Synthesis And Chromatographic Analysis Of Hetero Carbon Clusters

Since the discovery of bulk production of fullerenes,synthetic chemists have conducted chemical modifications for the all-carbon cages.Besides exohedral and endohedral fullerene derivatives,heterofullerene represents the third fundamental group of modified fullerenes,where one or more carbon atoms are replaced by non-carbon atoms.Heterofullerenes is a new and young branch of fullerene chemistry. Due to the replacement of several atoms,structure and electron property of fullerene cages may be improved,and in turn,pushes their potential application in various fields such as superconductors,photoelectron devices and organic ferromagnets.We adopted a popular plasma technology,i.e.arc discharge,to synthesize heterofullerene.Any carbon atoms of the fullerene cage may be substituted by foreign atoms to form heterofullerene in the chaos of fullerene products.The procedure is such that the graphite with BN is discharged in the atmosphere of N₂/He,followed by soxhlet extraction of the soot with toluene for further characterization.The elemental analysis shows that the content of extracted sample by toluene is (%):C,59.77;N,6.957;H,4.749.Together with the isotope patterns in the related mass spectra,therefore,we can confirm the element of B has been doped in the clusters.Furthermore,the mass spectrometry demonstrates a series of doped clusters with m/z 100-500,and multistage mass spectrometry(MSⁿ) indicates that the series of doped clusters accord with the 'magic numbers' of cluster chemistry.Every cluster molecule can be derived from its parent cluster,depending on the high voltage electron stream,which is apparently different from polycyclic aromatic hydrocarbons. We also find that an appropriate amount of silver in the graphite favors the formation of doped fullerene.Unfortunately,we still can't find an available way to separate them effectively.To accurately identify the clusters,we utilized HPLC to separate the pristine sample.HPLC-MS-UV/Vis technology was employ to analyze the sample with methanol/ethanol/cyclohexane as gradient mobile phase.On the C₁₈ column,C₆₀ were eluted at five different retention times,while C₇₀ were eluted at three different retention times.The evidences implied the possible existence of fullerenes(C₆₀,C₇₀) isomers or their derivatives.Furthermore,some structures with(quasi)molecular ion peaks such as 822 and 846 m/z remained to be identified.In addition,we also found some higher fullerenes and their isomers,including C₇₆,C₇₈,C₈₂,C₈₄,et al.The isomers of C₇₆ in the sample can be confirmed in terms of comparing the UV/Vis spectra with those of previous references.One of the isomers at the time of 103.6 min is D₂-C₇₆,which is consistent with the UV/Vis from the references.Another one at the retention time of 78.4 min is a new isomer of C₇₆,which has never been reported before.Similarly,the fullerenes of C_2v-C₇₈,D_3h-C₇₈ and D_2d-C₈₄ were also identified by the HPLC-MS-UV/Vis chromatogram.Unfortunately,likely due to the instability of heterofullerenes,we did not macroscopically isolate the possible heterofullerene C₅₈BN that ever was detected in our primary experiment.Compared to C₆₀,C₅₈BN has a smaller HOMO-LUMO gap, a lower ionization potentials and a lower stabilization energy,all of which may be the reason why C₅₈BN has not yet been separated until now.Besides arc discharge,some other reaction systems can be employed for synthesizing heterofullerene also,e.g,CVD method based on the reaction between C₆₀ with NH₃ and B₂O₃,traditional organic synthesis strategy with the reactions of some nitro compounds with C₆₀.