| Ligand-protected nanoclusters are widely applied in production and life.The thiolate-protected gold nanoclusters are important representatives of them,which have been applied in catalysis,sensing,optics,biomedicine and other fields.However,the precise controllable synthesis of ligand-protected nanoclusters at the atomic level is still an unsolved problem,and the cause of the "magic size"phenomenon is also unclear.These seriously limit the development of nanocluster science.Our previous studies showed that ligand plays an important role in the formation of nanoclusters.Therefore,based on density functional theory,the"magic size",structures and properties of gold nanoclusters[Au-(p-/m-/oMBT)]1-8 protected by para-/meta-/ortho-methylbenzenethiol ligands were systematically studied in this paper,focusing on the effect of different ligands on the nanoclusters.The research results will contribute to understand the formation mechanism and provide theoretical basis for the controllable preparation of ligandprotected nanoclusters.The main research contents of this paper are as follows:(1)Firstly,the structures,stabilities and surface properties of three isomerized ligands p-/m-/o-MBT were systematically studied,focusing on the comparison of similarities and differences among them.The different position of methyl groups in the p-/m-/o-MBT ligands on the benzene ring result in different steric hindrance effects of the ligands.By calculating the interaction of these three structures,it is found that the interaction in the o-MBT is stronger because the methyl group is close to the sulfur atom,resulting in slight change in partial bond lengths,bond angles and dihedral angles compared withp-/m-MBT.In addition,the total energy,the bond energy,the surface electrostatic potential,the average local ionization energy and the local electron affinity energy of the three systems were studied,and it was found that the three ligands have slight differences in these aspects.(2)On the basis of previous studies of p-/m-/o-MBT ligands,the ligandprotected gold nanoclusters[Au-(p-/m-/o-MBT)]1-8 have been systematically studied.Results show that the gold-sulfur skeleton of[Au-(/p-/m-/o-MBT)]1-8 tend to form closed ring structures with increasing degree of distortion,except for[Au(p-/m-/o-MBT)]1,2.Interestingly,it is found that the[Au-(p-/m-/o-MBT)]1,2 could serve as the basic building blocks for the larger[Au-(p-/m-/o-MBT)]3-8 nanoclusters.Based on the comparison,it is found that the bond length,bond angle and dihedral angle of[Au-(o-MBT)]1-8 are significantly different from that of[Au(p-/m-MBT)]1-8,which may be due to the stronger interaction in o-MBT.Furthermore,ligands also change their angles and orientations more obviously to cope with the dense packing between ligands in[Au-(o-MBT)]1-8.(3)By studying the relative stabilities and molecular surface properties of[Au-(p-/m-/o-MBT)]1-8 nanoclusters,it is found that the total energies of[Au-(oMBT)]1-8 are higher than those of[Au-(p-/m-MBT)]1-8,and the difference of total energy between them increases with the size increasing.The stabilities of[Au-(oMBT)]1-8 are relatively lower compared with other types of nanoclusters,which is also caused by the strong steric hindrance effect of o-MBT ligand and is consistent with the results above.Finally,in order to study the surface properties and growth patterns of[Au-(p-/m-/o-MBT)]1-8,the average binding energy,the HOMO-LUMO energy gap,the average local ionization energy and the local electron affinity energy of[Au-(p-/m-/o-MBT)]1,2 were calculated.It is found that they have strong chemical activity and can be used as the basic building block of large size nanocluster[Au-(p-/m-/o-MBT)]3-8. |
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