In this structural use, the coordination number counts nearest neighbouring constituents. State which neighbours are counted and which ionic crystal structure is being described; it is not an ion's electric charge number.
Eight nearest neighbours at cube corners around a central site; fluorite structure cations have this arrangement.
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Coordination number refers to the number of ligand atoms or ions that are directly bonded to a central atom or ion in a coordination complex. It is an important concept in coordination chemistry and helps in understanding the structure and stability of coordination compounds. For example, in a metal complex such as [Co(NH₃)₆]³⁺, the cobalt ion (Co³⁺) is surrounded by six ammonia (NH₃) ligands.