Problem 50 - General Chemistry

Question

Give the IUPAC name for each of the following. a. \(\left[\mathrm{W}(\mathrm{CO})_{8}\right]\) b. \(\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}(\mathrm{en})_{2}\right]\left(\mathrm{SO}_{4}\right)_{3}\) c. \(\mathrm{K}\left[\mathrm{Mo}(\mathrm{CN})_{8}\right]\) d. \(\left[\mathrm{CrO}_{4}\right]^{2-}\)

Step-by-Step Solution

Answer

a. Octacarbonyl tungsten(0). b. Diaqua bis(ethylendiamine) cobalt(III) sulfate. c. Potassium octacyanomolybdate(III). d. Tetraoxochromate(VI).

Step 1: Identify the central metal and ligands

For each complex, first identify the central metal atom and the ligand(s) bonded to it. - a) For \( [\text{W(CO)}_8] \), tungsten (W) is the central metal and carbonyl (\(\text{CO}\)) is the ligand.- b) For \( [\text{Co(H}_2\text{O})_2(\text{en})_2]\text{(SO}_4\text{)}_3 \), cobalt (Co) is the central metal ion, with water (\(\text{H}_2\text{O}\)) and ethylenediamine (en) as ligands.- c) For \( \text{K[Mo(CN)}_8] \), molybdenum (Mo) is the central metal, and cyanide (\(\text{CN}^-\)) is the ligand.- d) For \( [\text{CrO}_4]^{2-} \), chromium (Cr) is the central metal with oxide (\(\text{O}^{2-}\)) ligands in a tetrahedral arrangement.

Step 2: Determine the oxidation state of the metal

Calculate the oxidation state of the metal by considering the charge of the complex and the charge contributed by each ligand.- a) In \( [\text{W(CO)}_8] \), the \(\text{CO}\) ligands are neutral, so W is in the zero oxidation state.- b) In \( [\text{Co(H}_2\text{O})_2(\text{en})_2]\) with \((\text{SO}_4)_{3}\), \(\text{H}_2\text{O}\) and \(\text{en}\) are neutral. The three sulfate ions imply a +6 oxidation state for Co (since each sulfate is \(-2\)).- c) In \( \text{K[Mo(CN)}_8] \), each \(\text{CN}^-\) contributes \(-1\), and with K contributing +1 and overall complex being neutral, Mo is +3.- d) In \( [\text{CrO}_4]^{2-} \), each \(\text{O}\) contributes \(-2\), so Cr must be +6.

Step 3: Apply IUPAC naming rules

Name each complex by arranging the ligand names alphabetically, followed by the metal name and its oxidation state in Roman numerals.- a) \([\text{W(CO)}_8]\) is named as octacarbonyl tungsten(0) because 'carbonyl' comes eight times, followed by 'tungsten' and its zero oxidation state.- b) \([\text{Co(H}_2\text{O})_2(\text{en})_2]\text{(SO}_4\text{)}_3 \) is cobalt(III) with ligands 'aqua' and 'ethylendiamine'; since two en groups are present, 'bis' is used: diaqua bis(ethylendiamine) cobalt(III) sulfate.- c) \( \text{K[Mo(CN)}_8] \) is potassium octacyanomolybdate(III).- d) \([\text{CrO}_4]^{2-}\) is named as tetraoxochromate(VI).

Key Concepts

Coordination Chemistry

Coordination chemistry focuses on the study of compounds that consist of a central atom or ion, usually a metal, surrounded by molecules or ions known as ligands. These ligands donate pairs of electrons to form coordinate bonds with the central atom. This type of chemical bonding is key for the formation of coordination complexes, which are found in various forms of matter, ranging from biological molecules to industrial catalysts.

• Central Metal Ion: The central part of the complex, typically a transition metal, which has empty orbitals to accept electron pairs.
• Ligands: Molecules or ions that donate a pair of electrons to the metal. They can be neutral, like H\(_2\)O, or anionic, like Cl\(^-\).

Coordination chemistry plays a crucial role in areas such as catalysis, bioinorganic chemistry, and materials science. Each complex has unique properties that arise from the combination of the central metal and its ligands, influencing reactivity, magnetism, and color.

Oxidation State Determination

Determining the oxidation state of the metal within a coordination complex is vital for understanding the electronic structure and reactivity of the compound. The oxidation state is essentially the charge that the central atom would have if all the ligands were removed along with the electron pairs shared in the bonds.To calculate the oxidation state:

• Start by knowing the charge of the entire complex.
• Identify the charge of the ligands involved. For instance, in \(\text{CN}^-\), the charge is \(-1\); for \(\text{CO}\), the charge is neutral \((0)\).
• Subtract the total charge contributed by the ligands from the overall charge of the complex to find the oxidation state of the metal.

This process is crucial for predicting the chemical behavior of the complex and aids in their IUPAC naming. Understanding the oxidation state is also pivotal when studying redox reactions and the catalytic capabilities of coordination complexes.

Transition Metal Complexes

Transition metal complexes are unique due to their ability to form multiple oxidation states and coordinate geometries. They are characterized by the d-block elements from the periodic table, which can exhibit a variety of oxidation states and can form complexes with unusual shapes. These complexes can exhibit different properties such as:

• Color: Due to d-d electronic transitions and charge transfer interactions, transition metal complexes often have vivid colors.
• Catalytic Activity: Transition metals can accelerate chemical reactions, making them invaluable as catalysts in industrial chemical processes.
• Magnetism: Depending on the arrangement of their d-electrons, they can be paramagnetic or diamagnetic.

Transition metal complexes are crucial in both biological systems, such as hemoglobin's iron complex, and industrial applications, like catalysis in the production of polymers. This versatility is largely due to the unique electronic configuration and chemistry of transition metals.