Dimerization in KC60 and RbC60

A Theoretical Structure Study Infrared Spectra of C60O Isomers Through Ab Initio Method

The infrared spectra of C60O isomers have been calculated through ab initio method. It has been observed that the simulated spectrum of one of C60O isomers is matching with the available experimental data in literature, while the other isomers are not matching so much. One can easily understand the basic physical properties of C60O by knowing of their vibration and geometric structures with their interrelation between these properties. It is found that the isomeric structures of C60O are very sensitive to electron correlation treatment with basis set that are employed. So the structure of C60O will not calculate from semi-empirical methods such as modified neglect of differential overlap (MNDO) or AM1 for more accuracy. The simulated spectra show different bands that rarely found all bands simultaneously in single experiment.

Fullerene monolayer formation by spray coating

Many large molecular complexes are limited in thin film applications by their insufficient thermal stability, which excludes deposition via commonly used vapour phase deposition methods. Here we demonstrate an alternative way of monolayer formation of large molecules by a simple spray coating method under ambient conditions. This technique has been successfully applied on C(60) dissolved in toluene and carbon disulfide. Monolayer thick C(60) films have been formed on graphite and gold surfaces at particular deposition parameters, as confirmed by atomic force and scanning tunnelling microscopies. Structural and electronic properties of spray coated C(60) films on Au(111) have been found comparable to thermally evaporated C(60). We attribute the monolayer formation in spray coating to a crystallization process mediated by an ultrathin solution film on a sample surface.

Reversible phase transformation and doubly charged anions at the surface of simple cubic RbC60

The simple cubic phase of a RbC60 thin film has been studied using photoelectron spectroscopy. The simple cubic-to-dimer transition is found to be reversible at the film surface. A sharp Fermi edge is observed and a lower limit of 0.5 eV is found for the surface Hubbard U, pointing to a strongly correlated metallic character of thin-film simple cubic RbC60. A molecular charge state is identified in the valence band and core-level photoemission spectra which arises from C60(2-) anions and contributes to the spectral intensity at the Fermi level.

Ionic and Neutral C60 Complexes with Coordination Assemblies of Metal Tetraphenylporphyrins, MIITPP2·DMP (M = Mn, Zn). Coexistence of (C60-)2 Dimers Bonded by One and Two Single Bonds in the Same Compound

Coordination assemblies of metal tetraphenylporphyrins, MIITPP2.DMP (M=Mn, Zn) were shown to form ionic multicomponent and neutral complexes with fullerene, {(MnIITPP)2.DMP}.(C60-)2.(DMETEP+)2.(C6H4Cl2)5 (1) and {(ZnTPP)2.DMP}.(C60)2.(C6H5Cl)4 (2), where DMP=N,N'-dimethylpiperazine and DMETEP+=the cation of N,N'-dimethyl-N'-ethylthioethylpiperazine. The crystal structure of 1 contains zigzag chains of the (C60-)2 dimers alternating with the DMETEP+ cations in the channels formed by the (MnIITPP)2.DMP units, whereas in 2 zigzag chains of the C60 molecules are separated by the (ZnTPP)2.DMP units and C6H5Cl molecules. The (MIITPP)2.DMP assemblies (M=Mn, Zn) have axial M-N(DMP) bonds of 2.315(2) and 2.250(2) A length, average equatorial M-N(DMP) bonds elongated to 2.141(3) and 2.077(2) A, and MII atoms displaced from the porphyrin plane toward the ligand by 0.677 and 0.485 A, respectively. The single-bonded sigma-(C60-)2 dimer coexists in 1 with the (C60-)2 dimer bonded by two single bonds with 86/14 occupancy factors. The sigma-(C60-)2 dimers are unusually stable and begin to dissociate only above a temperature of 320-330 K that results in the increase of the magnetic moment of 1 from 8.33 microB (320 K) to 8.66 microB (360 K). The electron paramagnetic resonance (EPR) signal of the dimeric phase (T<320 K) with the features spread over the range of 0-0.7 T was attributed to the interacting Mn2+ centers in the (MnIITPP)2.DMP units. The dissociation of the sigma-(C60-)2 dimers to the EPR-active C60*- radical anions manifests a new broad Lorenz signal above 320 K with g=2.0179 and DeltaH=65.5 mT. This signal can appear due to the exchange coupling between paramagnetic (MnIITPP)2.DMP and C60*- species. The vis-NIR spectrum of the sigma-(C60-)2 dimers is discussed.

