1-Phenyl-1,2-dicarba-closo-dodecaborane, 1-Ph-1,2-closo-C(2)B(10)H(11). Synthesis, Characterization, and Structure As Determined in the Gas Phase by Electron Diffraction, in the Crystalline Phase at 199 K by X-ray Diffraction, and by ab Initio Computations

The compound 1-phenyl-1,2-dicarba-closo-dodecaborane(12), 1-C(6)H(5)-1,2-closo-C(2)B(10)H(11) (1), has been synthesized and characterized by a complete assignment of its (11)B NMR spectrum via (11)B{(1)H}/(11)B{(1)H} (COSY), (1)H{(11)B(selective)} and (1)H{(11)B}/(1)H{(11)B} (COSY) spectroscopy. An electron- and X-ray diffraction investigation of 1, complemented by ab initio calculations, has been undertaken. The gas-phase electron-diffraction (GED) data can be fitted by several models describing conformations which differ in the position of the phenyl ring with respect to the carborane cage. Local symmetries ofC(2)(v)() and D(6)(h)() for the 1,2-C(2)B(10) and C(6) moieties, respectively, were adopted in the GED model in order to simplify the problem. In addition, constraints among the close-lying C-C and B-B bonds were employed. However, even though such simplifications led to satisfactory refinements (R(G) = 0.069-0.071), a unique, definitive solution could not be gained. The (C-C)(mean), (C-B)(mean) and (B-B)(mean) bond lengths,r(a), are ca. 1.44, 1.72, and 1.78 ?, respectively. The C(6) hexagon, with r(a)(C-C) = ca. 1.394 ?, either eclipses the C(1)-C(2) vector (overall C(s)() symmetry) or more or less eclipses the C(1)-B(4) cluster bond (overall C(1) symmetry). In contrast, in the solid at 199 K, the ring lies at a position intermediate between the two GED positions, as determined by X-ray crystallography [C(8)H(16)B(10), monoclinic P2(1)/a: a = 12.047(3) ?, b = 18.627(4) ?, c = 12.332(5) ?, beta = 110.09(4) degrees, Z = 8]. The C-B distances span the range 1.681(6)-1.743(5) ?, and B-B lengths lie between 1.756(6) and 1.795(6) ?. A similar conformation was found for the theoretical (RHF/6-31G level) structure which was fully optimized in C(1) symmetry. The r(e) distances are consistent with the dimensions derived in the experimental studies. IGLO calculations of the (11)B chemical shifts, in addition to SCF single-point energies of the GED structures, further support these observations.     

Glass transition temperatures of stereoblock,isotactic and atactic polypropylenes of various chain lengths

The effect of sample molecular weight on the glass transition temperature has been examined for isotactic, stereoblock and atactic polypropylene samples. Asymptotic values of T₉ (∞) (isotactic) = 272°K, T₉ (∞) (atactic) = 266°K, and T_g (∞) (stereoblock) = 266°K were found. Deviation from T_g (∞) was observed when M?_n was below 10⁴; the dependence of T_g on M?_n has been discussed in relation to the Gibbs-DiMarzio treatment of the glass transition. The possible effects of both tacticity and crystallinity on T_g were examined; comparison of the data obtained with those of other workers was made. It was concluded that molecular order in polypropylene samples could affect T_g significantly and that this was particularly obvious in short chain stereoblock fractions.     

Unusual ligand transformations initiated by dppm deprotonation in methylene-bridged Rh/Os complexes

The reaction of [RhOs(CO)(3)(μ-CH(2))(dppm)(2)][CF(3)SO(3)] (dppm = μ-Ph(2)PCH(2)PPh(2)) with 1,3,4,5-tetramethylimidazol-2-ylidene (IMe(4)) results in competing substitution of the Rh-bound carbonyl by IMe(4) and dppm deprotonation by IMe(4) to give the two products [RhOs(IMe(4))(CO)(2)(μ-CH(2))(dppm)(2)][CF(3)SO(3)] and [RhOs(CO)(3)(μ-CH(2))(μ-κ(1):η(2)-dppm-H)(dppm)] [3; dppm-H = bis(diphenylphosphino)methanide], respectively. In the latter product, the dppm-H group is P-bound to Os while bound to Rh by the other PPh(2) group and the adjacent methanide C. The reaction of the tetracarbonyl species [RhOs(CO)(4)(μ-CH(2))(dppm)(2)][CF(3)SO(3)] with IMe(4) results in the exclusive deprotonation of a dppm ligand to give [RhOs(CO)(4)(μ-CH(2))(μ-κ(1):κ(1)-dppm-H)(dppm)] (4) in which dppm-H is P-bound to both metals. Both deprotonated products are cleanly prepared by the reaction of their respective precursors with potassium bis(trimethylsilyl)amide. Reversible conversion of the μ-κ(1):η(2)-dppm-H complex to the μ-κ(1):κ(1)-dppm-H complex is achieved by the addition or removal of CO, respectively. In the absence of CO, compound 3 slowly converts in solution to [RhOs(CO)(3)(μ-κ(1):κ(1):κ(1)-Ph(2)PCHPPh(2)CH(2))(dppm)] (5) as a result of dissociation of the Rh-bound PPh(2) moiety of the dppm-H group and its attack at the bridging CH(2) group. Compound 4 is also unstable, yielding the ketenyl- and ketenylidene/hydride tautomers [RhOs(CO)(3)(μ-κ(1):η(2)-CHCO)(dppm)(2)] (6a) and [RhOs(H)(CO)(3)(μ-κ(1):κ(1)-CCO)(dppm)(2)] (6b), initiated by proton transfer from μ-CH(2) to dppm-H. Slow conversion of these tautomers to a pair of isomers of [RhOs(H)(CO)(3)(μ-κ(1):κ(1):κ(1)-Ph(2)PCH(COCH)PPh(2))(dppm)] (7a and 7b) subsequently occurs in which proton transfer from a dppm group to the ketenylidene fragment gives rise to coupling of the resulting dppm-H methanide C and the ketenyl unit. Attempts to couple the ketenyl- or ketenylidene-bridged fragments in 6a/6b with dimethyl acetylenedicarboxylate (DMAD) yield [RhOs(κ(1)-CHCO)(CO)(3)(μ-DMAD)(dppm)(2)], in which the ketenyl group is terminally bound to Os.     

