(i) What type of isomerism is shown by the complex [Co(NH₃)₆][Cr(CN)₆]?

(ii) Why a solution of [Ni(H₂O)₆]²⁺ is green while a solution of [Ni(CN)₄]^2– is colourless? (At. No. of Ni = 28)

(iii) Write the IUPAC name of the following complex : [Co(NH₃)₅(CO₃)]Cl.

(i) The type of isomerism shown by the complex is coordination isomerism . This type of isomerism arises from the interchange of ligands between cationic and anionic entities of different metal ions present in a complex. Its isomer is [Cr(NH₃)₆][Co(CN)₆] .

(ii) d-d transition is responsible for colour of compounds. Both have 3d⁸ configuration of Ni and unpaired electrons. But In the first case, d-d transition occurs. T₂g has 6 electrons and e_g has 2 electrons, with octahedral structure, because it contains unpaired electrons due to pairing with weak H₂O ligand. In the second case, Ni is paired with strong ligand , hence has no unpaired electrons, no d-d transition , and no colour. Strong ligands make unpaired elctrons pair up.

(iii) 5 ammonia groups, 1 carbonate group and its cobalt chloride. So, its called pentaaminecarbonatocobalt(III)chloride.