Answer :

(i) The complex is an anion with chromium as central atom, 2 water molecules and 2 oxolate ions with -2 negative charge each. Balance overall charge as 0, we get oxidation state of Cr as:

X + 2(0) + 2(-2) = -1


X = + 3.


Name of compound: potassium diaquadioxolatochromate(III) trihydrate.


Electronic configuration of Cr: 3d3, t2g3



Co-ordination no. Of complex: 6 (as oxolate ion is bidentate ligand)


As both the water molecule and oxolate ion are weak field ligand, so they do not cause pairing up of electron.


μ = [n(n + 2)]1/2


μ = [3×5]1/2


μ = 4BM.


(ii) The complex is a cation with cobalt as central atom, five neutral ammonia molecules and one chloride ion. Balance overall charge as 0, we get,


X + 5(0) + 1(-1) = + 2


X = + 3.


Oxidation state of cobalt is + 3.


Name of compound is pentaamminechloridocobalt(III) chloride.


Coordination no. is 6.


Electronic configuration of cobalt: 3d6


As ammonia is a strong field ligand so it causes pairing of the electron. No. Of unpaired electrons:0


μ = [n(n + 2)]1/2


μ = [0]1/2


μ = 0BM.



(iii) The complex is neutral with chromium as central atom, three chloride ions and 3 pyridine molecules which are neutral.


Name of compound is trichloridotripyridinechromium(III).


Balance overall charge as 0.


X + 3(-1) + 3(0) = 0


X = + 3.


Oxidation state of chromium is + 3.


Electronic configuration:3d3


Coordination no. Is 6.


As chloride ion and pyridine molecule botha re weak field ligand so they do not cause pairing of electron.



μ = [n(n + 2)]1/2


μ = [3×5]1/2


μ = 4BM


(iv) The complex is anion with iron as central atom, and 4 chloride ions. Balance overall charge:


X + 4(-1) = -1


X = + 3


Oxidation state of Fe: + 3.


Electronic configuration:3d6


Name of compound: Caesium tetrachloridoferrate(III).


Coordination no. is 4.


As chloride ion is weak field ligand ,it does not cause pairing of electron.


μ = [n(n + 2)]1/2


μ = [4×6]1/2


μ = 5BM


Steriochemistry is optically inactive as it is a tetrahedral complex and the relative position of each ligand will be same in all condition.



(v) The complex is anion with manganese as central atom , and six cyanide ions with each unit ngative charge. Balance overall charge


X + 6(-1) = -4


X = + 2


Oxidation state of Mn = + 2


Electronic configuration of Mn:3d3


Name of compound: potassium hexacyanoferrate(III)


Coordination no. Is 6.


As cyanide ions are strong field ligand , they cause pairing of electrons.


No. Of unpaired electrons is 1.


μ = [n(n + 2)]1/2


μ = [1×3]1/2


μ = 1.732BM.


Steriochemistry: optically inactive .


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