Search

Reaction of C(60) with CF(3)I at 550 degrees C, which is known to produce a single isomer of C(60)(CF(3))(2,4,6) and multiple isomers of C(60)(CF(3))(8,10), has now been found to produce an isomer of C(60)(CF(3))(6) with the C(s)-C(60)X(6) skew-pentagonal-pyramid (SPP) addition pattern and an epoxide with the C(s)-C(60)X(4)O variation of the SPP addition pattern, C(s)-C(60)(CF(3))(4)O. The structurally similar epoxide C(s)-C(60)(C(2)F(5))(4)O is one of the products of the reaction of C(60) with C(2)F(5)I at 430 degrees C. The three compounds have been characterized by mass spectrometry, DFT quantum chemical calculations, Raman, visible, and (19)F NMR spectroscopy, and, in the case of the two epoxides, single-crystal X-ray diffraction. The compound C(s)-C(60)(CF(3))(6) is the first [60]fullerene derivative with adjacent R(f) groups that are sufficiently sterically hindered to cause the (DFT-predicted) lengthening of the cage (CF(3))C-C(CF(3)) bond to 1.60 A as well as to give rise to a rare, non-fast-exchange-limit (19)F NMR spectrum at 20 degrees C. The compounds C(s)-C(60)(CF(3))(4)O and C(s)-C(60)(C(2)F(5))(4)O are the first poly(perfluoroalkyl)fullerene derivatives with a non-fluorine-containing exohedral substituent and the first fullerene epoxides known to be stable at elevated temperatures. All three compounds demonstrate that the SPP addition pattern is at least kinetically stable, if not thermodynamically stable, at temperatures exceeding 400 degrees C. The high-temperature synthesis of the two epoxides also indicates that perfluoroalkyl substituents can enhance the thermal stability of fullerene derivatives with other substituents.

The vibrational structure of the endohedral cluster fullerene Sc(3)N@C(78) is studied by FTIR spectroscopy, Raman spectroscopy and DFT-based quantum chemical calculations. Remarkably good agreement between experimental and calculated spectra is achieved and a full assignment of the Sc(3)N-based vibrational modes is given. Significant differences in the vibrational structure of the endohedral cluster fullerene Sc(3)N@C(78) and the empty, charged C(78) (6-): 5 (D(3h)') are rationalized by the strong coupling between the Sc(3)N cluster and the fullerene cage. This coupling has its origin in a significant overlap of the Sc(3)N and C(78) molecular orbitals, and causes atomic-charge and bond-length redistributions compared to the neutral C(78) and the C(78) (6-) anion. An ionic model is not sufficient to describe the electronic, geometric and vibrational structure of the Sc(3)N@C(78) nitride cluster fullerene.

IR and Raman spectra of two fluorofullerenes, C60F48 and C60F36, are thoroughly studied. Assignment of the experimental spectra is provided on the basis of density functional theory (DFT) computations. Perfect correspondence between experimental and computed spectra enabled us to confirm that the major isomer of C60F48 has D3 symmetry. It was found that as-synthesized samples of C60F36 consist mainly of C3 and C1 isomers in ca. 2:1 ratio and 2-3% of T-symmetric structures. Extensive AM1 and DFT computations have shown that all three structures are the most stable isomers of C60F36. Previous structural assignment of the C3 isomer (Gakh, A. A.; Tuinman, A. A. Tetrahedron Lett. 2001, 42, 7137-7139) was confirmed by the vibrational data.

Reaction of C70 with ten equivalents of silver(I) trifluoroacetate at 320-340 degrees C followed by fractional sublimation at 420-540 degrees C and HPLC processing led to the isolation of a single abundant isomer of C70(CF3)n for n = 2, 4, 6, and 10, and two abundant isomers of C70(CF3)8. These six compounds were characterized by using matrix-assisted laser desorption ionization (MALDI) mass spectrometry, 2D-COSY and/or 1D 19F NMR spectroscopy, and quantum-chemical calculations at the density functional theory (DFT) level. Some were also characterized by Raman spectroscopy. The addition patterns for the isolated compounds were unambiguously found to be C1-7,24-C70(CF3)2, C1-7,24,44,47-C70(CF3)4, C2-1,4,11,19,31,41-C70(CF3)6, Cs-1,4,11,19,31,41,51,64-C70(CF3)8, C2-1,4,11,19,31,41,51,60-C70(CF3)8, and C1-1,4,10,19,25,41,49,60,66,69-C70(CF3)10 (IUPAC numbering). Except for the last compound, which is identical to the recently reported, crystallographically characterized C70(CF3)10 derivative prepared by a different synthetic route, these compounds have not previously been shown to have the indicated addition patterns. The largest relative yield under an optimized set of reaction conditions was for the Cs isomer of C70(CF3)8 (ca. 30 mol % of the sublimed mixture of products based on HPLC integration). The results demonstrate that thermally stable C70(CF3)n isomers tend to have their CF3 groups arranged on isolated para-C6(CF3)2 hexagons and/or on a ribbon of edge-sharing meta- and/or para-C6(CF3)2 hexagons. For Cs- and C2-C70(CF3)8 and for C2-C70(CF3)6, the ribbons straddle the C70 equatorial belt; for C1-C70(CF3)4, the para-meta-para ribbon includes three polar hexagons; for C1-7,24-C70(CF3)2, the para-C6(CF3)2 hexagon includes one of the carbon atoms on a C70 polar pentagon. The 10.3-16.2 Hz 7JF,F NMR coupling constants for the end-of-ribbon CF3 groups, which are always para to their nearest-neighbor CF3 group, are consistent with through-space Fermi-contact interactions between the fluorine atoms of proximate, rapidly rotating CF3 groups.

