[Show abstract][Hide abstract] ABSTRACT: A family of highly stable (poly)perfluoroalkylated metallic nitride cluster fullerenes was prepared in high-temperature reactions and characterized by spectroscopic (MS, (19)F NMR, UV-vis/NIR, ESR), structural and electrochemical methods. For two new compounds, Sc(3)N@C(80)(CF(3))(10) and Sc(3)N@C(80)(CF(3))(12,) single crystal X-ray structures are determined. Addition pattern guidelines for endohedral fullerene derivatives with bulky functional groups are formulated as a result of experimental ((19)F NMR spectroscopy and single crystal X-ray diffraction) studies and exhaustive quantum chemical calculations of the structures of Sc(3)N@C(80)(CF(3))(n) (n = 2-16). Electrochemical studies revealed that Sc(3)N@C(80)(CF(3))(n) derivatives are easier to reduce than Sc(3)N@C(80), the shift of E(1/2) potentials ranging from +0.11 V (n = 2) to +0.42 V (n = 10). Stable radical anions of Sc(3)N@C(80)(CF(3))(n) were generated in solution and characterized by ESR spectroscopy, revealing their (45)Sc hyperfine structure. Facile further functionalizations via cycloadditions or radical additions were achieved for trifluoromethylated Sc(3)N@C(80) making them attractive versatile platforms for the design of molecular and supramolecular materials of fundamental and practical importance.
Journal of the American Chemical Society 02/2011; 133(8):2672-90. DOI:10.1021/ja109462j · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
[Show abstract][Hide abstract] ABSTRACT: The first endohedral trianion captured: Sc3N@C 80(CF3)2 (see figure) exhibits three reversible reductions and two reversible oxidations and affords the facile generation of the monocation, monoanion, and trianion in solution, which can be characterized by ESR and absorption spectroscopies. This is the first time that such a broad range of charged states of any endohedral fullerene has been spectroscopically characterized. (Chemical Equation Presented)
Chemistry - A European Journal 03/2010; 16(16):4721-4. DOI:10.1002/chem.201000205 · 5.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The tetrahedral array of four scandium atoms with oxygen atoms capping three of the four faces found in Sc(4)(mu(3)-O)(3)@I(h)-C(80) is the largest cluster isolated to date inside a fullerene cage.
Chemical Communications 01/2010; 46(2):279-81. DOI:10.1039/b918731f · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report the synthesis and electronic stabilization of La(3)N@C(79)N. Unsuccessful efforts to encapsulate bulky La(3)N clusters in small C(80) cages have been attributed to large ionic radii. The preferred species for La(3)N clusters in all-carbon cages is La(3)N@C(96). A surprising finding is the synthesis of La(3)N@C(79)N, a new metallofullerene present in higher abundance than La(3)N@C(96). This reduction in cage size from 96 to 80 atoms reflects the significance and role of electronic effects. To understand the geometric and electronic properties of this first metallic nitride azafullerene (M(3)N@C(79)N, M = La), density functional theory (DFT) investigations were performed on a number of isomers. Results indicate a preferred N-substitution at the 665 junction site on the cage in lieu of a 666 substitution. The relative stabilities of different isomers can be well reproduced by using the minimum distance between the metal atom and the nitrogen atom of the cage (R(N'M)(min)). Long R(N'M)(min) values indicate distant contacts between six atoms that bear significantly large positive charges: the three metal atoms and the three carbon atoms bonded with the nitrogen atom in the cage, which are favored. These results suggest a dominant electronic effect on the stabilities of metalloazafullerenes. Interestingly, spin densities of the 665 substitution isomers of La(3)N@C(79)N are located predominantly in the metal cluster, while spin densities of the 666 substitution isomers are primarily on the cage.
Journal of the American Chemical Society 12/2009; 131(49):17780-2. DOI:10.1021/ja908370t · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Gold nanoparticles and multi-functional acrylate (TMPTA) were incorporated into a photopolymerized thiol-ene (TMPMP–APE) network as a physical and chemical approach to intentionally control sub-Tg aging. The degree of the restriction effect was evaluated by differential cooling rate measurements allowing the quantification of the apparent activation energy for enthalpy relaxation (Δh*) upon sub-Tg aging. Incorporation of gold nanoparticles (0.01 to 1wt%) into the TMPMP–APE network increased Tg and decreased ΔCp at Tg due to molecular mobility restrictions. The extent of enthalpy relaxation and apparent activation energy for enthalpy relaxation (Δh*) clearly indicated the significant restrictive effect of the gold nanoparticles on the molecular mobility in the thiol-ene network. A TMPMP–APE–TMPTA ternary system was investigated in order to correlate Δh* and network uniformity as a chemical approach. TMPTA, being capable of homopolymerization as well as TMPMP–TMPTA copolymerization, was incorporated into a TMPMP–APE network structure, thereby decreasing the network uniformity and significantly affecting the sub-Tg aging. The extent of enthalpy relaxation decreased and the distribution was drastically broadened as a function of TMPTA content due to molecular mobility restrictions, which were also quantified by measuring values for the apparent enthalpy relaxation activation energy (Δh*).
