Theoretical Design And Application Of New Concept Superatoms

Due to the importance of clusters in basic research and the possibility ofassembling nanostructured materials with tunable properties, cluster science hasbecome a most active research field. One of the most exciting developments of clusterscience was the introduction of the concept that selected stable clusters with suitablesize and composition can mimic the chemical properties of atoms in the periodic table.Such intriguing species are termed as “superatoms”. In this thesis, three new kinds ofsuperatoms are designed and investigated by the quantum chemical method. Theirgeometrical structures, electronic structures, and other properties are systemically anddetailedly dicussed. In addition, we have studied the practical potential of superalkalisin designing novel nonolinear optical materials, and successfully desgined severalseries of alkalides of new type. The main contributions of this thesis are as follows:1. Based on the Jellium model of clusters, a novel superatom, namely Al12Be,exhibiting behaviors akin to chalcogens is proposed in this thesis. It is revealed thatthe lowest-energy Al12Be is a compact quasi-icosahedron with the Be atom lying atthe center of the Al-cage. The quasi-chalcogen characteristics of Al12Be is verified bythe prominent stability and electronic behavior of (Al12Be)Li2among the (Al12Be)Lin(n=1–5) series, the largest HOMO-LUMO gap of (Al12Be)Be among (Al12Be)M (M=Li, Be, B, C, N, O, and F) compounds, comparison of the dissociation energies of(Al12Be)M compound with those of corresponding diatomic oxides/sulfide, similaritybetween (Al12Be)Ca/(Al12Be)(FLi3) compounds and CaO/CaS molecules, and further,by the formation of (Al12Be)2dimer akin to O2or S2molecule. Finally, the origin ofthese quasi-chalcogen characteristics of Al12Be is clarified by the molecular orbitalsanalysis. This study will not only further enrich the superatom chemistry but alsoprovide a novel building block for designing and synthesizing cluster-assembledmaterials with tailored properties.2. Utilizing cyclo-N5–as new ligand, a series of mononuclear M(N5)k+1–(M=Li, Be, B) and dinuclear M2(N5)2k+1–(M=Li, Be) aromatic hyperhalogen anions havebeen achieved here for the first time. Calculations based on the density functionaltheory revealed that the N5–subunits preserve their structural and electronic integrityas well as aromatic characters in these anions. Especially, the vertical electrondetachment energies (VDEs) of these anionic molecules can reach as high as6.76–7.86eV, which are even larger than that of5.63eV for the N5–superhalogenbuilding-block, confirming their hyperhalogen nature. Moreover, the stability of thesestudied anions was guaranteed by their large HOMO LUMO gaps and positivedissociation energies of predetermined fragmentation pathways. This work can notonly provide an approach to obtain more aromatic hyperhalogens of new type, butalso stimulate experimental efforts to synthesize and characterize such aromaticpolynitrogen species in laboratory.3. The systematic calculations on the polynuclear MLin+1+cations show thataromatic superatoms can be designed by combination of suitable aromatic anions andalkali metal cations. Herein, the selected aromatic anions include metallic,non-metallic, and organic species. It is found that, except for N42–and C4H42–, all thearomatic anions retain their identities inside the resulting MLin+1+cations. Thearomatic MLin+1+proposed here possess low electron affinities and represent a newkind of superalkali or pseudoalkali cations. They also show pretty largeHOMO–LUMO gaps, as well as thermodynamic stability against dissociation.Besides, it is also possible for the MLin+1+cations to combine with (super)halogensanions and consequently form stable superatom compounds. The theoretical designand characterization of these aromatic superatoms may open a new branch ofsuperatom chemistry, and provide meaningful references to the further design of novelsuperatoms with aromatic building blocks.4. Superalkali Li3dissolved in gaseous ammonia is investigated by densityfunctional theory. Similar to the lithium atom, Li3can coordinate up to four ammoniamolecules. Among the structural isomers of Li3(NH3)n(n=1–4), the one withseparately distributed NH3ligands is preferred. Most of the Li3(NH3)nspecies possessthe alkalide characteristics and exhibit considerably large static first hyperpolarizabilities (β0) up to3.9×105au. Especially, for the lowest-energyLi3(NH3)ncomplexes, a prominent coordination number dependence of β0is found asfollows:12608(n=1)<38564(n=2)<121726(n=3)<391149au (n=4). Inaddition, the case of introducing a Na atom into such superalkali-ammonia systemshas been considered and the resulting Li3(NH3)nNa (n=1–4) complexes are studied inthe same vein. It is revealed that the β0values of Li3(NH3)nNa are influenced by boththe coordination number and the relative position of NH3ligands. This study not onlyprovides a new type of alkalides, but also evokes the possibility of exploring a fresh,thriving area, i.e. superalkali solutions with solvents of all sorts.5. A series of superalkali-based compounds, namely, Li3+(calix[4]pyrrole)M–,Li3O+(calix[4]pyrrole)M–, and M3O+(calix[4]pyrrole)K–(M=Li, Na, and K) havebeen designed and systemically studied by density functional theory method. Thealkalide characteristics of these compounds are demonstrated by the analyses of NBOcharges, VIE values, and their HOMOs. Compared with the alkali-metal-basedalkalides, these novel alkalides exhibit the structural diversity as well as largercomplexation energies. Interestingly, in all the resulting alkalides, the superalkaliclusters preserve their identities and behave just like alkali metal atoms. The positionof the upper M–anion is closely related to its atomic number, but seems almostunaffected by the species of inserted superalkali. Likewise, the change of M–has littlebearing on the geometrical structure of the superalkali subunit. The superalkali-basedalkalides show large NLO responses with considerable hyperpolarizabilities (0),especially for the potassides. Besides, the insertion of lower IP superalkalis also has apositive effect on enhancing the0values of the investigated alkalides. Hence, thesuperalkali clusters may be potential candidates for designing non-traditional alkalideswith remarkable and tunable NLO responses. This work will promote furtherapplication of superalkalis and, on the other hand, attract more research interest andefforts in exploring new, unconventional alkalides.6. Under density functional theory (DFT) computations, a new series ofsuperalkali-based alkalides, namely,(FLi2+@aza222)K,(OLi3+@aza222)K,(NLi4+@aza222)K, and (Li3+@aza222)K were achieved by encapsulating superalkali clusters into aza222cage-complexant. These species possess diverseisomeric structures, in which the encapsulated superalkalis preserve their identitiesand behave as alkali metal atoms. All these alkalides exhibit remarkably large firsthyperpolarizabilities (0) up to504739au. Especially, a prominent structuraldependence of0is observed for these studied compounds. Herein, how the geometricfactors affect the nonlinear optical (NLO) response of such alkalides is detailedlyinvestigated.