The laser assisted formation of silicon nanocrystals in SiNx films deposited on quartz and silicon substrates is studied. The Raman spectroscopy revealed creation of the Si cluster and crystallite after excimer laser treatments. Photoluminescence signal from the samples was detected at room temperatures. I-V and C-V measurements were carried out to examine carries transfer through dielectrics film as well as recharging of electronics states.

The spectroelectrochemical behavior in situ of some polymers of polythiophene series, polybithiophene (PBT) and poly-3-phenylthiophene (P3PhT), is studied in the processes of anodic and cathodic doping. It is confirmed that in the case of PBT and P3PhT, the cathodic evolution of the absorption spectra, which is characteristic of the cathodic doping process, occurs in solutions of tetrabutylammonium salts, but not in solutions of lithium salts. It is shown that polymers of a more complicated structure than that of PBT, e.g. P3PhT, feature additional absorption bands, as compared to PBT, which demonstrates a single absorption band. Moreover, in the case of P3PhT, two color transitions can be observed by sight in the process of doping-undoping, unlike the single transition observed in the case of PBT and most other electron-conducting polymers. On the basis of quantum-mechanical calculations, an assumption is made that such a behavior of P3PhT is due to the decrease of the local symmetry of polythiophene chain in the presence of a bulky substituent, which causes the activation of the transitions in the electronic spectra that are forbidden in more symmetrical structures.

Several high‐level quantum chemical methods are used to calculate the vibrational properties of fullerenes, and the PBE/tz2p approach is shown to be the optimal one. The model to simulate the vibrational spectra of fullerenes polymers from the quantum chemical calculations of their finite fragments was analyzed. The complete interpretation of the spectra of 1D and 2D polymerized fullerenes is fulfilled.

Infrared spectra of a number of C60 cycloaddition products, namely, fullerenopyrroline and fullerenopyrazolines with the substituents in the heterocyclic fragments have been studied experimentally and employing DFT calculations. Complete vibrational assignment is proposed.

Infrared and Raman scattering spectra of the chloro‐ and bromofullerenes C60Cl6, C60Br6, C60Br8, C60Br24, C70Cl10, and C70Br10 have been studied both experimentally and theoretically employing first‐principle calculations. Complete vibrational assignment for these molecules is proposed.

Differential scanning calorimetry and IR-spectroscopy have been used to study the depolymerization of the 2D tetragonal (T) polymerized phase of C60 at p = 1 atm. The depolymerization enthalpy obtained was 17.7 ± 1.7 kJ per mole of C60. Experimental enthalpies of depolymerization along with the lattice energies calculated by the atom–atom potential method were combined into the thermochemical cycles to account for the trends in the relative stability of the polymerized phases of C60. Surprisingly low depolymerization enthalpy of 2D rhombohedral (R) phase compared to 1D orthorhombic (O) and 2D T-phases was explained by the unfavorable packing energy of the isolated rhombohedral layers into R-crystal lattice, though the averaged C60 = C60 bond energy was also lower for R- than for O- and T- phases, being 31, 42 and 43 kJ/mol, respectively. Results of DFT quantum chemical calculations of the energetics of C60 polymers were in qualitative agreement with this trend. The mechanism of depolymerization appeared to be significantly different for R-phase compared to other polymers. While decomposition of O- and T-phases occurred in one step without any IR-detectable intermediate species, depolymerization of R-phase was found to be at least a two-step process. Comparison of experimental and DFT simulated IR-spectra suggested that intermediate species were cyclic trimers or similar oligomers.

