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Tetrahedral complexes of Co2+ are quite common. Use d -orbital splitting diagram to rationalize the stability of Co2+ tetrahedral complex ions.

Short Answer

Expert verified
The tetrahedral crystal field stabilization energy (CFSE) for Co^2+ ions is larger than the octahedral CFSE due to the high number of unpaired electrons (5 in the eg set and 2 in the t2 set) and the smaller splitting between the eg and t2 sets, in the tetrahedral geometry. This makes the tetrahedral complexes of Co^2+ more stable compared to octahedral ones.

Step by step solution

01

Recall d-orbital energy levels and the octahedral crystal field theory

Octahedral crystal field theory considers the arrangement of ligands around the central metal ion. It helps to explain the differences in color, magnetism, and stability of coordination complexes. In an octahedral complex, the energy levels of the d-orbitals split into two sets, with the lower energy set called the t2g set and the higher energy set called the eg set.
02

Apply the octahedral crystal field theory to tetrahedral complexes

In the case of tetrahedral complexes, the energy levels of the d-orbitals also split, but in a different way compared to octahedral complexes. In tetrahedral complexes, the lower energy level set is called the eg set while the higher energy level set is called the t2 set.
03

Consider the d-electron configuration of Co^2+

For cobalt, the atomic number is 27 and the electron configuration is [Ar] 4s^2 3d^7. A Co^2+ ion is formed by removing two electrons, resulting in the electron configuration [Ar] 3d^7. Recall that the number of unpaired electrons affects the stability of the complex.
04

Create the d-orbital splitting diagram for the tetrahedral Co^2+ complex

Based on the tetrahedral crystal field theory, here's how you create the energy splitting diagram for Co^2+: 1. Place the three d-orbitals of lower energy (the eg set) at the bottom, and the two higher energy d-orbitals (the t2 set) at the top. 2. Put the seven d-electrons into the diagram following Hund's rule, with a maximum number of unpaired electrons. The first five will fill the eg orbitals with unpaired electrons, and the remaining two will fill the t2 orbitals.
05

Rationalize the stability of the Co^2+ tetrahedral complex ions

The d-orbital splitting diagram shows that the Co^2+ ion has five unpaired electrons in its eg set and two in its t2 set. This high number of unpaired electrons leads to a stronger crystal field stabilization energy (CFSE) in the tetrahedral geometry, compared to the alternative octahedral geometry. Moreover, the splitting between the t2 and eg sets is smaller in a tetrahedral complex than in an octahedral one. The combined effect of a larger CFSE and a smaller splitting makes the tetrahedral geometry more favorable for the Co^2+ ion, thus explaining the stability of its tetrahedral complexes.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Tetrahedral Complex Ions
The arrangement of molecules or ions around a central atom in a complex or coordination compound is called its coordination geometry. One such geometry is the tetrahedral arrangement, where four ligands are positioned at the corners of a tetrahedron around the central metal ion.

Tetrahedral complexes stand out due to their smaller ligand field splitting compared to other geometries such as octahedral. This is because in a tetrahedral complex, the approaching ligands exert a lesser degree of repulsion on the d-orbitals of the central metal atom; the orbitals facing directly towards the ligands (the eg set) actually have lower energy while the orbitals directed between the ligands (the t2 set) are of higher energy. This is the opposite of what is observed with octahedral complexes.

Ease the Visualization with Splitting Diagrams

In the context of the Co^2+ ion, understanding tetrahedral d-orbital splitting can be facilitated by a visual diagram representing the energy levels. This diagram serves to rationalize the population of d-electrons in these energy states and thus explains the particular properties, like color and magnetism, of a tetrahedral complex ion.
Crystal Field Theory
Crystal Field Theory (CFT) is a model that describes the electronic structure of metal complexes. It accounts for the interaction between the central metal ion and the surrounding ligands which are presumed to be point charges. According to CFT, ligands disrupt the degeneracy of the d-orbitals on the metal ion, leading to unequal energy levels, a phenomenon known as crystal field splitting.

Importance of Crystal Field Splitting

The theory provides insight into the color, magnetism, and reactivity of metal complexes by considering the varying energy levels that electrons would occupy in an external field. A key takeaway is that the difference in splitting has a significant effect on the stability of the complex, making it a crucial factor in predicting complex behavior.
Co^2+ Ion Stability
Stability in metal complexes can be a complex affair, often influenced by a variety of factors such as charge, ligand types, and geometry. For the Co^2+ ion, its stability in tetrahedral complexes is quite remarkable.

The stability of Co^2+ ions in tetrahedral complexes can be comprehended through its electronic configuration ([Ar] 3d^7) and the effects of crystal field splitting. When the Co^2+ ion forms a complex, the d-orbitals' energy levels split into two sets, eg and t2, with the former lying lower in energy than the latter in a tetrahedral arrangement.

Crystal Field Stabilization Energy (CFSE)

An impressive aspect of the stability comes from CFSE. For the Co^2+ ion in a tetrahedral complex, the presence of a high number of unpaired electrons gives rise to a considerable CFSE. This is a stabilizing energy that arises from the electrons being placed in the lower-energy eg orbitals according to Hund's rule. In addition, the smaller energy gap between the t2 and eg sets compared to their octahedral counterparts contributes to the favorability of the tetrahedral arrangement for Co^2+ ions. It showcases how electronic arrangement and geometry coalesce to influence the stability of metal complexes.

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Most popular questions from this chapter

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