A theoretical study on the dihydrogen bonding interactions in various MgH 2 and BeH 2 complexes

Abstract

The dihydrogen bonding (DHB) interactions were studied theoretically between the hydrogen atoms of BeH₂ (1) and MgH₂ (2) with those of HC≡CX where X = H (3), CH₃ (4), F (5), Cl (6) to form the complexes H-Be-H ... HC≡CX (7–10) and H-Mg-H …HC≡CX (11–14), respectively. The structures of compounds 1–14 were optimized at MP2 method using 6-311++G(d,p) basis set. The most negative binding energy was measured for structure 4 among isolated analogues 3–6. The complexes 9 and 14 indicated the most negative BSSE corrected ΔE_{dihydrogen bonding} values among BeH₂ and MgH₂ dihydrogen bonded compounds, respectively. A linear relationship was obtained between the H …H distance and (ΔE_{dihydrogen bonding} + BSSE) values in which the energy increases with lengthening the H …H distance. All of the ΔG_interaction and ΔG^#_interaction were positive confirming the DHB interactions for all complexes at both transition state and final optimized forms are endergonic indicating they are non-spontaneous interactions. The smaller band gaps of complexes 7–14 compared to those of their related isolated acetylene derivatives 3–6 reveals the increase in electrical conductivities upon formation of dihydrogen bonds. The QTAIM computations supported the covalent/shared character of the C–H, C≡C, C-Cl bonds, the intermediate character of Be-H, Mg-H, C-F bonds while the electrostatic nature of H ... H interactions.