A MP2 and CCSD(T) theoretical investigation on the weak dihydrogen-bonded interactions between HBBH (1Δg) and HM (M = Li, Na, K, BeH, MgH or CaH)

The weak dihydrogen-bonded interactions are found between HBBH (1Δg) and HM (M = Li, Na, K, BeH, MgH or CaH) using MP2 and CCSD(T) methods with 6-311++G(3df,2p) and aug-cc-pVTZ basis sets. The binding energies follow the order of HBBH⋯HK > HBBH⋯HNa > HBBH⋯HLi > HBBH⋯HCaH > HBBH⋯HMgH > HBBH⋯HBeH. The interactions in HBBH⋯HM are weaker than those in HCCH⋯HM. The calculated binding energies correlate with the H⋯H distance, the elongation of the BH bond and the charge density at the H⋯H bond critical point. The analyses of the natural bond orbital (NBO), atoms in molecules (AIM) and electron density shifts reveal the nature of the dihydrogen-bonded interaction. In these interactions, many of the lost densities from HM or the hydridic hydrogen of HM are shifted toward the BH bond or the H atom of the BH moiety. The polarization of the BB double-bond plays a role in the formation of the dihydrogen-bonded interaction. Thus, the concept of dihydrogen bond is extended to MHδ−⋯+δHBBH system where the BH group can be as the proton donor.