Theoretical Studies On Delocalization Of Several Inorganic Clusters

Aromatic through-space conjugation has been widely recognized and exploitedin organic compounds and ions, while it hasn't been applied to explain the bondingsof inorganic compounds and ions. In the dissertation, we have shown, by means ofquantum chemistry, that a series of inorganic compounds and ions, whose structureshave been long-known and characterized, are aromatic due to through-spaceconjugations. This is the first time that the aromatic through-space conjugation isfound in inorganic compounds and ions with known structures. The main pointsobtained read as follows:1. Pericyclic Tansition-state-like (PTS-like) aromaticity in Se₂I₄²⁺ and S₂O₄^2-Our theoretical calculations reveal that Se₂I₄²⁺ and S₂O₄^2- are aromatic resultingfrom 6c-10e through-space conjugation. Since no linkage exists between the twoconjugated V-shaped units, the aromaticity arising from the 6c-10e through-spaceconjugation can be termed as PTS-like aromaticity, analogous to the aromaticthrough-space conjugations disclosed previously for the Diels-Alder transition state.2. PTS-like aromaticity in I₄²⁺, S₆N₄²⁺ and N₂O₂ Our theoretical studies concerned I₄²⁺, S₆N₄²⁺ and N₂O₂ reveal that there existsaromatic through-space conjugation between the two I₂⁺ units , the opposite S-S unitson the two trans-five-member ring and the two NO units. Between the two conjugatedunits there is no saturated linkages, therefore, the aromaticity resulting from 6Ï€econjugation also termed as PTS-like aromaticity with similarity to the first point.3. Homoaromatic inorganic ions 6c-10e S₈²⁺,Se₈²⁺Our calculations disclose that between the two transannular units of X2X3X4and X6X7X8(X=S or Se) exists 10Ï€e aromatic through-space conjugation with eachunit contributing 5Ï€e. The saturated linkages of -S- or -Se- between two conjugatedunits partially disturb the conjugation of two conjugated units,S₈²⁺ and Se₈²⁺ are stillaromatic , thus belong to homoaromatic system.4. homoaromaticity in Te₆²⁺ with 4c-6e conjuationBy our calculations, the 4c-6e through-space conjugation is revealed to induce adiatropic (aromatic) ring current in the central Te4 (Te3-Te4…Te5-Te6) plane. Sincethe central two pairs ofTe atoms are connected bytwo apical Te atoms (Te1 andTe4)that are not explicitly involved in the through-space conjugation, the boat-shapedTe62+ isbishomoaromaticinnature.5.Possibilityofdualbishomoaromaticityin S4N4andSe4N4Aftercarefullyanalyzingtheelectronsandatomicorbitalsthatarenotinvolvedinthe formation of the frameworks of X4N4 (X=S, Se) molecules, we propose that theyhave dual bishomoaromaticity. Two separated N-X-N species within the top half ofthe X4N4 molecule, each containing five-electrons, form a bishomoaromatic systemwith totally ten-electrons that fulfills the (4n+2)e Hückel rule. Similarly, the bottomhalf of the X4N4 molecule contains another ten-electrons bishomoaromatic systemFurthermore, the two fused bishomoaromatic systems are orthogonal and, hence,should contribute synergetically to the overall aromaticity. However, the clearpicuture of two orthogonal orbital is not found in X4N4(X=S, Se) real orbital, hence,their contribution to the overall aromaticiy can't be available, and the dualbishomoaromaticityisapossibility.6.Sphericallyaromatic inorganicions:X64+(X=Te,Se,S)In terms of molecular orbital and VB analysis, 6c-8e through-space conjugationbetween two Te32+ units is 3-dimensional (3D) conforms to the 2(N+1)2 rule ofspherical aromaticity, thus, molecule is spherical aromaiticityin nature. The sphericalaromaticity of this tetracation is also manifested by the NICS value from calculationand by grouping its MOs according to spherical harmonics. Similarly, two hypothetictetracations Se64+ and S64+ , the lighter homologues of Te64+, are also sphericalaromaticity.We have presented new conceptual applications of aromatic through-spaceconjugations that were well-established in organic chemistry to a lot of inorganicsystems that have through-space ?Ï€?*- ?Ï€?* bonding(s) between two weakly interactedradical subunits. Of particular interest are the spherical aromatic through-spaceconjugation of Te64+, which is new conjugated form and has not been reported before.Consequently,thisstudynotonlyextendsthearomaticthrough-spaceconjugationintoinorganic field but also expands the concept of aromatic through-space conjugationitself.7.ExperimentalandtheoreticalstudyonAuCn-(1≤n≤10)clustersA series of AuCn- clusters were generated by laser vaporization on home-madetime-of-flight mass spectrometer and the abundance of AuCn- display odd-evenalternation with even-n clusters being relatively more abundant. The structure andstabilityof AuCn- (n≤12) has been studied using B3lyp method with Lan2dz basis setfor Au atom and 6-31G(d) for C atom. For even-n AuCn- cluster, the geometricalmutation fromlinearAuC2- tobentAuCn-(n=4,6,8,10,12)andthecontrarygeometriesbetween neutral and anionic even-n geometries are well interpreted usingMullican–Walsh model. The structural change with carbon chain extends and thecomparison with CnH- clusters was also analyzed. The calculated incremental energy,adiabatic electron affinity (AEA) and vertical detachment energy (VDE) show thesame odd-even pattern with n=even higher than n=odd, which is consistent with theobserved odd-even alternation of the TOF signal intensities. This parity effects areattributed to electronic configuration of AuCn- that even-n ones have closed shell andmostofodd-noneshavenot-fully-filledelectronicshell.8.TheoreticalstudyonstructuresandpropertiesofC2Sn-(5≤n≤10)Systematic density functional calculation reveals that the ground geometries ofC2Sn-(5≤n≤10) clusters are classified into three type ring-like structures, respectivelywith two separated carbon atoms in the ringor with two adjacent carbon atoms partlyor completely in the ring, corresponding to C2Sn-(5≤n≤8), C2S9- and C2S10-. Thestabilized factors that underlie these favorable structures are discovered, includingtheweak S…S bond, excess electron andÏ€electrons delocalization, the relief of stericringstrain.Key Words: aromaticity, aromatic through-space conjugation in inorganicclusters,aromaticityofinorganiccluster,dopedcarbonclusters.