Coordination compounds plays many important roles in animals and plants. The are essential in the storage and transport of oxygen as electrons transfer agents as catalysts and in photosynthesis Wide range of application in daily life takes place through formation of complexes Photographic fixing qualitative and quantitative analysis purification of water metallurgical extraction are some specific worth mentioning
Arrange of the following in order of decreasing number of unpaired electrons
(I) `[Fe(H_(2)O))_(6)]^(2+)`
(II) `[Fe(CN)_(6)]^(3-)`
(III) `[Fe(CN)_(6)]^(4-)`
(IV) `[fe(H_(2)O)_(6)]^(3+)`
(a) IV,I,II,III
(b) `I,II,III,IV`
(c) `III,II,IIV`
(d) II,III,I,IV` .

Answer

A

Explanation

`[Fe^(2+)(H_(2)O)_(6)]^(2+),Fe^(2+) =3d^(6)`
`H_(2)O` is a weak field ligand so, no pairing of elctrons occurs
(II) `[Fe^(3+)(CN)_(6)]^(3-),Fe^(3+) =3d^(5)`
Since cyanide ion is a strong field ligand, hence pairing occurs
(III) `[Fe^(2+) (CN)_(6)]^(4-),Fe^(2+) =3d^(6)`
Pairing occurs
(IV) `[Fe^(3+)(H_(2O))_(6)]^(3+),fe^(3+) =3d^(5)`
pairing does not occur
The decreasing number of unpaired electrons is
`IV gtIgtIIgtIII(5 gt4gt1gt0)`