REMOVAL REVIEW (Part 3) Flashcards
How does CFT explain the magnetic properties of [Fe(CN)6]4- and [Fe(CN)6]3-?
Crystal Field Theory (CFT) explains magnetic properties by considering how ligands surrounding a metal ion affect the energy levels of its d-orbitals.
The strength of the ligand field determines the energy splitting of d-orbitals, which in turn dictates the electron pairing and ultimately the magnetic properties of the complex.
[Fe(CN)6]4- which has a Fe(II) central metal ion. Its electron configuration is [Ar] 3d6. CN- is a strong-field ligand. This means it causes a large splitting of the d-orbitals of the Fe(II) ion. Since all of its electrons are paired, it is diamagnetic.
[Fe(CN)6]3- has a Fe(III) central metal ion. Its electron configuration is [Ar] 3d5. CN- as a strong-field ligand, electrons will preferentially fill the t2g orbitals before pairing up. Five electrons will occupy the d-orbitals, with one unpaired electron remaining in the t2g set. Since it has 1 unpaired electron, it is paramagnetic.
Predict the geometry of [Ni(CN)4]2- and explain how Ligand Field Theory (LFT) supports this prediction.
Ligand Field Theory (LFT) is a model that describes the bonding, orbital arrangement, and other characteristics of coordination complexes. It builds upon Crystal Field Theory (CFT) by incorporating covalent interactions between the metal and ligands. LFT can help predict the geometry of a coordination complex by considering how the ligand field affects the energy levels of the metal’s d-orbitals.
[Ni(CN)4]2- has a square planar geometry. It is diamagnetic and its hybridization is dsp2. CN- is a strong-field ligand: Creates a large crystal field splitting.
In a square planar geometry, the d-orbitals split into three lower energy levels and two higher energy levels.
The strength of the ligand field significantly influences the splitting of d-orbitals and, consequently, the preferred geometry of the complex.
Explain the importance of the spectrochemical series in predicting the electronic configurations and magnetic properties of coordination compounds.
Electron Configuration
The spectrochemical series helps predict whether a complex will adopt a high-spin or low-spin configuration, particularly for d⁴ to d⁷ electron configurations in octahedral complexes.
Strong-field ligands: Favor electron pairing in the lower energy d-orbitals before occupying higher energy orbitals (low-spin complexes). This often leads to fewer unpaired electrons and diamagnetism.
Weak-field ligands: Favor maximizing the number of unpaired electrons in the d-orbitals (high-spin complexes), resulting in paramagnetism.
Magnetic properties
The presence of unpaired electrons makes a complex paramagnetic (attracted to a magnetic field). Complexes with all electrons paired are diamagnetic (repelled by a magnetic field).
Explain the role of ligands in altering the electronic configuration and overall stability of a coordination complex. Use the example of [Fe(CN)6]4-.
Ligands play a crucial role in altering the electronic configuration and overall stability of a coordination complex.
Ligand Field Strength: Ligands differ in their ability to split the d-orbitals of the central metal ion. Strong-field ligands (like CN-) cause a large energy gap between the d-orbitals, forcing electrons to pair up in the lower energy levels (low-spin configuration). Weak-field ligands result in a smaller energy gap and favor maximizing the number of unpaired electrons (high-spin configuration).
[Fe(CN)6]4- Example: In this complex, Fe(II) has six d-electrons. CN- is a strong-field ligand. The large ligand field splitting forces all six electrons to pair up in the lower energy d-orbitals, resulting in a diamagnetic (no unpaired electrons) low-spin configuration.
Compare and contrast CFT and Ligand Field Theory (LFT) in explaining the bonding in coordination compounds.
Crystal Field Theory (CFT) sees ligands as point charges with electrostatic interactions. Thus, while both are used to explain bonding in coordination complexes, they approach the interaction differently - CFT uses an electrostatic model, while LFT uses a model based on molecular orbitals.
Crystal field theory is an electrostatic model which predicts that the d orbitals in a metal complex are not degenerate. The pattern of splitting of the d orbitals depends on the crystal field, this being determined by the arrangement and type of ligands.
Ligand field theory is an extension of crystal field theory which is freely parameterized rather than taking a localized field arising from point charge ligands. Ligand field, like crystal field theory, is confined to the role of d orbitals, but unlike the crystal field model, the ligand field approach is not a purely electrostatic model. It is a freely parameterized model, and uses oct and Racah parameters which are obtained from electronic spectroscopic data.
Identify the color associated with each of the following coordination compounds: [Cu(H2O)6]2, [Cu(NH3)4]2, and [CuCl4]2-; a. deep blue/purple, b. yellow/green, and c. blue. Explain the role of the ligands in causing the observed colors.
Copper (Cu) is a transition metal with a flexible coordination sphere, meaning it can adopt many coordination geometries, and therefore have various colored complexes.
The nature of the ligand surrounding the central metal ion significantly influences the energy gap between the d-orbitals. This, in turn, determines which wavelengths of light are absorbed and, consequently, the observed color of the complex.
[Cu(H2O)6]2+ is Blue Hexaaquacopper(II) chloride.
In [Cu(H2O)6]2+, the central copper(II) ion is surrounded by six water molecules, forming an octahedral arrangement. This creates an octahedral ligand field. In this complex, water molecules act as weak-field ligands. This causes a relatively small splitting of the d-orbitals of the copper(II) ion. When the complex absorbs light in the red-orange region of the spectrum, electrons in the lower-energy d-orbitals are excited to the higher-energy d-orbitals. The transmitted light, which appears blue, is what we perceive.
