Dear Student
I) The metal ligand bond arises by donation of pair of electrons by ligands to the central metal atom.
II) To accommodate these electrons the metal ion must possess  requisite number of vacant orbitals of equal energy. These orbitals of  the metal atom undergo hybridisation to give hybrid orbitals.
III) Sometimes the unpaired (n-1)d orbitals pair up before bond  formation making (n-1)d orbitals vacant. The central metal atom makes  available number of d-orbitals equal to its co-ordination number.
iv) The metal ligand bonds are thus formed by donation of electron  pairs by the ligands to the empty hybridized orbitals. These bonds are  equal in strength and directional in nature.
v) Octahadral, square planar and tetrahedral complexes are formed as a result of d2sp3 (or sp3 d2), dsp2 and sp3 hybridization respectively.
 
Octahedral Complexes
     
Tetrahedral Complexes
     The tetrahedral arrangement of four ligands surrounding the metal ions.
Square Planar Complexes
     
      
 
All the best.                                                           
AKASH GOYAL
AskiitiansExpert-IIT Delhi
 
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