Improved synthetic and isolation procedures have been developed that resulted in the preparation of pure C60F20 in sufficient amounts for comprehensive vibrational spectroscopic studies. The FTIR spectrum, the first Raman spectrum, and DFT vibrational calculations of the two possible D5d-symmetry isomers of C60F20 provide compelling evidence in favor of the previously proposed Saturn-like structure of this fluorofullerene. Excellent agreement between the experimental and simulated spectra allowed a complete vibrational assignment for C60F20 to be made.

The IR and Raman spectra of the bromofullerene C 60 Br 24 were thoroughly studied and assigned on the base of Hartree–Fock ab initio calculations. A complete interpretation of the spectra is proposed within a conventional potential energy distribution analysis as well as employing the projection technique to follow the genetic relationships of the carbon cage vibrations in C 60 Br 24 molecule with those in parent C 60 . Such analysis has shown that the vast majority of bromofullerene vibrations could be regarded as the vibrations of its carbon skeleton stringed inside a motionless sphere of bromine atoms.

Vibrational spectroscopies have been employed to study the fluorofullerenes of formula C60F18, C60F36, and C60F48. For the first time, the Raman spectra of C60F18, C60F36, and C60F48 as well as infrared (IR) spectra of their gaseous molecules isolated in cryogenic matrices have been obtained. The results were discussed and compared with the infrared spectra of the corresponding solids. In the case of C60F18, experimental data were supported by theoretical calculations.

Empty fullerenes are known to have very fast intersystem crossing with near 100% yield of the T1 state, which results in very low quantum yield of fluorescence and relatively short fluorescence lifetimes (less than 1 ns). In endohedral metallofullerenes, the intersystem crossing is even faster due to the internal heavy-atom effect, and hence fluorescence can hardly be expected. However, Y3N@C80 is known to exhibit reasonably high yield of fluorescence (1%) and unusually long lifetimes of 800 ns.1, 2 Such unusual photophysical parameters indicate that simple fluorescence mechanism cannot explain experimental facts. In this contribution we describe steady-state and lifetime luminescence as well as light-induced electron paramagnetic resonance studies of Y3N@C80 at different temperatures aimed at clarification of photophysical properties of Y3N@C80. 1. Bharadwaj, L.; Novotny, L., Plasmon-Enhanced Photoemission from a Single Y3N@C80 Fullerene. J. Phys. Chem. C 2010, 114, 7444-7447. 2. Toth, K.; Molloy, J. K.; Matta, M.; Heinrich, B.; Guillon, D.; Bergamini, G.; Zerbetto, F.; Donnio, B.; Ceroni, P.; Felder-Flesch, D., A Strongly Emitting Liquid-Crystalline Derivative of Y3N@C80: Bright and Long-Lived Near-IR Luminescence from a Charge Transfer State. Angew. Chem.-Int. Edit. Engl. 2013, 52, 12303-12307.

Electronic properties of endohedral metallofullerenes (EMFs) and especially their behavior in the charge transfer processes have been in the focus since the middle of 1990s, when sufficient amounts of EMFs became available. The Closed carbon shell of EMF represents itself as a suitable environment for stabilization of different exotic metal species, including dimetallic clusters with metal-metal bond. Here we report the electrochemical properties of M2@C82 clustersfullerenes (2 cage isomers of C82: with C3v and Cs symmetry; M=Lu, Er, Sc) . UV-Vis and NIR absorption spectroscopy data and theoretical calculations expose the unique structure of M2@C82 EMFs with two M2+ions inside the cage, connected with metal-metal bonding (despite the fact that in majority of EMFs lanthanides demonstrate oxidation state 3+). Electrochemical experiments along with theoretical calculations have proved that metal-metal bonding orbital in EMFs is always one of the frontier orbitals, and its energy to a great extant determines the redox behavior of the molecule. For M2@C82 family metal-metal bonding orbital presents itself as a HOMO. The cyclic voltammetry has revealed the cathodic shift* of the first oxidation potential for Sc2- and Er2-EMFs in comparison with corresponding isomers of Lu2@C82, caused by the significant difference in position of the HOMO. Monocation of Sc2@C82-C3v, generated by chemical oxidation, has been studied with EPR spectroscopy as well. Due to the spd-character of metal-metal bonding orbital, the spin density at the nuclei is extremely high, that provides the second order effects in line position and variations of the signal line width.

