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.
(a) [CrF6]3-
(b) [V(H2O)6]3+
(c) [Fe(CN)6]3-
Ch.21 - Transition Elements and Coordination Chemistry
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McMurry 8th EditionCh.21 - Transition Elements and Coordination ChemistryProblem 21.112
McMurry 8th EditionCh.21 - Transition Elements and Coordination ChemistryProblem 21.112Chapter 21, Problem 21.112
Draw a crystal field energy-level diagram for a square planar complex, and explain why square planar geometry is especially common for d8 complexes.
Verified step by step guidance1
Identify the metal ion and its oxidation state in the square planar complex. This will help determine the electron configuration and the number of d electrons present.
Understand that in a square planar complex, the ligands are positioned at the corners of a square in the xy-plane, leading to a specific splitting pattern of the d orbitals.
Recognize that the d orbitals split into different energy levels due to the ligand field. For a square planar complex, the order of increasing energy is typically: dz2, dxy, dyz = dxz, and dx2-y2.
Place the d electrons into the energy levels according to Hund's rule and the Pauli exclusion principle, starting from the lowest energy level. For a d8 complex, fill the lower energy orbitals first.
Explain that square planar geometry is common for d8 complexes because it allows for a stable electron configuration with lower energy, minimizing electron repulsion and maximizing ligand field stabilization energy.
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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 a square planar geometry, the ligands are positioned in a way that causes specific splitting of the d-orbitals, leading to distinct energy levels. This theory helps predict the electronic structure and color of coordination complexes.
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01:18
The study of ligand-metal interactions helped to form Ligand Field Theory which combines CFT with MO Theory.
d<sup>8</sup> Electron Configuration
The d<sup>8</sup> electron configuration refers to transition metal complexes that have eight electrons in their d-orbitals. This configuration is particularly stable in square planar complexes, as it allows for optimal pairing of electrons and minimizes electron-electron repulsion. Common examples include complexes of metals like nickel(II) and platinum(II).
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01:33Electron Configuration Example
Ligand Field Stabilization Energy (LFSE)
Ligand Field Stabilization Energy (LFSE) is the energy difference between the actual electronic configuration of a complex and the hypothetical configuration where all d-electrons are in the highest energy level. In square planar complexes, d<sup>8</sup> configurations can achieve a high LFSE due to effective pairing and lower energy arrangements, making this geometry energetically favorable.
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02:40Strong-Field Ligands result in a large Δ and Weak-Field Ligands result in a small Δ.
Related Practice
Textbook Question
Draw a crystal field energy-level diagram, assign the electrons to orbitals, and predict the number of unpaired electrons for each of the following.
(a) [Cu(en)3]2+
(b) [FeF6]2-
(c) [Co(en)3]3+ (low spin)
Textbook Question
The Ni2+(aq) cation is green, but Zn2+(aq) is colorless. Explain.
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.
(a) [Pt(NH3)4]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)