Coordination Complexes : Videos & Practice Problems

Coordination Complexes Example

To determine the formula for a coordination complex, we start by identifying the complex ion and the counter ion. In this case, we have a complex cation and a counter anion. When combining these ions, we treat them as charged entities. If the charges of the ions differ, we use a crisscross method to balance them. This means that the magnitude of the charge of one ion becomes the subscript of the other ion.

For example, if the complex ion has a charge of +2 and the counter ion has a charge of -1, we would crisscross the charges. The +2 charge from the complex ion becomes the subscript for the anion, while the -1 charge from the anion becomes the subscript for the cation. Thus, the formula is constructed by placing the complex cation first, followed by the anion.

In this scenario, the resulting formula for the coordination complex would be represented as follows: if the complex ion is denoted as [Complex] and the anion is F₂, the final formula would be [Complex]F₂. This notation indicates that the complex ion is present in a 1:2 ratio with the anion, reflecting the balance of charges in the coordination complex.

Correctly label all the components of the coordination complex: [Mn(NH₃)₄Cl₂]Br.

• A. Mn is the metal cation, NH₃ and Br are the ligands, and Cl is the counterion.
• B. Mn is the metal anion, Cl and Br are the ligands, and NH₃ is the counterion.
• C. Mn is the metal cation, NH₃ and Cl are the ligands, and Br is the counterion.
• D. Mn is the metal atom, NH₃ and Cl are the ligands, and Br is the counterion.
• E. Mn is the metal atom, NH₃ and Br are the ligands, and Cl is the counterion.

Answer: (C)

Which of the following statements is/are true about the coordination complex of: Na₂[SnCl₆].
I) The coordination complex contains 8 ligands.
II) The metal cation of the complex ion has an overall charge of +6.
III) The sodium ion represents the counterion.
IV) The complex ion has an overall charge of –2.

• A. I only
• B. II and III
• C. I, III, and IV
• D. III and IV
• E. IV only

Answer: (D)

Here's what students ask on this topic:

What is a coordination complex and how is it structured?

A coordination complex is an ionic compound composed of a complex ion and a counter ion that together maintain electrical neutrality. The complex ion is a charged species, either a cation or an anion, and is always written within brackets. The counter ion has the opposite charge to balance the overall charge of the compound. For example, in the coordination complex ${[}_{\mathrm{Ni}}{(}_{\mathrm{NH}}{4}_{]}{3+}^{}$Cl^-, the complex ion is $[Ni(NH\_3)\_4]^\{3+\}$ and the counter ion is Cl^-. The complex ion contains a central metal ion bonded to ligands, while the counter ion balances the charge to form a neutral compound.

How do you identify the complex ion and counter ion in a coordination complex?

In a coordination complex, the complex ion is always the portion enclosed in brackets. It can be either positively or negatively charged. The counter ion is the ion outside the brackets that balances the charge of the complex ion to maintain overall neutrality. For example, in $[Ni(NH\_3)\_4]^\{3+\}Cl\_3^\{-\}$, the complex ion is $[Ni(NH\_3)\_4]^\{3+\}$ and the counter ion is Cl^-. The charge on the complex ion determines the number and charge of the counter ions needed. Identifying the complex ion and counter ion is essential for understanding the compound's formula and properties.

Why are complex ions written in brackets in coordination complexes?

Complex ions are written in brackets to clearly distinguish them from the counter ions in coordination complexes. The brackets indicate that the species inside is a single charged entity composed of a central metal ion bonded to ligands. This notation helps to identify the complex ion as a unit with a specific charge, separate from the counter ion that balances the overall charge. For example, in $[Ni(NH\_3)\_4]^\{3+\}Cl\_3^\{-\}$, the brackets around $Ni(NH\_3)\_4$ show it is the complex ion, while Cl^- outside the brackets is the counter ion.

How do you determine the charge on a complex ion in a coordination compound?

The charge on a complex ion is determined by summing the charges of the central metal ion and its ligands. Ligands can be neutral (like NH₃) or charged (like Cl^-). For example, in $[Ni(NH\_3)\_4]^\{3+\}$, nickel has a charge of +3, and each NH₃ ligand is neutral, so the overall charge of the complex ion is +3. The charge on the complex ion dictates the number and charge of counter ions needed to balance the compound. Understanding this helps in writing correct formulas for coordination complexes.

What role do counter ions play in coordination complexes?

Counter ions balance the charge of the complex ion in coordination complexes to ensure the overall compound is electrically neutral. If the complex ion is positively charged, the counter ion will be negatively charged, and vice versa. For example, in $[Ni(NH\_3)\_4]^\{3+\}Cl\_3^\{-\}$, the complex ion has a +3 charge, so three Cl^- counter ions are needed to balance the charge. Counter ions do not coordinate directly to the metal center but are essential for the stability and neutrality of the compound.