A large family of dysprosium-scandium (Dy-Sc) mixed-metal nitride clusterfullerenes (MMNCFs), Dy(x)Sc(3-x)N@C2n (x = 1, 2, 2n = 68, 70, 76-86) have been successfully synthesized and isolated. Among these, the C70 and C82-based MMNCFs are two new cages that have never been isolated for MMNCFs. Synthesis of Dy(x)Sc(3-x)N@C2n was accomplished by the "selective organic solid" route using guanidinium thiocyanate as the nitrogen source, and their isolation was fulfilled by recycling HPLC. UV/Vis-NIR spectroscopic study indicates that almost all Dy(x)Sc(3-x)N@C2n MMNCFs are kinetically stable fullerenes with optical band gaps beyond 1 eV. This feature is distinctly different to their counterparts Dy3N@C2n (78≤2n≤88), whose for optical band-gaps are below 1 eV for relatively large cages such as C84 and C86. An FTIR spectroscopic study in combination with DFT calculations enables reasonable assignments of the cage isomeric structures of all isolated Dy(x)Sc(3-x)N@C2n (x = 1, 2, 2n = 68, 70, 76-86) MMNCFs. The carbon cage size distribution of Dy(x)Sc(3-x)N@C2n (2n = 68, 70, 76-86) is compared to the reported Dy3N@C2n (78≤2n≤8) homogeneous NCF and Dy(x)Sc(3-x)N@C2n (78≤2n≤88) MMNCF families, revealing that the medium-sized Dy metal plays a crucial role on the expanded cage size distribution of MMNCFs. As a result, Dy(x)Sc(3-x)N@C2n MMNCFs are the largest MMNCF family reported to date.

In endohedral metallofullerenes (EMFs), the carbon cage shields the endohedral species from the surrounding environment and can stabilize unusual clusters that otherwise would not exist. This review is focused on the behavior of the metal/π-system interface in EMFs under electron transfer conditions. We show that the stabilizing role of the fullerene cage can be extended from unusual clusters to the peculiar spin and charge states obtained via endohedral electron transfer. For such redox processes, the role of the fullerene cage can be understood as that of an innocent ligand. This review is specifically focused on four groups of EMFs with different kinds of endohedral redox activity: (i) dimetallofullerenes, (ii) Sc3N@C80 and its derivatives, (iii) titanium-based EMFs, and (iv) cerium-based nitride clusterfullerenes. Frontier orbitals of dimetallofullerenes usually have pronounced metal–metal bonding character, and therefore electron transfer affects the metal–metal bonding character in such molecules. T...

The synthesis and single-crystal X-ray structural characterization of the first endohedral metallofullerene to contain a heptagon in the carbon cage are reported. The carbon framework surrounding the planar LaSc2N unit in LaSc2N@Cs(hept)-C80 consists of one heptagon, 13 pentagons, and 28 hexagons. This cage is related to the most abundant Ih- C80 isomer by one Stone-Wales-like, heptagon/pentagon to hexagon/hexagon realignment. DFT computations predict that LaSc2N@Cs(hept)-C80 is more stable than LaSc2N@D5h-C80, and suggests that the low yield of the heptagon-containing endohedral fullerene may be caused by kinetic factors. According to the IUPAC definition, fullerenes are "Com- pounds composed solely of an even number of carbon atoms, which form a cage-like fused-ring polycyclic system with twelve five-membered rings and the rest six-membered rings", although the broadened definition also includes any closed cage structures consisting of three-coordinate carbon atoms. (1) The number of pentagons in this definition follows from Eulers theorem as applied to a polyhedron comprising only pentagons and hexagons. Furthermore, it was found that adjacent pentagons are strongly destabilizing, and hence the isolated pentagon rule (IPR) was formulated. (2) The IPR requires that each pentagon be surrounded by five hexagons and is rooted in the anti-aromaticity of the pentalene fragment and its high curvature, thus leading to the significant strain in an sp 2 -based carbon system.

The low-temperature magnetic properties of the endohedral metallofullerene HoSc2N@C-80 have been studied by superconducting quantum interference device (SQUID) magnetometry. Alternating current (ac) susceptibility measurements reveal that this molecule exhibits slow relaxation of magnetization in a small applied field with timescales in the order of milliseconds. The equilibrium magnetic properties of HoSc2N@C-80 indicate strong magnetic anisotropy. The large differences in magnetization relaxation times between the present compound and the previously investigated DySc2N@C-80 are discussed.

Iron in Graphene Carbon or other covalently bonded materials, like boron nitride, can form two-dimensional sheets because of the strong bonding between the atoms. In contrast, metals share electrons in a three-dimensional delocalized way, and this could preclude the formation of thin stable sheets. Nevertheless, Zhao et al. (p. 1228 ) observed pure iron membranes suspended across the pores in a graphene sheet. This phenomenon was discovered when an iron chloride solution, used to process the graphene, decomposed to form pure iron films across the pores.

