Theoretical Study on the Structures and Properties of NCBBH•••HNa(H2O)n and CNBBH•••HNa(H2O)n (n=1∼5)

In this paper, our main aim is to examine the solvation effect on the dihydrogen-bonded complex in which the electron-deficient B-H group is as proton donor. NCBBH center dot center dot center dot HNa and CNBBH center dot center dot center dot HNa as well as their hydrated complexes NCBBH center dot center dot center dot HNa(H2O)(n) and CNBBH center dot center dot center dot HNa(H2O)(n) (n=1 similar to 5) have been fully optimized using DFT-B3LYP/6-311++G** method. The intermolecular interactions have been investigated at CCSD(T)/6-311++G** level. The topological electron charge density has been analyzed by AIM (atom in molecule) method to characterize the property of the H center dot center dot center dot H bond. The frontier molecular orbitals are presented in order to reveal the nature of the formation of the H-H covalent bonds in the hydrated complexes. The result shows that, with the increase of the number of surrounding water molecules, the B-H bond length is increased while the H center dot center dot center dot H distance is decreased accompanied by the conversion of the H center dot center dot center dot H bonding nature from the ionic bond to the covalent bond. When the number of the surrounding water molecules is up to 4, the dihydrogen-bonded interaction and that between the water molecules and NCB=BH center dot center dot center dot HNa are increased to -374.21 and -306.50 kJ.mol(-1), respectively, and the H-H covalent bond is formed. The dehydrogenation reaction for the hydrated complexes of dihydrogen-bonded system involving the electron-deficient B-H group as proton donor might be more difficult than that for FH center dot center dot center dot HLi(H2O)(n).