Natural bond orbital analysis resonance stabilization

Ab initio calculations (MP2/6-31G ) of the parent compound of 8 revealed that the most stable arrangement of the dimer adopts Dih symmetry (Fig. 5). Interestingly, the four Li ions and the two phosphorus centers constitute an octahedral skeleton with relatively short Li-Li and Li-P distances of 2.645 and 2.458 A, respectively. Charge analysis (22) undoubtedly supports the electrostatic bonding model for this system because of the high net charges of the natural atomic orbitals (NBO) at Li (+0.768) and P (-1.583), while NBO-Lewis resonance structures support stabilization through delocalization (Fig. 5). 

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