Valence shell charge topology, atomic graphs, and electric field gradients in one- to four-bonded nitrogen atoms

The atomic graph containing the extremes of the Laplacian of the charge distribution -del(2) rho(r) of the valence shell for each type of coordinated N atom in some nitriles, imines, diimides, planar and nonplanar amines, and substituted ammonium ions was obtained. Each bonding configuration showed specific correlations between the values of -del(2) rho(r) at some of the extremes present in the N atomic graph and the components of the electric field gradient (EFG) tensor. It was found that the q(zz) principal component of the EFG was generated mainly by the nonbonding charge concentration ''lone pair'' of the N valence shell for coordination one to three studied in this work. For the four-coordinated N atom with T-d symmetry, a relationship was obtained with a difference between the values of -del(2) rho(r) at the bonded maxima corresponding to the different bonds. The asymmetry parameter of the EFG was found to be connected with the atomic graphs through the values of -del(2) rho(r) at specific sets of saddle points of the N valence shell. For each type of N coordination, a particular set was found linking the values of -del(2) rho(r) at these points and the asymmetry parameter.