A theoretical study on the dihydrogen bonding interactions in various MgH2 and BeH2 complexes

The dihydrogen bonding (DHB) interactions were studied theoretically between the hydrogen atoms of BeH2 (1) and MgH2 (2) with those of HCCX where X = H (3), CH3 (4), F (5), Cl (6) to form the complexes H-Be-H HCCX (7-10) and H-Mg-H HCCX (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 AEdihydrogen bonding values among BeH2 and MgH2 dihydrogen bonded compounds, respectively. A linear relationship was obtained between the H H distance and (AEdihydrogen bonding + BSSE) values in which the energy increases with lengthening the H center dot center dot center dot H distance. All of the AiGinieraction and AG#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, CC, C-Cl bonds, the intermediate character of Be-H, Mg-H, C-F bonds while the electrostatic nature of H center dot center dot center dot H interactions.