Na⋅⋅⋅B Bond in NaBH3−: Solving the Conundrum.

Bonding in the recently synthesized NaBH3− cluster is investigated using the high level Valence Bond BOVB method. Contrary to earlier conclusions, the Na−B bond is found to be neither a genuine dative bond, nor a standard polar‐covalent bond at equilibrium. It is rather revealed as a split and polarized weakly coupled electron‐pair, which allows this cluster to be more effectively stabilized by a combination of (major) dipole‐dipole electrostatic interaction and (secondary) resonant one‐electron bonding mechanism. Our analysis of this unprecedented bonding situation extends to similar clusters, and the VB model unifies and articulates the previously published variegated views on this exotic "bond". [ABSTRACT FROM AUTHOR]