Question

Among the following species the ones having square planar geometry for central atom are 1\. \(\mathrm{XeF}_{4}\) 2\. \(\mathrm{SF}_{4}\) 3\. \(\left[\mathrm{NiCl}_{4}\right]^{2-}\) 4\. \(\left[\mathrm{PdCl}_{4}\right]^{2-}\) (a) 1 and 4 (b) \(\mathrm{l}\) and 2 (c) 2 and 3 (d) 3 and 4

Short answer

The correct answer is (a) 1 and 4.

Step-by-step solution

Understand Square Planar Geometry

Square planar geometry occurs when there are four bonds arranged equally around a central atom in a single plane, with an angle of 90° between each bond. This geometry is typically found in certain coordination complexes involving transition metals with filled or partially filled d-orbitals.

Analyze XeF4

The molecule \( \mathrm{XeF}_{4} \) has a central Xenon atom surrounded by four fluorine atoms in a square planar formation. Xenon has 8 valence electrons, two of which are lone pairs, leading to the square planar shape according to VSEPR theory. Thus, \( \mathrm{XeF}_{4} \) has a square planar geometry.

Analyze SF4

The molecule \( \mathrm{SF}_{4} \) has a central Sulfur atom bonded to four fluorine atoms and one lone pair. According to VSEPR theory, its geometry is seesaw (or distorted tetrahedral) due to one lone pair occupying one position, not allowing for a square planar structure. Hence, \( \mathrm{SF}_{4} \) does not have a square planar geometry.

Analyze [NiCl4]^{2-}

The \( \left[\mathrm{NiCl}_{4}\right]^{2-} \) complex has a Nickel atom at the center, coordinated by four chlorine atoms. Nickel typically forms tetrahedral complexes in this type of configuration, especially given the electronic configuration of the Ni(II) ion. Hence, \( \left[\mathrm{NiCl}_{4}\right]^{2-} \) does not have a square planar geometry.

Analyze [PdCl4]^{2-}

The \( \left[\mathrm{PdCl}_{4}\right]^{2-} \) complex has Palladium in the center, which is known to form square planar complexes due to the presence of d8 electronic configuration (making use of dsp2 hybridization). Therefore, \( \left[\mathrm{PdCl}_{4}\right]^{2-} \) is square planar.

Determine the Correct Answer

After analysis, the species that have square planar geometries are \( \mathrm{XeF}_{4} \) and \( \left[\mathrm{PdCl}_{4}\right]^{2-} \). Therefore, the correct option from the given choices is (a) 1 and 4.

Key concepts

VSEPR theory

The VSEPR (Valence Shell Electron Pair Repulsion) theory is a simple model used to predict the geometry of molecules based on the repulsion between electron pairs in the valence shell of an atom. Key to understanding this model is recognizing that electron pairs will arrange themselves around a central atom in a way that minimizes repulsions, creating a specific geometric shape.

- **Lone Pairs and Bonding Pairs**: Lone pairs have stronger repulsive effects compared to bonding pairs. This is crucial in determining molecular geometry as they occupy more space. - **Example: XeF extsubscript{4}**: In the case of XeF extsubscript{4}, the central xenon atom has 6 electron pairs: 4 forming bonds with fluorine atoms and 2 as lone pairs. To minimize repulsion, the molecule adopts a square planar shape, positioning the lone pairs opposite each other.

Coordination Complexes

Coordination complexes are structures where a central metal atom is bonded to surrounding ligands through coordinate covalent bonds. These complexes have distinctive geometries influenced by various factors such as the type of ligands, the oxidation state of the metal, and the nature of metal's d-orbitals.

- **Complex Formation**: Coordination complexes form when ligands donate a pair of electrons to the metal. In some instances, the complex may form a square planar geometry if particular d-orbital configurations are favorable, as seen with metals like palladium. - **Example: [PdCl extsubscript{4}] extsuperscript{2−}**: This complex has palladium at its center coordinated with four chloride ions, forming a plane. The square planar shape arises from dsp2 hybridization common in metals with a d8 configuration like Palladium.

d-orbitals

d-orbitals are five degenerate orbitals found in transition metals that can host electrons beyond the s and p orbitals. These orbitals play a crucial role in determining the geometry and properties of coordination complexes.

- **Influence on Geometry**: The filling of d-orbitals influences the complex's geometry as it affects how the metal ion interacts with ligands. - **d8 Configuration**: Metals with a d8 configuration, like palladium, are typically square planar. This happens because electronic repulsions within the d-orbitals are minimized when the metal forms a square planar complex.

Transition Metals

Transition metals are elements known for their ability to form various oxidation states and complexes due to their partially filled d-orbitals. Their unique properties make them crucial in chemistry, particularly in forming coordination compounds.

- **Variable Oxidation States**: Transition metals can exhibit multiple oxidation states, allowing them to bond with various ligands and form diverse complex geometries. - **Example: Nickel and Palladium**: Nickel, often found in tetrahedral complexes like in [NiCl extsubscript{4}] extsuperscript{2−}, does not typically form square planar shapes. In contrast, palladium forms square planar complexes like [PdCl extsubscript{4}] extsuperscript{2−} due to its electronic configuration, demonstrating how different transition metals create distinct shapes.