| The chemistry of carboranes and metallacarboranes has received considerable attention since their emergence in the 1960s. Efforts of almost half a century in this area have resulted in the extensive studies on the synthesis, structure, reactivity and application of these clusters. Carborane, an important specie of borane derivatives, obtained by replacing BH or BH- group with C or CH, have applied in many fields due to its representative structure and special bond. Recently, with the development of nonlinear optical (NLO) study and the prospect of NLO material application, the theoretical computations on carborane derivatives as NLO material have received more attention. Allis et al designed a series of molecules linking icosahedral crborane polyhedra as bridge, employed semiempirical methods to optimize the structures and calculate their first hyperpolarizability. And the results indicated that the rigid cage structure of icosahedral carborane polyhedra is in favor of the first hyperpolarizability. This paper employed density functional theory (DFT) B3LYP method to optimize the molecules using n-vertex bis-substituted carborane (n=5, 6, 7) as bridge and as acceptors combined with finite field (FF) formalism to calculate the first hyperpolarizability. Meanwhile, the same method is employed to optimize the structures of 14-vertex closo-carborane clusters and analyzed the stabilities. The results as follow:1. The structures of n-vertex bis-substituted carborane (n=5, 6, 7) are changed due to bridged donor and acceptor moieties. The distances between two C atoms are becoming longer. And changing substituted position of C atoms influences the stability and dipole moment. The isomers with the substituents connecting with C atoms of lower coordination number have better stability and larger values of polarizability. One-dimensional structure of the molecules bridged through n-vertex bis-substituted carborane (n=5, 6, 7) is in favor of intramolecular charge-transfer. Meanwhile, the isomer with a larger change of dipole moment has larger value of the first hyperpolarizability during the charge-transfer process.2. The structures of the moleculars combined ferrocene with n-vertex bis-substituted carborane (n=5, 6, 7) are more stable with the lager bond length between carborane and phenyl. The less negative charge distribution of carborane is more favorable to the stability of the molecular. The trends of the dipole moment, the polarizability and the first hyperpolarizability are similar and the value increase with decreasing the distance between C atoms. The energy levels are close and decrease with the distance between C-C atoms decreasing; the HOMO-LUMO gaps also have the same changes. Meanwhile, the less gap values, the largerβvalues.3. The stable structures of nine C2B12H14 isomers were obtained and their molecular backbone structures remained that of B14H142-and the structure of 1,14-C2B12H14 is squeezed along the axial compared with that of B14H142-. Besides the stability of 1,14-C2B12H14 with two C atoms substituted for B atoms in axial position, the stabilities increase with the distances between the two C atoms increasing. The substitution of C atoms for B atoms in the higher coordination number position decreases the stability. The negative charge of each isomer is distributed mainly among the C atoms and the rest is among the axial B atoms, and the positions of C atoms and the axial B atoms may become the active regions of the nucleophilic reaction. The trend of HOMO energy levels of the isomers is coincided with their stabilities, and the isomer having lower HOMO energy level is more stable.
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