Energy and geometry of boron compounds. Halides BHHal2, BHal3 and their disproportionation

Analysis of structural and thermodynamic parameters of boron halogen derivatives was conducted on the basis of structural-thermochemical (ST) model. Equilibrium interatomic B-H distances were specified for gaseous BHF2, BHCl2 and BHBr2 molecules. They were equal to 1.199±0.002, 1.175±0.003 and 1.79±0.01 A respectively. Formation heat was determined for BHI2: ΔfH298 (BHI2(hg) = 72±5 kJ/mol. Qualitative analysis of thermodynamics of reactions of boron halide disproportionation was performed in the framework of ST-model: BHal3 + 4BHal3. It was shown that halogen atoms weakened B-H-H bridges, halogens formed weak bridges in intermediate nonstable dimers