Question
What is ligand? Explain classification of ligand.
✓
Answer
$\rightarrow$ "Ligands are atom or ions which donates electron pairs to the central metal ion."
$(OR)$
$\rightarrow $ "The ions or molecules bound to the central atom/ion in the coordination entity are called ligands."
$\rightarrow$ These may be simple ions such as $Cl,$ small molecules such as $H_2O$ or $NH3,$ larger molecules such as $\ce{H_2NCH_2CH_2NH_2or N(CH_2CH_2NH_2)_3}$ or even macromolecules, such as proteins.
Classification of Ligands:
$(1)$ Unidentate ligands:
$\rightarrow$ "When a ligand is bound to a metal ion through a single donor atom, the ligand is said to be unidentate."
Example :
(a) Neutral: $\ce{H _2 \ddot{ O }$, : $NH _3,: CO ,: NO , CH _3 \ddot{N}H_2, C _5 H _5\ddot{N}} \ ($py$)$
(b) Negative ion: $\ce{{-} OH , F ^{-}, Cl ^{-}, Br ^{-}, I^{-} ,{ }^{-} CN , {}^{-}NH_2,}$
$\ce{NO _3^{-}, NO _2^{-}, NCH _3 COO ^{-}\left( AcO ^{-}\right), O ^{2-}, S ^2, N^{3-}}$
$(2)$ Didentate ligands:
$\rightarrow$ "When a ligand is bound to a metal ion through a two donor atom, the ligand is said to be didentate ".
$(3)$ Tridentate ligands:
$\rightarrow$ "When a ligand is bound to a metal ion through a three donor atom, the ligand is said to be Tridentate,"
Example:
$(4)$ Hexadentate ligands:
$\rightarrow$ When a ligand is bound to a metal ion through a six donor atom, the ligand is said to be hexadendate
Example: Ethylenediaminetetraacetate ion $\left(\text{EDTA} ^{4-}\right)$
$(OR)$
$\rightarrow $ "The ions or molecules bound to the central atom/ion in the coordination entity are called ligands."
$\rightarrow$ These may be simple ions such as $Cl,$ small molecules such as $H_2O$ or $NH3,$ larger molecules such as $\ce{H_2NCH_2CH_2NH_2or N(CH_2CH_2NH_2)_3}$ or even macromolecules, such as proteins.
Classification of Ligands:
$(1)$ Unidentate ligands:
$\rightarrow$ "When a ligand is bound to a metal ion through a single donor atom, the ligand is said to be unidentate."
Example :
(a) Neutral: $\ce{H _2 \ddot{ O }$, : $NH _3,: CO ,: NO , CH _3 \ddot{N}H_2, C _5 H _5\ddot{N}} \ ($py$)$
(b) Negative ion: $\ce{{-} OH , F ^{-}, Cl ^{-}, Br ^{-}, I^{-} ,{ }^{-} CN , {}^{-}NH_2,}$
$\ce{NO _3^{-}, NO _2^{-}, NCH _3 COO ^{-}\left( AcO ^{-}\right), O ^{2-}, S ^2, N^{3-}}$
$(2)$ Didentate ligands:
$\rightarrow$ "When a ligand is bound to a metal ion through a two donor atom, the ligand is said to be didentate ".
$(3)$ Tridentate ligands:
$\rightarrow$ "When a ligand is bound to a metal ion through a three donor atom, the ligand is said to be Tridentate,"
Example:
$(4)$ Hexadentate ligands:
$\rightarrow$ When a ligand is bound to a metal ion through a six donor atom, the ligand is said to be hexadendate
Example: Ethylenediaminetetraacetate ion $\left(\text{EDTA} ^{4-}\right)$
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