What is the Difference Between Coordination Entity and Coordination Sphere?

The main difference between a coordination entity and a coordination sphere lies in the components they represent in a coordination compound.

• Coordination Entity: This is the collection of components of a coordination compound, including the central atom or ion and the ligands. The ligands are bonded to the central atom or ion via coordinate covalent bonds, which are formed when electron-rich molecules or ions donate their lone electron pairs to the central atom or ion. For example, in the coordination entity [CoCl3(NH3)3], the cobalt ion is surrounded by three ammonia molecules.
• Coordination Sphere: This refers to the central atom or ion and the ligands attached to it enclosed in square brackets. The coordination sphere represents the coordination entity along with the net charge on the coordination entity. For example, in the complex K4[Fe(CN)6], the coordination entity is [Fe(CN)6]4-, and the coordination sphere is represented by the same expression.

In summary, a coordination entity consists of the central atom or ion and the ligands, while a coordination sphere includes the central atom or ion, the ligands, and the net charge on the coordination entity.

Comparative Table: Coordination Entity vs Coordination Sphere

Here is a table highlighting the differences between a coordination entity and a coordination sphere:

A coordination entity is a central metal atom or ion bonded to a fixed number of ions or molecules, such as ligands. In contrast, a coordination sphere includes the central atom/ion, the ligands directly attached to it, and the counter ions (ions outside the coordination entity). The coordination sphere is enclosed in square brackets and indicates the net charge on the coordination entity.