A theoretical study of some possible alkyllithium hexamers

Using ab initio SCF calculations we optimized three possible structures of hexameric methyllithium each having a near octahedral geometry of lithium atoms with capping methyl groups. The isomer in which the vacant faces of the octahedron are trans to each other is the most stable. The alternative structure with the vacant faces in apical contact is 8.8 kcal/mol (6-31G^*//4-31G) higher in energy while the edge contact isomer is 26.3 kcal/mol more energetic than the trans structure. The methyl groups were found not to be faced centered. These results are rationalized electrostatically.