On the nature of the trimer, tetramer, and pentamer of ammonia borane

摘要: A stochastic search of stable configurations for ammonia borane trimers, tetramers, and pentamers affords very rich complex potential energy surfaces. Structural preferences three-dimensional, compact geometries \(n\ge 4\) at the second-order perturbation theory level with an extended basis set, MP2/6–311++G(d, p), is inferred. Molecular units in clusters interact via four different types non-conventional intermolecular contacts: heteropolar N–\(\hbox {H}\cdots \)H–B dihydrogen bonds (the main stabilizing factor), homopolar B–\(\hbox bonds, B\(\cdots \)H–N N\(\cdots hydrogen bonds. Despite perceived weak nature case polymers studied here, they lead to unusually strong interactions, exceeding by more than 20 kcal mol−1 stabilization energies reported water same molecularities . We provide evidence suggest that all cases, arise from charge transfer between orbitals general \(\sigma _{\mathrm{B-H}}\rightarrow \sigma ^*_{\mathrm{N-H}}\) type.