Identify transition metal complexes which are not octahedral in shape

(A) \([Co(NH_3)_6]^{3+}\)

(B) \([Ni(CO)_4]\)

(C) \([CoCl(NH_3)_5]^{2+}\)

(D) \([CoCl_2(NH_3)_4]^{+}\)

(E) \([PtCl_4]^{2-}\)

Choose the correct answer from the options given below:

(B) and (E) only

The correct answer is option 2. (B) and (E) only.

Let us look at each of the given complexes:

(A) \([Co(NH_3)_6]^{3+}\):

This complex is formed by cobalt \((Co)\) coordinated with six ammonia \((NH_3)\) ligands. The coordination number is \(6\), indicating that there are six ligands surrounding the central cobalt atom. In this case, the complex adopts an octahedral geometry because ammonia is a weak field ligand, which doesn't cause significant splitting of the d orbitals. Therefore, the complex has a symmetric octahedral arrangement

(B) \([Ni(CO)_4]\):

This complex is formed by nickel \((Ni)\) coordinated with four carbon monoxide \((CO)\) ligands. The coordination number is \(4\), indicating that there are four ligands surrounding the central nickel atom. In this case, the complex adopts a tetrahedral geometry because carbon monoxide is a strong field ligand, causing significant splitting of the d orbitals. The ligands approach the central metal atom along the axes of a tetrahedron, resulting in a tetrahedral geometry.

(C) \([CoCl(NH_3)_5]^{2+}\):

This complex is formed by cobalt \((Co)\) coordinated with one chloride ion \((Cl^-)\) and five ammonia \((NH_3)\) ligands. The coordination number is 6, indicating that there are six ligands surrounding the central cobalt atom. In this case, the complex adopts an octahedral geometry because ammonia is a weak field ligand, similar to option (A).

(D) \([CoCl_2(NH_3)_4]^{+}\):
This complex is formed by cobalt \((Co)\) coordinated with two chloride ions \((Cl^-)\) and four ammonia \((NH_3)\) ligands. The coordination number is 6, indicating that there are six ligands surrounding the central cobalt atom. Similar to options (A) and (C), the complex adopts an octahedral geometry due to the weak field nature of the ligands.

(E) \([PtCl_4]^{2-}\):
This complex is formed by platinum \((Pt)\) coordinated with four chloride ions \((Cl^-)\). The coordination number is 4, indicating that there are four ligands surrounding the central platinum atom. In this case, the complex adopts a square planar geometry because chloride ions are strong field ligands, causing significant splitting of the d orbitals. The ligands approach the central metal atom in the plane of the molecule, resulting in a square planar geometry.

In summary, option (B) \([Ni(CO)_4]\) forms a tetrahedral complex, and option (E) \([PtCl_4]^{2-}\) forms a square planar complex, while the other options form octahedral complexes.