[Show abstract][Hide abstract] ABSTRACT: The compounds Sc(3)N@(C(80)-I(h)(7))(CF(3))(14) (1) and Sc(3)N@(C(80)-I(h)(7))(CF(3))(16) (2) were prepared by heating Sc(3)N@C(80)-I(h)(7) and Ag(CF(3)CO(2)) to 350 degrees C in a sealed tube. The structures of 1 and 2 were determined by single-crystal X-ray diffraction. They are the first X-ray structures of any endohedral metallofullerene with more than four cage C(sp(3)) atoms. The structures exhibit several unprecedented features for metallic nitride fullerenes, including multiple cage sp(3) triple-hexagon junctions (four on 1 and eight on 2), no cage disorder and little (2) or no (1) endohedral atom disorder, high-precision (C-C esd's are 0.005 A for 1 and 0.002 A for 2), an isolated aromatic C(sp(2))(6) hexagon on 2, and two negatively charged isolated aromatic C(sp(2))(5)(-) pentagons on 2 that are bonded to one of the Sc atoms. DFT calculations are in excellent agreement with the two Sc(3)N conformations observed for 2 (DeltaE(calc) = 0.36 kJ mol(-1); DeltaE(exp) = 0.26(2) kJ mol(-1)).
Journal of the American Chemical Society 11/2009; 131(48):17630-7. DOI:10.1021/ja9069216 · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Metallic nitride fullerenes (MNFs) and oxometallic fullerenes (OMFs) react quickly with an array of Lewis acids. Empty-cage fullerenes are largely unreactive under conditions used in this study. The reactivity order is Sc(4)O(2)@I(h)-C(80) > Sc(3)N@C(78) > Sc(3)N@C(68) > Sc(3)N@D(5h)-C(80) > Sc(3)N@I(h)-C(80). Manipulations of Lewis acids, molar ratios, and kinetic differences within the family of OMF and MNF metallofullerenes are demonstrated in a selective precipitation scheme, which can be used either alone for purifying Sc(3)N@I(h)-C(80) or combined with a final high-performance liquid chromatography pass for Sc(4)O(2)@I(h)-C(80), Sc(3)N@D(5h)-C(80), Sc(3)N@C(68), or Sc(3)N@C(78). The purification process is scalable. Analysis of the experimental rate constants versus electrochemical band gap explains the order of reactivity among the OMFs and MNFs.
[Show abstract][Hide abstract] ABSTRACT: The adhesive properties, as measured by bulk tack analysis, are found to decrease in blends of isomerically pure Sc3N@I(h)-C80 metallic nitride fullerene (MNF) and polystyrene-block-polyisoprene-block-polystyrene (SIS) copolymer pressure-sensitive adhesive under white light irradiation in air. The reduction of tack is attributed to the in situ generation of 1O2 and subsequent photooxidative cross-linking of the adhesive film. Comparisons are drawn to classical fullerenes C60 and C70 for this process. This work represents the first demonstration of 1O2 generating ability in the general class of MNFs (M3N@C80). Additional support is provided for the sensitizing ability of Sc3N@I(h)-C80 through the successful photooxygenation of 2-methyl-2-butene to its allylic hydroperoxides in benzene-d(6) under irradiation at 420 nm, a process that occurs at a rate comparable to that of C(60). Photooxygenation of 2-methyl-2-butene is found to be influenced by the fullerene sensitizer concentration and O2 flow rate. Molar extinction coefficients are reported for Sc3N@I(h)-C80 at 420 and 536 nm. Evaluation of the potential antimicrobial activity of films prepared in this study stemming from the in situ generation of 1O2 led to an observed 1 log kill for select Gram-positive and Gram-negative bacteria.
[Show abstract][Hide abstract] ABSTRACT: The remarkably large cluster Sc4(mu3-O)2 has been obtained trapped inside an Ih-C80 cage by conducting the vaporization of graphite rods doped with copper(II) nitrate and scandium(III) oxide in an electric arc under a low pressure helium atmosphere with an added flow of air. The product has been isolated by chromatography and identified by high-resolution mass spectrometry. The structure of Sc4(mu3-O)2@Ih-C80 has been determined by X-ray crystallography on a crystal of Sc4(mu3-O)2@Ih-C80.NiII(OEP).2(C6H6). The Sc4(mu3-O)2 unit consists of a distorted tetrahedron of scandium atoms with oxygen atoms bridging two of its faces. The Sc-Sc distances range from 2.946(7) to 3.379(7) A.
