High spin and low spin complex are two possible classifications of spin states that occur in a coordination compound.
- Before going to this topic we must have an idea about strong ligand and weak ligand. To know which ligand is strong and which ligand is weak, we must go through spectrochemical series i.e.
- The spectrochemical series : (weak end)O22−< I− < Br− < S2− < SCN− (S–bonded) < Cl− < N3− < F−< NCO− < OH− < C2O42− < H2O < NCS− (N–bonded) < CH3CN < gly (glycine) < py (pyridine) < NH3 < en (ethylenediamine) < bipy (2,2′-bipyridine) < phen (1,10-phenanthroline) < NO2− < PPh3 < CN− < CO < CH2(strong end)
- The ligands which are present on the left of the series are consider to be strong ligahds and those which are present on the right of the series are consider to be weak ligand
High spin complex:
- It is also called spin free complex.
- The complex having a maximum number of unpaired electrons are called high-spin or spin-free complex.
- In the high spin complex, first all the d-orbital are singly filled and then pairing occour .
- Strong ligand i.e. ligands which are on the left of the spectrochemical series are always form high spin or spin free complex.
Low spin complex:
- It is also called spin paired complex.
- The complex having a minimum number of unpaired electron i.e. more number of paired electrons are called low spin or spin paired complex.
- In a low spin octahedral complex pairing of d electrons take place from the initial condition.
- Weak ligand i.e. ligands which are present on the right of the spectrochemical series always form low spin or spin paired complex.