ABSTRACT
The repulsions are at a minimum if the distribution of ions is as symmetrical as possible. Thus ions which are 3-coordinated have their neighbours at 120° in a triangular arrangement, 4-coordinated ions have a tetrahedral, 6-coordinated ions an octahedral, and 8-coordinated ions a cubic arrangement. In addition, some coordination numbers, such as five, which do not pack regularly in a solid are not observed in ionic crystals.
