Question

Explain with two examples of each of the following: coordination entity, ligand, coordination number, coordination polyhedron, homoleptic, and heteroleptic.

Answer 1

Neutral molecules or anions bond to a central metal atom or ion in a Lewis acid-base reaction, the product formed in this reaction is coordination complex. The bond which is involved in the formation of the coordination complex is a coordination covalent bond.

Complete step by step solution:
(1) Coordination entity: this is an electrical charge radical species with a positive or negative charge. In this coordination entity, the suitable number of neutral molecules or negative ions is called ligands which are surrounded by the central metal atom or ion.
${{[Ni{{(N{{H}_{3}})}_{6}}]}^{2+}}$ - Cationic complex
${{[Ag{{(CN)}_{2}}]}^{-}}$ - Anionic complex
$Ni{{[CO]}_{4}}$ - Neutral complex
(2) Ligands: it is an atom or ion or molecule that can donate a pair of electrons to central metal atoms and forms coordination covalent bonds with a metal atom in coordination complex compounds. This may be neutral molecules or negatively charged ions bonded to the central metal atom in a coordination entity.
For example, $O{{H}^{-}},C{{l}^{-}},{{H}_{2}}O,N{{H}_{3}}$
(3) Coordination number: In a coordination compound, the total number of ligands attached to the central metal atom or ion.
For example,${{[Ni{{(N{{H}_{3}})}_{6}}]}^{2+}}$, the coordination number $N{{i}^{+2}}$ is 6.
$Fe{{[CO]}_{5}}$, the coordination number of Fe is 5.
(4) coordination polyhedron: this is about the central metal atom defined as the spatial arrangements of ligand atoms bonded to the central metal atom or ion in the coordination sphere.
For example, $Fe{{[CO]}_{5}}$is a mononuclear complex that has trigonal bipyramidal geometry.
(5) Homoleptic complexes: in the coordination sphere, if the central metal atom or ion attached to the same kind of ligand or donor group are called homoleptic complexes.
For example: ${{[PtC{{l}_{4}}]}^{2-}}$ , ${{[Co{{(N{{H}_{3}})}_{6}}]}^{3+}}$
(6) Heteroleptic complexes: in a coordination complex, the central metal atom or ion bonded to more than one kind of ligands or donor groups.
For example, $[CoC{{l}_{3}}{{(N{{H}_{3}})}_{3}}],[NiC{{l}_{2}}{{({{H}_{2}}O)}_{4}}]$

Note: Coordination compounds and double salts are differing in the property of dissociation when dissolved in water. Both are formed by the combination of two or more stable compounds in the stoichiometric ratio. While double salts like Mohr’s salt, potash
alum dissociate completely into ions when dissolved in water. But complex compounds do not dissociate into complexions.