期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 19, 期 47, 页码 15941-15954出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201302181
关键词
bond energy; carbenes; carbones; cumulenes; density functional calculations
资金
- Deutsche Forschungsgemeinschaft
- U.S. Department of Energy, Office of Basic Energy Sciences, Combustion Program [DE-FG02-97ER14748]
- U.S. National Science Foundation
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1152357] Funding Source: National Science Foundation
The ground electronic state of C(BH)(2) exhibits both a linear minimum and a peculiar angle-deformation isomer with a central B-C-B angle near 90 degrees. Definitive computations on these species and the intervening transition state have been executed by means of coupled-cluster theory including single and double excitations (CCSD), perturbative triples (CCSD(T)), and full triples with perturbative quadruples (CCSDT(Q)), in concert with series of correlation-consistent basis sets (cc-pVXZ, X=D, T, Q, 5, 6; cc-pCVXZ, X=T, Q). Final energies were pinpointed by focal-point analyses (FPA) targeting the complete basis-set limit of CCSDT(Q) theory with auxiliary core correlation, relativistic, and non-Born-Oppenheimer corrections. Isomerization of the linear species to the bent form has a minuscule FPA reaction energy of 0.02kcalmol(-1) and a corresponding barrier of only 1.89kcalmol(-1). Quantum tunneling computations reveal interconversion of the two isomers on a timescale much less than 1s even at 0K. Highly accurate CCSD(T)/cc-pVTZ and composite c approximate to CCSDT(Q)/cc-pCVQZ anharmonic vibrational frequencies confirm matrix-isolation infrared bands previously assigned to linear C(BH)(2) and provide excellent predictions for the heretofore unobserved bent isomer. Chemical bonding in the C(BH)(2) species was exhaustively investigated by the atoms-in-molecules (AIM) approach, molecular orbital plots, various population analyses, local mode vibrations and force constants, unified reaction valley analysis (URVA), and other methods. Linear C(BH)(2) is a cumulene, whereas bent C(BH)(2) is best characterized as a carbene with little carbone character. Weak B-B attraction is clearly present in the unusual bent isomer, but its strength is insufficient to form a CB2 ring with a genuine boron-boron bond and attendant AIM bond path.
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