Convergence of nuclear magnetic shieldings and one-bond 1J(11B1H) indirect spin-spin coupling constants in small boron molecules

Self-consistent field Hartree-Fock (SCF-HF), density functional theory (B3LYP, KT1, KT2, and KT3), and coupled-cluster calculations of the nuclear magnetic shielding constants of BH and BH3 molecules have been conducted to characterize the convergence of individual results obtained with correlation- and polarization-consistent basis sets. The individual B-11 and H-1 NMR parameters were estimated in the complete basis set limit and compared with benchmark literature results. The SCF-HF and density functional theory B3LYP predicted boron shieldings and shielding anisotropies of BH significantly differed from the results obtained by coupled-cluster with single, double, and perturbative treatment of triple excitations, CCSD(T) approach. The best agreement between the CCSD(T)/complete basis set limit estimated boron shieldings was obtained for KT3 density functional (similar to 5.7ppm). The H-1 NMR parameters predicted at B3LYP and CCSD(T) levels of theory differed by less than 1ppm, and the SCF-HF calculated proton shieldings and shielding anisotropies also nicely agreed with our coupled-cluster results. The (1)J((BH)-B-11-H-1) parameters, calculated with B3LYP and KT3 functionals, accurately reproduced the earlier reported benchmark value for BH molecule. The SCF-HF, B3LYP, and KT3 calculated boron shieldings of BH3 differed from the CCSD(T) values by 13.2, -16.8, and -2.1ppm, respectively.