are interpreted in terms of slow rotation around the C–1? C–2 and C–3? N bonds discernible at room temperature. O-protonated forms of the secondary enamino ketones undergo further reaction on C–2 yielding pyridinium salts. The mechanism of formation of the quaternary salts is interpreted and the additivity parameters of the ¹³C n.m.r. chemical shifts in the pyridinium ions is briefly discussed.     

The determination of mercury in air samples by flameless atomic absorption

A method is described for the determination of mercury in air by furnace atomic absorption. The porous graphite cups used ordinarily fail to adsorb mercury vapors from the air. When these same porous graphite cups are plated on the inner surface with a thin layer of gold the retention of mercury from an air sample passed through the cup is shown to be quantitative. The sensitivity of the analytical system is 3 × 10^?10 g which is equivalent to 0.6 $\text{μg}\text{m}{}^3$ for a 500 cm³ air sample. Relative S.D. is 11.2%. The method described should also prove useful for other types of flameless devices.     

Some symmetry aspects of layered-clathrate structures formed by Ni (NCS)2 (4-methylpuridine)4

The crystal structures of layered clathrate inclusion compounds of Ni(CNS)₂ (4-methylpyridine)₄ with 1-bromonaphthalene (I) and azulene (II) were analyzed by x-ray single-crystal diffractometry [crystal data: I–C₄₆H₄₂N₆S₂Br₂Ni; a=11.88(1), b=11.82(1), c=32.79(3), =102.0(1), Z=4, P2₁/c; II–C₄₆H₄₄N₆S₂Ni; a=11.51(2), b=11.64(1), c=32.98(2), =103.4, Z=4, P2₁/n]. Disordering of guest molecules in I is concluded, based on x-ray study, and positions of the guest (each of the two symmetry independent molecules disordered over two orientations) have been refined. In II disoder of guest-azulene is also observed but only one from the two symmetrically independent guest molecules could be located from the x-ray data. The empirical force field calculations were performed for I and II. The results were used for location of the second azulene molecule and for discussion of the disorder mole (short or long-range).     

Chemical Manganese Dioxide (CMD): its application to the oxidative iodination of benzene, halobenzenes and some deactivated arenes

After comparing our previous and newer results for numerous oxidative aromatic iodination experiments using various brands of active MnO2 as the oxidants,we recommend the use of a Chemical Manganese Dioxide (Aldrich CMD; 90 +% MnO2) as the oxidant of choice, since it is satisfactorily pure and chemically active, and is notably less costly than other options.     

Asymptotic Distribution of Eigenvalues for a Class of Second-Order Elliptic Operators with Irregular Coefficients in R d

Let A=A ₀+v(x) where A ₀ is a second-order uniformly elliptic self-adjoint operator in R ^d and v is a real valued polynomially growing potential. Assuming that v and the coefficients of A ₀ are Hölder continuous, we study the asymptotic behaviour of the counting function N(A,) () with the remainder estimates depending on the regularity hypotheses. Our strongest regularity hypotheses involve Lipschitz continuity and give the remainder estimate N(A,)O({}^–), where may take an arbitrary value strictly smaller than the best possible value known in the smooth case. In particular, our results are obtained without any hypothesis on critical points of the potential.