Reactions of CH(3)F have been surveyed systematically at room temperature with 46 different atomic cations using an inductively coupled plasma/selected-ion flow tube tandem mass spectrometer. Rate coefficients and product distributions were measured for the reactions of fourth-period atomic ions from K(+) to Se(+), of fifth-period atomic ions from Rb(+) to Te(+) (excluding Tc(+)), and of sixth-period atomic ions from Cs(+) to Bi(+). Primary reaction channels were observed corresponding to F atom transfer, CH(3)F addition, HF elimination, and H(2) elimination. The early-transition-metal cations exhibit a much more active chemistry than the late-transition-metal cations, and there are periodic features in the chemical activity and reaction efficiency that maximize with Ti(+), As(+), Y(+), Hf(+), and Pt(+). F atom transfer appears to be thermodynamically controlled, although a periodic variation in efficiency is observed within the early-transition-metal cations which maximizes with Ti(+), Y(+), and Hf(+). Addition of CH(3)F was observed exclusively (>99%) with the late-fourth-period cations from Mn(+) to Ga(+), the fifth-period cations from Ru(+) to Te(+), and the sixth-period cations from Hg(+) to Bi(+) as well as Re(+). Periodic trends are observed in the effective bimolecular rate coefficient for CH(3)F addition, and these are consistent with expected trends in the electrostatic binding energies of the adduct ions and measured trends in the standard free energy of addition. HF elimination is the major reaction channel with As(+), while dehydrogenation dominates the reactions of W(+), Os(+), Ir(+), and Pt(+). Sequential F atom transfer is observed with the early-transition-metal cations, with the number of F atoms transferred increasing across the periodic table from two to four, maximizing at four for the group 5 cations Nb(+)(d(4)) and Ta(+)(d(3)s(1)), and stopping at two with V(+)(d(4)). Sequential CH(3)F addition was observed with many atomic cations and all of the metal mono- and multifluoride cations that were formed.

Endohedral metallofullerenes (EMFs) are novel derivatives of fullerenes that can encapsulate metal atoms or clusters in their inner space.[1] Owing to their extraordinary properties attributed to significant electron transfer from the metal atoms to the fullerene cage, [2] EMFs have attracted wide interests since the discovery of fullerenes.[3] For instance, lanthanide metallofullerenes have been suggested for use as encapsulated contrasting agents for magnetic resonance imaging. [4] In EMFs, the internal metal atoms always donate electrons to the fullerene cage and carry considerable positive charges. It is interesting and highly significant to investigate the possible formation of metal-metal bonds between these metal atoms in EMFs. [5][6][7] From a theoretical point of view, the study of metal-metal bonds in EMFs gives an in-depth perspective of the metal-metal interaction and provides an approach for further experimental and theoretical explorations of metal-metal interactions. [6,8] On the other hand, in contrast to the fact that several kinds of metal-metal bonds have been studied, in other fields, [9] up to now only rare examples of metal-metal bonds are reported in fullerene chemistry.[7] Furthermore, the presence of metal-metal bonds produces unique structures and fascinating electronic properties of EMFs, which may extend their promising applications in electronics, magnetism, and photovoltaics. [7,10] Most importantly, previous studies have indicated that the encapsulated metal atoms can move around in fullerene cage at room temperature.[11] This dynamic motion makes it possible to design these EMFs as functional molecular devices with new magnetic and electronic properties. [12] It is also an interesting question whether other novel dynamic motion of the encapsulated metals exists in fullerene cage.Lots of efforts have been devoted to metal-metal bonds in EMFs during the past decades, but only a few single metal-metal bonds have been found and confirmed. [6][7][8][13][14][15] In fact, Stevenson et al. suggested the presence of a Sc À Sc bond between the shortest Sc À Sc distance with a newly experimentally determined structure of Sc 4 O 2 @C 80 .[14] Two kinds of metal-metal bonds have been found between Y atoms so far: one two-electron bond in the Y 2 @C 82 , [7] and another long single-electron bond in Y 2 @C 79 N.[15] In addition, a single-electron bond between Tb atoms was also proposed in Tb 2 @C 79 N.[15]Herein we present a thorough investigation on a newly isolated dimetallofullerene Lu 2 @C 76 , [16] and find that the two lutetium atoms prefer to bind together to form an unprecedented single metal-metal bond, in a formal valence state of [Lu 2 ] 4 + @C 76 4À by means of combined quantum chemical and statistical thermodynamic approaches. More interestingly, it is shown that the Lu atoms can hop rapidly between six equivalent configurations in the fullerene cage at room temperature, giving rise to a trajectory as a tetrahedron in C 76 (T d ). Systematic calculations on the di-, tetra-, he...

