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The part of coordination compound present in the square bracket is called coordination sphere. It is non-ionizable part. The part present outside the square bracket is called ionization sphere. It is ionizable.
Example 1) K3 [Fe(CN)6] —–> 3K+ + [Fe (CN)6]3-
coordination sphere is [Fe (CN)6]3-
Ionization sphere is K+
Example 2) [Co(NH3)6]Cl3 ——> [Co (NH3)6]3+ +3Cl–
[Co (NH3)6]3+ ——> co-ordination sphere
Cl– ——-> ionization sphere
The number of ligands attached to central metal ion or atom is called Coordination number.
Coordination number of Fe is 6 because six ligands (CN) are attached to central metal Fe.
Nomenclature of Coordination Compound :
Rules for IUPAC are given below:-
1) If the coordination compound is ionic, then cation is named first then anion.
2) In the complex ion the name of ligands are written first, then name of central metal atom.
3) Complex ion may be anion or cation. Their names are written in different way.
Example 1) In K4[Fe(CN)6] , complex ion is [Fe(CN)6]4-
a) If coordination sphere or complex ion is a cation or neutral, then name of metal is written as it is.
b) If complex ion is anion, then ‘ate’ is used after the name of metal.
4) Oxidation number of metal is calculated and is indicated by roman number after the name of metal.
Ex . copper(II), Nickel(0), Ferrate(III).
Naming of ligands:
The ligands may be negative , neutral or positive.
1) The negative ligands whose names end with ‘ide’ have this suffix replaced by ‘O’.
Ex. Cl– (chloro) , CN– (cyano), Br– (bromo) , O— (oxo), OH– (hydroxo)
2) The negative ligands whose names end with ‘ite’ or ‘ate’ become ‘ito ‘ & ‘ato’ respectively .
CO3– – (carbonato), CH3COO– (acetato), SCN– (thiocyanato), SO4— (sulphato), C2O4— (oxalato) , NO2– (nitrito) .
3 ) The name of neutral molecule is written as CO (carbonyl) , H2N CH2.CH2NH2 ( ethylenediamine ) , H2O (aqua), NH3 (amine).
4) The name of positive ligand ends with ‘ium’.
NH2NH3+ (hydrazinium), NO2+ (nitronium), NO+ (nitrosonium).
According to the number of ligands- prefix mono, di, tri etc are used before the name of ligand. Ligands are written in alphabetical order. If di ,tri tetra ,penta , hexa etc are present in the name of ligand , then bis , tris , tetrakis, pentakis,hexakis is used before the name of ligand respectively.