Would you expect the Mg3[Cr (CN) 6]2 to be diamagnetic or paramagnetic? Explain your reasoning.

paramagnetic

Explanation:

The complex ion is : [Cr (CN) ₆]³⁻

Oxidation state of Cr in [Cr (CN) ₆]³⁻ is:

x + (-1) 6 = - 3

x = + 3

CN⁻ is a strong field ligand which can result in pairing of the electrons.

The electronic configuration of Cr is:

1s²2s²2p⁶3s²3p⁶3d⁵4s¹

The electronic configuration of Cr³⁺ is:

1s²2s²2p⁶3s²3p⁶3d³

These 3 electrons will be singly present in the 3 degenerate t₂g orbitals and per Hund's rule, pairing will not occur in the same level energy orbitals. So, no. of unpaired electrons will be 3 and the complex will be paramagnetic.