Structure and properties of 1,2-, 1,7-, and 1,12-dicarba-closo-dodecaboranes(12): A quantum chemical study

Abstract

The molecular and electronic structures and thermodynamic parameters of 1,2 , 1,7 , and 1,12 dicarba closo dodecaborane(12) molecules in the singlet ground state were calculated by the Hartree-Fock, DFT, and MP2 (including B3LYP/6 311G(2d,2p) and MP2/6 311+G(d,2p) methods). The energies and character of spatial localization of the fron tier MOs in o , m , p carboranes(12) correlate with the changes in the configuration stabilities and reactivities in the reactions of carboranes with electrophilic and nucleophilic agents and bases. The electrostatic potential distributions in the molecules and the atomic charge distribu tion of hydrogen atoms correlate with the known chemical properties of carboranes(12). The thermodynamic parameters of two isomerization reactions, o C 2 B 10 H 12 m C 2 B 10 H 12 and m C 2 B 10 H 12 p C 2 B 10 H 12 , calculated for the temperature range 298-1000 K agree with experimental data within the limits of measuring error. The values of the electron density and the Laplacian of the electron density at the (3, -1) critical points of the B-H and C-H bonds correlate with the reactivities of the title compounds.The electronic structures of closo carboranes(12), C 2 B 10 H 12 , and their derivatives has been studied by theo retical 1-8 and experimental 9 methods. In most cases the results of calculations of the molecular structures and relative stabilities of these compounds are compared with the experimental data. Only a few attempts to relate the electronic structure characteristics to the configuration stability, regularities of the electrophilic and nucleo philic reactions, and the acidities of carboranes were re ported. 10-12 Usually, the Mulliken charges on the cage atoms are used as a criterion for assessment of the reactiv ity. 10,12 However, this is not always true when studying the title compounds. 1 Analysis of the electron density distribution function in the vicinity of reaction centers is of paramount importance; 12 however, the computational cost of such calculations is very high. Advances made in this field of chemistry of boranes and carboranes have been documented in a review. 8 In this work we carried out the HF, DFT, and MP2 (including B3LYP/6 311G(2d,2p) and MP2/6 311+G(d,2p)) quantum chemical calculations and determined the thermodynamic characteristics of the isomers of carboranes(12) for the temperature range 298-1000 K and established parameters of their ground state electronic structure, which correlate with the con figuration stability and with characteristic features of elec trophilic and nucleophilic reactions. These are the ener gies and the structures of the frontier MOs, the electro static potential, the atomic charges of hydrogens in the molecules under study, and the characteristics of the total electron density function at the (3, -1) critical points of the B-H and C-H bonds. Calculation ProcedureQuantum chemical calculations of the molecules of o , m , and p carboranes were carried out by the Hartree-Fock and density functional (B3LYP) methods, at the second o...

Self-Assembly of Carboranethiol Isomers on Au{111}: Intermolecular Interactions Determined by Molecular Dipole Orientations

“…Strong dipole−dipole interactions within SAMs influence adlayer structures and functions. , Thus, it is important to calculate the magnitudes and directions of the molecular dipole moments in the carboranethiol species in order to gain insight into the relative intermolecular forces within the SAM. While complete active space with second-order perturbation theory (CASPT2) and higher-level theories would provide better treatment of electron delocalization in carborane derivatives, density functional theory (DFT) has been shown to balance computation cost and efficiency for carboranes of moderate size. , Using DFT with the 6-31G basis set, we calculated the dipole moments for M1 and M9 in the gas phase to be 1.06 and 4.08 D, respectively. For comparison, calculations were also performed at the Hartree−Fock (HF) and MP2 levels, both with the 6-31G basis set (Supporting Information Table 1).…”

“…While complete active space with second-order perturbation theory (CASPT2) and higher-level theories would provide better treatment of electron delocalization in carborane derivatives, density functional theory (DFT) has been shown to balance computation cost and efficiency for carboranes of moderate size. 57,60 Using DFT with the 6-31G basis set, we calculated the dipole moments for M1 and M9 in the gas phase to be 1.06 and 4.08 D, respectively. For comparison, calculations were also performed at the HartreeϪFock (HF) and MP2 levels, both with the 6-31G basis set (Supporting Information Table 1).…”