Curtis E. Coumbe

Poly(perfluoroalkylation) of Metallic Nitride Fullerenes Reveals Addition-Pattern Guidelines: Synthesis and Characterization of a Family of Sc3N@C80(CF3)n (n = 2−16) and Their Radical Anions

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.

Redox-Tuning Endohedral Fullerene Spin States: From the Dication to the Trianion Radical of Sc3N@C80(CF3)2 in Five Reversible Single-Electron Steps

Synthetic/separation procedures for endohedral fullerenes, especially nitride cluster fullerenes M3N@C2n (NCFs), have progressed to the point in which sufficient amounts are now available for the exploration of their electronic and chemical properties. NCFs were recently found to be superior to C60 in stabilizing charge-separated states in donor–acceptor dyads. In contrast to the wealth of information about oxidized (cationic) and reduced (anionic) C60 derivatives, much less is known about NCF cations and anions, and even less is known about their derivatives. NCFs exhibit electrochemically irreversible reductions, at slow scan rates, that are chemically reversible. On the other hand, some M3N@C80(X)n derivatives have reversible electron-transfer steps even at low scan rates (hereinafter C80 shall specifically denote the C80-Ih(7) cage). Spectroscopic data for NCF ions are limited to 1) ex situ ESR spectra of Sc3N@C80 [3] and the monoanion of a pyrrolidino cycloadduct of Y3N@C80 [4] and 2) in situ ESR/Vis/NIR spectra of Sc3N@C68 + and Sc3N@C68 . The trifluoromethylation of NCFs was recently developed and several Sc3N@C80ACHTUNGTRENNUNG(CF3)n derivatives were isolated and characterized by mass spectrometry, UV/Vis and NMR spectroscopy, and single-crystal X-ray diffraction. We now report the existence of the monoand dications and the mono-, di-, and trianions of the simplest derivative, Sc3N@C80ACHTUNGTRENNUNG(CF3)2 (I), and an in-depth study of three of them by ESR and Vis/NIR spectroelectrochemistry. The cyclic voltammetry of I, shown in Figure 1, exhibits three reversACHTUNGTRENNUNGible one-electron reductions at 1.16, 1.65, and 2.04 V versus Fe(Cp)2 + /0 and two reversible one-electron oxidations at 0.47 and 0.60 V versus Fe(Cp)2 + . The dotted lines show that I has a smaller + / electrochemical gap than Sc3N@C80 (II); the 0/ and + /0 E1/2 values for I are shifted, respec[a] Dr. A. A. Popov, A. L. Svitova, Prof. Dr. L. Dunsch Department of Electrochemistry and Conducting Polymers Leibniz Institute for Solid State and Materials Research Dresden 01069 (Germany) Fax: (+49) 351-4659-745 E-mail : a.popov@ifw-dresden.de l.dunsch@ifw-dresden.de [b] N. B. Shustova, Prof. S. H. Strauss, Dr. O. V. Boltalina Department of Chemistry, Colorado State University Fort Collins, CO 80523 (USA) Fax: (+1) 970-491-1801 E-mail : olga.boltalina@colostate.edu steven.strauss@colostate.edu [c] M. A. Mackey, C. E. Coumbe, Prof. J. P. Phillips, Prof. S. Stevenson Department of Chemistry and Biochemistry University of Southern Mississippi, Hattiesburg, MS 39406 (USA) Fax: (+1) 601-266-6075 E-mail : janice.phillips@usm.edu steven.stevenson@usm.edu Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201000205. Figure 1. Cyclic voltammetry of Sc3N@C80 ACHTUNGTRENNUNG(CF3)2 (1,2-C6H4Cl2 (0.1 m), TBABF4, 25 8C, 20 mV s ). The dotted lines show the E1/2 values of Sc3N@C80 at fast scan rates. [3b, 7] The inset shows Vis/NIR absorption spectra of a) Sc3N@C80ACHTUNGTRENNUNG(CF3)2 and b) Sc3N@C80 in toluene.

Sc3N@(C-80-I-h(7))(CF3)(14) and Sc3N@(C-80-I-h(7))(CF3)(16). Endohedral Metallofullerene Derivatives with Exohedral Addends on Four and Eight Triple-Hexagon Junctions. Does the Sc3N Cluster Control the Addition Pattern or Vice Versa?

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 esds 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)).

Evidence for Singlet-Oxygen Generation and Biocidal Activity in Photoresponsive Metallic Nitride Fullerene−Polymer Adhesive Films

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.

Effect of copper metal on the yield of Sc3N@C80 metallofullerenes.

The yield of Sc3N@C80 metallofullerene and fullerene extract is dramatically increased via filling cored graphite rods with copper and Sc2O3 only; when compared to 100% Sc2O3 packed rods, improvements of factors of approximately 3 and approximately 5 have been achieved for Sc3N@C80 and fullerene extract produced, respectively, with the weight percent of Cu added to the rod affecting the type and amount of fullerene produced.

Reducing hazardous material and environmental impact through recycling of scandium nanomaterial waste

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.