X-ray study of the electron density distributions for hexagonal and

Abstract

The electron density distributions of and , which include icosahedral clusters, have been studied by a single-crystal x-ray diffraction method. The maximum-entropy method (MEM) is used to construct the electron density distribution (EDD). In the EDD maps, strongly covalent bonds between Al atoms and transition metal (TM) atoms are visible. As regards the chemical bonding, has an icosahedral bonding environment, whereas does not. The number of electrons belonging to each atom and the charge transfer from Al atoms to TM atoms have been derived from the EDD maps. The negative valences were estimated to be -1.25 and -1.26 for Co atoms and -1.00 for a Mn atom. These negative valences can be understood to be the charge transfer due to the covalent bond with strongly ionic character. These results were compared with pair-potential calculations and band-structure calculations.