Question

How many chelate rings are present in: \((a)\left[\operatorname{Ru}(\mathrm{ox})_{3}\right]^{3-}\); (b) \(\left[\mathrm{Fe}(\text { trien) }]^{3+}\right.\) (trien is triethylenetetramine); (c) \(\left[\mathrm{Cu}(\mathrm{dien})_{2}\right]^{2+}\) ?

Short answer

Complex (a) has 6 chelate rings, complex (b) has 4 chelate rings, and complex (c) has 4 chelate rings.

Step-by-step solution

Identify Chelating Ligands

Chelating ligands are those that can form more than one bond with the central metal ion, creating a ring structure. The ligands in question are oxalate (ox), which can form two bonds, triethylenetetramine (trien), which can form four bonds, and diethylenetriamine (dien), which can form three bonds.

Determine the Number of Chelating Ligands and Their Dentate Nature

In complex (a), oxalate (ox) is bidentate and there are three oxalate ligands. In (b), trien is tetradentate with only one trien ligand. In (c), dien is tridentate and two dien ligands are present.

Calculate Chelate Rings in Each Complex

In complex (a), each oxalate forms two rings so 3 oxalates give 3*2=6 rings. In complex (b), one trien forms four rings. In complex (c), each dien forms two rings and with two dien ligands, gives 2*2=4 rings.

Key concepts

Chelating Ligands

Chelating ligands are a crucial concept in the study of coordination chemistry. These are molecules that can form multiple bonds to a single central metal ion. Imagine a lobster's claw that can grasp something from two points; similarly, a chelating ligand grips the metal atom at two or more places, creating a more stable and robust structure called a 'chelate ring'.

These ligands are like the power players in molecular binding because they use their multiple 'teeth' or 'donor atoms' to form rings with the metal ion at the center. This multi-toothed approach is not only fascinating but also incredibly important because it significantly affects the stability and reactivity of metal complexes. In essence, chelating ligands could be thought of as the molecular equivalent of a multi-point seatbelt that provides enhanced protection and stability for the metal ion passenger within its embrace.

For instance, ethylenediamine (en), oxalate (ox), and diethylenetriamine (dien) are common examples of chelating ligands you might come across. These play a big role in creating complex structures that are essential in various applications, from medicinal chemistry to industrial catalysis.

Bidentate Ligand

A bidentate ligand is a type of chelating ligand with exactly two donor atoms available to bond to a central metal ion. Think of them as having two arms, with each arm reaching out to grab the metal ion. When both arms are attached, they form a ring structure including the metal at the center. This formation greatly enhances the stability of the resulting complex.

It's like a dancer holding firmly onto their partner with both hands during a performance, ensuring that they move together flawlessly, without falling apart. The term 'bidentate' itself comes from the Latin bi-, meaning 'two', and dentate, meaning 'teeth'. So, a bidentate ligand is essentially a molecule with two 'teeth' that can bite onto the metal ion.

An example that features prominently in coordination chemistry is ethylenediamine (en), but in our original exercise, oxalate (ox) is asked about and it's also a prime example of a bidentate ligand because it binds through two oxygen atoms. The ability of bidentate ligands to form stable chelate rings makes them especially valuable in the realm of chemistry.

Coordination Chemistry

Diving into the world of coordination chemistry is like exploring the heart of molecular relationships. It's the branch of chemistry that studies the way in which 'central' metal ions come together with surrounding molecules or ions - called 'ligands'. This is not a fleeting relationship; instead, the ligands coordinate, or bind, to the metal ion, creating complex but incredibly well-organized structures known as coordination compounds or complexes.

The beauty of this process lies in the intricacies of the metal-ligand bond. Think of the central metal ion as the star of a show, around which a cast of ligands gathers, contributing their unique characteristics to the overall performance. The coordination number of a metal ion - that is, the number of ligand 'hands' holding onto it - along with the type of ligands involved, dictate the function and properties of the entire ensemble.

For example, hemoglobin is a biological coordination complex where an iron ion (Fe) is held in place by surrounding nitrogen atoms from a heme group. Coordination chemistry is not just an elegant theoretical concept; it has practical implications in many fields, including medicine, environmental science, and materials engineering, where understanding and manipulating these molecular ballets can lead to significant advancements.