Coordination Complexes : Videos & Practice Problems

Coordination complexes are ionic compounds consisting of a complex ion and a counter ion, ensuring overall neutrality. The complex ion, indicated by brackets, can be either a cation or an anion, while the counter ion balances the charge. For example, in a complex like [Ni(NH₃)₄]³⁺Cl^-, [Ni(NH₃)₄] is the complex ion, and Cl^- is the counter ion. Understanding the charge and structure of these ions is crucial for grasping the properties of coordination compounds.

Coordination Complexes I and II

Coordination complexes are specialized ionic compounds that consist of a complex ion and a counter ion, which together maintain electrical neutrality. In the nomenclature of ionic compounds, the cation is listed first, followed by the anion. In a coordination complex, the complex ion acts as the cation and is enclosed in brackets, indicating its distinct identity within the compound.

For example, consider a coordination complex where the complex ion is represented as [Ni(NH₃)₄]. The brackets signify that this is the complex ion, which carries a charge of +3, as indicated by the overall charge of the complex. The counter ion, in this case, is Cl^-, which is derived from group 7A and has a charge of -1. The charge balance is achieved by combining the +3 charge of the complex ion with the -1 charge of the counter ion, resulting in a neutral compound.

In another example, if the complex ion is an anion, it will be written second in the formula. For instance, if we have a complex ion represented as [Co(NH₃)₆]^2-, the lithium counter ion (Li⁺) from group 1A balances the -2 charge of the complex ion. Here, the brackets again denote the complex ion, which is crucial for identifying its role in the coordination complex.

In summary, a coordination complex consists of a complex ion, which can be either a cation or an anion, and a counter ion that has an opposing charge. This combination results in a neutral ionic compound, showcasing the unique properties of coordination chemistry.

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 are coordination complexes?

Coordination complexes, also known as coordination compounds, are molecules that consist of a central metal atom or ion (usually a transition metal) surrounded by a number of surrounding molecules or ions, known as ligands. These ligands can be anions or neutral molecules that donate pairs of electrons to the metal atom or ion, forming coordinate covalent bonds. The central metal atom or ion with its attached ligands is referred to as the coordination sphere, and it can have various geometries such as octahedral, tetrahedral, or square planar, depending on the number and arrangement of the ligands.

The coordination number of a complex is the number of ligand donor atoms that are bonded to the central metal ion. Coordination complexes play a vital role in various areas of chemistry and biochemistry, including catalysis, the functioning of enzymes, and the transport of ions within cells. They are also significant in industrial applications such as the purification of metals and in materials science.

How can coordination complexes be drawn?

Coordination complexes can be drawn by following a systematic approach:

1. Identify the Central Metal Ion: Start by writing the symbol of the central metal ion in the center of your drawing.
2. Determine the Oxidation State: Indicate the oxidation state of the metal ion, which is often given in the complex's formula or can be deduced from it.
3. Add the Ligands: Draw lines (bonds) from the central metal ion to represent the ligands. Ligands are atoms, ions, or molecules that donate a pair of electrons to the metal ion. If the ligand is polydentate (binds through multiple points), make sure to represent all the binding sites.
4. Indicate Geometry: The geometry of the complex depends on the number of ligands and the electronic configuration of the metal ion. Common geometries include linear, square planar, tetrahedral, square pyramidal, trigonal bipyramidal, and octahedral.
5. Show Charge: If the coordination complex has an overall charge, indicate this outside the brackets that enclose the complex.
6. Add Counter-Ions (if necessary): If the complex is part of an ionic compound, draw the counter-ions outside the brackets.
7. Include Lone Pairs and Multiple Bonds (if necessary): If the ligands have lone pairs or multiple bonds, include these in your drawing to accurately represent the structure.

How do you name coordination complexes?

Naming coordination complexes involves a series of rules set by the International Union of Pure and Applied Chemistry (IUPAC). Here's a simplified guide to help you name them correctly:

1. Name the Ligands First: Start with the ligands in alphabetical order. Use prefixes like di-, tri-, tetra-, etc., to indicate the number of identical ligands. Anionic ligands end in '-o' (e.g. chloride becomes chlorido), neutral ligands are often named as the molecule (e.g. water is aqua or aquo), except for a few like ammonia, which is called ammine.
2. Name the Metal: After the ligands, name the central metal atom/ion. If the complex is an anion, the metal ends with the suffix '-ate' (e.g. iron becomes ferrate).
3. Oxidation State: Indicate the oxidation state of the metal in Roman numerals in parentheses immediately following the metal's name.
4. Cation Before Anion: If the complex is part of a larger ionic compound, name the cation before the anion.
5. Polyatomic Complexes: For polyatomic complexes, use the suffixes '-ite' or '-ate' for less or more oxygen atoms, respectively, and prefixes like 'hypo-' and 'per-'.

How can coordination complexes be drawn in ChemDraw?

To draw coordination complexes in ChemDraw, follow these steps:

1. Open ChemDraw and select the 'Bond Tool' to draw the central metal atom with its associated ligands. You can use the 'Text Tool' to add the appropriate atomic symbols.
2. For ligands that are simple ions or molecules, use the 'Bond Tool' to connect them directly to the metal center. For polydentate ligands (ligands that attach at multiple points), ensure you draw the connecting atoms and the points of attachment to the metal.
3. To represent coordinate bonds (dative covalent bonds), where both electrons are donated by the ligand, use the 'Bond Tool' to draw an arrow from the donor atom to the metal. The arrowhead should point towards the metal center.
4. If you need to show geometric isomers (like cis or trans), use the 'Structure Perspective Tool' to adjust the angles between ligands or to bring ligands to the front or back of the plane.
5. For charge notations, use the 'Text Tool' to add the charge near the metal center or the entire complex as needed.
6. Finally, use the 'Clean Up Structure' feature to automatically adjust the drawing for aesthetic presentation.

Remember to refer to IUPAC naming conventions for the correct representation of coordination complexes in your drawings.