ENTHALPIES OF FORMATION AND BOND-ENERGIES IN LITHIUM, BERYLLIUM, AND BORON DERIVATIVES - A THEORETICAL ATTEMPT FOR DATA RATIONALIZATION

For a set of small XYH(n) molecules (where X stands for Li, Be, or B and Y is one of the second-row atoms), we have calculated the enthalpies of formation at the MP4 = SDTQ/6-311++G(3df,2p) level of theory by using MP2 = FULL/6-31 G(d,p) fully optimized structures. The obtained values are expected to be in the range of the so-called "chemical accuracy" (+/- 1 kcal/mol). Some alkyl derivatives of the previous XYH(n) compounds have been studied at the RHF/6-31G* level (with fully optimized geometries). The theoretical enthalpies of formation reproduce most of the available experimental results in a quite satisfactory manner. All the collected (experimental or theoretical) data are used to build a bond-energy table, which includes lithium, beryllium, and boron atoms.