X-ray derived experimental charge density distribution in GaF₃ and VF₃ solid systems

The electronic structure and bonding features of metal and transition metal fluorides in low oxidation states, GaF₃ and VF₃, have been studied from precise single crystal X-ray diffraction data using multipole and maximum entropy methods. The topology of the charge density is analyzed and the (3,−1) bond critical points are determined. Existences of ionic nature of bonding in low valent fluorine compounds are clearly evident. The spherical core of metal atom and aspherical or twisted core of transition metal atom reveal the fact that GaF₃ is much more rigid than VF₃. Aspherical cores of the polarized ligand atoms are also visible in the two-dimensional density distribution pictures. The true valence charge density surfaces with encapsulating the atomic basins maps are elucidated. An elongated saddle with mid-bond density of 0.6191 e/ų, observed in the compound VF₃, shows that its lattice is less rigid and has more ionic character than GaF₃.