Explain with two examples each of the following: coordination entity, ligand, coordination number, coordination polyhedron, homoleptic and heteroleptic.
Coordination entity: A coordination entity constitutes a central metal atom or ion bonded to a fixed number of ions or molecules. For example, [CoCl₃(NH₃)₃] is a coordination entity where cobalt ion is surrounded by three ammonia molecules and three chloride ions. Another example is [Ni(CO)₄].
Ligand: The ions or molecules bound to the central atom/ion in the coordination entity are called ligands. These may be simple ions such as Cl⁻, small molecules such as H₂O or NH₃, or larger molecules such as H₂NCH₂CH₂NH₂. Examples include Cl⁻ and NH₃.
Coordination number: The secondary valence is equal to the coordination number and is fixed for a metal. The ions/groups bound by secondary linkages to the metal have characteristic spatial arrangements corresponding to different coordination numbers. Examples include [Co(NH₃)₆]³⁺ with coordination number 6 and [Ni(CO)₄] with coordination number 4.
Coordination polyhedron: The spatial arrangement of the ligand atoms which are directly attached to the central atom/ion defines a coordination polyhedron about the central atom. Examples include [Co(NH₃)₆]³⁺ which is octahedral and [Ni(CO)₄] which is tetrahedral.
Homoleptic and heteroleptic: Homoleptic complexes have a metal bound to only one kind of donor groups, e.g., [Co(NH₃)₆]³⁺ and [Ni(CO)₄]. Heteroleptic complexes have a metal bound to more than one kind of donor groups, e.g., [Co(NH₃)₄Cl₂]⁺ and [CoCl₃(NH₃)₃].
Explanation
The answer provides definitions and examples for each term as per the NCERT textbook context. For coordination entity, the context provides clear definition and multiple examples. For ligand, the definition and examples are explicitly stated. For coordination number, the context relates it to secondary valence; examples are inferred from coordination entities where the fixed number of ligands corresponds to the coordination number. For coordination polyhedron, the definition and examples are clearly provided. For homoleptic and heteroleptic, definitions are provided with one example each; additional examples are identified by applying the definitions to other coordination entities mentioned in the context.