Problem 38 - Chemistry: The Central Science in SI Units, Global Edition

Question

Write names for the following coordination compounds: (a) \(\mathrm{Na}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NO}\right]\) (b) \(\left[\mathrm{CoO}\left(\mathrm{NH}_{3}\right)_{5}\right] \mathrm{Br}\) (c) \(\mathrm{Na}_{2}\left[\mathrm{NiBr}_{4}\right]\) (d) \(\left[\mathrm{Rh}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]\left[\mathrm{Ag}(\mathrm{CN})_{2}\right]_{3}\)

Step-by-Step Solution

Answer

The names for the coordination compounds are: (a) Pentaamminecyanidonitrosyliron(III) (b) Pentaammineoxocobalt(III) bromide (c) Tetrabromidonickel(II) sodium (d) Hexaaquarhodium(III) tris(dicyanoargentate(I))

Step 1: (a) Naming Na3[Fe(CN)5NO]

First, identify the metal and its oxidation state. In this compound, the metal is iron (Fe). The ligands include five cyanides (CN-) and one nitrosyl (NO). The total charge of the coordination complex is -3, as there are three sodium ions (Na+) in the compound. Iron's oxidation state is +3, which balances the charge. The name for the coordination compound is then: Pentaamminecyanidonitrosyliron(III)

Step 2: (b) Naming [CoO(NH3)5]Br

Identify the metal and its oxidation state. In this compound, the metal is cobalt (Co). The ligands include one oxide (O2-) and five ammonia (NH3) molecules. The total charge of the coordination complex is +1, as there is one bromide ion (Br-) in the compound. Cobalt's oxidation state is +3, which balances the charge. The name for the coordination compound is: Pentaammineoxocobalt(III) bromide

Step 3: (c) Naming Na2[NiBr4]

Identify the metal and its oxidation state. In this compound, the metal is nickel (Ni). The ligands include four bromides (Br-). The total charge of the coordination complex is -2, as there are two sodium ions (Na+) in the compound. Nickel's oxidation state is +2, which balances the charge. The name for the coordination compound is: Tetrabromidonickel(II) sodium

Step 4: (d) Naming [Rh(H2O)6][Ag(CN)2]3

In this compound, there are two coordination complexes: [Rh(H2O)6] and [Ag(CN)2]. Identify the metal and its oxidation state in [Rh(H2O)6]. The metal is rhodium (Rh), and the ligands include six water (H2O) molecules. The charge of this complex is +3, which gives Rh an oxidation state of +3. The name for this coordination complex is: Hexaaquarhodium(III) Identify the metal and its oxidation state in [Ag(CN)2]. The metal is silver (Ag), and the ligands include two cyanides (CN-). The charge of this complex is -1, which gives Ag an oxidation state of +1. The name for this coordination complex is: Dicyanoargentate(I) Putting both names together, the name for the full coordination compound is: Hexaaquarhodium(III) tris(dicyanoargentate(I))

Key Concepts

Ligand Naming

In coordination chemistry, ligands play a crucial role, working as donor molecules that attach to the central metal atom or ion. Naming these ligands correctly is important to accurately describe the coordination compound. Ligands can be anions, neutral molecules, or even cations. To ensure clarity, different types of ligands follow specific naming rules.

• Anionic ligands: These often end in '-o'. For example, a chloride ion (Cl^-) is named chloro, and a cyanide ion (CN^-) is cyano.
• Neutral ligands: These are usually called by their common names, such as "aqua" for water (H₂O) and "ammine" for ammonia (NH₃).
• Cationic ligands: These are rare but follow similar rules to anionic and neutral ligands.

When naming coordination compounds, list the ligands alphabetically before naming the central metal. Prefixes like 'di-', 'tri-', 'tetra-', etc., are used to indicate the number of each type of ligand present. This nomenclature helps convey the structure and composition of the complex clearly.

Oxidation State Determination

Determining the oxidation state of the central metal atom or ion in a coordination compound is a vital aspect. The oxidation state provides key information about the electronic state and overall charge balance within the coordination compound.

In step-by-step terms:

• Summing Up Ligand Charges: Begin by adding up the charges provided by each ligand. For instance, the cyanides (CN^-) each contribute a charge of -1.
• Determining the Overall Charge: Next, look at the overall charge of the coordination complex bracketed entity. For example, a coordination complex with a charge of -3 signifies that the sum of all components must equal -3.
• Calculating Metal Charge: Using the known charge on the ligands and the overall charge of the complex, solve for the oxidation state of the metal. For Na₃[Fe(CN)₅NO], with a complex charge of -3, and knowing each CN^- is -1 and NO is neutral, iron's oxidation state calculates to +3.

These calculations balance the charges within the complex and determine the oxidation number that rounds out the metal's electron configuration.

Complex Ion Formation

Complex ion formation occurs when ligands attach to a central metal atom or ion, creating a structured complex that behaves as a single charged entity in solution. This formation is key to the unique properties and functionality of coordination compounds.

• Central Metal Atom: This is usually a transition metal that can accept electrons from the ligands because of its availability of d-orbitals.
• Ligands: These molecules or ions donate at least one pair of electrons to form a coordinate covalent bond with the metal. Their arrangement around the metal atom creates the geometry of the complex, such as octahedral, tetrahedral, or square planar.
• Coordination Number: This signifies the number of ligand donor atoms bonded to the central metal atom. For example, in [Rh(H₂O)₆][Ag(CN)₂]₃, rhodium has a coordination number of 6, indicating an octahedral arrangement.

The resultant complexes exhibit unique chemical and physical properties, such as color, magnetism, and reactivity, driven by the nature of the ligand and the metal's electron configuration. Understanding the intricacies of complex ion formation provides insight into the behavior and application of these compounds in areas such as catalysis, medicine, and material science.