Coordination Co...

A colorless solid (A) dissolves in water to a yellowish brown solution. The solution gives a white ppt. with $$BaCl_2$$ solution, the white ppt. is insoluble in HCl or $$HNO_3$$. When $$NH_4OH$$ or $$NaOH$$ is added to a solution of (A), a brown ppt. is formed which does not dissolve in $$NaOH$$ solution. The brown ppt. dissolve in conc. HCl to give a reddish brown solution which gives a blue ppt. with $$[K_4Fe(CN)_6]$$ solution. When solid (A) is heated, a colourless gas is evolved and a brown residue is left.

A colorless solid (A) dissolves in water to a yellowish brown solution. The solution gives a white ppt. with $$BaCl_2$$ solution, the white ppt. is insoluble in HCl or $$HNO_3$$. When $$NH_4OH$$ or $$NaOH$$ is added to a solution of (A), a brown ppt. is formed which does not dissolve in $$NaOH$$ solution. The brown ppt. dissolve in conc. HCl to give a reddish brown solution which gives a blue ppt. with $$[K_4Fe(CN)_6]$$ solution. When solid (A) is heated, a colourless gas is evolved and a brown residue is left.

When crystals of $$CuS{ O }_{ 4 }\cdot 4N{ H }_{ 3 }$$ are dissolved in water, there is hardly any evidence for the presence of $$Cu^{2+}$$ ions or ammonia molecules. A new ion, $${ \left[ Cu{ \left( N{ H }_{ 3 } \right)  }_{ 4 } \right]  }^{ 2+ }$$, is furnished in which ammonia molecules are directly linked with the metal ion. Similarly, the aqueous solution of $$Fe\left( CN \right) _{ 2 }\cdot 4KCN$$ does not gives tests of $$Fe^{2+}$$ and $$CN^{-}$$ ions but gives test of a new ion. $${ \left[ Fe{ \left( { CN }\right)  }_{ 6 } \right]  }^{ 4- }$$. The ions $${ \left[ Cu{ \left( N{ H }_{ 3 } \right)  }_{ 4 } \right]  }^{ 2+ }$$ and $${ \left[ Fe{ \left( { CN }\right)  }_{ 6 } \right]  }^{ 4- }$$ are called complex ions. These ions are represented as :

An aqueous solution of an inorganic compound (X) gives the following reactions:
(i) With an aqueous solution of $$BaCl_2$$, a precipitate insoluble in dilute HCl is obtained.
(ii) Addition of excess of KI give a brown precipitate which turns white on addition of excess hypo solution 
(iii) With an aqueous solution of potassium ferrocyanide a chocolate colored ppt. is obtained.

When crystals of $$CuS{ O }_{ 4 }\cdot 4N{ H }_{ 3 }$$ are dissolved in water, there is hardly any evidence for the presence of $$Cu^{2+}$$ ions or ammonia molecules. A new ion, $${ \left[ Cu{ \left( N{ H }_{ 3 } \right)  }_{ 4 } \right]  }^{ 2+ }$$, is furnished in which ammonia molecules are directly linked with the metal ion. Similarly, the aqueous solution of $$Fe\left( CN \right) _{ 2 }\cdot 4KCN$$ does not gives tests of $$Fe^{2+}$$ and $$CN^{-}$$ ions but gives test of a new ion. $${ \left[ Fe{ \left( { CN }\right)  }_{ 6 } \right]  }^{ 4- }$$. The ions $${ \left[ Cu{ \left( N{ H }_{ 3 } \right)  }_{ 4 } \right]  }^{ 2+ }$$ and $${ \left[ Fe{ \left( { CN }\right)  }_{ 6 } \right]  }^{ 4- }$$ are called complex ions. These ions are represented as :