High-spin complexes are a type of coordination compound where the metal center has the maximum possible number of unpaired electrons in its valence shell, resulting in a high total spin quantum number. This spin state is favored when the ligand field splitting energy is relatively weak compared to the pairing energy of the electrons.
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High-spin complexes have the maximum possible number of unpaired electrons in the metal center's valence shell, which results in a high total spin quantum number.
The spin state of a complex is determined by the relative strength of the ligand field splitting energy and the pairing energy of the electrons.
High-spin complexes are favored when the ligand field splitting energy is relatively weak compared to the pairing energy, allowing the electrons to occupy the higher-energy d-orbitals individually.
High-spin complexes exhibit characteristic magnetic and spectroscopic properties, such as high magnetic moments and distinctive electronic absorption spectra.
The spin state of a complex can be influenced by factors such as the nature of the ligands, the oxidation state of the metal, and the geometry of the complex.
Review Questions
Explain the relationship between the ligand field splitting energy and the pairing energy in determining the spin state of a coordination complex.
The spin state of a coordination complex is determined by the relative strength of the ligand field splitting energy and the pairing energy of the electrons. When the ligand field splitting energy is relatively weak compared to the pairing energy, the system favors a high-spin configuration, where the electrons occupy the higher-energy d-orbitals individually, resulting in the maximum possible number of unpaired electrons. This high-spin state is characterized by a high total spin quantum number. Conversely, when the ligand field splitting energy is strong enough to overcome the pairing energy, the system will adopt a low-spin configuration, where the electrons pair up in the lower-energy d-orbitals.
Describe the characteristic magnetic and spectroscopic properties of high-spin complexes and explain how they are related to the electronic configuration.
High-spin complexes exhibit distinct magnetic and spectroscopic properties due to their electronic configuration. The presence of a large number of unpaired electrons in the metal center's valence shell results in a high magnetic moment, which can be observed through magnetic susceptibility measurements. This high magnetic moment arises from the uncompensated spin angular momentum of the unpaired electrons. Additionally, high-spin complexes display characteristic electronic absorption spectra, with transitions occurring at relatively lower energies compared to low-spin complexes. This is because the d-orbital splitting is smaller in high-spin complexes, leading to smaller energy gaps between the d-orbitals and, consequently, lower-energy electronic transitions.
Analyze how the nature of the ligands and the geometry of the complex can influence the spin state of a coordination compound.
The spin state of a coordination complex is influenced by both the nature of the ligands and the geometry of the complex. The strength of the ligand field splitting energy, which is a key factor in determining the spin state, is affected by the identity and arrangement of the ligands. Stronger field ligands, such as carbonyl or cyanide, tend to favor low-spin configurations, while weaker field ligands, such as chloride or water, are more likely to result in high-spin complexes. Additionally, the geometry of the complex can also play a role, as different geometries (e.g., octahedral, tetrahedral) can lead to varying degrees of d-orbital splitting and, consequently, influence the spin state preference. By carefully selecting the ligands and controlling the complex geometry, chemists can tune the spin state of coordination compounds to achieve desired magnetic and spectroscopic properties.
A model that describes the electronic structure of coordination complexes, focusing on the splitting of the metal d-orbitals due to the presence of ligands.
Pairing Energy: The energy required to pair two electrons in the same orbital, which opposes the formation of high-spin complexes.