Adsorption of neutral and protonated Lewis bases on Na8-nanocluster: basicity enhancement of the Lewis bases

Structural and energetic properties of Na n ( n = 1 –8) nanoclusters were studied employing the B3LYP method and using 6-31+(d,p) basis set. Comparison of the calculated binding energies per atom ( E b ) of the cluster shows that the Na 8 cluster with D 2 d symmetry group is the most stable structure among the Na n clusters. Adsorption of neutral and protonated forms of ammonia, methylamine, ethylamine, hydrazine, guanidine, pyridine, methanolamine, and methanimine on Na 8 cluster was studied. Interaction of the neutral Lewis bases with Na 8 was very weak such that the interaction energies were smaller than - 50 kJ mol - 1 . However, the protonated bases interact with Na 8 more strongly with interaction energies generally in the range of - 90 to - 350 kJ mol - 1 . The protonated forms of methanolamine undergo dissociative adsorption on Na 8 with adsorption energies of about - 800 kJ mol - 1 . Since the protonated bases are stabilized more than the corresponding neutral ones upon adsorption on Na 8 cluster, the basicity of the Lewis bases enhances in the presence of Na 8 . The calculated proton affinities of the isolated Lewis bases were smaller than 990 kJ mol - 1 while in the presence of the Na 8 cluster, the basicity increases so that the calculated proton affinities were higher than 1000 kJ mol - 1 . GRAPHICAL ABSTRACT SYNOPSIS Adsorption of neutral amines on Na 8 is very weak while protonated amines are more strongly adsorbed on Na 8 . These results showed that the Na 8 cluster stabilizes the protonated amines better than the corresponding neutral ones. Therefore, basicity of the amines is enhanced in the presence of the Na 8 cluster.