How would you Account for the following: (i) Of the d^4 species, Cr^(2+) is strongly reducing while manganese (III) is strongly oxidising, (ii) Cobalt (II) is stable in aqueous solution but in the presence of complexing reagents, it is easily oxidised. (iii) The d^1 configuration is very unstable in ions.

How would you Account for the following: (i) Of the d^4 species, Cr^(

1.	How would you Account for the following: (i) Of the d^4 species, Cr^(2+) is strongly reducing while manganese (III) is strongly oxidising, (ii) Cobalt (II) is stable in aqueous solution but in the presence of complexing reagents, it is easily oxidised. (iii) The d^1 configuration is very unstable in ions.
Answer» Solution :(i) `E^0` vlaue for `Cr^(3+)//Cr^(2+)` is negative (-0.41 V) whereas `E^0` value for `Mn^(3+)//Mn^(2+)` is positive(+1.57V). Thus, `Cr^(2+)` ions can easily undergo oxidation to give `Cr^(3+)` ions and, therefore, acts as strong reducing agent. On the other hand, `Mn^(3+)` can easily undergo reduction to give `Mn^(2+)` and hence act as oxidising agent (ii) Co (III) has greater tendency to form co-ordination complexes than Co (II). Thus, in the PRESENCE of ligands, Co (II) changes to Co (III). i.e., is easily oxidised (iii) The ions with `d^1` configuration have the tendency to lose the only ELECTRON present in d-subshell to acquire stable `d^0` configuration. Therefore, they are UNSTABLE and undergo oxidation or DISPROPORTION.