Structure and bonding in the isoelectronic series CnHnP5-n+: is phosphorus a carbon copy?

The relative stabilities of different isomers of the isoelectronic series C(n)H(n)P(5-n)(+) have been investigated using G3X theory. The results indicate that all species containing one or more phosphorus atom adopt a three-dimensional nido geometry, in marked contrast to the planar structure favoured by the all-carbon analogue. Within isomeric nido clusters, a strong correlation between total energy and the nucleus-independent chemical shift (NICS) indicates that three-dimensional aromaticity plays a significant role in determining the stability of the cluster. In the context of these nido clusters, the extent to which phosphorus is a carbon copy proves to be highly dependent on the global electronic environment. The first isolobal substitution of CH by P causes a complete switch from localised to delocalised bonding, accompanied by a transition from a two- to a three-dimensional structure, with the phosphorus atom showing a strong preference for the unique apical site. In contrast, further increasing the phosphorus content causes no further change in structure or bonding, suggesting that, at the basal sites, phosphorus is a rather better carbon copy. The low-energy pathways for interconversion of apical and basal atoms previously identified in C(2)H(2)P(3)(+) prove to be a general feature of all members of the series.     

Synthesis of analogue structures of the p-quinone methide moiety of kendomycin

[reaction: see text] The synthesis of two model p-quinone methide ring systems of the antibiotic and antiosteoporotic compound kendomycin is reported. Two approaches were examined in detail, and the two-step (i) demethylation and (ii) DMDO oxidation were found to be reliable and generally applicable. Additionally, it was found that oxidation of a benzofuran by NaIO(4) on silica produced a long-lived semiquinone radical.     

Complete characterization of an (Sb2O3)n/SWNT inclusion composite

The detailed inclusion crystallography of a one-dimensional valentinite Sb₂O₃ crystal incorporated within a helical (21, ?8) single-walled carbon nanotube (SWNT) was identified from a phase image that was recovered via a modified object wave restoration scheme. A detailed analysis of asymmetric fringe contrast in the tube walls provided strong evidence for the chiral sense of the tube itself. Due to the good agreement of the observed wall periodicity with the determined absolute focus values and power spectra obtained from single-pixel line traces along both tube walls, we were able to determine the chiral sense of the SWNT and the tilt angle of the Sb₂O₃/SWNT composite relative to the electron beam. The angle between the optimum $\left\langle {10\bar 1} \right\rangle $ viewing direction of the crystal fraction and the tube axis, which is aligned with the $\left\langle {4\bar 12} \right\rangle $ direction of the Sb₂O₃ crystal, is 78.3°. Since small deviations from this viewing direction make an insignificant difference to the observed contrast, a tube inclination of 15° is plausible for both the Sb₂O₃ crystal and the assigned (21, ?8) SWNT, which is the mirror image of a (13, 8) SWNT.     

The preparation of organically functionalized chromium and nickel nanoparticles

Nanoparticles of chromium or nickel have been prepared by the reduction of either CrCl2 or Ni(acac)2 (acac = pentane-2,4-dionate) at elevated temperatures in various Lewis base solvents; the effect of the Lewis base, which acts as both a reaction solvent and passivating ligand on morphology are apparent; the nanostructures have been analysed by NMR, IR, TEM and XRD.     

On the Affine Temperley-Lieb Algebras

The paper describes the cell structure of the affine Temperley–Liebalgebra with respect to a monomial basis. A diagram calculusis constructed for this algebra.     

Discrete Series Characters for GL(n, q)

The discrete series characters of the finite general linear group GL(n, q) are expressed as uniquely defined integral linear combinations of characters induced from linear characters on certain subgroups Hd, n of GL(n, q). The coefficients in these linear combinations are determined (for all n, q) by a family of polynomials r(T) Z[T] indexed by the set of all partitions .