CSIR UGC NET Dec-15 (Q-4)

Using crystal field theory, identify from the following complex ions that shows same µ_eff (spin only) values:

(A) [CoF₆]^3- , (B) [IrCl₆]^3- , (C) [Fe(H2O)₆]²⁺

(a) A and B 
(b) B and C 
(c) A and C 
(d) A, B and C

Ans:
All the complex are d⁶ and contain weak field ligand but except Ir all form high spin complex 

*[4d and 5d metals never form high spin complex] Hence spin only magnetic moment will be same for Co(III) and Fe(II)

The magnitude of the paramagnetism is expressed as an effective magnetic moment, μeff.

Magnetochemistry is concerned with the magnetic properties of chemical compounds. Magnetic properties arise from the spin and orbital angular momentum of the electrons contained in a compound. Compounds are diamagnetic when they contain no unpaired electrons. Molecular compounds that contain one or more unpaired electrons areparamagnetic. The magnitude of the paramagnetism is expressed as an effective magnetic moment, μeff.

Reference : Figgis&Lewis, pp. 424, 432