Theoretical Design Of Novel Superatoms And Superatom Compounds

In the past few decades,people have shown great interest in exploring various types of superatomic clusters because they constitute basic elements of a third dimension of the traditional periodic table and may serve as versatile building blocks for promising nanoscale assemblies and materials.In recent years,new progress has been made in identifying and characterizing superatom motifs.The main contributions of this thesis are as follows:1.An quasi-chalcogen superatom Ge9Be with the form of an endohedral Zintl cluster was theoretically designed and studied.It is found that the most stable configuration of Ge₉Be has C_3v symmetry.The Ge₉ skeleton of Ge₉Be is quite similar to Ge₉^2-.The lowest-energy structure of Ge₉Be^2-is an ideal mono-capped square antiprism with C_4v symmetry.It is more similar in geometry to the valence isoelectronic Zintl anion Ge₉^4-.The quasi-chalcogen characteristics of Ge₉Be are demonstrated from the following aspects:The electronic structure features of Ge₉Be and its daughter anion Ge₉Be^2-lay the foundation for their quasi-chalcogen characteristics;Like oxygen-group elements,Ge₉Be exhibits highly exothermic first electron affinity(EA)and less endothermic second EA;Ge₉Be tends to combine with two Li atoms to form a Li₂O-like compound,to couple with a(super)alkaline-earth atom to mimic the ionically bound Ca O molecule or to unite with multiple valence superatom Al₇^-to make up a compound analogue of oxocarbon.Besides,the binding energy of the(Ge₉Be)M(M=Li,Be,B,C,N,O,and F)series evolves in a manner quite similar to those of diatomic molecules MO and MS.Moreover,close parallels have also been found between(Ge9Be)2-based compounds and common peroxides,further evidencing the superatom characteristics of Ge9Be.2.Based on the experimentally identified Sn₈^6-anion,superatom Li2Sn8Be has been designed and its compounds have been studied in terms of geometrical structure,bonding,and stability.Results show that,despite having two lithium ligands,the Li2Sn8Be cluster resembles group VIA elements in many respects.First of all,Li2Sn8Be has higher exothermic first electron affinity and lower endothermic second electron affinity than oxygen group elements.Second,Li2Sn8Be behaves just like chalcogen elements and prefers to bind with two(super)alkali metals forming stable ionic compounds(Li2Sn8Be)Li₂,(Li2Sn8Be)(Li₃O)₂,and(Li2Sn8Be)(Ca₂F₃)₂.Li2Sn8Be also has the potential to form stable compound analogues of alkaline-earth-metal chalcogenides.Besides,compound analogues of CO,O₂^2-,H₂O₂,and Li₂O₂ can also be obtained with Li₂Sn₈Be serving as the building block.3.Be₁₁ cluster shares a similar electronic configuration with dual valence superatoms Al₇^-and Al₇Li.Thus,we consider that Be₁₁ is also apt to lose two or four electrons to achieve a stable closed-shell electronic configuration of 20 or 18 electrons,respectively.It has been found that the Be₁₁C/O and Be₁₁I_n(n=2,4)compounds exhibit particular stability among the Be₁₁M(M=Li/Na/K,Be/Mg/Ca,B/Al/Ga,C/Si/Ge,N/P/As,O/S/Se,F/Cl/Br)and Be₁₁I_n(n=1-6)series,respectively,reflecting the dual-oxidation-state feature of Be₁₁.Besides,Be₁₁is able to form stable ionic compounds such as Be₁₁O₂,Be₁₁Cl₂,Be₁₁(OH)₂,Be₁₁Cl₄,and Be₁₁(OH)₄,which are analogous to typical oxides,halides,and hydroxides of carbon group elements.The nearest atomic counterpart of Be₁₁ in group IVA is probably Sn or Pb since their compounds share like characteristics.4.With the aid of density functional theory(DFT)calculations,we found that compounds formed by combining quasi-chalcogen superatom Ge₉Be with superalkalis M(M=Mg₂F₃,Ca₂F₃,and Ca₃F₅)can exhibit novel chemical and tunable electronic features.It has been revealed that superatoms Ge₉Be and M maintain their respective configurations in all interacting systems.Results also show that the(Ge₉Be)M₂,(Ge₉Be)M₃,and(Ge₉Be)₂M₅⁺clusters are analogues of Li₂O,Li₃O,and Li₂O₅⁺molecules,respectively.Note that all the low-lying isomers of(Ge₉Be)M₃ have low first ionization potential of 2.87-4.87 e V,which are lower or comparable to that of alkali atoms.Hence,(Ge₉Be)M₃ can be regarded as an ultra alkali motif.Interestingly,with Ge₉Be and M serving as superatomic building blocks,(Ge₉Be)M₂(M=Mg₂F₃,Ca₂F₃)has been recognized as a strongly bound molecule that can be assembled into ring or chain superatom assemblies[(Ge₉Be)(M)₂]_n.This finding puts forward various superatom assemblies and opens the door to characteristics-oriented design and synthesis of stable superatom motifs by utilizing stable superatoms as building blocks.5.The ability of superhalogens to oxidize aromatic heterocyclic molecules has been examined on the basis of ab initio and density functional theory calculations.It is found that superhalogens Al F₄,Mg F₃,Li F₂,and Li Cl₂ are able to form stable charge-transfer compounds with pyrrole,furan,and thiophene.As for the pyridine molecule,it can only be ionized and form strongly bound compound when combined with superhalogen Sb F₆.This conclusion is supported by analysis of the the following(i)structure relaxation of heterocyclic molecules in the resulting L/X(L=C₄H₅N,C₄H₄O,C₄H₄S,and C₅H₅N;X=Al F₄,Mg F₃,Li F₂,and Li Cl₂)compounds(ii)charge flow between aromatic heterocyclic molecules and superhalogens(iii)spin density distribution of the L/X compounds,and(iv)binding energy calculated for the compounds.