Co-ordination Compounds- II

Types of Complexes-
1. Homoleptic complexes-
Complexes in which the metal atom or ion is linked to only one kind of donor atoms, are called homoleptic complexes e.g., [Co(NH3)6]3(+ve ions).
2. Heteroleptic complexes-
Complexes in which the metal atom or ion is linked to more than one kind of donor atoms are called heteroleptic complexes e.g., [Co(NH3)4CI2](1 +ve ion).
3. Labile and Inert complexes-
Complexes in which the ligand substitution is fast are known as labile complexes and in which ligand substitution is slow, are known as inert complexes.
Effective Atomic Number (EAN) – 
This concept was proposed by Sidgwick. In a complex, the EAN of metal atom is equal to the total number of electrons present in it.
EAN = Z – ON of metal + 2 * CN
(where, Z = atomic number of metal atom
ON = oxidation number of metal
and CN = coordination number of complex).
An ion with central metal atom having EAN equal to next inert gas will be more stable.
IUPAC Naming of Complex Compounds –
Naming is based on set of rules given by IUPAC.
1. Name of the compound is written in two parts (i) name of cation, and (ii) name of anion.
2. The cation is named first in both positively and negatively charged coordination complexes.
3. The dissimilar ligands are named in au alphabetical order before the name of central metal atom or ion.
4. For more then one similar ligands. the prefixes di, tri, tetra, etc are added before its name. If the di, tri, etc already appear in the complex then bis, tris, tetrakis are used.
5. If the complex part is anion, the name of the central metal ends with suffix ‘ate’.
6. Names of the anionic ligands end in ‘0’, names of positive ligands end with ‘ium’ and names of neutral ligands remains as such. But exception are there as we use aqua for H2O, ammine for NH3, carbonyl for CO and nitrosyl for NO.
7. Oxidation state for the metal in cation, anion or neutral coordination compounds is indicated by Roman numeral in parentheses.
8. The name of the complex part is written as one word.
9. If the complex ion is a cation, the metal is named same as the element.
10. The neutral complex molecule is named similar to that of the complex cation.
Some examples are
(i) [Cr(NH3)3(H2O)3]Cl3
triamminetrichlorochromium (III) chloride
(ii) [Co(H2CH2CH2H2)3]2(SO4)3
tris (ethane-l,2-diamine) cobalt (III) sulphate
(iii) [Ag(NH3)2] [Ag(CN)2]
diamminesilver (I) dicyanoargentate(I)
(iv) K4 [Fe(CN)6]
potassium hexacyanoferrate

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