Steven Stevenson

The Shape of the Sc2(μ2-S) Unit Trapped in C82: Crystallographic, Computational and Electrochemical Studies of the Isomers, Sc2(μ2-S)@Cs(6)-C82 and Sc2(μ2-S)@C3v(8)-C82

Single-crystal X-ray diffraction studies of Sc(2)(μ(2)-S)@C(s)(6)-C(82)·Ni(II)(OEP)·2C(6)H(6) and Sc(2)(μ(2)-S)@C(3v)(8)-C(82)·Ni(II)(OEP)·2C(6)H(6) reveal that both contain fully ordered fullerene cages. The crystallographic data for Sc(2)(μ(2)-S)@C(s)(6)-C(82)·Ni(II)(OEP)·2C(6)H(6) show two remarkable features: the presence of two slightly different cage sites and a fully ordered molecule Sc(2)(μ(2)-S)@C(s)(6)-C(82) in one of these sites. The Sc-S-Sc angles in Sc(2)(μ(2)-S)@C(s)(6)-C(82) (113.84(3)°) and Sc(2)(μ(2)-S)@C(3v)(8)-C(82) differ (97.34(13)°). This is the first case where the nature and structure of the fullerene cage isomer exerts a demonstrable effect on the geometry of the cluster contained within. Computational studies have shown that, among the nine isomers that follow the isolated pentagon rule for C(82), the cage stability changes markedly between 0 and 250 K, but the C(s)(6)-C(82) cage is preferred at temperatures ≥250 °C when using the energies obtained with the free encapsulated model (FEM). However, the C(3v)(8)-C(82) cage is preferred at temperatures ≥250 °C using the energies obtained by rigid rotor-harmonic oscillator (RRHO) approximation. These results corroborate the fact that both cages are observed and likely to trap the Sc(2)(μ(2)-S) cluster, whereas earlier FEM and RRHO calculations predicted only the C(s)(6)-C(82) cage is likely to trap the Sc(2)(μ(2)-O) cluster. We also compare the recently published electrochemistry of the sulfide-containing Sc(2)(μ(2)-S)@C(s)(6)-C(82) to that of corresponding oxide-containing Sc(2)(μ(2)-O)@C(s)(6)-C(82).

Redox-active scandium oxide cluster inside a fullerene cage: Spectroscopic, voltammetric, electron spin resonance spectroelectrochemical, and extended density functional theory study of Sc4O2@C80 and its ion radicals

The clusterfullerene Sc(4)O(2)@C(80) with a mixed redox state of scandium was found to be an exciting molecule for endohedral electrochemistry as demonstrated by means of an in situ electron spin resonance (ESR) spectroelectrochemical study of the spin density distribution in its electrochemically generated cation and anion radicals. The compound exhibits two reversible reduction and oxidation steps with a relatively small electrochemical gap of 1.10 V. The ESR spectra of the ion radicals have a rich hyperfine structure caused by two pairs of equivalent Sc atoms. The Sc-based hyperfine structure with large hyperfine coupling constants shows that both oxidation and reduction of Sc(4)O(2)@C(80) are in cavea redox processes, which is the subject of endohedral electrochemistry. The assignment of the experimentally determined a((45)Sc) values to the two types of Sc atoms in the Sc(4)O(2) cluster was accomplished by extended density functional theory and molecular dynamics simulations. Sc atoms adopting a divalent state in the neutral Sc(4)O(2)@C(80) exhibited an especially large coupling constant of 150.4 G in the cation radical, which is the record high a((45)Sc) value for Sc-based endohedral metallofullerenes. Such a high value is explained by the nature of the highest occupied molecular orbital (HOMO) localized on the six-atom Sc(4)O(2) cluster. This HOMO is a Sc-Sc bonding MO and hence has large contributions from the 4s atomic orbitals of Sc(II). We claim that ESR spectroelectrochemistry is an invaluable experimental tool in the studies of metal-metal bonding in endohedral metallofullerenes and in endohedral electrochemistry.

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.

Bis-1,3-dipolar Cycloadditions on Endohedral Fullerenes M3N@Ih-C80 (M = Sc, Lu): Remarkable Endohedral-Cluster Regiochemical Control.

In this work, we briefly report some attempts to control regioisomeric bisadditions on Sc3N@Ih-C80 and Lu3N@Ih-C80 using the tether-controlled multifunctionalization method. We then describe the use of independent (nontethered) bis-1,3-dipolar cycloaddition reactions and the characterization of 5 new bisadducts, 3 for Sc3N@C80 and 2 for Lu3N@C80, which have never been reported before. Unexpectedly and remarkably, 4 of these compounds exhibit relatively high symmetry and 2 of these bisadducts are the first examples of intrinsically chiral endohedral compounds, due to the addition pattern, not to the presence of chiral centers on the addends. Since an analysis of the statistically possible number of bisadduct isomers on an Ih-C80 cage has not been reported, we present it here.

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.