(i) [CoNH₃CI(en)₂]²⁺
amminechloridobis(ethane-1,2-diamine)cobalt (Ill) ion

Co³⁺ : 4s⁰3d⁶ 
(ii) [Ni(H₂O)₂(OX)₂]^2-
diaquadioxalatonickelate (II) ion
Ni²⁺ : 4s⁰3d⁸

Unidentate Ligands: Those ligands which can form only one coordinate bond are called unidentate ligands, e.g. NH₃ , CN^- Didentate Ligands: Those ligands which can form two coordinate bonds are called bidentate ligands,\(\overset { { COO }^{ - } }{ \underset { { COO }^{ - } }{ | } } \)  (ox), H₂NCH₂CH₂NH₂(en). Ambidentate Ligands: Those ligands which can form bond through either of the two donor atoms are called ambidentate ligands, e.g. CN^- , NO₂^-  etc.

Let us assume that the six ligands are positioned symmetrically along the cartesian axes, with metal atom at the origin. As the ligands approach, first there is an increase in energy of d-orbitals relative to that of the free ion just as would be the case in a spherical field  The orbitals lying along the axes (\({ d }_{ { z }^{ 2 } }\)nd \({ d }_{ { x }^{ 2 }-{ y }^{ 2 } }\))get repelled more strongly than dx¹ d and d_yz and d_zx orbitals which have lobes directed between the axes. The \({ d }_{ { z }^{ 2 } }\)and  orbitals get raised in energy and d_xy d_yz d _xz orbitals are lowered in energy relative to the average energy in the spherical crystal field. Thus, the degenerate set of d-orbitals get split into two sets : the lower energy orbitals set and the higher energy orbitals eg set. The energy is separated by t_2g and the higher energy orbitals e_g set. The energy is separated by \({ \Delta }_{ 0 }\)

(a) [Cr(C₂O₄)₃]^3-

(b) [PtCl₂(en)₂]²⁺
 
(c) [Cr(NH₃)₂Cl₂(en)]⁺

(i) It does not explain why a metal ion in particular oxidation state forms low spin or high spin complexes.
(ii) It cannot justify magnetic behaviour in some cases.
(iii) It cannot explain colour shown by complex compounds.
(iv) It does not give idea about thermodynamic and kinetic stability of complex compound.
(v) It is based on assumptions which may not be true.
(vi) There is no quantitative interpretation of magnetic moment. 

(i) Potassium hexacyanomaganate (II). It has octahedral shape  and is paramagnetic in nature.
(ii) Pentaamine chloridocobalt (III) chloride. It has octahedral  shape and is diamagnetic in nature.
(iii) Potassium tetracyano nickelate (II). It has square planar shape and is diamagnetic in nature.