The paramagnetic NMR study of HoM2N@C-80-I-h and Ho2MN@C-80-I-h nitride cluster fullerenes (M = Sc, Lu, Y) reveals strong dependence of Ho-induced paramagnetic shifts (delta(para)) in C-13 NMR spectra on the size of the diamagnetic metal in the cluster. In particular, the delta(para) value in HoY2N@C-80 is almost doubled in comparison to that in HoSc2N@C-80. X-ray magnetic circular dichroism studies show that all Ho-nitride cluster fullerenes have the same magnetic ground state of Ho3+. Point-charge ligand-field splitting calculations show that the increase of the M3+ radius in going from Sc to Y results in a considerable increase of the energy splitting between different J(z) states. This leads to a 19% higher magnetic anisotropy of Ho3+ in HoY2N@C-80 than in HoSc2N@C-80 at 300 K. Variations of the molecular geometry and cluster dynamics with the size of the cluster are found to have even greater influence on delta(para) values. This work shows that the magnetic properties of the species confined inside the fullerene cages can be tuned using the geometrical factors such as the cluster and the cage size.

Thermal behavior of two hydrofullerenes, C 60 H 36 and C 60 H 18 , was studied by means of Knudsen cell mass-spectrometry and infrared spectroscopy. Vapor pressures and enthalpies of sublimation at T =550–685 K were measured. Sublimation of the hydrofullerenes was accompanied by partial loss of hydrogen. Decomposition of C 60 H 36 was confirmed to be a stepwise process with formation of C 60 H 18 as an intermediate product. The material of the Knudsen cell strongly affected the partial pressures and mass-spectra of the hydrofullerene vapor species.

Redox behavior of endohedral metallofullerenes, in particular their oxidation process, can be classified as a fullerene-based or endohedral species-based process according to the mechanism of the electron transfer. Here we report on the phenomenon of the strain-driven electrochemical behavior achieved by encapsulating the cerium-containing clusters into a series of carbon cages ranging from C78 to C88. The Ce-based mixed metal nitride clusterfullerenes CexM3-xN@C2n (x = 1, 2; M = Sc or Y; 2n = 78-88) were synthesized and characterized. The magnitude of the inherent strain caused by the limited inner space of the carbon cage for the relatively large nitride clusters can be varied by choosing different scaffold metals (Sc, Lu, or Y) to tailor the size of the encaged CexM3-xN cluster and by matching the nitride cluster with different fullerene cages in the size range from C78 to C88. The redox properties of CexM3-xN@C2n were investigated by cyclic and square wave voltammetry. The mechanism of the electrochemical oxidation of Ce-based mixed metal nitride clusterfullerenes, in particular whether the fullerene-based oxidation or the Ce(III) → Ce(IV) process is observed, is found to be dependent on the scaffold metal and the size of the fullerene cage. The endohedral oxidation of Ce(III) to Ce(IV) was observed for a number of compounds as revealed by the negative shift of their oxidation potentials with respect to the values measured for the non-Ce analogues. Experimental studies are supported by DFT calculations. We conclude that the prerequisites for the Ce-based endohedral oxidation process are suitable inherent cluster-cage strain and sufficiently high oxidation potential of the fullerene cage.

The selective substitution of the antipodal F atom in 1-Me-CB(11)F(11)- with a SiPh(3) moiety led to the isolation and structure determination of the cesium(I) and silver(I) salts of the 1-Me-12-SiPh(3)-CB(11)F(10)- anion. The silver salt contains both a nearly trigonal-planar Ag(arene)(3)+ cation and the first example of a Ag(arene)(4)+ cation.

The characteristic features of the continuous-wave lasing spectra near 3.3 µm of multimode InAsSbP/InAsSb/InAsSbP double-heterostructure diode lasers are shown. The observation of mode switching to longer and shorter wavelengths at cryogenic temperatures is reported. It is shown that suppression of the longitudinal side modes closest to the main mode results in large mode jumps in energy during mode tuning by current. The characteristics which were observed are explained by gain spectrum inhomogeneity due to spectral hole burning in narrow-gap semiconductors. The intraband charge-carrier relaxation times in the active region are estimated.

The performance of the InAsSbP/InAs lasers for absorption spectroscopy of ammonia at 3370–3660 cm−1 was first shown. These continuous wave lasers based on the III–V semiconductor are alternative to a widespread utilised Pb-salt device and were first investigated in closed-cycle He-cryostat at temperatures of 32–85 K. The spectral and tuning characteristics of the laser were considered versus both heatsink temperatures and drive currents in viewpoint of applications in molecular laser spectroscopy, with best device performance being found at 45–65 K. The preliminary experiments to record spectra of the ammonia absorption with the diode were undertaken.

Individual gaseous species of fullerene chlorides have been successfully generated in a molecular beam. Knudsen cell mass spectrometry has been used to detect C 60 Cl 2 n ( n =0…9), C 70 Cl 2 m ( m =0…7) in the vapour over the system C 60 /C 70 (extract) with CrCl 3 , FeCl 3 ·6H 2 O, FeCl 3 (anhydrous) and CuCl 2 (anhydrous) at temperatures from 520 to 720 K. Bond dissociation enthalpies for the fullerene chlorides have been estimated.