Single-walled carbon nanotubes (SWNTs) were subjected to alkylation using alkyl bromide and alkyl dibromide, and the photoluminescence (PL) properties of the resulting alkylated SWNTs were characterized. Two new PL peaks were observed along with the intrinsic PL peak at 976 nm when alkyl bromide was used (SWNT-Bu: ∼1095 and 1230 nm, SWNT-Bn: 1104 and 1197 nm). In contrast, the use of α,α'-dibromo-o-xylene as an alkyl dibromide primarily resulted in only one new PL peak, which was observed at 1231 nm. The results revealed that the Stokes shift of the new peaks was strongly influenced by the addition patterns of the substituents. In addition, the time-resolved PL decay profiles of the alkylated SWNTs revealed that the PL peaks possessing a larger Stokes shift had longer exciton lifetimes. The up-conversion PL (UCPL) intensity of the alkylated SWNTs at excitation wavelengths of 1100 and 1250 nm was estimated to be ∼2.38 and ∼2.35 times higher than that of the as-dispersed SWNTs, respectively.

The encapsulations of fullerene C 70 by carbon-nanorings are of great interest because, unlike the spheroidal C 60 , several distinct geometrical orientations are possible. Additionally, due to experimental difficulties, there is a great deal of opportunity for the computational efforts to deeply explore the intrinsic nature of π−π noncovalent interactions of the CPP carbon-nanoring⊃fullerene host−guest systems. In this paper, the structures and properties of the host−guest complexes formed with nanoring host [n]cycloparaphenylene (n =10, 11, and 12) ([n]CPP) and guest fullerene C 70 were detailed and explored by theoretical calculations. The results showed that three different kinds of quasi-inclusion configurations can be obtained for [10]CPP⊃C 70 and [11]CPP⊃C 70 host−guest complexes in which C 70 is lying, half-lying, and standing in the cavities of the hosts, respectively. However, there are only two kinds of stable configurations for [12]CPP⊃C 70 host−guest complexes in which C 70 is half-lying and standing in the cavities of the host [12]CPP, respectively. According to the relative values of the binding energies and thermodynamic information, the guest C 70 is apt to adopt lying, standing, and half-lying orientations in the cavities of [10]CPP, [11]CPP, and [12]CPP, respectively. The host−guest interaction regions were detected and visualized in real space based on the electron density and reduced density gradient (RDG). Additionally, IR, UV−visible−NIR, and 1 H NMR spectra of the hosts before and after the formations of the complexes have been simulated and discussed qualitatively, which may be helpful for further experimental investigations in the future.

The reaction mechanism and regioselectivity of the Diels-Alder reactions of C68 and Sc3N@C68, which violate the isolated pentagon rule, were studied with density functional theory calculations. For C68, the [5,5] bond is the most favored thermodynamically, whereas the cycloaddition on the [5,6] bond has the lowest activation energy. Upon encapsulation of the metallic cluster, the exohedral reactivity of Sc3N@C68 is reduced remarkably owing to charge transfer from the cluster to the fullerene cage. The [5,5] bond becomes the most reactive site thermodynamically and kinetically. The bonds around the pentagon adjacency show the highest chemical reactivity, which demonstrates the importance of pentagon adjacency. Furthermore, the viability of Diels-Alder cycloadditions of several dienes and Sc3N@C68 was examined theoretically. o-Quinodimethane is predicted to react with Sc3N@C68 easily, which implies the possibility of using Diels-Alder cycloaddition to functionalize Sc3N@C68.

No abstract

No abstract

Successful isolation and unambiguous crystallographic assignment of a series of higher carbide cluster metallofullerenes present new insights into the molecular structures and cluster-cage interactions of endohedral metallofullerenes. These new species are identified as LaC@C(41)-C, LaC@D(85)-C, LaC@C(132)-C, LaC@C(157)-C, and LaC@C(175)-C. This is the first report for these new cage structures except for D(85)-C. Our experimental and theoretical results demonstrate that LaC are more inclined to exist stably in the carbide form LaC@C rather than as the dimetallofullerenes La@C, which are rationalized by considering a synergistic effect of inserting a C unit into the cage, which ensures strong metal-cage interactions by partially neutralizing the charges from the metal ions and by fulfilling the coordination requirement of the La ions as much as possible.