The copolymerisation of 2,4-dicyanobut-1-ene with N-vinyl carbazole

The copolymerisation of the monomers 2,4-dicyanobut-1-ene and N-vinyl carbazole has been studied. The presence of a charge transfer complex from these two monomers with a 1:1 stoichiometry has been established, and a value of 0.22 dm³ mol⁻¹ at 298 K for the equilibrium constant for complex formation has been obtained from NMR measurements. The copolymer composition data have been analyzed allowing for the participation of the complex in the propagation reactions; the results have been compared with the predictions of two simpler terminal models and with the penultimate model.     

Miscibility enhancement in blends of polystyrene and polyisoprene modified with electron donor–electron acceptor groups

The use of electron donor–electron acceptor groups to enhance miscibility in polymer blends has been investigated, using the immiscible binary pair polystyrene and polyisoprene as the basic materials. These polymers have been modified by copolymerization with monomers that are either donor or acceptor groups. The copolymers synthesized were poly(styrene-stat-N-itaconimidyl-3,5-dinitrobenzoate), which contains the electron acceptor, and poly[isoprene-stat-N-(2-hydroxyethyl) carbazole methacrylate], which contains the electron donor. Blends were examined using differential scanning calorimetry and dynamic mechanical thermal analysis. The criterion of miscibility was taken to be the presence of only one glass transition temperature in the binary blend, and it was established that at least 20 mol% of the donor–acceptor units had to be incorporated into each chain before a stable one-phase blend was obtained. Miscible blends were observed to undergo a “decomplexation” reaction above the blend T_g, to form partially phase separated blends, with each phase rich in one component and diluted by the second. The value of the blend T_g was above that expected from a weighted average of those of the components, indicating that specific intermolecular interactions, probably charge-transfer complexes, which led to nonbonding crosslinking were present in the blend and stabilized the one-phase system.     

Orbital Angular Momentum in Scalar Diquark Model and QED

We compare the orbital angular momentum of the ‘quark’ in the scalar diquark model as well as that of the electron in QED (to order α) obtained from the Jaffe–Manohar decomposition to that obtained from the Ji relation. We estimate the importance of the vector potential in the definition of orbital angular momentum.     

Glass and sub-glass transitions in methylphenyl and chlorophenyl polyitaconic acid esters

Two series of ring substituted poly(di-phenyl itaconate)s have been prepared and characterized. The 2-, 3-, and 4-methylphenyl and chlorophenyl derivatives were studied and the glass transition temperatures (Tg) of the 3-substituted polymers were found to be lower than those of the 2- or 4-substituted polymers in each series. Some suggestion of polar effects contributing to Tg was evident in the poly(di-(4-chlorophenyl)itaconate). Dynamic mechanical studies revealed prominent damping peaks in the glassy state of the poly(di(methylphenyl)itaconate)s which can be attributed to methyl group relaxation. The chloro-derivatives showed fewer features, although in the 4-chloro compound there is evidence of restricted ring oscillation in the glass.     

The local structure of SO2 and SO3 on Ni(1 1 1)

The normal incidence X-ray standing wave (NIXSW) technique, supported by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS), has been used to determine the local adsorption geometry of SO₂ and SO₃ on Ni(1 1 1). Chemical-state specific NIXSW data for coadsorbed SO₃ and S, formed by the disproportionation of adsorbed SO₂ after heating from 140 K to 270 K, were obtained using S 1s photoemission detection. For adsorbed SO₂ at 140 K the new results confirm those of an earlier study [Jackson et al., Surf. Sci. 389 (1997) 223] that the molecule is located above hollow sites with its molecular plane parallel to the surface and the S and O atoms in off-atop sites; corrections to account for the non-dipole effects in the interpretation of the NIXSW monitored by S 1s and O 1s photoemission, not included in the earlier work, remove the need for any significant adsorption-induced distortion of the SO₂ in this structure. SO₃, not previously investigated, is found to occupy an off-bridge site with the C_3v axis slightly tilted relative to the surface normal and with one O atom in an off-atop site and the other two O atoms roughly between bridge and hollow sites. The O atoms are approximately 0.87 Å closer to the surface than the S atom. This general bonding orientation for SO₃ is similar to that found on Cu(1 1 1) and Cu(1 0 0) both experimentally and theoretically, although the detailed adsorption sites differ.