A definition of coordination and its relevance in the structure types AlB₂ and NiAs

The largest gap in the list of reciprocal interatomic distances is used to limit the coordination polyhedra. For the structure types AIB₂ and NiAs, the polyhedra are evaluated according to c/a. In plots of c/a versus r_A/r_B, the various coordination types correspond to actually observed families of representatives. These results as well as others from more than 50 structure types support the view that coordination as limited by the largest gap is a realistic factor.