Theoretical Design And Recognition Of Superhalogen Anions

Specific clusters,which possess even higher electron affinities?EA?than halogen atoms owing to collective effects,are termed as superhalogens.Superhalogens can mimic the chemical behavior of halogen atoms and serve as elementary building units to construct unusual chemical compounds.Moreover,they play an important role in chemistry given their strong electron-accepting ability.In recent years,the field of superhalogens has drawn numerous attention from both theoretical and experimental research groups,and a great deal of superhalogens and their anions have been characterized.In this thesis,two types of novel superhalogen anions were designed and explored by quantum chemical methods.The structural features and electronic structure of these superhalogen anions were analyzed.In addition,we have studied the recognition of superhalogen anions by using density functional theory.The main contributions of this dissertation are as follows:1.Hetero-binuclear superhalogen anions,namely MM?F₄^-and MM?F₅^-?M=Li,Na;M?=Be,Mg,Ca;M?=B,Al,Ga?,have been theoretically characterized at the MP2?FULL?/6-311+G?3df?level.It is found that two central atoms can be linked by at most three fluorine ligands.The large vertical electron detachment energies?VDEs,7.45-8.98 eV?verify the superhalogen identity of these anions.The VDEs of both MM?F₄^-and MM?F₅^-decrease when the atomic size of M increases whereas increase with the size of M?and M?.Besides,the extra electron distribution also has effect on the VDEs of such superhalogen anions.We hope that the results of this study not only provide further understanding of multi-nuclear superhalogens but also stimulate more efforts in the research area of intriguing superatoms.2.A series of hetero-binuclear superhalogen anions involving cyanide and/or isocyanide ligands have been theoretically characterized.Large VDEs?5.83-8.41 eV?confirm the superhalogen nature of these anions.A smaller M or a larger M?central atom can bring a larger VDE value to such anions.The LiMgL₄^--B?L=CN/NC?isomer possesses the largest VDE value because its extra electron is evenly shared by the three bridging L ligands.For the other anions,the isomers possess relatively larger VDE values when the extra electron is localized on the terminal cyanide instead of isocyanide ligand.We hope that our findings can further enrich the superhalogen chemistry and provide potential agents for chemical processes where strong electron acceptors are needed.3.The recognition of a series of superhalogen anions by the calix[4]pyrrole and calix[6]pyrrole molecules has been theoretically investigated at the B97D/6-31++G?d,p?level.The structures and properties of the complexes C4P:X^-?X=LiF₂,BeF₃,BF₄,SiF₅,BO₂,PO₃,ClO₄,SO₃F?and C6P:X^-?X=LiF₂,BeF₃?have been characterized.NBO analysis reveals that there is charge-transfer interaction between calix[4]pyrrole/calix[6]pyrrole host molecules and superhalogen anion guests.Meanwhile,all the studied complexes possess large binding energies,indicating strong H bond interactions between the host molecules and superhalgen anion guests.The geometrical structures of the studied complexes do not change much when solvent effect is taken into account.In the presence of non-polar solvent?chloroform?molecules,although the binding energies of C4P:X^-and C6P:X^-complexes reduce,the dynamic stabilities of the complexes are enhanced.In addition,it is found that the larger the center cavity the host molecules contain and the smaller the superhalogen anions,the stronger the H bond interactions between the host molecules and the superhalogen anion guests.We hope that conclusions of this study can not only expand the scope of supramolecular chemistry,but also extend the research of anion recognition to the field of superatoms and provide valuable theoretical information for related experimental studies.