Question

The species having tetrahedral shape is: (a) \(\left[\mathrm{PdCl}_{4}\right]^{2-}\) (b) \(\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}\) (c) \(\left[\mathrm{Pd}(\mathrm{CN})_{4}\right]^{2-}\) (d) \(\left[\mathrm{NiCl}_{4}\right]^{2-}\)

Short answer

Option (d) \(\left[\mathrm{NiCl}_{4}\right]^{2-}\) is tetrahedral.

Step-by-step solution

Determine Coordination Geometry

For a molecule to be tetrahedral, it typically needs a coordination number of four and no lone pairs influencing the geometry. You need to examine the ligands and the central atom's electronic configuration.

Analyze Each Compound

**(a) \(\left[\mathrm{PdCl}_{4}\right]^{2-}\)**- Palladium generally forms a square planar complex with strong field ligands such as Cl.**(b) \(\left[\mathrm{Ni}(abla{CN})_{4}\right]^{2-}\)**- Nickel in the +2 oxidation state with strong field ligands like CN tends to form a square planar structure.**(c) \(\left[\mathrm{Pd}(abla{CN})_{4}\right]^{2-}\)**- Like option (b), palladium with four ligands often forms a square planar complex due to CN being a strong field ligand.**(d) \(\left[\mathrm{NiCl}_{4}\right]^{2-}\)**- Nickel with chloride (Cl), a weaker field ligand, forms a tetrahedral complex due to the less strong field causing a different d-orbital splitting compared to CN.

Consider Ligand Field Strength

Strong field ligands like CN usually result in square planar geometry, especially with metals like Ni and Pd. Weaker field ligands like Cl do not cause the same extent of splitting, leading to tetrahedral geometry.

Conclude the Geometry Based on Analysis

From analyzing the geometry and field strength of the ligands:- (d) \(\left[\mathrm{NiCl}_{4}\right]^{2-}\) forms a tetrahedral complex.- The other options with stronger field ligands form square planar complexes.

Key concepts

Tetrahedral geometry

In coordination chemistry, tetrahedral geometry is one of the possible spatial arrangements of molecules where a central atom is surrounded by four ligands placed at the vertices of a tetrahedron. This arrangement is commonly seen when the central metal atom is in a high spin state and is paired with weaker field ligands, which do not significantly affect the d-orbital splitting.

- **Key Characteristics:** - The angles between the ligands are roughly 109.5°. - Tetrahedral geometry avoids lone pair or steric interactions if the central atom has no lone electron pairs.
An everyday example of tetrahedral geometry is found in compounds like \[\mathrm{NiCl}_{4}\]^{2-}\, where the chloride ions are weaker field ligands allowing for a more equal distribution of electrons across energy levels, resulting in tetrahedral geometry instead of square planar geometry.

Ligand field theory

Ligand field theory (LFT) is an extension of crystal field theory that helps explain the behavior and properties of transition metal complexes. It considers ligands as point charges that create an electrostatic field affecting the distribution of electrons in the d-orbitals of the metal ion.

- **Important Aspects:** - Strong field ligands can split d-orbitals significantly, leading to low-spin configurations that favor square planar or octahedral geometries. - Weaker field ligands such as chlorides cause less splitting, allowing for higher spin states and often leading to tetrahedral arrangements.
LFT helps in predicting the geometry of a complex by analyzing the ligand's field strength. For example, in \[\mathrm{NiCl}_{4}\]^{2-}\, the weaker influence of Cl leads to a smaller splitting of the metal’s d-orbitals, resulting in a tetrahedral configuration.

Coordination number

The coordination number is the number of ligand atoms bonded directly to the central metal atom, an essential concept for understanding the structure and geometry of complexes. It typically ranges from 2 to 6 in coordination compounds.

- **Key Points to Consider:** - A coordination number of 4 can lead to either tetrahedral or square planar geometries, depending on the electrochemical properties of the ligands and the metal ion. - The type and arrangement of bonding significantly affect the compound's geometry and stability.
For instance, \[\mathrm{NiCl}_{4}\]^{2-}\, having a coordination number of 4, forms a tetrahedral shape due to the interaction of nickel with four chloride ions, which are weaker field ligands, allowing for the natural expansion and dispersion of the orbital box.

Square planar complex

Square planar geometry is a type of coordination arrangement found commonly in certain metal complexes, particularly with transition metals paired with strong field ligands like cyanide (CN).

- **Characteristics of Square Planar Complexes:** - Metal ions with dye configurations, such as dd^8 are particularly suited to forming square planar complexes. - This geometry generally has 90° angles between the ligands, creating a flat, square-like arrangement around the central atom.
An example of square planar geometry can be seen in the \[\mathrm{PdCl}_{4}\]^{2-}\ complex, often occurring with palladium or nickel ions, especially when strong electronic field ligands such as CN are involved, significantly affecting the splitting and stabilization of the involved d-orbitals.