High-Level Electron Correlation of the Indirect Nuclear Spin-Spin Coupling Constants in Some Small Diboranes and Lithium-Doped Diboranes

We have investigated the spin-spin coupling constants (SSCC's) of diborane(4) and diborane(6), their Li-doped counterparts, and the dimerization of diborane(6), using the second order polarization propagator approximation with coupled cluster singled and double [SOPPA(CCSD)] substitutions. We employed an adapted basis set to perform the calculations of their SSCC's. Energetically, from optimized structures at second-order Moller-Plesset perturbation theory, our results indicate that the stable isomers of diborane(4) may exist as independent molecular entities, separate by similar to 20 kJ/mol, obtained in our best level of calculation. Distinct geometric configurations and energetic stability are well related to the nuclear coupling mechanism in these diborane compounds. We found that dimerization of diborane(6) is possible with different symmetries, although it does not significantly change the geometric parameters of the monomers. This is also confirmed by the SSCC's calculations with SOPPA(CCSD).