Probing the interactions between cations and borazine analogue complexes.

CONTEXT: The bond nature of X+  - E13 upon X+  - E13 = NL2 (X = H, Li, Na, K, Al, Cu, Ag, E13 = B, Al, Ga, In, and L = H, F, OH, CH3, SiH3) complexation was investigated theoretically. The well characterized covalency order of these cations H+  > Cu+  > Ag+  > Al+  > Li+  > Na+  > K+ was used as a criterion to estimate the characteristics of X+ - E13 binding. The topological analysis is valid for all the X+ - E13 = NL2, except X+ - Al = NL2. localized orbital locator study reveals that this is due to the non-uniform distribution of electron density and longer distance between X+ - Al. Orbital components of these complexes were quantified. The associated charge transfer and NOCV orbital energies reveal bonding strength follows as H+  > Ag+  > Cu+ > Al+  > Li+  > Na+  > K+. Two more bonding orbitals between Cu+ and E13 = NL2 share interaction energies, as well as charge transfer, leaving the major pairwise orbital bonding energies and charge transfer lesser than those of Ag+. CDA analysis demonstrates no orbital bonding between X+ and E13 = NL2 (X = Li, Na, K), weak orbital bonding for the interactions in the other compunds, especially strong orbital bonding between H+  and E13 = NL2. All the result demonstrated that E13 = NL2 series act as qualified Lewis bases upon X+ - E13 = NL2 complexation, and the covalency of X+ - E13 follows the traditional criterion. METHODS: The structural optimizations of cation/molecule interactions of X+ - E13 = NL2 were optimized at the level of M062X/def2tzvp using Gaussian 09 program. The nature of X+ - E13 was investigated by Quantum Theory of Atoms in Molecules (QTAIM). Specifically, the signs of Laplacian density ( ∇ 2 ρ ) and energy density H(r) were used to discriminate covalency from non-covalency; the electron density ρ(r) was used to detect the bonding strength. Localized orbital locator (LOL) was used to show the color-filled maps of the electron densities of some species of interest. Charge decomposition analysis (CDA) and natural orbital o for chemical valence (NOCV) calculations were also performed. AIM, MESP, the plotting of the color-filled maps of LOL, CDA, and NOCV calculations were performed with the Multiwfn software.