The Na+ decorated bicyclo[2.2.1]hepta-2,5-diene hydrogen adduct: a theoretical investigation

At the MP2/6-311 + + G(d, p) computational level, the interactions among bicyclo[2.2.1]hepta-2,5-diene (BCH), sodium ion (Na + ), and multiple hydrogen molecules (nH 2 , where n ranges from 1 to 13) were explored through ab initio calculations. The study revealed that the C = C double bonds within the BCH molecule potentially enable the adsorption of Na(H 2 ) n + adducts, resulting in the formation of (BCH)Na(H 2 ) n + aggregates. The findings show that larger (BCH)Na(H 2 ) n + complexes can form by sequential addition of H 2 molecules to the initial (BCH)Na + adduct. These additional hydrogen molecules bind through Na…H 2 , C-H…H 2 , or H 2 …H 2 interactions to the (BCH)Na + base complex. Notably, Na + is limited to interact directly with up to 5H 2 molecules through sodium bonding. Comparison of interactions shows that Na…H 2 bonding is stronger than the C-H…H 2 interaction, while the H 2 …H 2 bonding is the weakest of this set. As the number of hydrogen molecules increases, the interaction energy per H 2 molecule decreases, indicating weaker binding for later ( n = 6–13) added H 2 molecules. Analysis of vibrational spectra shows characteristic shifts as: C = C stretching frequencies experience redshifts, while H 2 stretching modes exhibit blue shifts upon complex formation. The study also evaluated diminutive effects within the (BCH)Na(H 2 ) n + aggregates. Using Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) theoretical approaches, the detailed electronic structures of complexes were analyzed.