Question

How many chelate rings are present in each of the following complexes? Assume that all the donor atoms are involved in coordination. (a) \([\mathrm{Cu}(\operatorname{trien})]^{2+}\) (b) \(\left[\mathrm{Fe}(\mathrm{ox})_{3}\right]^{3-} ;(\mathrm{c})\left[\mathrm{Ru}(\mathrm{bpy})_{3}\right]^{2+}\); (d) \(\left[\mathrm{Co}(\operatorname{dien})_{2}\right]^{3+}\) (e) \([\mathrm{K}(18-\text { crown }-6)]^{+}\)

Short answer

(a) 3 chelate rings, (b) 3 chelate rings, (c) 3 chelate rings, (d) 4 chelate rings, (e) 1 chelate ring.

Step-by-step solution

Understanding Chelate Rings

Chelate rings form when a ligand with multiple donor atoms coordinates with a metal center, creating a ring structure. Each donor atom that forms a bond with the metal contributes to a chelate ring.

Analyzing [Cu(trien)]^{2+} Complex

The trien ligand is triethylenetetramine, which contains four nitrogen donor atoms. These Nitrogens coordinate to the copper, forming three chelate rings as follows: one with N1 and N2, another with N2 and N3, and the last one with N3 and N4.

Analyzing [Fe(ox)_{3}]^{3-} Complex

The oxalate ion (ox) has two donor oxygens per ligand. Each oxalate forms one chelate ring with the metal, totaling three chelate rings in the complex, as there are three oxalate ligands.

Analyzing [Ru(bpy)_{3}]^{2+} Complex

The bpy ligand is 2,2'-bipyridine, which has two nitrogen donor atoms. Each bpy forms one 5-membered ring with Ruthenium, and since there are three bpy ligands, the complex has three chelate rings.

Analyzing [Co(dien)_{2}]^{3+} Complex

The dien ligand is diethylenetriamine, containing three nitrogen atoms. Each dien forms two chelate rings with Cobalt. With two dien ligands, this results in a total of four chelate rings.

Analyzing [K(18-crown-6)]^{+} Complex

The 18-crown-6 is a cyclic compound with six donor oxygen atoms. It forms one ring by itself when coordinating with a potassium ion, resulting in one large chelate ring.

Key concepts

Coordination Chemistry

Coordination chemistry is a fascinating branch of chemistry focused on the study of complex compounds made from a central metal atom or ion bonded to surrounding molecules or ions, known as ligands. This central atom, often a transition metal, acts as a magnet for the ligands, resulting in a structured formation called a coordination complex.
These complexes are significantly important in both biological systems and industrial applications. For instance, hemoglobin, which carries oxygen in the blood, is a coordination complex of iron. Also, coordination chemistry can help in the design of new materials and catalysts used in chemical reactions.
Coordination numbers, which represent how many ligand atoms are directly attached to the central metal, play a crucial role in determining the structure and reactivity of the coordination complex. Familiarizing yourself with these concepts will help in understanding how ligands influence the physical and chemical properties of complexes.

Ligands

Ligands are molecules or ions that bind to a central metal atom in coordination complexes. The role of ligands is quite essential as they determine the properties and stability of these complexes. Most ligands possess one or more donor atoms, which are the atoms within the ligand that carry lone pairs of electrons used to bond to the metal center.

• Monodentate Ligands: These attach to the metal atom via a single donor atom. An example is the chlorine ion, Cl^-.
• Bidentate Ligands: These have two donor atoms and can form two bonds with the central atom. Oxalate ("ox" in the step-by-step solution) is an example.
• Polydentate Ligands: Involve ligands with more than two donor atoms. They can form multiple bonds, creating ring structures referred to as chelates. Trien and dien are examples mentioned in the exercise.

Understanding the type of ligand is crucial for predicting the geometry and number of chelate rings within a complex. The more avenues a ligand has to bond, the more stable the complex becomes, often resulting in fascinating geometrical configurations.

Transition Metal Complexes

Transition metal complexes form a significant part of coordination chemistry. These complexes consist of a central transition metal atom surrounded by ligands. Transition metals, situated in the center of the periodic table, have d orbitals that can accept electrons from ligands.
The unique feature of transition metals is their ability to exist in multiple oxidation states and form colored complexes, which arise due to d-d electron transitions that absorb visible light. Such properties find applications in a wide range of fields, including catalysis, material science, and even in biological systems.
Understanding transition metal complexes involves not just recognizing the types of metal and ligands but also comprehending concepts like chelate effects, which refers to the increased stability of complexes due to ligand ring formation. The broader the understanding of these principles, the better one can grasp how chelate rings form and function in complex coordination structures.