Question

The geometry and magnetic behaviour of the complex `[Ni(CO)_4]` are
A. square planar geometry and paramagnetic
B. tetrahedral geometry and diamagnetic
C. square planar geometry and diamagnetic
D. tetrahedral geometry and paramagnetic

Answer 1

Correct Answer - B
Key Concept The complexes having `sp^(3)`-hybridisation are tetrahedral while having `dsp^(2)`-hybridisation are square planar. The magnetic behaviour of complexes can be paramagnetic and diamagnetic based on the presence and absence of upaired electrons, respectively.
Electronic configuration of Ni(Z=28) is `[Ar]_(18)3d^(8)4s^(2)`. Due to presence of CO (neutral ligand), oxidation state of Ni in `[Ni(CO)_(4)]` is 0.

Since, CO is a strong field ligand, it pair up the unpaired electrons of Ni.

There is no unpaired electron, hence, `Ni(CO)_(4)` is diamagnetic with tetrahedral geometry.