Probing the interactions between cations and borazine analogue complexes

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.

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 ( ${\nabla }^2\rho$ ) 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.