#coordination complex

Most 6-coordinate complexes adopt an octahedral geometry, in which the six ligand donor atoms are positioned at the vertices of an octahedron (figure 13.13).

For example, the coordination complex [Ni(NH3)4]²+ is formed from reaction of Ni²+ with four NH3 ligands, according to the equation:

Coordination bonds typically form between polyvalent cations and carbon compounds – for example, complexes between copper ions and tartaric acid (Figure 13.16A) or between magnesium ions and chlorophyll a (Figure 13.16B). (...) Calcium ions can also form coordination complexes with the polygalacturonic acid of cell walls (Figure 13.16C).