Structural aspects of two-stage dimerization in an ionic C60complex with bis(benzene)chromium: Cr(C6H6)2·C60·C6H4Cl2

Single crystals of the ionic C60 complex with bis(benzene)chromium: {Cr(I)(C6H6)2(.+)}.(C60.-)).C6H4Cl2 (1) were obtained. The crystal structure of 1 shows the presence of monomeric C60.- radical anions at 250 K and the formation of single-bonded (C60-)2 dimers at 90 K. The dimerization is realized in two types of the C60.-) pairs with different interfullerene center-to-center distances of 10.052 and 10.279 A arranged in zigzag chains along the a-direction. As a result, two symmetrically independent (C60-)2 dimers found in 1 at 90 K have different environments, intercage C-C bond lengths and C60- center-to-center distances. Such differences should provide different thermal stability of these dimers and result in the appearance of two stages at the dimerization. Indeed, according to SQUID measurements, the magnetic moment of 1 decreases stepwise at the dimerization in two temperature ranges at 240-200 and 200-160 K.

Formation of single-bonded (C60-)2 and (C70-)2 dimers in crystalline ionic complexes of fullerenes

New ionic complexes of fullerenes C(60) and C(70) with decamethylchromocene Cp*(2)Cr.C60.(C(6)H(4)Cl(2))(2) (1), Cp*(2)Cr.C60.(C(6)H(6))(2) (2); the multicomponent complex of (Cs(+))(C70-) with cyclotriveratrylene CTV.(Cs)(2).(C70)(2).(DMF)(7).(C(6)H(6))(0.75) (3); bis(benzene)chromium Cr(C(6)H(6))(2).C60.(C(6)H(4)Cl(2))(0.7) (4), Cr(C(6)H(6))(2).C60.C(6)H(5)CN (5), Cr(C(6)H(6))(2).C70.C(6)H(4)Cl(2) (6), Cr(C(6)H(6))(2).C60 (7); cobaltocene Cp(2)Co.C60.C(6)H(4)Cl(2) (8), Cp(2)Co.C70.(C(6)H(4)Cl(2))(0.5) (9); and cesium Cs.C70.(DMF)(5) (10) have been obtained. The complexes have been characterized by the elemental analysis, IR-, UV-vis-NIR spectroscopy, EPR and SQUID measurements. It is shown that C(60)(.-) exists as a single-bonded diamagnetic (C60-)2 dimer in 1, 2, 4, 5, and 8 at low temperatures (1.9-250 K). The dimers dissociate above 160-250 K depending on donor and solvent molecules involved in the complex. C60(.-) dimerizes reversibly and shows a small hysteresis (<2 K) at slow cooling and heating rates. The single-bonded diamagnetic (C70-)2 dimers are also formed in 6, 9, and 10 and begin to dissociate only above 250-360 K. The IR and UV-vis-NIR spectra of sigma-bonded negatively charged fullerenes are presented.

Dimer to monomer phase transition in alkali-metal fullerides: magnetic susceptibility changes

Ab initio calculations have been employed to investigate the peculiar change in magnetic property (from diamagnetic to paramagnetic) of the dianionic C60-dimer phase in a rapidly cooled AC60 samples ( A: alkali metal). We first note that the triplet state of (C60)-22 which was never considered previously is nearly degenerate with the singlet state, and the transition barrier between the two states is reasonably small. This explains the susceptibility increase with an increase in temperature and the magnetic phase transition in the process of the dimer to monomer phase transition.

Electron spin density distribution in the polymer phase of CsC60: assignment of the NMR spectrum

We present high resolution 133Cs-13C double resonance NMR data and 13C-13C NMR correlation spectra of 13C enriched samples of the polymeric phase of CsC60. These data lead to a partial assignment of the lines in the 13C NMR spectrum of CsC60 to the carbon positions on the C60 molecule. A plausible completion of the assignment can be made on the basis of an ab initio calculation. The data support the view that the conduction electron density is concentrated at the C60 "equator," away from the interfullerene bonds.

COMPUTATIONAL APPROACH TO THE PHYSICAL CHEMISTRY OF FULLERENES AND THEIR DERIVATIVES

A critical review is presented of results obtained with different computational methods (mainly ab initio) on C60, C70, and specific fullerene derivatives, also in comparison with experimental data. From the discussion of diverse systems, the (often underestimated) complexity of their physical and chemical behavior emerges, and hence the importance of an accurate description and the need for a careful inspection of the experimental data, with which comparison is often intrinsically difficult. The ambition of this review is to help establish a basis not only for a nonsuperficial reading of the existing literature, but also for a constructive approach with computations to the challenge posed by recent promising applications of fullerenes in nanotechnology, optoelectronics, and biology.

The LUMO-derived band of the [Formula: see text] phases

The LUMO-derived band of the [Formula: see text] compound was investigated by means of x-ray and UV photoemission and photoelectric yield spectroscopies. A double-peak structure is found, with peak maxima at 1.1 eV and 0.35 eV. The relative magnitude of the two peaks is strongly temperature dependent: a large transfer of spectral weight from the lower- to the higher-binding-energy peak takes place upon cooling to 110 K. The peaks are tentatively attributed to the dimer and the polymeric phase respectively. However the behaviour as a function of temperature does not agree with the metastability of the dimer phase at room temperature. The position of the Fermi level is compatible with a correlated system on the border of the metal - insulating transition.