Single-Crystal X-ray Diffraction Studies of Solvated Crystals of C60 Reveal the Intermolecular Interactions between the Component Molecules.

The solid-state structures of seven solvates of C60 (C60·4tetrachloroethylene, C60·2tetrachloroethylene, C60·3benzene, C60· n-pentane, C60·diethyl ether, C60·chlorobenzene, and C60·benzene·dichloromethane) were determined by single-crystal X-ray diffraction at low temperature. At 90 K, the fullerene and solvate components are generally well-ordered and do not show the orientational disorder that plagues similar structures determined at room temperature. Interactions between the solvate molecules and the fullerene and between adjacent C60 molecules were examined and analyzed. Van der Waals and weak charge-transfer interactions are important to help to organize the individual components in these structures. The weak Lewis acid behavior of C60, such as when it cocrystallizes with diethyl ether or chlorinated solvents, is apparent. In addition, π-stacking interactions are prevalent. The solvates of C60 reported here were frequently obtained from attempts to cocrystallize C60 with another chemical compound. Although the desired cocrystals were never formed, the unincorporated molecules influenced solvate formation.

2-Aminoethanol Extraction as a Method for Purifying Sc3N@C80 and for Differentiating Classes of Endohedral Fullerenes on the Basis of Reactivity.

Extraction with 2-aminoethanol is an inexpensive method for removing empty cage fullerenes from the soluble extract from electric-arc-generated fullerene soot that contains endohedral metallofullerenes of the type Sc3N@C2n (n = 34, 39, 40). Our method of separation exploits the fact that C60, C70, and other larger, empty cage fullerenes are more susceptible to nucleophilic attack than endohedral fullerenes and that these adducts can be readily extracted into 2-aminoethanol. This methodology has also been employed to examine the reactivity of the mixture of soluble endohedral fullerenes that result from doping graphite rods used in the Krätschmer-Huffman electric-arc generator with the oxides of Y, Lu, Dy, Tb, and Gd. For example, with Y2O3, we were able to detect by mass spectrometry several new families of endohedral fullerenes, namely Y3C108 to Y3C126, Y3C107 to Y3C125, Y4C128 to Y4C146, that resisted reactivity with 2-aminoethanol more than the empty cage fullerenes and the mono- and dimetallo fullerenes. The discovery of the family Y3C107 to Y3C125 with odd numbers of carbon atoms is remarkable, since fullerene cages must involve even numbers of carbon atoms. The newly discovered families of endohedral fullerenes with the composition M4C2n (M = Y, Lu, Dy, Tb, and Gd) are unusually resistant to reaction with 2-aminoethanol. Additionally, the individual endohedrals, Y3C112 and M3C102 (M = Lu, Dy, Tb and Gd), were remarkably less reactive toward 2-aminoethanol.

Synthesis, characterization, and antibacterial activity of structurally complex 2-acylated 2,3,1-benzodiazaborines and related compounds.

A set of 2-acylated 2,3,1-benzodiazaborines and some related boron heterocycles were synthesized, characterized, and tested for antibacterial activity against Escherichia coli and Mycobacterium smegmatis. By high-field solution NMR, the heretofore unknown class of 2-acyl-1-hydroxy-2,3,1-diazaborines has been found to be able to exist in several interconvertable structural forms along a continuum comprised of an open hydrazone a, a monomeric B-hydroxy diazaborine b, and an anhydro dimer c. X-Ray crystallography of one of the anhydro dimers, 17c, revealed it to have an unprecedented structure featuring a double intramolecular O→B chelation. The crystal structure of another compound, 37, showed it to be based on a new pentacyclic B heterocycle framework. Nine compounds were found to possess activities against E. coli, and two others were active against M. smegmatis. The finding that these two contain isoniazid covalently embedded in their structures suggests that they might possibly be acting as prodrugs of this well-known antituberculosis agent in vivo.

1-Hydroxy-1H-benzo[d][1,2,6]oxazaborinin-4(3H)-one.

The structure of the title compound, C(7)H(6)BNO(3), a new boron heterocycle, prepared by the condensation of (2-ethoxycarbonylphenyl)boronic acid and hydroxylamine, reveals the specific mode of intramolecular condensation between a phenylboronic acid and an ortho hydroxamic acid substituent. The crystal structure shows that dehydration occurs to form a planar oxazaborinine ring possessing both phenol-like B-O-H and lactam functional groups. In the extended structure, intermolecular hydrogen bonding generates a 14-membered ring. To our knowledge, this is the first crystal structure determination involving a six-membered ring that exhibits consecutive B-OH, O, NH, and C=O functional groups.

A zwitterion produced by a strong intramolecular N→B interaction in 1-hydroxy-2-(pyridin-2-ylcarbonyl)benzo[d][1,2,3]diazaborinine.

2-Acylated 2,3,1-benzodiazaborines can display unusual structures and reactivities. The crystal structure analysis of the boron heterocycle obtained by condensing 2-formylphenylboronic acid and picolinohydrazide reveals it to be an N→B-chelated zwitterionic tetracycle (systematic name: 1-hydroxy-11-oxo-9,10,17λ(5)-triaza-1λ(4)-boratetracyclo[8.7.0.0(2,7).0(12,17)]heptadeca-3,5,7,12,14,16-hexaen-17-ylium-1-uide), C13H10BN3O2, produced by the intramolecular addition of the Lewis basic picolinoyl N atom of 1-hydroxy-2-(pyridin-2-ylcarbonyl)benzo[d][1,2,3]diazaborinine to the boron heterocycle B atom acting as a Lewis acid. Neither of the other two pyridinylcarbonyl isomers (viz. nicotinoyl and isonicotinoyl) are able to adopt such a structure for geometric reasons. A favored yet reversible chelation equilibrium provides an explanation for the slow D2O exchange observed for the OH resonance in the (1)H NMR spectrum, as well as for its unusual upfield chemical shift. Deuterium exchange may take place solely in the minor open (unchelated) species present in solution.