The number of unpaired spins in the `[Cr(en)_(3)]^(2+)` ion is

Options

A. two
B. four
C. three
D. zero

Answer

A

Explanation

The magnetic properties of a complex ion depend on the number of unpaired electrons present. The actual number of unpaired electrons (or spins) in a complex ion can be found by magnetic measurments, and in general experimental findings supports predictions based on crystal field splitting. However a distinction between low and high spin complexes can be made only if the metal ion contains more than three and fewer than eight d electrons. The ground state electron configuration of `Cr^(2+)` is `[Ar]3d^(4)` . Since en is a strong field ligand, we expect `[Cr(en)_(3)]^(2+)` to be a low spin complex. According to crystal field orbital energy level diagram, all four electrons will be place in the lower d orbitals `(d_(xy), d_(yz)` and `d_(xz))` and there will be a total of two unpaired spins: