Optical constants and integrated intensities of liquid hexafluorobenzene between 4000 and 250 cm at 25 °C

The optical constants (real and imaginary refractive indices) of hexafluorobenzene were determined at 25 °C via transmission measurements. Experimental absorbance spectra measured on a Nicolet Impact 410 FTIR were converted to imaginary refractive indices using methods described in the literature. The real refractive indices were obtained by Kramers–Kronig transformation of the imaginary refractive indices. From the complex refractive indices, the molar absorption coefficient (E_m) and complex molar polarizability spectra were calculated. The integrated intensities for the E_1u fundamentals were obtained from the areas under the bands in the spectrum. These integrated intensities are compared to those for benzene and benzene-d₆ in the literature.     

Carbon-fluorine bond activation coupled with carbon-hydrogen bond formation alpha to iridium: kinetics, mechanism, and diastereoselectivity

Reactions of iridium(fluoroalkyl)hydride complexes CpIr(PMe(3))(CF(2)R(F))Y (R(F) = F, CF(3); Y = H, D) with LutHX (Lut = 2,6-dimethylpyridine; X = Cl, I) results in C-F activation coupled with hydride migration to give CpIr(PMe(3))(CYFR(F))X as variable mixtures of diastereomers. Solution conformations and relative diastereomer configurations of the products have been determined by (19)F{(1)H}HOESY NMR to be (S(C), S(Ir))(R(C), R(Ir)) for the kinetic diastereomer and (R(C), S(Ir))(S(C), R(Ir)) for its thermodynamic counterpart. Isotope labeling experiments using LutDCl/CpIr(PMe(3))(CF(2)R(F))H and CpIr(PMe(3))(CF(2)R(F))D/LutHCl) showed that, unlike a previously studied system, H/D exchange is faster than protonation of the alpha-CF bond, giving an identical mixture of product isotopologues from both reaction mixtures. The kinetic rate law shows a first-order dependence on the concentration of iridium substrate, but a half-order dependence on that of LutHCl; this is interpreted to mean that LutHCl dissociates to give HCl as the active protic source for C-F bond activation. Detailed kinetic studies are reported, which demonstrate that lack of complete diastereoselectivity is not a function of the C-F bond activation/H migration steps but that a cationic intermediate plays a double role in loss of diastereoselectivity; the intermediate can undergo epimerization at iridium before being trapped by halide and can also catalyze the epimerization of kinetic diastereomer product to thermodynamic product. A detailed mechanism is proposed and simulations performed to fit the kinetic data.     

Large effects of ion pairing and protonic-hydridic bonding on the stereochemistry and basicity of crown-, azacrown-, and cryptand-222-potassium salts of anionic tetrahydride complexes of iridium(III)

The compounds [K(Q)][IrH(4)(PR(3))(2)] (Q = 18-crown-6, R = Ph, (i)Pr, Cy; Q = aza-18-crown-6, R = (i)Pr; Q = 1,10-diaza-18-crown-6, R = Ph, (i)Pr, Cy; Q = cryptand-222, R = (i)Pr, Cy) were formed in the reactions of IrH(5)(PR(3))(2) with KH and Q. In solution, the stereochemistry of the salts of [IrH(4)(PR(3))(2)](-) is surprisingly sensitive to the countercation: either trans as the potassium cryptand-222 salts (R = Cy, (i)Pr) or exclusively cis (R = Cy, Ph) as the crown- and azacrown-potassium salts or a mixture of cis and trans (R = (i)Pr). There is IR evidence for protonic-hydridic bonding between the NH of the aza salts and the iridium hydride in solution. In single crystals of [K(18-crown-6)][cis-IrH(4)(PR(3))(2)] (R = Ph, (i)Pr) and [K(aza-18-crown-6)][cis-IrH(4)(P(i)Pr(3))(2)], the potassium bonds to three hydrides on a face of the iridium octahedron according to X-ray diffraction studies. Significantly, [K(1,10-diaza-18-crown-6)][trans-IrH(4)(P(i)Pr(3))(2)] crystallizes in a chain structure held together by protonic-hydridic bonds. In [K(1,10-diaza-18-crown-6)][cis-IrH(4)(PPh(3))(2)], the potassium bonds to two hydrides so that one NH can form an intra-ion-pair protonic-hydridic hydrogen bond while the other forms an inter-ion-pair NH.HIr hydrogen bond to form chains through the lattice. Thus, there is a competition between the potassium and NH groups in forming bonds with the hydrides on iridium. The more basic P(i)R(3) complex has the lower N-H stretch in the IR spectrum because of stronger N[bond]H...HIr hydrogen bonding. The trans complexes have very low Ir-H wavenumbers (1670-1680) due to the trans hydride ligands. The [K(cryptand)](+) salt of [trans-IrH(4)(P(i)Pr(3))(2)](-) reacts with WH(6)(PMe(2)Ph)(3) (pK(alpha)(THF) 42) to give an equilibrium (K(eq) = 1.6) with IrH(5)(P(i)Pr(3))(2) and [WH(5)(PMe(2)Ph)(3)](-) while the same reaction of WH(6)(PMe(2)Ph)(3) with the [K(18-crown-6)](+) salt of [cis-IrH(4)(P(i)Pr(3))(2)](-) has a much larger equilibrium constant (K(eq) = 150) to give IrH(5)(P(i)Pr(3))(2) and [WH(5)(PMe(2)Ph)(3)](-); therefore, the tetrahydride anion displays an unprecedented increase (about 100-fold) in basicity with a change from [K(crypt)](+) to [K(crown)](+) countercation and a change from trans to cis stereochemistry. The acidity of the pentahydrides decrease in THF as IrH(5)(P(i)Pr(3))(2)/[K(crypt)][trans-IrH(4)(P(i)Pr(3))(2)] (pK(alpha)(THF) = 42) > IrH(5)(PCy(3))(2)/[K(crypt)][trans-IrH(4)(PCy(3))(2)] (pK(alpha)(THF) = 43) > IrH(5)(P(i)Pr(3))(2)/[K(crown)][cis-IrH(4)(P(i)Pr(3))(2)] (pK(alpha)(THF) = 44) > IrH(5)(PCy(3))(2)/[K(crown)][cis-IrH(4)(PCy(3))(2)]. The loss of PCy(3) from IrH(5)(PCy(3))(2) can result in mixed ligand complexes and H/D exchange with deuterated solvents. Reductive cleavage of P-Ph bonds is observed in some preparations of the PPh(3) complexes.     

