The d- and f- B...

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 :