Question

Out of [CoF₆]^3- and [Co(en)₃]³⁺, which one complex is
(i) paramagnetic
(ii) more stable
(iii) inner orbital complex and
(iv) high spin complex
(Atomic no. of Co = 27) 

Answer 1

Co (Z=27)=1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷

Co⁺³ =1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁷ 

F^- is weak field ligand: 
[CoF₆]^3-

(i) [CoF₆]^3- is paramagnetic due to the presence of four unpaired electrons 

(ii) [Co(en)₃]³⁺ is more stable due to chelation

(iii) [Co(en)₃]³⁺ forms inner orbital complex (d²sp³)

(iv) [CoF₆]³⁺ Forms high spin complex (sp³d²)