Haemoglobin
Haemoglobin is a coordination compound of iron (Fe) and it regulates the respiration process.
A Coordination compound or metal complex consists of an atom or ion (usually metallic), bonded to a surrounding array of molecules or anions. Coordination refers to the "coordinate covalent bonds"(dipolar bonds) between the ligands and the central atom (metal). The earliest known coordination compound is the alizarin dye. It is bright red in color and used as dying agent for clothes by the ancient Persians and Egyptians. Certain biological compounds haemoglobin and chlorophyll are coordination compounds with Fe and Mg as central metal ions respectively.
Copper complex ion
Many metal containing compounds retain their identity in solution, such metal compounds are called as metal complexes. Coordinate compounds when dissolved do not form simple ions but form complex ions (i.e., remain intact). Complex ions are shown by the use of square brackets. The net charge is written on the right hand top corner of the square bracket.
Example:
Therefore a coordinate compound or coordinate complex comprises of a complex anion/cation and a simple ionizable anion/cation [or] a complex anion/cation and a non ionizable molecular compound. These Coordinate Complexes are not double salts. Double salts loose their identity when dissolved in water. Example for an double salt is Mohr's salt, [(NH4)2SO4.FeSO4. 6H2O].