David R. M. Walton

The chemistry of fullerenes

Initially envisaged as rather unreactive, aromatic-like molecules, the fullerenes instead undergo a wide variety of reactions characteristic of alkenes. The many derivatives of C60, and the few of C70, that have now been reported offer new directions for organic chemistry.

Electronic spectra and transitions of the fullerene C60

Abstract Absorption spectra of C60 have been measured in the ranges (a) 190–700 nm in n-hexane solutions at 300 K, (b) 390–700 nm in n-hexane and in 3-methylpentane solutions at 77 K. 40 vibronic bands were observed. They exhibit a large range of bandwidths and intensities, whose significance is discussed. Assignment of electronic transitions has been carried out using the results of theoretical calculations. Vibronic structures have been analyzed within the framework of theories of electronic transitions of polyatomic molecules applied to the Ih symmetry group. Nine allowed 1T1u−1Ag transitions have been assigned in the 190–410 nm region. Observed and calculated allowed transition energies and oscillator strengths are compared. Detailed vibronic analyses of the 1 1T1u−1 1Ag and 2 1T1u−1 1Ag transitions illustrate the role of Jahn-Teller couplings. Orbitally forbidden singlet-singlet transitions are observed between 410 and 620 nm. Their vibronic structures were analyzed in terms of concurrent Herzberg-Teller and Jahn-Teller vibronic interactions. The 77 K spectra provided useful information on hot bands and on other aspects of the analyses. Vibronic bands belonging to triplet←singlet transitions were detected between 620 and 700 nm.

Silylation as a protective method for terminal alkynes in oxidative couplings : A general synthesis of the parent polyynes H(CC)nH (n = 4–10, 12)☆

Abstract Individual polyynes in the series H(CC)n (n = 4–10, 12) have been prepared in solution by sequences involving Cu-catalysed oxidative couplings (Hay technique) of silyl-protected terminal alkynes, partial cleavage (desilylation) of the products by alkali, recoupling and complete desilylation. Thus using the conditions established in a model coupling, Et3SiCCH(I) → Et3Si(CSiEt3(II), coupling of the silyidiyne Et3Si(CC)2H(II) gives Et3Si(CC)4SiEt3(IV) which upon controlled cleavage yields a chromatographically separable mixture of IV, Et3Si(CC)4H (V) and H(CC)4H (VI). Coupling of V in turn gives Et3Si(CC)18SiEt3 (VII) which upon cleavage yields Et3Si(CC)8H (VIII) and H(CC)8H (IX), and coupling of VIII gives the bissilylhexadecaacetylene Et3Si(CC)16SiEt3(X). Hexa- and dodecaacetylene may be synthesized analogously: Et3Si(CC)3SiEt3 (XII) → Et3Si(CC)3H (XI) → Et3Si(C)6SiEt3 (XIII) → Et3Si(CC)6H (XIV) → H(CC)6H (XV); XIV → Et3Si(CC)12SiEt3 (XVI) → H(CC)12H (XVII). Other members of the series are prepared via mixed couplings: I + V → Et3Si(CC)5SiEt3 (XVIII) → H(CC)5H (XIX): I + XIV → Et3Si(CC)7SiEt3 (XX) → H(CC)7H (XXI); I + VIII → Et3Si(CC)9SiEt3 (XXII) → H(CC)9H (XXIII): III + VIII → Et3Si(CC)10SiEt3 (XXIV) → H(CC)10H (XXV). The principal UV light absorption maxima of compounds IV → XXV within each of the series Et3Si(CC)nSiEt3, Et3Si(C)nH and H(CC)nH correlate excellently with relationships previously established for polyyne spectra: λ2 = kn (λ = longest wavelength high intensity band) and Δλ = k′n (Δλ = average vibrational spacing of the intense bands).

Friedel-crafts reactions of bis(trimethylsilyl)polyynes with acyl chlorides; a useful route to terminal-alkynyl ketones

Abstract Bis(trimethylsilyl)acetylenes, Me 3 Si(CC) n SiMe 3 , react with acyl chloride-aluminium chloride complexes, XC 6 H 4 COCl·AlCl 3 in methylene chloride at 0–20° to form the corresponding ketones XC 6 H 4 CO(CC) n SiMe 3 in excellent ( n = 1) or moderate ( n = 2, 4) yield. Treatment of the products with aqueous methanolic borax results in virtually quantitative liberation of the terminal alkynyl ketones XC 6 H 4 CO(CC) n H. The method provides the first practical route to the ketotetraynes ( n = 4) and usefully supplements existing oxidative methods for keto-monoyne and -diyne synthesis. The oxalyl chloride-aluminium chloride complex reacts with Me 3 SiCCSiMe 3 to give the novel silyl-substituted heterocycle (I):

Tungsten oxide tree-like structures

Abstract An interesting micrometer scale tree-like structure has been generated by heating a W foil, partly covered by a SiO 2 plate, in an Ar atmosphere at ca. 1600°C. Upon sonication, the trees are broken into nanoneedles (ca. 5–50 nm wide and 20–200 nm long) and planar polyhedral nanoparticles (ca. 10–50 nm cross-section). Structural analysis, using ED, EDX, XRD, and HRTEM, showed that: (1) the trees consist of well-crystallised WO x phases ( x =0–3); (2) the nanoneedles are composed mainly of monoclinic W 18 O 49 phases; and (3) the nanoparticles consist primarily of WO 3 . The tree growth is thought to arise from the intrinsic crystalline feature of WO x , the planar defect or the shear structure of which is responsible for the breakdown of the trees.

