Textbook Question
Tris(2-aminoethyl)amine, abbreviated tren, is the tetradentate ligand N(CH2CH2NH2)3. Using to represent each of the three NCH2CH2NH2 segments of the ligand, sketch all possible isomers of the octahedral complex [Co(tren)BrCl]+.
Ch.21 - Transition Elements and Coordination Chemistry
Chapter 21, Problem 103
Use a sketch to explain why the dxy and dx2-y2 orbitals have different energies in an octahedral complex. Which of the two orbitals has higher energy?
Verified step by step guidance1
Step 1: Understand the geometry of an octahedral complex. In an octahedral complex, a central metal atom is surrounded by six ligands positioned at the corners of an octahedron. This arrangement leads to specific interactions between the metal's d orbitals and the ligands.
Step 2: Recall the five d orbitals: d_{xy}, d_{yz}, d_{zx}, d_{x^2-y^2}, and d_{z^2}. In a free atom, these orbitals are degenerate, meaning they have the same energy. However, in an octahedral complex, the presence of ligands causes a splitting of these energy levels.
Step 3: Consider the orientation of the d orbitals. The d_{xy} orbital lies in the xy-plane, while the d_{x^2-y^2} orbital also lies in the xy-plane but has lobes along the x and y axes. In an octahedral complex, ligands approach along the x, y, and z axes.
Step 4: Analyze the interaction with ligands. The d_{x^2-y^2} orbital has lobes that point directly towards the ligands along the x and y axes, leading to greater repulsion and higher energy. In contrast, the d_{xy} orbital's lobes are oriented between the axes, resulting in less direct interaction with the ligands and lower energy.
Step 5: Conclude which orbital has higher energy. Due to the direct interaction with the ligands, the d_{x^2-y^2} orbital experiences greater repulsion and thus has higher energy compared to the d_{xy} orbital in an octahedral complex.
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 its d-orbitals. In an octahedral complex, the ligands approach the metal ion along the axes, leading to a splitting of the d-orbitals into two energy levels: the lower-energy t2g set and the higher-energy eg set. This theory helps in understanding the electronic structure and stability 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-Orbital Splitting in Octahedral Fields
In an octahedral field, the five d-orbitals split into two groups due to the electrostatic interactions with surrounding ligands. The dxy and dx2-y2 orbitals are part of the eg set, which is higher in energy compared to the t2g set. The dx2-y2 orbital, oriented along the axes, experiences greater repulsion from the ligands than the dxy orbital, which is oriented between the axes, resulting in different energy levels.
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03:04The crystal field splitting pattern for octahedral complexes has the d orbitals on or along the axes as having the higher energy.
Ligand Field Strength
Ligand field strength refers to the ability of ligands to influence the energy levels of d-orbitals in a metal complex. Strong field ligands cause greater splitting of the d-orbitals, while weak field ligands result in smaller splitting. In the context of the dxy and dx2-y2 orbitals, the ligand field strength determines the extent of energy difference between these orbitals, with the dx2-y2 typically having higher energy due to its direct alignment with the ligands.
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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
Consider the octahedral complex [Co(en)(dien)Cl]2+, where dien = H2NCH2CH2NHCH2CH2NH2, which can be abbreivated
(a) The dien (diethylenetriamine) ligand is a tridentate ligand. Explain what is meant by 'tridentate' and why dien can act as a tridentate ligand.
(b) Draw all possible stereoisomers of [Co(en)(dien)Cl]2+ (dien is a flexible ligand). Which stereoisomers are chiral, and which are achiral?
Textbook Question
The reaction of the octahedral complex Co(NH3)3(NO2)3 with HCl yields a complex [Co(NH3)3(H2O)Cl2]+ in which the two chloride ligands are trans to one another.
(a) Draw the two possible stereoisomers of the starting material [Co(NH3)3(NO2)3]. (All three NO2- ligands are bonded to Co through the N atom.)
(b) Assuming that the NH3 groups remain in place, which of the two starting isomers could give rise to the observed product?
Textbook Question
In octahedral complexes, the choice between high-spin and low-spin electron configurations arises only for d4 - d7 complexes. Explain.