Crystal structure refinements with generalized scattering factors. III. Refinement of 1, 1′‐azobiscarbamide and melamine, 2,4,6‐triamino‐s‐ triazine, at the octopole level

摘要: Single crystal x‐ray diffraction data for 1,1′‐azobiscarbamide, C2H4N4O2, and melamine (2,4,6‐triamino‐s‐triazine), C3N6H6, have been refined using one‐center generalized scattering factors through the octopole level. This work is an extension of previous in which structures these compounds were dipole quadrupole population parameters two‐center monopole paramaters to account bonding electron density. The model accounts density more efficiently than model. Radial Slater‐type functions used compute also refined. In both compounds, radial about 7% smaller molecular optimized values found. Interatomic distances are not very sensitive melamine, all C–N increase by 0.004 A models with octopoles. Also, if octopoles on nitrogen atoms, N–H become approximately equal consistent centroid hydrogen atom being displaced 0.07–0.08 into bond. By symmetry applying appropriate linear constraints least‐squares matrix, dramatic improvements can be made over a spherical few additional parameters. Electric field gradients at nuclei (i.e., atomic positions determined refinement data) calculated atoms. These calculations included penetration integrals from multipole atoms within 7 radius.