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

The species \\([\mathrm{NiCl}_{4}]^{2-}\\) has a tetrahedral shape.

Step-by-step solution

Understanding the Problem

We need to determine which of the given complexes has a tetrahedral shape. Tetrahedral geometry is characteristic of complexes with low coordination numbers, typically 4, with specific electron count and ligand fields.

Analyzing Electronic Configuration

Let's consider the hybridization of the central metal atom. Tetrahedral coordination is common when metal complexes involve dsp3 or sp3 hybridization with weaker field ligands. We will examine each complex to determine its likely geometry.

Evaluating Complexes

a) \([\mathrm{PdCl}_{4}]^{2-}\): Palladium typically forms square planar complexes because it has a strong tendency towards dsp2 hybridization. Chloride is a weak field ligand, but Pd(II) still prefers square planar configuration, not tetrahedral. b) \([\mathrm{Ni}( ext{CN})_{4}]^{2-}\): CN- is a strong field ligand, leading to dsp2 hybridization in Ni(II), resulting in a square planar complex. c) \([\mathrm{Pd}( ext{CN})_{4}]^{2-}\): Similar to Ni(CN)4^{2-}, this complex will also be square planar due to strong field nature of CN-. d) \([\mathrm{NiCl}_{4}]^{2-}\): Chloride is a weak field ligand, allowing sp3 hybridization in Ni(II), which typically results in a tetrahedral complex.

Conclusion

Considering the hybridization and field strength of ligands, \([\mathrm{NiCl}_{4}]^{2-}\) is the species that has a tetrahedral geometry due to the presence of a weak field ligand like chloride enabling sp3 hybridization in nickel.

Key concepts

Coordination Compounds

Coordination compounds are unique chemical structures consisting of a central metal atom surrounded by molecules or ions called ligands. These ligands attach to the metal through coordinate covalent bonds, where electrons are donated by the ligands. Coordination compounds display fascinating properties and a broad range of geometries, which depend significantly on factors like ligand types and electron configurations.

When studying coordination compounds, understanding the coordination number is essential. This number corresponds to the count of ligand atoms bonded to the central metal. In most complexes, coordination numbers range from 2 to 9, with 4 and 6 being common. The geometry a compound takes—from tetrahedral to square planar or octahedral—is closely linked to this coordination number and the hybridization of orbitals in the metal atom.

For instance, in a four-coordinate metal complex, where the coordination number is 4, the shape may either be tetrahedral or square planar. This is determined mainly by the type of ligands present: weak field ligands tend to form tetrahedral complexes, whereas strong field ligands usually form square planar structures.

Hybridization

Hybridization refers to the mixing of atomic orbitals in a metal atom to form new hybrid orbitals. These hybrid orbitals are utilized for forming bonds with ligands in coordination compounds. Understanding hybridization is key to predicting the shapes and geometries of such compounds.

For four-coordinate complexes, two main types of hybridizations are possible: sp3 and dsp2. The type depends on the ligand field strength and electronic configuration of the central metal ion.

• sp3 hybridization occurs when there are four orbitals combining, resulting in a tetrahedral geometry. This is typical in environments where the ligands are weak field, such as chloride in iCl_{4}]^{2-} .
• dsp2 hybridization, on the other hand, involves merging one d orbital, one s orbital, and two p orbitals, resulting in a square planar shape, commonly seen with strong field ligands like CN-.

The understanding of these hybridizations helps determine the potential geometric shape of the coordination compound and further predict its chemical behavior and reactivity.

Geometric Shapes of Complexes

The geometric shape of a coordination complex is crucial in comprehending its chemical and physical properties. Different geometrical arrangements not only impact the stability of the complex but also its color, magnetism, and reactivity.

In coordination chemistry, common shapes include linear, tetrahedral, trigonal planar, square planar, and octahedral. For a tetrahedral shape, often seen with four-coordinate compounds, the atoms or ligands are positioned symmetrically around the central metal atom at approximately 109.5° angles. This geometry is frequently found in complexes with weak field ligands due to the simpler spatial arrangement that minimizes strain and repulsion.

Conversely, the square planar shape, also for four-coordinate complexes, involves ligands positioned in the same plane as the metal center. This geometry is typical with metal ions that prefer dsp2 hybridization, often supported by strong field ligands. Recognizing the driving factors behind these shapes aids in understanding complex formation rules and predicting the behavior of coordination compounds in various chemical reactions.