Among the following coordination complexes, how many have a spin-only magnetic moment greater than 3.5 BM ? [ Mn ( H ₂ O )₆ ]²⁺ , [ Fe ( CN )₆ ]³⁻ , [ CoF ₆ ]³⁻ , [ Ni ( NH ₃ )₆ ]²⁺ , [ Cu ( NH ₃ )₄ ]²⁺

Step-by-step solution

The spin-only magnetic moment is given by = n(n+2) BM , where n is the number of unpaired electrons. For > 3.5 BM , the complex must have n 3 unpaired electrons. [ Mn ( H ₂ O )₆ ]²⁺ : Mn ²⁺ is 3 d ^5 . H ₂ O is a weak field ligand. Configuration is t _ 2 g ^3 e _ g ^2 . n = 5 . = 35 5.92 BM . [ Fe ( CN )₆ ]³⁻ : Fe ³⁺ is 3 d ^5 . CN ^- is a strong field ligand. Configuration is t _ 2 g ^5 e _ g ^0 . n = 1 . = 3 1.73 BM . [ CoF ₆ ]³⁻ : Co ³⁺ is 3 d ^6 . F ^- is a weak field ligand. Configuration is t _ 2 g ^4 e _ g ^