Question

In which of the following metal complex, does the central metal atom have zero Oxidation state? (a) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{SO}_{4}\) (b) \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) (c) \(\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]\) (d) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]\)

Short answer

The complex with zero oxidation state is [Ni(CO)_4].

Step-by-step solution

Understanding Oxidation State Calculation

To determine the oxidation state of a central metal atom in a metal complex, we need to understand how oxidation states are calculated. Each ligand is assigned a charge, and we aim to balance the total charge of the complex.

Analyzing [Cu(NH_3)_4]SO_4

In this complex, the sulfate ion (SO_4) has a charge of -2, and ammonia (NH_3) is a neutral ligand. Therefore, the oxidation state of Cu is +2 to balance the -2 charge from the sulfate.

Evaluating K_3[Fe(CN)_6]

The CN^- ion has a charge of -1. Since there are six cyanide ions, the overall charge from the cyanides is -6. There must be an overall charge of -3, due to the three K^+ ions balancing it. Thus, iron (Fe) must have an oxidation state of +3.

Examining [Ni(CO)_4]

The CO ligand is a neutral molecule, contributing a charge of 0. Since there are four CO molecules and the complex is overall neutral, the oxidation state of Ni must be 0 to balance the charges.

Inspecting [Pt(NH_3)_2Cl_2]

Both NH_3 and Cl^- ligands are present. The NH_3 is neutral, and each Cl^- contributes -1. Hence, the total charge from two Cl^- ions is -2. This indicates the oxidation state of Pt is +2 to achieve a neutral complex.

Key concepts

Metal Complex Formation

Metal complex formation involves the interaction between a central metal atom and surrounding molecules or ions known as ligands. These ligands form coordinate bonds with the metal atom through their unshared pair of electrons. This gives rise to a coordinate structure where the metal acts as the atom around which the entire complex is organized.

Metal complexes play a crucial role in various fields like bioinorganic chemistry, catalysis, and material science. Understanding the basic formation process helps in grasping more complex concepts like oxidation states in these complexes. During the formation, the identity, number, and nature of ligands are crucial to the structural and chemical properties of the whole complex.

For example,

• In 'tetraamine copper sulfate' \((\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]\ \mathrm{SO}_{4})\), ammonia functions as a ligand coordinating to copper.
• In \hexa-cyanoferrate(III) complex \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\), cyanide ions serve as the ligands.

Ligand Charge

In metal complexes, ligands can either be neutral or charged, and their specific charge contributes to the overall charge of the complex. Knowing the charge of each ligand is essential for calculating the oxidation state of the central metal atom. Different ligands have specific charges, for instance, chloride ions (Cl\(^-\)) have a charge of \-1\, whereas ammonia (NH\(_3\)) is neutral.

When incorporating ligands into a metal complex, their individual charges play a significant role in defining the balance of the complex. For accurate oxidation state calculation, understanding and assigning the correct ligand charge is a critical step.

• For example, in \hexa-cyanoferrate(III), each cyanide ligand carries a charge of \-1\.
• Ammonia in \copper tetraamine sulfate acts as a neutral ligand.

Oxidation State Calculation

Calculating the oxidation state of a metal within a complex requires careful consideration of the charges associated with each component of the complex. The central idea is to ensure that the overall charge of the complex is balanced. This involves assigning charges to each ligand and setting up an equation where the sum of the ligand charges and the metal's oxidation state equals the charge of the entire complex.

Let's look at an example from the provided complexes: In \(\left[\mathrm{Ni}(\mathrm{CO})_4\right]\), all CO ligands are neutral, contributing no charge, resulting in a neutral overall complex. Thus, the oxidation state of Nickel is zero.

Neutral Ligands

Neutral ligands are those that do not contribute any charge to the metal complex. Despite having no charge, they still play a pivotal role in stabilizing the structure of metal complexes. These ligands typically coordinate through their lone electron pairs, forming bonds that drastically influence the properties of the metal complex.

Common examples of neutral ligands include ammonia (NH\(_3\)) and carbon monoxide (CO). For instance, in \(\left[\mathrm{Ni}(\mathrm{CO})_4\right]\), CO is a neutral ligand. It helps to stabilize the nickel center, but its neutrality means it does not affect the charge balance for oxidation state calculation.

Neutral ligands can significantly impact the geometry and electronic properties of the complexes they form without adding any charge factor, making them unique and vital in chemistry.

Charge Balance in Complexes

Maintaining charge balance in metal complexes is essential for their stability and to accurately deduce the oxidation state of the metal. The complete complex charge depends on the combination of the metal's oxidation state, ligand charges, and possible charges of other ions present.

To determine the correct oxidation state, one should balance the total ligand charge with the total charge of the complex. This approach allows understanding which ions or molecules maintain a neutral or charged complex when formed with the metal atom.

As demonstrated in \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]\), knowing that Cl\(^-\) contributes a charge of \-1\ helps figure out that Pt must have an oxidation state of +2 to balance the two chloride ions, ensuring the overall charge is zero. Understanding this balance concept is the key to mastering metal complex chemistry.