Terminology of coordination chemistry

 1) coordination no. :--- 

• It is the property of  central metal ion. 
• It is the total number of coordinate bond around the central atom. 

(2) coordination polyhedra:-- It is the 3D arrangement of ligand around the central atom. 

• Coordination polyhedra depends upon the coordination number. 

Co. No.                             Co. Polyhedra 

  2                                          Linear

 3.                                     Trigonal planar

4.                                Tetrahedral/square planar

5.                      Trigonal bipyramidal/ square.                                                            pyramidal 

6.                                      Octahedral.   

(3) classification of ligand:--- 

• Monodentate ligand 
• Polydentate ligand

(a)  monodentate ligand:--- Ligands which                                 have one donar side is called.                                    monodentate ligand. 

Types of monodentate ligand:---

(i)  neutral ligand:--- 

H2O.   ----- aqua

NH3.  ------- amino

RNH2. ------alkylamine

PR3.   ------- trialkyl phosphine

PPh3 -------- triphenyl phosphine

PH3 ---------- phosphine

CO.  ---------- carbonyl

(ii)  positively charged ligand:---

NO+  -------nitrosonium ion

NH2-NH3+   --------hydrazinium ion

(iii)  negatively charged ligand:---

X-    -------- halohalide

OH-           hydroxo

CN-           Cyano

O2-            oxo

O2^-      superoxo

O2^-2.   Peroxo

N3^-        azido

N^3-        nitrido

S^-2.        Sulphido

CO3^2-     carbonato

SO4^2-      sulphato

SO3^2-     sulphito

CH3COO-    acitato

NO3^-           nitrito

H^-                hydrido

(b)  Polydentate ligand:--- Ligands which                      have more than one donar side                          are called Polydentate ligand. 

Types of Polydentate ligand :--

• Ethylenediamine (en) -CH2(NH2)CH2(NH2)

           ( bidentate) 

• Diethylenetriamine(dien) - CH2(NH2)CH2(NH)CH2CH2(NH2)

            (tridentate) 

• EDTA^-4   ethylene diaminetetraacitato

            ( CH3COO-)2NCH2CH2N(CH3COO-)

             (hexadentate) 

There is a another type of ligand :--

Amphidentate ligand：--

Ligands which have more than one donar side but at the same time only one donar side is used to form coordinate bond with central metal called Amphidentate ligand. 

 

    -CN.      Cyano (donar site carbon) 

     -NC.   Isocyano(donar site nitrogen）

-ONO.     Nitrito（donar site oxygen) 

-NO2.    Nitro(donar site nitrogen) 

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