Chemical understanding of carbide cluster metallofullerenes: a case study on Sc2C2@C2v(5)-C80 with complete X-ray crystallographic characterizations

Little is known about the chemical properties of carbide cluster metallofullerenes (CCMFs). Here we report the photochemical reaction of a newly assigned CCMF Sc(2)C(2)@C(2v)(5)-C(80) with 2-adamantane-2,3-[3H]-diazirine (AdN(2), 1), which provides a carbene reagent under irradiation. Five monoadduct isomers (2a-2e), with respective abundances of 20%, 40%, 25%, 5%, and 10%, were isolated and characterized with a combination of experimental techniques including unambiguous single-crystal X-ray crystallography. Results show that the two Sc atoms of the bent Sc(2)C(2) cluster tend to move in most cases, whereas the C(2)-unit is almost fixed. Accordingly, it is difficult to explain the addition patterns by considering the strain and charge density on the cage with a fixed cluster, and thus a moving cluster may account for the addition patterns. These results show that the situation of CCMFs is more complicated than those in other metallofullerenes. Furthermore, a thermal isomerization process from 2b to 2c was observed, confirming that the most abundant isomer 2b is a kinetically favored adduct. Finally, it is revealed that the electronic and electrochemical properties of pristine Sc(2)C(2)@C(2v)(5)-C(80) have been markedly altered by exohedral modification.     

Projector Monte Carlo method based on Slater determinants: a new sampling method for singlet state calculations

A new sampling method is proposed for projector Monte Carlo (PMC) calculations based on Slater determinants (SD) in singlet states. Using the symmetry of the ?? and ?? electron determinants, the number of configurations to be considered can be about one-half of the original sampling. We applied the new sampling to the PMC-SD calculations of the H₂O molecule in the ground state. The results were always improved by the new sampling method both for the equilibrium and for bond-stretched structures.     

Reaction of Some Amides and Thioamides with Diazomethane Catalyzed by Silica Gel

Certain amides and thioamides can easily be methylated with diazomethane in the presence of silica gel.     

Effect of Acids on Crystallization of Lithium Borate Films

Lithium borate films in amorphous and crystalline (Li₂B₄O₇) states were prepared from alkoxide solutions hydrolyzed in the presence or absence of hydrochloric acid or acetic acid. The acids suppressed crystallization of the amorphous films into Li₂B₄O₇, with acetic acid being the stronger suppressor. In order to determine the suppressing mechanism, we investigated the distribution of boron-containing species in the solutions by¹¹B-NMR. Boron in the non-acidified solution existed as both B(OH) ₄ ⁻ and polyborate species, including B₄O₅(OH) ₄ ²⁻ , which is easily transformed into the crystal nucleous of Li₂B₄O₇. In the solutions containing hydrochloric acid or acetic acid, however, boron was present mainly as B(OH)₃ and the formation of the polyborate species was suppressed, leading in turn to the suppression of crystallization into Li₂B₄O₇. X-ray fluorescence analysis showed that acetic acid produced a larger amount of residual carbon in the films than did hydrochloric acid. We concluded that the residual carbon also inhibited crystallization of the films into Li₂B₄O₇.