Determination of inorganic chlorine stable isotopes by continuous flow isotope ratio mass spectrometry

Chlorine stable isotope analyses of inorganic samples were conducted using continuous flow isotope ratio mass spectrometry (CF-IRMS) coupled with gas chromatography (GC). Inorganic chloride was precipitated in the form of silver chloride (AgCl) by using silver nitrate in a standard methodology. Chlorine stable isotope analysis was carried out on methyl chloride (CH3Cl) after converting AgCl into CH3Cl by reacting it with methyl iodide (CH3I). The reaction between AgCl and CH3I took place in 20 mL size vials. Addition of CH3I was performed in a glove bag under helium flow. An Agilent 6890 gas chromatograph equipped with a CTC Analytics CombiPAL autosampler and a DB-5MS 60 m column was used to separate CH3Cl from CH3I. This new technique uses samples as small as 0.2 mg of AgCl (1.4 micromol of Cl-). The chlorine stable isotope analysis using continuous flow technology showed excellent precision and accuracy. The internal precision using pure CH3Cl gas is better than +/-0.04 per thousand (+/-STDV). The external precision using seawater standard is better than +/-0.07 per thousand (+/-STDV) for n=12. Moreover, the sample analysis time is much shorter and many more samples can be analyzed in one day than by using the conventional off-line techniques.     

The supercuspidal representations of <Emphasis Type="Italic">p</Emphasis>-adic classical groups

Let G be a unitary, symplectic or special orthogonal group over a locally compact non-archimedean local field of odd residual characteristic. We construct many new supercuspidal representations of G, and Bushnell–Kutzko types for these representations. Moreover, we prove that every irreducible supercuspidal representation of G arises from our constructions.     

The valence bands of model amorphous semiconductor structures

Using a basis of bonding orbitals, and tight-binding matrix elements which depend on the local topology, we calculate the valence band electronic structure of silicon on the diamond and ST12(GeIII) lattices, as well as on the continuous random networks of Polk and Boudreaux and Connell and Temkin. Results indicate the need for odd-membered rings to account for the experimentally observed features.     

Sums of Five, Seven and Nine Squares

Let r _k(n) denote the number of representations of an integer n as a sum of k squares. We prove that

Synthesis and photophysical behavior of a novel zinc phthalocyanine containing a single carboxylic acid and three phenylthio substituents

Zinc 2, (3)-tri-(phenylthio)-2, (3)-carboxy phthalocyanine (ZnPc(COOH)(SPh)₃), zinc 2, (3)-tetra-(phenylthio) phthalocyanine (ZnPc(SPh)₄) and 2, (3)-tetra-(phenylthio) phthalocyanine (H₂Pc(SPh)₄) were synthesized and their photophysical behavior were compared with those of a number of zinc phthalocyanine (ZnPc) derivatives. ZnPc(COOH)(SPh)₃ and ZnPc(SPh)₄ had similar fluorescence (Φ_F=0.14) and triplet state (Φ_T=0.65) quantum yields in dimethylsulfoxide, hence showing no effects of the replacement of one of the phenylthio groups with a carboxylic acid group. ZnPc(COOH)(SPh)₃ displayed a slightly shorter triplet lifetime (τ_T=331 μs) than ZnPc (τ_T=350 μs) in DMSO, but within the range of ZnPc derivatives. The triplet lifetime for ZnPc(COOH)(SPh)₃ is much longer than for the symmetrical derivative (ZnPc(SPh)₄) with τ_T=149 μs in DMSO.