Question

List examples of positive and negative ligands .

Answer 1

Hint: The positive and negative ligands are charged species present in coordinate complexes formed by a variety of transition metal ions. The nature of charge on those ligands helps distinguish the two kinds of ligands.

Complete answer:
A coordination complex is formed when a central metal ion gets surrounded by a group of ions or neutral molecules that stabilize the metal ion by forming partial covalent bonds which give rise to a specific geometry. These ions or molecules are known as ligands.
The central metal ion and the ligands are a Lewis acid-base pair where the metal ion is a Lewis acid and ligands are Lewis bases that donate at least one pair of electrons to the central metal forming a coordinate covalent bond.
In order to be a ligand, any molecule or ion should possess a minimum of one lone pair (unshared pair of electrons) or a bond pair that can be shared with a central metal ion.
The ionic ligands can be divided into the following two categories:
Negative ligand: ligands that carry a negative charge (anions) and usually contain suffixes like ‘ite’ or ‘ate’. When complexes are named according to the rules of IUPAC nomenclature, the suffixes are modified to ‘ito’ or 'ato’.
Examples of negative ligands are as follows:
\[C{O_3}^{2 - }(carbonato)\]
\[N{O_2}^ - (nitrito)\]
\[C{H_3}CO{O^ - }(acetato)\]
\[SC{N^ - }(thiocyanato)\]
\[S{O_4}^{2 - }(sulphato)\]
\[{C_2}{O_4}^ - (oxalato)\]
Positive ligand ligands that carry a positive charge (cations) and usually contain suffixes like ‘ium’. The IUPAC nomenclature rules state the suffix of positive ligands should not be modified or altered.
Examples of positive ligands are as follows:
\[N{H_2}N{H_3}^ + (hydrazinium)\]
\[N{O_2}^ + (nitronium)\]
\[N{O^ + }(nitrosonium)\]

Note:
Like positive ligands, most metal names end with the suffix ‘ium’ like potassium, magnesium and aluminium. Yet metal ions that are themselves positively charged cannot be used as positive ligands and they do not have the tendency to donate electrons rather they accept electrons.