Quantum Chemical Studies On The Structures And Chemical Bonding Of Charged Molecular Alloy Clusters [Zn₉Bi₁₁]^5- And [Bi₇Ge₄Bi₇]^4-

Molecular alloy clusters are of current interest in synthetic chemistry and corrdination chemistry.Their unique structures and novel chemical bonding are important topics in nanocluster science and theoretical chemistry as well.These synthetic cluster systems furher increases the complexity,uniqueness,and diversity in chemical bonding,which has attracted the attention from theoretical researchers.On the other hand,the vigorous development of cluster physical chemistry has introduced new scientific concepts such as superatoms,which can be extended to understand and rationalize inorganic synthetic phases at the chemical bonding level.The latter effort may further guide the rational design and synthesis of novel cluster compounds.This dissertation focuses on the use of quantum chemistry methods to elucidate the structural stability and nature of chemical bonding of several synthetic condensed phase compounds.The newly developed concepts such as superatoms can also be applied to synthetic systems.Specifically,we chose to deal with molecular alloy clusters containing Bi atoms,that is,the[Zn₉Bi₁₁]^5-and[Bi₇Ge₄Bi₇]^4-clusters,at the theoretical level of density functional theory.The main contents,results,and conclusions of this thesis are briefly described as follows:1.Chemical Bonding in Synthetic All-metal Charged Molecular Alloy[Zn₉Bi₁₁]^5-Cluster.In this work,we analyze the chemical bonding in a cage-like Bi-containing polyanionic[Zn₉Bi₁₁]^5-molecular alloy cluster.Electronic structure calculations are carried out at the PBE0/def2-TZVP level.An array of computational tools are applied to understand its nature of bonding,which include the canonical molecular orbital analysis,localized molecular orbital analysis,adaptive natural density partitioning,natural bond orbital analysis,and orbital composition calculations.The comprehensive computational data show that the caged-like[Zn₉Bi₁₁]^5-cluster should be best described as the fusion of five structural fragments:a central Zn Bi₄unit,3 five-element trapezoids on the periphery,and a Zn₃Bi tetrahedron on top.This overall structural model is unknown in the existing literature.These structural components are shown to be interconnected by as few as 6 single bonds on the“cage”surface,hinting that the so-called cage is largely a physical rather than chemical entity.The whole alloy cluster is stabilized by the central Zn Bi₄unit,whose bonding interactions with the outer components involve only 8 electrons.The concept of superatom can be utilized to rationalize this sophisticated compound cluster.Such a superatom conforms to the octet rule.2.Preliminary Chemical Bonding Analysis of Charged Molecular Alloy[Bi₇Ge₄Bi₇]^4-cluster.In this preliminary work,we use quantum chemical calculations to understand the structure and bonding of a synthetic rod-shaped molecular alloy C_2h[Bi₇Ge₄Bi₇]^4-cluster,which contains the Bi atoms of group 15 elements.Chemical bonding is elucidated herein using the CMO analysis,NBO calculations,and Ad NDP analysis.Quantum chemical data show that this molecular alloy cluster can be described as a metallic Ge₄chain embedded in between two Bi₇cages.Each Ge atom is coordinated to two Bi atoms to form a twisted planar quadrilateral Ge₄Bi₈central block.The CMO analysis shows that there are four Ge 4s²lone pairs and a Ge-Ge single bond,but this picture is too simplified and inconsistent with the calculated bond distances and bond orders.Detailed CMO and Ad NDP analyses show that a Ge center maintains a nonbonding 4s¹configuration,and the remaining four 4s¹electrons are used for Ge-Ge?bonds.The cluster has three Ge-Ge bonds.This expansion of lone pairs to single bonds effectively increases their occupation numbers(ONs)in Ad NDP analysis,thus further justifying the treatment.The[Bi₇Ge₄Bi₇]^4-cluster may be customized as[Bi₇]^-[Ge₄]^2-[Bi₇]^-,in which the Ge atoms are in the Ge^0.5-charge state.It is reiterated that the above data are in the preliminary stage.