The partial hydrogenation of small unsaturated molecules by osmium cluster compounds. The reaction of diispropylcarbodiimide with H2Os3(CO)10

The products (μ-H)[μ-η²-(CH₃)₂CHNHCNCH(CH₃)₂]Os₃(CO)₁₀, I, and (μ-H)- [μ-η²-(CH₃)₂CHNHCO]Os₃(CO)₉[CNCH(CH₃)₂], II have been obtained from the reaction of H₂Os₃(CO)₁₀ with diisopropylcarbodiimine. Both products have been investigated by infrared and ¹H NMR spectroscopies, and by single crystal X-ray diffraction analyses. For I: Space group, P2₁/c, a12.840(4), b  15.724(4), c 12.638(4) Å, β 106.91(2)°, V  2441(2) ų, Z4, ? calc  2.66 g/cc. For 2869 reflections, R  0.051 and R_w  0.052. I contains an N-hydrido, N-isopropylamidinyl ligand bridging one edge of a triangular cluster of three osmium atoms. It was apparently formed by the incorporation of one carbodiimide molecule into the coordination sphere of the cluster followed by the transfer of one hydride ligand to one of the nitrogen atoms. For II: Space group P2 ₁/n;a  13.936(7), b  12.146(2), c  15.509(6) Å, β  105.20(4)°, V  2533(3) Å, Z  4, ?calc  2.57 g/cc. For 3065 reflections, R  0.052 and R_w  0.057. II contains an N-hydrido, N-isopropylformamido ligand bridging one edge of a triangular cluster of three osmium atoms and an isopropylisocyanide ligand. The molecule appears to have been formed by the cleavage of an NCH(CH₃)₂ moeity from one carbodiimide molecule and the transfer of it together with one hydride ligand to the carbon atom of a carbonyl group. The resultant formamido ligand bridges an edge of the cluster. The remaining fragment of the carbodiimide molecule bonds to one of the metal atoms of the cluster as a terminal isocyanide ligand. When heated, I loses one mole of carbon monoxide and forms the new cluster complex (μ-H)[μ₃-η²-(CH₃)₂CHNHCNCH-(CH₃)₂]Os₃(CO)₉ III. On the basis of electron counting schemes, III is believed to contain a triply-bridging amidinyl ligand serving as a five electron donor. Most importantly, no II was formed from I indicating that it is not a precursor -to II. A mechanism for the formation of I and II is presented and discussed.     

High resolution capillary electrophoresis of carbon nanotubes

Purification of single-walled carbon nanotubes by capillary electrophoresis (CE) is demonstrated. Real-time Raman spectroscopy of the separation process and single-wavelength UV/vis detection show the ability of CE to provide high-resolution separations of nanotube fractions with baseline separation. AFM images of collected fractions demonstrate that separations are based on tube length. The separation method is suggested to be based on alignment of the nanotubes along the separation field.     

7,8‐(Dichloromethano)homo[70]fullerene,an Unusual,but Unexceptional,Methanoannulene

The crystal structure of 7,8‐(dichloromethano)homo[70]fullerene shows that addition of the dichlorocarbene (:CCl₂) to C₇₀ gives a surprisingly normal methano‐bridged [9]annulene. The structural changes caused by the addition are highly localized; the C(7)? C(8) distance lengthens by 0.705(2) Å but no other distance changes by more than 0.022(3) Å. Bond angles within the [9]annulene increase by as much as 7.8(1)°, but changes outside the C₉ ring are much smaller. The nearly ellipsoidal molecules form hexagonally close‐packed layers that interact in pairs through short Cl???C, and possibly short Cl???Cl and C???C, interactions.     

Synthesis, characterization, and structure of cyclopenta[c]thiophenes and their manganese complexes

1,3-Diaryl-4H-cyclopenta[c]thiophenes are efficiently prepared from 1,2-diaroylcyclopentadienes by use of Lawesson's reagent. eta5-Cyclopenta[c]thienyl complexes, [Mn(eta5-SC7H3-1,3-R2)(CO)3] (R = Me, Ph), are prepared in high yield by ligand substitution reactions of [MnBr(CO)5] with [SnMe3(SC7H3-1,3-R2)]. Alternatively, thiation with P4S10/NaHCO3 converts [Mn{eta5-1,2-C5H3(COR)2)(CO)3] to [Mn(eta5-SC7H3-1,3-R2)(CO)3] (R = Ph, 4-tolyl, 4-MeOC6H4, benzo[2,3-b]thienyl). The molecular structures of complexes with R = Me, Ph show planar eta5-cyclopenta[c]thienyl ligands, with the manganese atom slightly displaced away from the ring-fusion bond.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

Muon investigations of fullerenyl radicals

Four of the five possible isomeric C₇₀Mu radicals have been detected by transversefieldSR in a C₇₀ powder sample at 298 K. Their assignment is based on the results of semi-empirical MNDO calculations. There are significant changes in intensity and lineshape of the signals at low temperature. The first SR spectrum of a fullerenyl radical in solution has been obtained.