Nanotubes: A Revolution in Materials Science and Electronics

Nanotube theoretical and experimental research has developed very rapidly over the last seven years, following the bulk production of C60 and structural identification of carbon nanotubes in soot deposits formed during plasma arc experiments. This review summarises achievements in nanotube technology, in particular various routes to carbon nanotubes and their remarkable mechanical and conducting properties. The creation of novel nanotubules, nanowires and nanorods containing other elements such as B, N, Si, O, Mo, S and W is also reviewed. These advances are paving the way to nanoscale technology and promise to provide a wide spectrum of applications.

[Tris(trimethylsilyl)methyl]lithium: An alkyllithium compound of unusual stability

Abstract Tris(trimethylsilyl)methane readily undergoes metallation when treated with methyllithium in a mixture of tetrahydrofuran and diethyl ether, and the [tris(trimethylsilyl)methyllithium produced is remarkably stable in tetrahydrofuran. The ease of formation and the stability of the organolithium compound may be associated with stabilization of the carbanion (Me3Si)3C− by delocalization of the lone pair of electrons into the d-orbitals of the silicon atom. The organolithium compound can also be obtained by treatment of tris(trimethylsilyl)methyl chloride with lithium, methyllithium, or the n-butyllithiumN,N,N′,N′-tetramethylethylenediamine complex. It couples normally with the halides MeI, Me3SiCl, Me2HSiCl, Me3GeBr, and Me3SnCl, and gives the new acid (Me3Si)3CCO2H on carbonation.

Aligned CNx nanotubes by pyrolysis of ferrocene/C60 under NH3 atmosphere

Aligned CNx (x<0.1) nanotubes have been generated by pyrolyzing ferrocene/C60 mixtures at 1050 °C in an ammonia atmosphere. The structure and composition of the product were determined by high-resolution transmission electron microscopy and high spatial resolution electron energy-loss spectroscopy. The CNx tubes (15–70 nm diameter, <50 μm length) grown in large flakes (<3 mm2) consist of a reduced number of “graphitic” layers (<15 on either side) arranged in a bamboo-like structure. Areas of high nitrogen concentration were found within curved or corrugated “graphite-like” domains. The observation of a well-developed double peak in the σ* feature of the N K-edge suggests that the material has not undergone the transition to the fullerene-like phase known for nitrogenated carbons. Incorporation of nitrogen from the gas phase (NH3) into CNx nanotubes therefore leads to improved and more efficient N substitution into the network as compared to the synthesis with solid nitrogen-containing precursors reported ...

The microwave spectrum, substitution structure and dipole moment of cyanobutadiyne, HCCCCCN

Abstract Cyanobutadiyne (cyanodiacetylene), HCCCCCN, is sufficiently stable at low pressures to permit its rotational spectrum to be studied by microwave spectroscopy. The spectrum consists of a series of R-branch transitions typical of a linear molecule. The transitions with J = 9 to 14 which lie between 26.5 and 40.0 GHz have been measured for the vibrational ground state. Transitions have also been detected in natural abundance for all possible singly substituted 13C and 15N isotopic species. Deuteriated cyanobutadiyne, DCCCCCN, has also been synthesized and its ground state spectrum recorded. These measurements have enabled a complete substitution structure to be derived for the first time for a polyacetylene: r8(HCa) = 1.0569 ± 0.001, r8(CaCb) = 1.2087 ± 0.001, r8(CbCc) = 1.3623 ± 0.003, r8(CcCd) = 1.2223 ± 0.004, r8(CdCe) = 1.3636 ± 0.003, r 8 ( C e  N ) = 1.1606 ± 0.001 A (10 −10 m ) . The spectroscopic parameters for the ground state are B0 = 1331.3313 ± 0.001 MHz and D0 = 0.0257 ± 0.002 KHz. The dipole moment, determined from the Stark effects of the J = 9 and 10 lines, is 4.33 ± 0.03 Debye.

Detection of cyanohexatriyne, H(triple bond)/sub 3/CN, in Heiles's cloud 2

The J=9..-->..8 and 21..-->..20 rotational transitions of the heavy linear molecule cyanohexatriyne, H(triple bond)/sub 3/CN, have been detected in Heiless Cloud 2, a dark cloud at a distance of 115 pc in Taurus. This molecule, which contains eight heavy atoms and has a molecular weight of 99 amu, was synthesized specifically for the purpose of interstellar detection. Statistical-equilibrium calculations indicate a total column density of 2.7 x 10/sup 13/ molecules cm/sup -2/. This abundance is down by a factor of only 2 from that of H(CequivalentC)/sub 2/CN