EXPERIMENTAL-DETERMINATION OF THE ELECTRON-DENSITY TOPOLOGY IN A NONCENTROSYMMETRIC TRANSITION-METAL COMPLEX - [NI(H3L)][NO3][PF6] (2-HYDROXY-3-METHYLBUTYL)-1,4,7-TRIAZACYCLONONANE]

We have determined the experimental charge density of the title compou nd, a large pendant arm macrocyclic complex, by fitting a multipole mo del to high-resolution X-ray diffraction data. We find redistribution of the charge density from the ligating nitrogen and oxygen atoms to t he central nickel ion which considerably reduces the charge on the met al. While the d-orbital populations are in agreement with ligand-field theory, the charge density of the metal shows diffuse features which are ascribed to metal 4s and 4p participation in the metal-ligand bond ing. Additionally, the trigonal-planar arrangement of critical points in -del(2) rho(r) within the valence shell charge concentration (VSCC) of the ligating oxygen atom provides evidence for metal-oxygen pi-bon ding.