Journal of the American Chemical Society 10/2008; 130(36):11844-5. DOI:10.1021/ja803679u · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Alkyl thiols and alkenes (enes) polymerize via an extremely rapid step-growth, free-radical chain process, uninhibited by air, to give high-density networks with excellent mechanical and physical properties. These thiol−ene coatings are potentially useful for a wide variety of coatings, adhesives, and optical applications. In this work, a series of nanogold-containing UV-cured, thiol−ene coatings were prepared from trimethylolpropane tris(3-mercaptopropionate) (trithiol) and pentaerythritol allyl ether (triene) monomers using a unique procedure which facilitates precomplexation of the gold−thiol prior to photocuring. Irgacure 651 (1 wt %) was used as a photoinitiator, and nanogold was incorporated at 0−1 wt %, average 10 nm size particles by TEM. Physical and mechanical properties were characterized using bulk tack analysis and other standard techniques: DSC, TGA, pencil hardness, and gel fractions. In general, films were found to be low absorbing in the visible range and highly uniform and to contain well-dispersed nanogold particles. Although the rate of polymerization was modestly retarded by the presence of gold nanoparticles, functional group conversions (CC and S−H) and gel fractions were high. Increasing nanogold content resulted in an increase in Tg measured by DSC (−15 to −8 °C for 0−1 wt % nanogold, respectively) due to the increasing number of physical gold−thiol cross-links created. TGA analysis revealed a small negative impact of increasing nanogold composition on relative thermal stability. The 1 wt % nanogold-containing samples possessed appreciable electrostatic discharge (ESD) character, with ESD times of 1−10 s measured using a commercial charge plate analyzer.
Chemistry of Materials 07/2008; 20(16). DOI:10.1021/cm8007842 · 8.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The emerging use of scandium and the environmental impact from scandium-containing waste is a rising environmental and health concern. With the development of new materials in the last decade, toxicological studies on those new materials have also been increasing. An example of a process which employs scandium is the generation of metallic nitride fullerene nanomaterials. This process typically generates 99+% scandium waste, as only small amounts of scandium are actually incorporated into the target fullerene molecules. We demonstrate a safe method to recover the scandium content in the waste, reuse the recovered material and successfully demonstrate a comparable product distribution without detectable health and environmental concerns.
Journal of Environmental Science and Health Part A 04/2008; 43(4):357-60. DOI:10.1080/10934520701795483 · 1.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Electrochemical studies of the Ih isomer of Sc3N@C80 in acetonitrile/toluene solvent mixture were performed. Controlled potential electrolysis was used to increase the solubility of the compounds via reduction and all CV and DPV investigations were performed under the vapor pressure of the prevailing solvents. The reduction and oxidation processes were found to be electrochemically quasi-reversible by cyclic voltammetry techniques, suggestive of a nondegenerate LUMO and accessible LUMO+1. The electrochemical properties of Sc3N@C80 (Ih) were comparatively discussed with our previous results performed in o-dichlorobenzene and results published by other authors in an acetonitrile/toluene solvent mixture.
[Show abstract][Hide abstract] ABSTRACT: Electrochemical studies of the I h isomer of Sc 3 N@C 80 in acetonitrile/toluene solvent mixture were performed. Controlled potential electrolysis was used to increase the solubility of the compounds via reduction and all CV and DPV investigations were performed under the vapor pressure of the prevailing solvents. The reduction and oxidation processes were found to be electrochemically quasi-reversible by cyclic voltammetry techniques, suggestive of a nondegenerate LUMO and accessible LUMO + 1. The electrochemical properties of Sc 3 N@C 80 (I h) were comparatively discussed with our previous results performed in o-dichlorobenzene and results published by other authors in an acetonitrile/toluene solvent mixture.
Journal of Electroanalytical Chemistry 01/2008; · 2.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Goals are (1) to selectively synthesize metallic nitride fullerenes (MNFs) in lieu of empty-cage fullerenes (e.g., C60, C70) without compromising MNF yield and (2) to test our hypothesis that MNFs possess a different set of optimal formation parameters than empty-cage fullerenes. In this work, we introduce a novel approach for the selective synthesis of metallic nitride fullerenes. This new method is "Chemically Adjusting Plasma Temperature, Energy, and Reactivity" (CAPTEAR). The CAPTEAR approach with copper nitrate hydrate uses NOx vapor from NOx generating solid reagents, air, and combustion to "tune" the temperature, energy, and reactivity of the plasma environment. The extent of temperature, energy, and reactive environment is stoichiometrically varied until optimal conditions for selective MNF synthesis are achieved. Analysis of soot extracts indicate that percentages of C60 and Sc3N@C80 are inversely related, whereas the percentages of C70 and higher empty-cage C2n fullerenes are largely unaffected. Hence, there may be a "competitive link" in the formation and mechanism of C60 and Sc3N@C80. Using this CAPTEAR method, purified MNFs (96% Sc3N@C80, 12 mg) have been obtained in soot extracts without a significant penalty in milligram yield when compared to control soot extracts (4% Sc3N@C80, 13 mg of Sc3N@C80). The CAPTEAR process with Cu(NO3)2.2.5H2O uses an exothermic nitrate moiety to suppress empty-cage fullerene formation, whereas Cu functions as a catalyst additive to offset the reactive plasma environment and boost the Sc3N@C80 MNF production.
Journal of the American Chemical Society 01/2008; 129(51):16257-62. DOI:10.1021/ja077305z · 12.11 Impact Factor