The title compound, C70F30,which has crystallographic twofold symmetry, is one of four isomers of C60(CF3)10. It has an idealized C60–I h core, with the ten CF3 groups arranged on two symmetry-related para-para-para-meta-meta loops of five edge-sharing C6(CF3)2 hexagons. There are no cage Csp 3—Csp 3 bonds. There are intramolecular F...F contacts between pairs of neighboring CF3 groups, ranging from 2.523 (2) to 2.746 (2) Å.

The kinetics of structural relaxation in hydrogenated amorphous silicon (a-Si:H) deposited by various methods is investigated by differential scanning calorimetry. The experimental results are used to analyze the nature of the metastable states in a-Si:H and to investigate the relationship between structural relaxation and light-induced metastability (the Staebler-Wronski effect).

Cyclic voltammograms are reported for C 6 0 (CF 3 ) n derivatives for the first time. The compounds studied were 1,9-C 6 0 (CF 3 ) 2 and 3 isomers of C 6 0 (CF 3 ) 1 0 , including the structurally characterized derivative 1,3,7,10,14,-17,23,28,31,40-C6o(CF3) 1 0 (C 6 0 (CF 3 ) 1 0 -3). The compound 1,9-C 6 0 (CF 3 ) 2 exhibited 3 reversible reductions; C 6 0 -(CF3) 1 0 -3 exhibited 2 reversible reductions; the other 2 isomers of C 6 0 (CF 3 ) 1 0 each exhibited 1 reversible reduction. ESR and near-IR spectroelectrochemical experiments were performed to characterize some of the C 6 0 (CF 3 ) n - and C 6 0 (CF 3 ) n 2 - species generated by cyclic voltammetry. The ESR spectrum of the C 6 0 (CF 3 ) 1 0 -3- radical anion consisted of an envelope of 25 lines centered at g = 2.0032 (the apparent a value is ca. 0.5 G), evidence of coupling between the unpaired electron and a significant number of the CF 3 fluorine atoms. The most significant finding is that this radical anion has a half-life in solution at 25 °C of about 7 min.

In all metallofullerenes known before this work, metal atoms form single highly polar bonds with non-metal atoms in endohedral cluster. This is rather surprising for titanium taking into account the diversity of organotitanium compounds. Here we show that the arc-discharge synthesis of mixed titanium-lutetium metallofullerenes in the presence of ammonia, melamine or methane unexpectedly results in the formation of TiLu2C@Ih-C80 with an icosahedral Ih(7) carbon cage. Single-crystal X-ray diffraction and spectroscopic studies of the compound reveal an unprecedented endohedral cluster with a μ3-carbido ligand and Ti-C double bond. The Ti(IV) in TiLu2C@Ih-C80 can be reversibly reduced to the Ti(III) state. The Ti=C bonding and Ti-localized lowest unoccupied molecular orbital in TiLu2C@Ih-C80 bear a certain resemblance to titanium alkylidenes. TiLu2C@Ih-C80 is the first metallofullerene with a multiple bond between a metal and the central, non-metal atom of the endohedral cluster. Metallofullerenes typically have polar single bonds between metals and non-metals. Here, through arc-discharge experiments, the authors observe the formation of an endohedral fullerene with an encapsulated tri-coordinate μ3-carbon centre and a stable titanium-carbon double bond.

An irreducible norm closed semigroup of complex matrices is simultaneously similar to a semigroup of partial isometries if and only if (a) the norms of all nonzero members of it are uniformly bounded above and below, and (b) its idempotents commute. This is a generalization of the well-known result on bounded groups.

The influence of the cage as well as of the cluster size has been studied in Gd–Sc nitride cluster fullerenes, which have been synthesized and isolated for these studies. A series of carbon cages ranging from C78 to C88 have been synthesized, isolated, and characterized in detail using absorption and vibrational spectroscopy as well as electrochemistry and density functional theory calculations. Gd–Sc mixed-metal cluster fullerenes in carbon cages different from C80 were described for the first time. A review of their structures, properties, and stability is given. The synthesis was performed with melamine as an effective solid source of nitrogen, providing high fullerene yield and suppressing empty fullerene formation. Substitution of gadolinium by scandium imposes a noticeable influence on the electronic structure of nitride cluster fullerenes as revealed by electrochemical, spectroscopic, and computational methods.

