Problem 27 - A Complete Resource Book in Chemistry for JEE Main

Question

The water soluble complex among the following is (a) \(\left[\mathrm{Ni}(\mathrm{HDMG})_{2} \mathrm{Cl}_{2}\right]\) (b) \(\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]\) (c) \(\left[\mathrm{Ni}(\mathrm{HDMG})_{2}\right]\) (d) \(\left[\mathrm{Pd}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]\)

Step-by-Step Solution

Answer

(d) \([\mathrm{Pd}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}]\) is water-soluble.

Step 1: Identify Ligands and Solubility

Determine the ligands in each compound to assess their contribution to solubility in water. Water solubility often depends on the nature of ligands and the charge on the complex.

Step 2: Assess the Complexes

- (a) \([\mathrm{Ni}(\mathrm{HDMG})_{2} \mathrm{Cl}_{2}]\) contains non-polar ligands and no charge, making it insoluble.- (b) \([\mathrm{Ni}(\mathrm{CO})_{4}]\) is a neutral, non-polar complex, rendering it insoluble.- (c) \([\mathrm{Ni}(\mathrm{HDMG})_{2}]\) lacks polarization; hence, it is also insoluble.- (d) \([\mathrm{Pd}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}]\) contains polar ammonia ligands and can dissolve in water.

Step 3: Determine the Most Soluble Complex

Among the given options, \([\mathrm{Pd}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}]\) contains ammonia, which is polar and enhances water solubility. The presence of polar NH3 ligands suggests solubility in water.

Key Concepts

Water Solubility

Water solubility of coordination compounds is an important characteristic that often dictates their practical applications. The solubility in water is primarily influenced by the ligands attached to the central metal atom and the overall charge of the complex.
Polar ligands, such as amines like ammonia (\( ext{NH}_3\)), have a tendency to form hydrogen bonds with water molecules, increasing solubility. If a complex has a charge, either positive or negative, it will also attract water molecules, leading to higher solubility.

• More polar ligands or ionic charges result in higher water solubility.
• Neutral or non-polar complexes are generally insoluble in water.

Hence, understanding the structure and nature of the ligands can provide insights into how a complex behaves when in contact with water.

Ligands

Ligands play a pivotal role in the chemistry of coordination compounds. They are atoms or groups of atoms that bind to the central metal atom or ion, usually through coordinate covalent bonds. These are the bonds where both electrons come from the ligand. Different types of ligands exist, including:

• Monodentate ligands: Attach at a single bonding site (e.g., chloride ions, neutral ammonia molecules).
• Bidentate ligands: Attach at two different bonding sites (e.g., oxalate ions).
• Polydentate ligands: Attach at multiple sites (e.g., ethylenediaminetetraacetic acid (EDTA)).

The nature of ligands, whether they are strong field or weak field, affects the color, magnetic properties, and reactivity of the complex. Strong field ligands can significantly alter the d-orbital splitting of the metal center, influencing the complex's properties.

Complex Stability

Complex stability refers to how readily a complex dissociates in a solution. Stability is often directly correlated with the strength and nature of the ligands. Factors Affecting Stability:

• Chelation: Complexes formed with chelating ligands (ligands that form more than one bond with the metal) are typically more stable than those with monodentate ligands.
• Charge: Higher charge on the metal ion generally increases stability due to stronger electrostatic forces.
• Steric factors: Bulky ligands can sometimes hinder stability due to crowding.
• Ligand field effects: Strong field ligands can cause a change in d-electron configurations, enhancing stability.

Metal-ligand bond strength, as well as outer electronic configuration, are crucial parameters in determining how a complex will behave in different environments.

Polar and Non-Polar Ligands

Ligands can be categorized into polar and non-polar, which influences their behavior in forming complexes. Polar ligands include atoms or molecules with a significant difference in electronegativity between the bonded atoms, leading to a dipole moment. Ammonia is an example of a polar ligand since the unequal sharing of electrons between nitrogen and hydrogen atoms imparts a dipole.
Non-polar ligands, such as carbnoyl (\( ext{CO}\)), do not have such significant charge separations and hence cannot interact as effectively with polar solvents like water. When evaluating the solubility and reactivity of a complex:

• Polar ligands indicate better solubility and interaction with polar solvents.
• Non-polar ligands tend to form complexes that are sparingly soluble or insoluble in water.

Recognizing whether the ligands are polar or non-polar provides insights into not only solubility but also potential reactivity and applications of the complex.