PNNL

Abstract

We launched a combined negative ion photoelectron spectroscopy (NIPES) and multiscale theoretical investigation on the geometric and electronic structures of a series of acetonitrile-solvated dodecaborate clusters, i.e. B12H12 2-·nCH3CN (n = 1–4). The electron binding energies (EBEs) of B12H12 2-·nCH3CN are observed to increase with cluster size suggesting their enhanced electronic stability. B3LYP-D3(BJ)/ma-def2- TZVP geometry optimizations indicate each acetonitrile molecule binds to B12H12 2- via a threefold dihydrogen bond (DHB) B3–H3 ??? H3C–CN unit, in which three adjacent nucleophilic H atoms in B12H12 2- interact with the three methyl hydrogens of acetonitrile. The structural evolution from n = 1 to 4 can be rationalized by the surface charge redistributions through the restrained electrostatic potential (RESP) analysis. Notably, a super-tetrahedral cluster of B12H12 2- solvated by four acetonitrile molecules with twelve DHBs is observed. The post-Hartree-Fock DLPNO-CCSD(T) calculated vertical detachment energies (VDEs) agree well with the experimental measurements, confirming the identified isomers as the most stable ones. Further, the nature and strength of the intermolecular interactions between B12H12 2- and CH3CN are revealed by the quantum theory of atoms-in-molecules (QTAIM) and the energy decomposition analysis. Ab initio molecular dynamics (AIMD) simulations are conducted at various temperatures to reveal the great kinetic and thermodynamic stabilities of the selected B12H12 2-·CH3CN cluster. This study provides a molecular-level understanding of structural evolution for acetonitrile-solvated dodecaborate clusters and a fresh view by examining acetonitrile as a real HB donor to form strong HB interactions.