Problem 2 - Chemistry The Central Science

Question

(a) Draw the structure for \(\mathrm{Pt}(\mathrm{en}) \mathrm{Cl}_{2} .\) (b) What is the coordination number for platinum in this complex, and what is the coordination geometry? (c) What is the oxidation state of the platinum? [Section 23.2]

Step-by-Step Solution

Answer

The structure of the complex \(\mathrm{Pt}(\mathrm{en}) \mathrm{Cl}_{2}\) is: ``` Cl en \ / Pt------N | | ------- ``` The coordination number for platinum is 4, and the coordination geometry is square planar. The oxidation state of platinum in this complex is +2.

Step 1: Draw the structure of the complex

First, let's identify the components of the complex. Pt is the central metal atom, en (ethylenediamine) is the bidentate ligand, and Cl is the monodentate ligand. Ethylenediamine is represented as H2N-CH2-CH2-NH2. In the complex \(\mathrm{Pt}(\mathrm{en}) \mathrm{Cl}_{2}\), the two chlorines and the N atoms from the ethylenediamine molecule form bonds with the central platinum atom. So, the structure of the complex would look like this: ``` Cl en \ / Pt------N | | ------- ```

Step 2: Determine the coordination number and coordination geometry

The coordination number is the number of ligand atoms bonded to the central metal atom. In this complex, we have two Cl atoms, and the ethylenediamine molecule has two N atoms, which are bonded to Pt. So, the coordination number for platinum in this complex is 2 (Cl) + 2 (N) = 4. The coordination geometry is determined by considering how the ligands are arranged around the central metal atom. Since there are four ligands around Pt, the coordination geometry is square planar.

Step 3: Determine the oxidation state of platinum

To calculate the oxidation state of platinum in this complex, we need to determine the charges of all the ligands. Cl has an oxidation state of -1. Since the ethylenediamine molecule is neutral, it contributes no charge to the complex. The sum of charges in the complex is given by the sum of the oxidation state of platinum and the charges of the ligands. Let the oxidation state of platinum (Pt) be x: x + 0 (charge for en) + (-1) (charge for first Cl) + (-1) (charge for second Cl) = 0 x - 2 = 0 x = 2 Hence, the oxidation state of the platinum in the complex \(\mathrm{Pt}(\mathrm{en}) \mathrm{Cl}_{2}\) is +2.

Key Concepts

Coordination Number

The coordination number in coordination chemistry is a fundamental concept that refers to the number of ligand atoms directly bonded to a central metal ion. In coordination complexes like \(\text{Pt(en)Cl}_2\), each ligand forms bonds with the central metal ion.

• In this complex, ethylenediamine ("en") is a bidentate ligand, meaning it forms two bonds with the platinum (Pt) atom through its two nitrogen atoms.
• Additionally, two chlorine (Cl) atoms, each forming a single bond, bring the total to four coordinating atoms.

Thus, the coordination number for platinum in \(\text{Pt(en)Cl}_2\) is 4.By understanding the coordination number, you can predict properties such as reactivity and color of the complex.

Oxidation State

The oxidation state (or oxidation number) represents the charge that an atom would have if the compound was composed of ions. In the complex \(\text{Pt(en)Cl}_2\), determining the oxidation state of the central metal atom is crucial for understanding its chemical behavior.

• Each chlorine (Cl) has an oxidation state of -1.
• Ethylenediamine is a neutral ligand, thus it does not contribute to the overall charge.
• The sum of all charges in the complex must equal the overall charge of the complex, which is neutral (0 in this case).

For platinum in this complex, let its oxidation state be \(x\).

According to the charge balance equation:\[x + 0 \text{ (for en)} + (-1) + (-1) = 0\]Solving this gives \(x = +2\).

Therefore, the oxidation state of platinum is \(+2\), which helps in predicting the complex's reactivity and stability.

Coordination Geometry

Coordination geometry describes the spatial arrangement of ligands bonded to the central metal atom in a coordination compound. The coordination geometry affects the chemical and physical properties of the compound.

• In \(\text{Pt(en)Cl}_2\), with a coordination number of 4, the geometry is typically either tetrahedral or square planar.
• Platinum is a transition metal that commonly forms square planar complexes due to its electron configurations and preferences.

As such, \(\text{Pt(en)Cl}_2\) exhibits square planar geometry.Square planar complexes, like this one, lead to distinct properties. These include unique optical and magnetic characteristics due to the arrangement of the ligands around the metal.