Question

Which of the following is paramagnetic
A . [Ni(CO)4]
B . [Co(NH3)6]3+
C . [Ni(CN)4]2-
D . [NiCl4]2-

Answer 1

Hint: In this question we have to use the concept of paramagnetism of a coordination compound to find out which out of the following complexes is paramagnetic.
A substance's magnetic properties can be determined by looking at its electronic configuration. If all of its electrons are paired, a substance is considered to be diamagnetic and it is paramagnetic if its electrons are unpaired.


Complete answer:Paramagnetism is the magnetic state of an atom with one or more unpaired electrons. The magnetic field pulls the unpaired electrons in due to the magnetic dipole moments of the electrons. According to Hund's Rule, electrons must occupy an orbital alone before they can occupy it twice. As a result, there is a higher number of unpaired electrons in the atom.

Because they can spin, either way, unpaired electrons exhibit magnetic characteristics in both directions. This property makes paramagnetic atoms attracted to magnetic fields.
In [NiCl4]2- the oxidation number of Ni is +2. The atomic number of Ni = 28
Electronic Configuration of Ni = [Ar]3d84s2
Electronic Configuration of Ni2+ = [Ar]3d8
Chlorido is a weak field ligand, with no pairing
sp3 - Hybridization (tetrahedral)
There are two unpaired electrons, so the complex is paramagnetic.

 The correct answer is D.

Note: For [Ni(CO)4], the oxidation number of Ni is O. Atomic number of Ni = 28
Electronic Configuration of Ni = [Ar]3d84s2
[Ni(CO)4] has sp3 Hybridization (tetrahedral)
There are no unpaired electrons, so the complex is diamagnetic.
Spin magnetic moment = zero
Similarly, for [Ni(CN)4]2-, the oxidation number of Ni is +2. The atomic number of Ni = 28
Electronic Configuration of Ni = [Ar]3d84s2
Electronic Configuration of Ni2+ = [Ar]3d8
[Ni(CN)4]2- has dsp2 configuration. There are no unpaired electrons so, the complex is diamagnetic.
Spin magnetic moment = zero