Question

Give formulas for the following. a. Hexakis(pyridine)cobalt(III) chloride b. Pentaammineiodochromium(III) iodide c. Tris(ethylenediamine)nickel(II) bromide d. Potassium tetracyanonickelate(II) e. Tetraamminedichloroplatinum(IV) tetrachloroplatinate(II)

Short answer

The formulas of the given complex compounds are as follows: a. Hexakis(pyridine)cobalt(III) chloride: \[ [Co(C_5H_5N)_6]Cl_3 \] b. Pentaammineiodochromium(III) iodide: \[ [Cr(NH_3)_5I]I_2 \] c. Tris(ethylenediamine)nickel(II) bromide: \[ [Ni(C_2H_8N_2)_3]Br_2 \] d. Potassium tetracyanonickelate(II): \[ K_2[Ni(CN)_4] \] e. Tetraamminedichloroplatinum(IV) tetrachloroplatinate(II): \[ [Pt(NH_3)_4Cl_2][PtCl_4] \]

Step-by-step solution

Identify the metal, ligands, and their charges

The metal is cobalt with an oxidation state of +3, the ligands are pyridine (C5H5N, a neutral monodentate ligand), and the counterions are chloride.

Write the formula

Using the information above, we can write down the formula for hexakis(pyridine)cobalt(III) chloride as follows: \[ [Co(C_5H_5N)_6]Cl_3 \] b. Pentaammineiodochromium(III) iodide

Identify the metal, ligands, and their charges

The metal is chromium with an oxidation state of +3, the ligands are 5 molecules of ammonia (NH3, a neutral monodentate ligand) and 1 iodide ion (a monodentate ligand with a charge of -1), the counterions are iodide.

Write the formula

Using the information above, we can write down the formula for pentaammineiodochromium(III) iodide as follows: \[ [Cr(NH_3)_5I]I_2 \] c. Tris(ethylenediamine)nickel(II) bromide

Identify the metal, ligands, and their charges

The metal is nickel with an oxidation state of +2, the ligands are 3 molecules of ethylenediamine (C2H8N2, a neutral bidentate ligand), and the counterions are bromide.

Write the formula

Using the information above, we can write down the formula for tris(ethylenediamine)nickel(II) bromide as follows: \[ [Ni(C_2H_8N_2)_3]Br_2 \] d. Potassium tetracyanonickelate(II)

Identify the metal, ligands, and their charges

The metal is nickel with an oxidation state of +2, the ligands are 4 cyanide ions (CN-, a monodentate ligand with a charge of -1), and the counterions are potassium.

Write the formula

Using the information above, we can write down the formula for potassium tetracyanonickelate(II) as follows: \[ K_2[Ni(CN)_4] \] e. Tetraamminedichloroplatinum(IV) tetrachloroplatinate(II)

Identify the metal, ligands, and their charges for both cations and anions

There are two complex ions in this compound. For the cation: - The metal is platinum with an oxidation state of +4. - The ligands are 4 molecules of ammonia (NH3, a neutral monodentate ligand) and 2 chloride ions (Cl-, a monodentate ligand with a charge of -1). For the anion: - The metal is also platinum, but this time with an oxidation state of +2. - The ligands are 4 chloride ions (Cl-, a monodentate ligand with a charge of -1).

Write the formula

Using the information above, we can write down the formula for tetraamminedichloroplatinum(IV) tetrachloroplatinate(II) as follows: \[ [Pt(NH_3)_4Cl_2][PtCl_4] \]

Key concepts

Oxidation States

Oxidation state is a fundamental concept in coordination chemistry. It refers to the charge of the central atom when all ligands, which are molecules or ions bonded to a metal, are removed. This is essential in forming coordination compounds because it determines how many electrons the metal can accept or donate when interacting with ligands.
Many transition metals can have multiple oxidation states, which affects their ability to form various coordination compounds. For example, cobalt in `hexakis(pyridine)cobalt(III) chloride` is in the +3 oxidation state. In this context, +3 means cobalt can interact with ligands by donating three electrons.
To determine the oxidation state, one must add up the charges of all ligands and other connected ions, like chloride ions. These steps ensure that the sum balances to zero in a neutral compound. Understanding oxidation states is pivotal in writing accurate chemical formulas for coordination compounds.

Ligands

Ligands are atoms, ions, or molecules attached to the central metal atom in a coordination compound. They can be thought of as the surrounding framework that helps stabilize the metal by forming coordinate bonds, which are a special type of covalent bond.
Ligands come in various types, such as monodentate, bidentate, and polydentate, determined by how many sites on the ligand can attach to the metal. For example:

• Monodentate ligands attach through one site. Examples include ammonia (NH3) and iodide (I-).
• Bidentate ligands use two sites to attach, like ethylenediamine (C2H8N2).

Designating the nature of ligands, like in `tris(ethylenediamine)nickel(II) bromide`, directly influences the metal's coordination number, or how many bonds it forms with ligands. Hence, knowing ligand types is vital for writing precise chemical formulas.

Coordination Chemistry

Coordination chemistry refers to the study and understanding of coordination compounds. These compounds consist of a central metal atom or ion surrounded by molecules or ions known as ligands. This branch of chemistry is significant because it helps explain the behavior and properties of complex molecules.
Coordination compounds exhibit unique structural, electronic, and optical properties, fueling research in catalysis, material science, and bioinorganic chemistry. Nickel in `potassium tetracyanonickelate(II)`, serves as the center of a complex ion bonded with cyanide ligands.
Understanding coordination chemistry is essential, as it governs the formation and reactivity of diverse compounds in nature and industry. It helps in determining the stability, color, and electronic arrangement of compounds, which are crucially important in chemical reactions and applications.

Chemical Formulas

Chemical formulas in coordination compounds stand as a blueprint, describing the elements and their respective quantities within a molecule. Writing them correctly requires understanding the different components, like metals, ligands, and counterions.
To accurately construct these formulas, one must know how to balance charges between the central metal ion and surrounding ligands or counterions. The process involves:

• Identifying the charge of the metal.
• Counting the number and type of ligands.
• Including any necessary counterions to achieve charge balance.

For instance, in `tetraamminedichloroplatinum(IV) tetrachloroplatinate(II)`, proper assembly requires understanding the cations and anions separately, then combining them to maintain neutrality. Chemical formulas communicate not only the composition but also insights into the molecule’s structure and potential interactions. Properly handling these formulas is crucial for success in chemistry.