The visible spectrum of the Cr (acac) 3

complex is significantly different from the [Cr (en) 3]Br3 complex. Why?

The observable visible spectrum of Cr (acac) 3 complex is different from that of

[Cr (en) 3]Br3 due to strength of bonded ligand in the coordination sphere.

en is a strong field ligand compared to acac thus pairing occurs. In both the complexes

Cr is in + 3 state, configuration [Ar] 3d^3. There are 3 unpaired e in Cr (acac) 3 whereas 1 unpaired e in [Cr (en) 3]Br3 due to pairing.