Hydrogenated silicon-rich nitride (SiNx :H) film with stoichiometry parameter x close to 1.3 was deposited on Si substrate with the use of plasma-enhanced chemical vapor deposition at temperature 100 � C. Furnace annealing during 5 hours in Ar ambient at 1130 � C under atmospheric and high hydrostatic pressure (11 kbar, 1.1 GPa) was applied to modify the structure of the film. Its properties were studied using infrared absorption spectroscopy, Raman spectroscopy and photoluminescence. According to Raman spectroscopy data, the as-deposited film does not contain Si–Si bonds in amount which can be observed. Furnace annealing leads to segregation of excessive Si, so, local vibrations of Si–Si bonds were observed in Raman spectra. In the case of high pressure annealing, the amount of Si–Si bonds is higher compared with atmospheric pressure annealing. Surprisingly, after annealing with such high thermal budget, according to infrared spectroscopy data, the films contain hydrogen in the form of Si–H bonds. Peak due to absorbance by Si–H bond vibrations becomes even higher for the film annealed at atmospheric pressure. Dramatic changes in photoluminescence spectra and temperature dependence of photoluminescence were observed for the films annealed under high and atmospheric pressure.

Furnace annealing, cw- and pulse laser treatments were app lied for crystallization of amorphous Si nano-layers and Si nanoclusters in SiN x -Si 3 N 4 and Si-SiO 2 multilayer nanostructures. The as-deposite d and annealed structures were studied using optical methods and electron micros copy techniques. The influence of hydr ogen on crystallization and formation of Si nanoclusters was studied. Regimes for pulse laser crystallization of amorphous Si nanoclusters and nanolayers were found. This approach is applicable for the creation of dielectric films with semiconductor nanoclusters and silicon nanostructured films on non-refr actory substrates for all-silicon tandem solar cells. Keywords: Si based nanostructures, pulse laser crystallizatio n, Raman scattering, all-silicon tandem solar cells 1. INTRODUCTION Interest to dielectric films containing many periodical layers of Si nanoclusters or Si quantum wells is growing due to their perspectives of practical application [1]. For example, growing interest to crystallization of amorphous silicon films and silicon based heterostructures on non-refractory not expensive substrates is stimulated by demands of giant microelectronics. The enlargement of sizes of flat panel displays with active thin film transistor matrix can be described as “reverse Moor’s low” [2]. Dielectric films with amorphou s or crystalline Si clusters show promise as a material for optoelectronic and flash-memory applications. The most important application areas are silicon-based optoelectronic devices, non-volatile memory, and tandem solar cells based on lateral Si/SiO

Topology is familiar mostly from mathematics, but also natural sciences have found its concepts useful. Those concepts have been used to explain several natural phenomena in biology and physics, and they are particularly relevant for the electronic structure description of topological insulators and graphene systems. Here, we introduce topologically distinct graphene forms - graphene spirals - and employ density-functional theory to investigate their geometric and electronic properties. We found that the spiral topology gives rise to an intrinsic Rashba spin-orbit splitting. Through a Hamiltonian constrained by space curvature, graphene spirals have topologically protected states due to time-reversal symmetry. In addition, we argue that the synthesis of such graphene spirals is feasible and can be achieved through advanced bottom-up experimental routes that we indicate in this work.

We study self-adjoint semigroups of partial isometries on a Hilbert space. These semigroups coincide precisely with faithful representations of abstract inverse semigroups. Groups of unitary operators are specialized examples of self-adjoint semigroups of partial isometries. We obtain a general structure result showing that every self-adjoint semigroup of partial isometries consists of "generalized weighted composition" operators on a space of square-integrable Hilbert-space valued functions. If the semigroup is irreducible and contains a compact operator then the underlying measure space is purely atomic, so that the semigroup is represented as "zero-unitary" matrices. In this case it is not even required that the semigroup be self-adjoint., Comment: To appear in Semigroup Forum

It is easy to see that if $\cG$ is a non-abelian group of unitary matrices, then for no members $A$ and $B$ of $\cG$ can the rank of $AB-BA$ be one. We examine the consequences of the assumption that this rank is at most two for a general semigroup $\cS$ of linear operators. Our conclusion is that under obviously necessary, but trivial, size conditions, $\cS$ is reducible. In the case of a unitary group satisfying the hypothesis, we show that it is contained in the direct sum $\cG_1\oplus\cG_2$ where $\cG_1$ is at most $3\times 3$ and $\cG_2$ is abelian., Comment: To appear in Proceeding of the American Mathematical Society

Photoinduced charge generation (PCG) dynamics are notoriously difficult to correlate with specific molecular properties in device relevant polymer:fullerene organic photovoltaic blend films due to the highly complex nature of the solid state blend morphology. Here, this study uses six judiciously selected trifluoromethylfullerenes blended with the prototypical polymer poly(3-hexylthiophene) and measure the PCG dynamics in 50 fs–500 ns time scales with time-resolved microwave conductivity and femtosecond transient absorption spectroscopy. The isomeric purity and thorough chemical characterization of the fullerenes used in this study allow for a detailed correlation between molecular properties, driving force, local intermolecular electronic coupling and, ultimately, the efficiency of PCG yield. The findings show that the molecular design of the fullerene not only determines inter-fullerene electronic coupling, but also influences the decay dynamics of free holes in the donor phase even when the polymer microstructure remains unchanged.

