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Ch.21 - Transition Elements and Coordination Chemistry
All textbooksMcMurry 8th EditionCh.21 - Transition Elements and Coordination ChemistryProblem 21-113a
Chapter 21, Problem 21-113a

For each of the following complexes, draw a crystal field energy-level diagram, assign the electrons to orbitals, and predict the number of unpaired electrons.
(a) [Pt(NH3)4]2+ (square planar)

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Identify the geometry of the complex: For [Pt(NH3)4]2+, the given geometry is square planar. This information is crucial as it determines the arrangement and energy levels of the d orbitals.
Determine the oxidation state of the metal: Platinum (Pt) in this complex is in a +2 oxidation state. This is calculated by assuming the ammonia (NH3) ligands are neutral, which leads to the overall +2 charge being localized on the platinum.
Draw the crystal field splitting for a square planar complex: In square planar geometry, the d orbitals split into two groups due to the ligand field. The dx^2-y^2 orbital has the highest energy, followed by the dz^2 orbital. The dxy, dxz, and dyz orbitals are lower in energy.
Assign electrons to the orbitals: Platinum in the +2 oxidation state has a d^8 electron configuration. Begin filling the orbitals from lowest to highest energy according to Hund's rule and the Pauli exclusion principle, ensuring to fill each orbital with one electron before pairing them.
Predict the number of unpaired electrons: After filling the orbitals according to the electron configuration and the energy levels, count the number of unpaired electrons in the d orbitals. This will help in determining the magnetic properties of the complex.

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Key Concepts

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

Crystal Field Theory

Crystal Field Theory (CFT) explains how the arrangement of ligands around a central metal ion affects the energy levels of the d-orbitals. In octahedral and square planar complexes, the d-orbitals split into different energy levels due to the electrostatic interactions between the ligands and the d-electrons. Understanding this splitting is crucial for predicting the electronic configuration and magnetic properties of the complex.
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The study of ligand-metal interactions helped to form Ligand Field Theory which combines CFT with MO Theory.

Square Planar Geometry

Square planar geometry is a specific arrangement of ligands around a central metal ion, where four ligands are positioned at the corners of a square in the same plane. This geometry is commonly observed in d8 metal complexes, such as [Pt(NH3)4]2+. The unique arrangement influences the d-orbital splitting pattern, which is essential for determining the electron distribution and the number of unpaired electrons.
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Square planar complexes show the most complex splitting pattern.

Unpaired Electrons and Magnetism

Unpaired electrons are electrons that occupy an orbital singly rather than in pairs. The presence of unpaired electrons in a complex contributes to its magnetic properties; complexes with unpaired electrons are paramagnetic, while those with all paired electrons are diamagnetic. Identifying the number of unpaired electrons in a complex helps predict its magnetic behavior and is a key aspect of analyzing coordination compounds.
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Magnetic Quantum Example
Related Practice
Textbook Question

The Ni2+(aq) cation is green, but Zn2+(aq) is colorless. Explain.

Textbook Question

Draw a crystal field energy-level diagram for a square planar complex, and explain why square planar geometry is especially common for d8 complexes.

Textbook Question

For each of the following complexes, draw a crystal field energy-level diagram, assign the electrons to orbitals, and predict the number of unpaired electrons. 

(d) [Cu(en)2]2+ (square planar) 

Textbook Question

For each of the following complexes, draw a crystal field energy-level diagram, assign the electrons to orbitals, and predict the number of unpaired electrons.

(b) [MnCl4]2- (tetrahedral)

Textbook Question

For each of the following complexes, draw a crystal field energy-level diagram, assign the electrons to orbitals, and predict the number of unpaired electrons.

(c) [Co(NCS)4]2- (tetrahedral)

Textbook Question

Which of the following complexes are paramagnetic?

(a) [Mn(CN)6]3-

(b) [Zn(NH3)4]2+ (tetrahedral)

(c) [Fe(CN)6]4-

(d) [FeF6]4-