Question

The complex [fe(h2o)6] +2 is paramagnetic ,while[fe(cn)6}] -4 is diamagnetic -explain .

Answer 1

[Fe(H2O) 6]+2 in this complex water is weak field ligand so there is no pairing of electrons in 3d orbital iron in octahedral environment. So Iron in +2 state in presence of weak field ligand as electronic configuration 3d6 4s0 (t2g4 eg2) it has unpaired electron so it is paramagnetic. But in [Fe(CN) 6]-4 Fe is present in +2 state only but CN is strong field ligand so in presence of strong field ligand there is pairing of electron in 3d orbital of iron i.e it has electronic configuration 3d6 4s0 (t2g6 eg0), so it has completely filled due to absence of unpaired electron it is diamagnetic.