Density functional theory/finite perturbation theory calculations of nuclear spin-spin coupling constants for polyhedral carboranes and boron hydrides

An extensive study is presented of nuclear spin-spin coupling constants in 25 polyhedral boranes using density functional theory/finite perturbation t heory (DFT/FPT) methods to determine the Fermi contact term. Scalar couplin gs were obtained at either the UB3LYP/6-311G** or the UB3LYP/6-311(++)G** l evel, with molecular structures fully optimized at the B3LYP/6-31G* DFT lev el. The calculated results are in good agreement with the solution experime ntal data for a wide range of directly bonded, geminal, vicinal, and long-r ange coupling constants. The largest disparities occur for (1)J(B-11-H-1) a nd (1)J(C-13-H-1) values greater than 120 Hz. These are underestimated on a verage by about 5%, a value close to that expected (4%) from the effects of motional averaging on directly bonded coupling constants. The accurate pre diction of coupling constants in polyhedral boron compounds will be extreme ly helpful in their detailed NMR spectral analyses.