Coordination Complexes - Online Tutor, Practice Problems & Exam Prep

• Co-ordination complexes are ionic compounds composed of a complex ion and a counter ion.
• In a co-ordination complex, the complex ion is written in brackets and it can be either an anion or a cation.
• The counter ion balances the charge of the complex ion to maintain neutrality.
• The structure of a co-ordination complex consists of the complex ion and counter ion.
• The complex ion has a charge, which determines the number of counter ions required to balance it.
• In co-ordination complex one, the complex ion is a cation, and in complex ion two, it is an anion.
• The counter ion for co-ordination complex one is Cl-, which is -1 because it belongs to Group 7A.
• The counter ion for co-ordination complex two is Li+, which is +1 because it belongs to Group 1A.
• The charge of the complex ion and the number of counter ions can be determined by crisscrossing their charges.
• Combining the complex ion and counter ion creates a neutral ionic compound, which is the co-ordination complex.

Coordination Complexes I and II

Coordination complexes are ionic compounds composed of a complex ion connected to what we call a counter ion to maintain neutrality. Now recall that an ionic compound is written as cation first, anion second. In our coordination complex one which we have here, the complex ion equals a cation and is written first.

So if we take a look here at this structure, how do we spot the portion that is the complex ion? Remember key giveaway is that complex ions are always written in brackets, so this portion in brackets represents our complex ion. It is just a portion of the coordination complex overall. So if that's the complex ion, what does the CL represent? Well, the CL here represents our counter ion CL in Group 7A, so it's -1. Again it is our counter ion and we're going to say here where did this three originate? Well it came from the complex ion, so basically on crisscross the charges.

So our complex ion was in brackets NI(NH_3)4. It is a cation here since it's written first. So it was 3 plus. So this is our complex ion. Now over here on the other side we have what we have our complex ion 2. In the complex ion 2, the complex ion is the anion and it's written second, it is the portion again that's in brackets. Here lithium represents our counter ion. Lithium is a group 1A, so it's plus one and then this two. It originates from the complex ion.

The complex ion is an anion here, so that two was part of 2 -, O. This would be our complex ion. So just remember the entire structure itself for both those are coordination complexes. The coordination complex is composed of its complex ion which has a charge and then the counter ion which has an opposing charge. Overall, combining these two gives us a neutral ionic compound, otherwise known as our coordination complex.

Coordination Complexes Example

Here it says determine the formula for the coordination complex created between. Here we have our complex ion and this is our counter ion. In order to combine them to treat them just like 2 ions, which they are. The numbers in the charges are different, so when they're different they don't cancel out, they crisscross 2 would come here and one would come here.

So we write this out. Here is our complex ion. Since it's a cation, it has to be written first and then the fluorine which is the anion is written second. The two from the charge of the complex sign came down here O. This would represent the formula for our 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.

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

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.