Ch.23 - Transition Metals and Coordination Chemistry

Problem 4

Chapter 23, Problem 4

Four-coordinate metals can have either a tetrahedral or a square-planar geometry; both possibilities are shown here for [PtCl₂(NH₃)₂].
a. What is the name of this molecule?
b. Would the tetrahedral molecule have a geometric isomer?
c. Would the tetrahedral molecule be diamagnetic or paramagnetic?
d. Would the square-planar molecule have a geometric isomer?

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Identify the components of the complex [PtCl2(NH3)2]. Pt is platinum, Cl is chloride, and NH3 is ammonia.

Determine the oxidation state of platinum in the complex. Since each Cl is -1 and each NH3 is neutral, the overall charge of the complex is 0, which helps in determining the oxidation state of Pt.

Use the oxidation state of Pt and the known ligands to predict the geometry of the complex. Platinum complexes with a +2 oxidation state can adopt either tetrahedral or square-planar geometries.

Analyze the possibility of geometric isomers for both tetrahedral and square-planar geometries. Geometric isomers occur when there are different possible arrangements of ligands around the central metal atom that are not interconvertible by rotation but only by breaking and reforming bonds.

Consider the magnetic properties based on the electron configuration of the metal center. If all the d-orbitals are paired, the complex is diamagnetic; if unpaired electrons are present, it is paramagnetic.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Coordination Geometry

Coordination geometry refers to the spatial arrangement of ligands around a central metal atom in a coordination complex. In the case of four-coordinate metals, the two common geometries are tetrahedral and square-planar. The geometry affects the properties of the complex, including its reactivity and stability, and is determined by factors such as ligand size, charge, and electronic effects.

Geometric Isomerism

Geometric isomerism occurs when molecules with the same molecular formula have different spatial arrangements of atoms. In coordination complexes, this can lead to distinct isomers, such as cis and trans forms in square-planar complexes. Tetrahedral complexes typically do not exhibit geometric isomerism due to their symmetrical arrangement, while square-planar complexes can have geometric isomers based on the relative positions of the ligands.

Magnetism in Coordination Complexes

The magnetic properties of coordination complexes, such as being diamagnetic or paramagnetic, depend on the presence of unpaired electrons in the metal's d-orbitals. Diamagnetic complexes have all electrons paired and are not attracted to a magnetic field, while paramagnetic complexes contain unpaired electrons and are attracted to magnetic fields. The geometry and ligand field strength influence the electron configuration and, consequently, the magnetic behavior of the complex.

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Coordination Complexes Example

Related Practice

Open Question

Draw the structure for Pt (en) Cl₂ and use it to answer the following questions: a. What is the coordination number for platinum in this complex? b. What is the coordination geometry? c. What is the oxidation state of the platinum? d. How many unpaired electrons are there? [Find more in Sections 23.2 and 23.6.]

Open Question

Complete the exercises below. a. A compound with formula RuCl₃ • 5H₂O is dissolved in water, forming a solution that is approximately the same color as the solid. Immediately after forming the solution, the addition of excess AgNO₃ (aq) forms 2 mol of solid AgCl per mole of complex. Write the formula for the compound, showing which ligands are likely to be present in the coordination sphere.

Textbook Question

Which of these crystal-field splitting diagrams represents:

a. a weak-field octahedral complex of Fe³⁺ ,

b. a strong-field octahedral complex of Fe³⁺

c. a tetrahedral complex of Fe³⁺

d. a tetrahedral complex of Ni²⁺ (The diagrams do not indicate the relative magnitudes of ∆. ) [Find more in Section 23.6.]

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Textbook Question

In the linear crystal-field shown here, the negative charges are on the z-axis. Using Figure 23.28 as a guide, predict which of the following choices most accurately describes the splitting of the d orbitals in a linear crystal-field? [Find more in Section 23.6.]

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