The endohedral metallofullerene (EMF) self-assembly process in Sc/carbon vapor in the presence and absence of an inert cooling gas (helium) is systematically investigated using quantum chemical molecular dynamics simulations. It is revealed that the presence of He atoms accelerates formation of pentagons and hexagons and reduces the size of the self-assembled carbon cages in comparison to analogous He-free simulations. As a result, the Sc/C/He system simulations produce a larger number of successful trajectories (i.e. leading to Sc-EMFs) with more realistic cage-size distribution than simulations of the Sc/C system. The main Sc encapsulation mechanism involves nucleation of several hexagons and pentagons with Sc atoms already at the early stages of the carbon vapor condensation. In such proto-cages, both Sc–C σ-bonds and coordination bonds between Sc atoms and the π-system of the carbon network are present. Sc atoms are thus rather labile and can move along the carbon network, but the overall bonding is sufficiently strong to prevent dissociation even at temperatures around 2000 Kelvin. Further growth of the fullerene cage results in encapsulation of one or two Sc atoms within the fullerene. In agreement with experimental studies, extension of the simulations to Fe and Ti as the metal component showed that Fe-EMFs are not formed at all, whereas Ti is prone to form Ti-EMFs with small cage sizes, including Ti@C28-Td and Ti@C30-C 2v (3).

Polycrystalline silicon films on polyimide substrates were obtained by a method based on the crystallization of amorphous films under the impact of nanosecond pulses of excimer laser radiation. Characteristics of the film structure were studied by methods of Raman scattering and high-resolution electron microscopy. For the laser crystallization regimes employed, nanocrystalline silicon films with an average grain size of 5 nm were obtained. The results are of interest for the development of large-scale microelectronic devices (active thin-film transistor matrices) on cheap flexible substrates.

Endohedral metallofullerenes (EMFs) are able to encapsulate up to four metal atoms. In EMFs, metal atoms are positively charged because of the electron transfer from the endohedral metal atoms to the carbon cage. It results in the strong Coulomb repulsion between the positively charged ions trapped in the confined inner space of the fullerene. At the same time, in many EMFs, such as Lu2@C76, Y2@C79N, M2@C82 (M = Sc, Y, Lu, etc.), Y3@C80, or Sc4O2@C80, metals do not adopt their highest oxidation states, thus yielding a possibility of the covalent metal–metal bonding. In some other EMFs (e.g., La2@C80), metal–metal bonding evolves as the result of the electrochemical or chemical reduction, which leads to the population of the metal-based LUMO with pronounced metal–metal bonding character. This article highlights different aspects of the metal–metal bonding in EMFs. It is concluded that the valence state of the metal atoms in dimetallofullerenes is not dependent on their third ionization potential, but is determined by their ns2(n − 1)d1 → ns1(n − 1)d2 excitation energies. Peculiarities of the metal–metal bonding in EMFs are described in terms of molecular orbital analysis as well as topological approaches such as Quantum Theory of Atoms in Molecules and Electron Localization Function. Interplay of Coulomb repulsion and covalent bonding is analyzed in the framework of the Interacting Quantum Atom approach.

The sequential addition of CN(-) or CH3(-) and electrophiles to three perfluoroalkylfullerenes (PFAFs), C(s)-C70(CF3)8, C1-C70(CF3)10, and C(s)-p-C60(CF3)2, was carried out to determine the most reactive individual fullerene C atoms (as opposed to the most reactive C=C bonds, which has previously been studied). Each PFAF reacted with CH3(-) or CN(-) to generate metastable PFAF(CN)(-) or PFAF(CH3)2(2-) species with high regioselectivity (i.e., one or two predominant isomers). They were treated with electrophiles E(+) to generate PFAF(CN)(E) or PFAF(CH3)2(E)2 derivatives, also with high regioselectivity (E(+)=CN(+), CH3(+), or H(+)). All of the predominant products, characterized by mass spectrometry and (19)F NMR spectroscopy, are new compounds. Some could be purified by HPLC to give single isomers. Two of them, C70(CF3)8(CN)2 and C70(CF3)10(CH3)2(CN)2, were characterized by single-crystal X-ray diffraction. DFT calculations were used to propose whether a particular reaction is under kinetic or thermodynamic control.