B11H14(-) - A NIDO CAGE WITH NO H...H INTERACTION

The structural and dynamic properties of the B11H14- anion has been in vestigated by solution and solid-state NMR methods and by HF ab initio calculations, focusing on the interaction between the three endo hydr ogens (H(endo)). T1 and isotope perturbation of resonance studies do n ot support the nonclassical structure that has been considered for the H(endo), in which a triangular (H(endo))3 caps the pentagonal face of the nido B11H11 cage. The experimental and theoretical results are in agreement with a classical ground-state structure with no H...H inter actions. Full gradient optimization of 1-CB10H14 and B11H14- shows tha t the structure is similar to that suggested by Shore et al. with one terminal and two edge-bridging H(endo). The transition state for the h ydrogen exchange has been identified and shown to lie only 1.4 kcal/mo l higher than the ground state; it too lacks H...H interactions. The r eason for the low barrier is that the H(endo) centers remain equally b onded to the boron atoms during the rearrangement.