Chapter 21: Problem 64
The complex ion NiCl \(_{4}^{2-}\) has two unpaired electrons, whereas \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\) is diamagnetic. Propose structures for these two complex ions.
Short Answer
Expert verified
The structures of NiCl鈧劼测伝 and Ni(CN)鈧劼测伝 are both tetrahedral with Ni虏鈦 as the central atom. NiCl鈧劼测伝 has two unpaired electrons due to weak field ligand Cl鈦, while Ni(CN)鈧劼测伝 is diamagnetic with no unpaired electrons due to strong field ligand CN鈦. The d-electrons fill the orbitals differently in each complex ion, resulting in the observed differences in magnetism.
Step by step solution
01
Determine the d-electron configuration of Ni虏鈦
First, we need to find out the electron configuration of the central metal ion, Ni虏鈦. The Nickel (Ni) atom has 28 electrons, but since it loses 2 electrons to form Ni虏鈦, it now has 26 electrons. The electron configuration for Nickel (Ni) is [Ar] 3d鈦4s虏, therefore for Ni虏鈦 it becomes [Ar] 3d鈦 (since 2 electrons are removed from 4s shell).
02
Identify the Ligand Field Chemistry of Cl鈦 and CN鈦
The two ligands, Cl鈦 and CN鈦, differ in their ligand field strength: Cl鈦 is a weak field ligand and CN鈦 is a strong field ligand. Weak field ligands tend to not create a large energy gap between the d-orbitals, while strong field ligands create a large split between the d-orbitals.
03
Construct the Crystal Field Splitting Diagram of NiCl鈧劼测伝
Since Cl鈦 is a weak field ligand, the crystal field splitting diagram for a tetrahedral complex would look like this:
1. There would be no splitting in the 4s and 4p orbitals.
2. The d-orbitals will be split into a lower energy set (dxy, dxz, and dyz) containing three orbitals and a higher energy set (dz虏 and dx虏-y虏) with two orbitals.
3. The d-electrons from Ni虏鈦 ([Ar] 3d鈦) will fill up the orbitals according to Hund's rule (first fill the lower energy orbitals, then the higher energy orbitals with a maximum of two unpaired electrons).
In this scenario, the Ni虏鈦 ion has 8 d-electrons: 6 will fill the lower energy orbitals, and 2 will fill the higher energy orbitals, leaving 2 unpaired electrons. This aligns with the fact that NiCl鈧劼测伝 has 2 unpaired electrons.
04
Construct the Crystal Field Splitting Diagram of Ni(CN)鈧劼测伝
Since CN鈦 is a strong field ligand, the crystal field splitting diagram for a tetrahedral complex would look like this:
1. There would be no splitting in the 4s and 4p orbitals.
2. The d-orbitals will be split into a lower energy set (dxy, dxz, and dyz) containing three orbitals and a higher energy set (dz虏 and dx虏-y虏) with two orbitals.
3. The d-electrons from Ni虏鈦 ([Ar] 3d鈦) will fill the orbitals according to the Aufbau principle (starting from the lowest available energy orbitals).
In this scenario, the Ni虏鈦 ion has 8 d-electrons: all 8 electrons will fill the lower energy orbitals, leaving no unpaired electrons. This aligns with the fact that Ni(CN)鈧劼测伝 is diamagnetic.
05
Propose Structures
Now that we know how the d-electrons are filled in each complex ion, we can propose structures for both.
NiCl鈧劼测伝:
- Central atom: Ni虏鈦
- Ligands: 4 Cl鈦 ions
- Geometry: Tetrahedral
- Bonding: Ni虏鈦 will form covalent bonds with the Cl鈦 ions through the filled d-orbitals.
Ni(CN)鈧劼测伝:
- Central atom: Ni虏鈦
- Ligands: 4 CN鈦 ions
- Geometry: Tetrahedral
- Bonding: Ni虏鈦 will form covalent bonds with the CN鈦 ions through the filled d-orbitals.
Thus, the structures of NiCl鈧劼测伝 and Ni(CN)鈧劼测伝 are both tetrahedral, with the difference being the ligands and how the d-electrons are filled in each case. NiCl鈧劼测伝 has two unpaired electrons, while Ni(CN)鈧劼测伝 is diamagnetic with no unpaired electrons.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Ligand Field Strength
Ligand field strength is a crucial concept in understanding how different ligands influence the electronic arrangements in complex ions. Ligands can be classified as either weak-field or strong-field based on their ability to split the d-orbitals of the central metal ion.
**Weak-field Ligands:**
**Weak-field Ligands:**
- Examples include halides like Cl鈦.
- They create a small energy difference between the d-orbitals.
- Because of this smaller energy gap, the pairing energy of electrons remains relatively high.
- Examples include CN鈦 and CO.
- They induce a large separation between the higher and lower sets of d-orbitals.
- This larger splitting overcomes the electron pairing energy.
Complex Ions
Complex ions consist of a central metal ion bonded to surrounding molecules or ions called ligands. The formation of complex ions involves the overlap of atomic orbitals from both the metal and ligands, creating covalent bonds.
In a complex such as NiCl鈧劼测伝:
In a complex such as NiCl鈧劼测伝:
- The central ion is Ni虏鈦, which coordinates with four chloride ions.
- This results in a tetrahedral shape due to the spatial arrangement of ligands.
- Nickel again acts as the central ion, surrounded by four cyanide ions.
- This also forms a tetrahedral configuration.
Electron Configuration
Electron configuration in transition metal complexes is significantly impacted by ligand field strength. Understanding electron configuration helps predict properties such as color and magnetism.
For Ni虏鈦 (28 electrons as Ni, but 26 as Ni虏鈦):
For Ni虏鈦 (28 electrons as Ni, but 26 as Ni虏鈦):
- Initial configuration as Ni is [Ar] 3d鈦4s虏.
- As Ni虏鈦, it loses 2 electrons resulting in [Ar] 3d鈦.
- With Cl鈦 as a weak ligand, the d-orbitals fill giving rise to unpaired electrons.
- With CN鈦 as a strong ligand, electrons pair fully in lower energy d-orbitals.
Magnetic Properties
Magnetic properties in complexes are determined by the spin states of electron configurations. The number of unpaired electrons plays a key role in defining whether a complex is paramagnetic or diamagnetic.
**Paramagnetic Complexes:**
**Paramagnetic Complexes:**
- Contain one or more unpaired electrons.
- Show attraction to magnetic fields.
- Example: NiCl鈧劼测伝, due to its two unpaired electrons.
- All electrons are paired.
- Show a weak repulsion from magnetic fields.
- Example: Ni(CN)鈧劼测伝, as no unpaired electrons are present.