Problem 15 - Chemistry and Chemical Reactivity

Question

Name the following ions or compounds. (a) \(\left[\mathrm{Ni}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2-}\) (c) \(\left[\mathrm{Co}(\mathrm{en})_{2}\left(\mathrm{NH}_{3}\right) \mathrm{Cl}\right]^{2+}\) (b) \(\left[\mathrm{Co}(\mathrm{en})_{2} \mathrm{Br}_{2}\right]^{+}\) (d) \(\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\)

Step-by-Step Solution

Answer

(a) Diaqua bis(oxalato)nickelate(II). (b) Dibromo bis(ethylenediamine) cobalt(III). (c) Chlorido bis(ethylenediamine) ammine cobalt(III). (d) Diamminoxalatoplatinum(II).

Step 1: Identify complex ion parts

First, identify the parts of each complex ion: the central metal atom, ligands, and any charges present.

Step 2: Name coordination compounds

For each compound, follow IUPAC naming rules for coordination complexes. List ligands in alphabetical order, specify the number with prefixes (di-, tri-, etc.), and name the metal atom. Add oxidation state of the metal if needed.

Step 3: Name part (a) - Nickel oxalate complex

For (a) \([\mathrm{Ni}(\mathrm{C}_{2} \mathrm{O}_{4})_{2}(\mathrm{H}_{2} \mathrm{O})_{2}]^{2-}\), this includes oxalate ligands (bidentate), water ligands (aqua), and nickel. The full name is "Diaqua bis(oxalato)nickelate(II)."

Step 4: Name part (b) - Cobalt ethylenediamine bromide

For (b) \([\mathrm{Co}(\mathrm{en})_{2} \mathrm{Br}_{2}]^{+}\), 'en' is shorthand for ethylenediamine (bidentate). Name as "Dibromo bis(ethylenediamine) cobalt(III)." The charge of \(+1\) is usually implicit.

Step 5: Name part (c) - Cobalt Ethylenediamine Ammonia complex

For (c) \([\mathrm{Co}(\mathrm{en})_{2}(\mathrm{NH}_{3}) \mathrm{Cl}]^{2+}\), the ligands are ethylenediamine (en), ammonia (ammine), and chloride. Name it "Chlorido bis(ethylenediamine) ammine cobalt(III)."

Step 6: Name part (d) - Platinum ammonia oxalate complex

For (d) \(\mathrm{Pt}(\mathrm{NH}_{3})_{2}(\mathrm{C}_{2} \mathrm{O}_{4})\), ammonia ligands (ammine) and oxalate interact with platinum. Name this "Diamminoxalatoplatinum(II)."

Key Concepts

IUPAC Naming Conventions

The International Union of Pure and Applied Chemistry (IUPAC) sets the standards for chemical nomenclature. When it comes to naming coordination compounds, specific rules are applied to provide a systematic name that clearly identifies the compound's structure. Here are some key points to remember:

• First, list the ligands in alphabetical order before the metal center. Ignore any prefixes like "di-" or "tri-" when determining this order.
• Prefixes indicate the number of each type of ligand present: "di-" for two, "tri-" for three, etc.
• If the ligand is an anion, its name usually ends in "-o" (e.g., chloride becomes chlorido).
• The metal atom follows the ligands in the name, and its oxidation state is indicated in Roman numerals in parentheses.

These rules ensure consistency and clarity across the scientific community when dealing with complex structures.

Ligands

Ligands are ions or molecules that donate at least one pair of electrons to the central metal atom to form a coordination complex. They are crucial in determining the properties and reactivity of these complexes. Here are some important aspects to understand about ligands:

• Nature of Ligands: Ligands can be neutral molecules (like water or ammonia) or anions (like chloride or bromide).
• Bidentate Ligands: Some ligands, such as oxalate (\( ext{C}_2 ext{O}_4^{2-}\)) or ethylenediamine ('en'), can form two bonds with the central metal, providing greater stability to the complex.
• Role in Naming: In IUPAC names, ligands are mentioned before the metal center and usually appear in their abbreviated forms if they are complex, such as 'en' for ethylenediamine.

Handling ligands correctly in names and formulas is crucial for representing a coordination complex accurately.

Oxidation State

The oxidation state of the central metal ion in a coordination compound is an important characteristic that defines the number of electrons the metal has lost, gained, or shared. This is significant because:

• Determination: To find it, consider the charge on the ligands and the overall charge of the complex. The oxidation state can often be deduced through this stoichiometric balance.
• Part of the Name: In the IUPAC system, the oxidation state of the metal is given in the name using Roman numerals in parentheses after the metal's name. For instance, cobalt in "cobalt(III)" indicates a +3 oxidation state.
• Influence on Properties: The oxidation state affects the metal’s chemical properties, including electrical charge, magnetism, and reactivity.

Therefore, accurately determining the oxidation state is essential for understanding and naming coordination compounds.

Complex Ions

Complex ions consist of a central metal ion bonded to a surrounding array of ligands. These can be either positively or negatively charged depending on the nature of the ligands and the oxidation state of the metal. Key points about complex ions include:

• Formation: Complex ions form through coordinate covalent bonds where ligands donate electron pairs to the metal ion.
• Charge Calculation: The total charge of a complex ion is the sum of the oxidation state of the metal and the charges on the ligands.
• Role in Compounds: Complex ions often form the central structure in coordination compounds, which might be surrounded by additional ions to balance their charges.
• Naming: When naming these ions as part of a coordination compound, it's crucial to account for both the metal and the ligands to understand the structure and charge distribution.

Understanding complex ions, their charge, and structure is fundamental for navigating the world of coordination chemistry.