[Cu(NH3)4]2+ is Deep blue/purple Tetraamminecopper(II). The central copper(II) ion is surrounded by 4 ammonia molecules, forming a square planar arrangement.
Ammonia is a stronger-field ligand compared to water. This results in a larger splitting of the d-orbitals. The complex absorbs light in the orange-yellow region, leading to a deep blue/purple color.
[CuCl4]2- is Yellow/green Tetrachlorocopper(II). The central copper(II) ion is surrounded by 4 chloride molecules, forming a tetrahedral arrangement.
Chloride ions are weaker-field ligands than water. The smaller splitting of the d-orbitals in this complex leads to the absorption of light in the violet region, resulting in a yellow/green color.
Analyze the correct naming of [Co(NH3)6]Cl3 and explain the significance of each part of the name.
Hexaamminecobalt(III) chloride. Hexaammine because it has 6 ammonia ligands. Cobalt(III) because the central metal ion is cobal and its oxidation charge is 3. Lastly, chloride because there is a Cl3 chlorine counter ion outside the coordination sphere.
Explain the difference in naming between [Pt(NH3)2Cl2] and [Pt(NH3)4]Cl2 and provide their names.
[Pt(NH3)2Cl2] is Diamminedichloroplatinum(II). It is Diammine because of its 2 ammonia ligands. Dichloro because it has 2 chlorine ligands. Platinum(II) because its central metal ion is platinum with an oxidation charge of 2.
Meanwhile [Pt(NH3)4]Cl2 is Tetraammineplatinum(II) chloride. Tetraammine because of its 4 ammonia ligands. Platinum(II) because its central metal ion is platinum with an oxidation charge of 2. Lastly, chloride because there is a Cl2 chlorine counter ion outside the coordination sphere.
Their differences are in the identity of the ligands, number of ligands, and if a counter ion exists outside the coordination sphere.
Explain the naming convention for the complex K3[Fe(C2O4)3] and determine its name.
K3[Fe(C2O4)3] is named Potassium Trioxalatoferrate(III). Potassium because it has a K3 counter ion. Then Trioxalato because of its 3 oxalate ligands. Lastly, Ferrate(III) because its central metal ion is Iron (Fe) with an oxidation charge of 3.
Explain how a coordination compound acts as a catalyst in the hydroformylation of alkenes.
A catalyst increases the rates of processes by introducing new pathways with lower Gibbs energies of activation. In hydroformylation an alkene, CO, and H2 react to form an aldehyde containing one more C atom than in the original alkene. Both cobalt and rhodium complexes are used as catalysts. Aldehydes produced by hydroformylation are normally reduced to are normally reduced to alcohols that are used as solvents and plasticizers, and in the synthesis of detergents. Coordination compounds, particularly those of transition metals like rhodium and cobalt, play a crucial role in catalyzing the hydroformylation reaction.
Coordination compounds, particularly those of transition metals like rhodium and cobalt, catalyze the hydroformylation of alkenes. These catalysts bind to the alkene, activate it, and facilitate the addition of carbon monoxide and hydrogen to form aldehydes. Key features of these catalysts include high activity, selectivity for desired products, and stability under reaction conditions. This process is crucial for the industrial production of valuable chemicals like alcohols and plastics.
Analyze the role of ligand in modifying the catalytic activity of a coordination compound in a hydrogenation reaction.
One of the most studied catalytic systems is the Rh(I) complex [ RhCl (PPh3)3 ], which is often referred to as Wilkinson’s catalyst. It involves the oxidative addition of H2 to the 16 electron complex RhCl (PPh 3 )3] (A), to form the 18 electron dihydrido complex (B)
Hydrogenation is a chemical reaction where hydrogen (H₂) is added to another compound or element, usually in the presence of a catalyst
Wilkinson’s catalyst is renowned for its ability to catalyze the hydrogenation of alkenes (compounds with a carbon-carbon double bond). This reaction adds hydrogen (H2) across the double bond, converting it into an alkane (a compound with only single bonds).
The ability of the rhodium center to coordinate with ligands, undergo changes in oxidation state, and facilitate bond-breaking and bond-forming processes is crucial for the efficient hydrogenation of alkenes.
How do coordination compounds enhance the rate of hydrolysis reactions in biochemical systems? Provide an example.
Hydrolysis is a chemical reaction in which water is used to break down a larger molecule into smaller ones.
Coordination compounds enhance the rate of hydrolysis reactions in biochemical systems by acting as Lewis acids, bringing reactants together, and activating water molecules.
For example, the zinc ion in carbonic anhydrase polarizes the CO2 molecule and activates water, facilitating the conversion of CO2 to bicarbonate.
Zinc in the active site of carbonic anhydrase coordinates with a water molecule. This coordination significantly increases the water molecule’s acidity, making it easier to lose a proton (H+). This results in the formation of a hydroxide ion (OH-) bound to the zinc.
The hydroxide ion (OH-) acts as a strong nucleophile. It attacks the carbon atom of carbon dioxide (CO2), initiating the conversion of CO2 into bicarbonate (HCO3-).
In essence, the zinc ion in carbonic anhydrase acts as a Lewis acid to polarize the CO2 molecule and activates a water molecule, facilitating the rapid interconversion between CO2 and bicarbonate.
Zinc in Carbonic Anhydrase: This enzyme catalyzes the reversible hydration of carbon dioxide to bicarbonate. The zinc ion in the enzyme’s active site plays a crucial role by:
Polarizing the C=O bond of CO2: This weakens the bond, making it more susceptible to attack by a water molecule.
Activating a water molecule: The zinc ion coordinates with a water molecule, increasing its nucleophilicity.
