Coordination Compounds

(a) [FeCl4]−
Fe⇒[Ar]3d64s2
Fe+3⇒[Ar]3d54s0
Cl−is weak field ligand, So pairing does not take place.
∴ In [FeCl4]−[Fe(CO)4]2−
Fe⇒[Ar]3d64s2
Fe−2⇒[Ar]3d84s2
∴ In [Fe(CO)4]2−(b) [Co(CO)4]−
Co⇒[Ar]3d74s2
Co−1⇒[Ar]3d84s2
∴‌‌In[Co(CO)4]−[CoCl4]2−
Co⇒[Ar]3d74s2
Co+2⇒[Ar]3d74s0
∴ In [CoCl4]2−(c) [Ni(CO)4]
Ni⇒[Ar]3d84s2
Ni0⇒[Ar]3d84s2
∴ In [Ni(CO)4][Ni(CN)4]2−
Ni⇒[Ar]3d84s2
Ni+2⇒[Ar]3d84s0
CN−is strong field ligand, so pairing does not take place.
∴ In [Ni(CN)4]2−(d) [Cu(py)4|+
Cu⇒[Ar]3d104s1
Cu+⇒[Ar]3d104s0
∴ In [Cu(py)4]+[Cu(CN)4]3−
Cu⇒[Ar]3d104s1
Cu+⇒[Ar]3d104s0
CN−is so pairing occurs.
∴ In[ [Cu(CN)4]3−