Coordination Complex

A coordination complex comprises a core atom or ion called the coordination centre, which is usually metallic, and a surrounding array of bonded molecules or ions called ligands or complexing agents. Many metal-containing compounds, particularly those containing transition metals (elements in the d-block of the Periodic Table, such as titanium), are coordination complexes. A dative bond, also known as a coordinate bond, develops when a Lewis base and a Lewis acid combine. Coordination is the word describing the donation of a Lewis base to a Lewis acid without any other bonding modifications.

Classification

Almost all metal compounds are metal complexes, commonly known as coordination compounds. All alkali and alkaline earth metals, transition metals, lanthanides, actinides, and metalloids are studied in “coordination chemistry,” which is the study of “inorganic chemistry.” As a result, most of the periodic table’s chemistry comes under coordination chemistry. Metals and metal ions are only found in condensed phases, surrounded by ligands.

Nomenclature of coordination complexes

Ligands are Lewis bases, and according to the Lewis base theory, they may transfer electrons to the central metal atom. On the other hand, metals are Lewis acids because they receive electrons. A ligand and a metal core cation makeup coordination complexes. A positive, negative, or neutral total charge is possible. Coordination compounds, for example, are complicated or include complex ions.

An anion or a neutral molecule that provides an electron pair to the complex is referred to as a ligand (NH3, H2O, Cl–). Whether a ligand is monodentate or polydentate is determined by how many ligands can be attached to a metal. 

Here are some considerations to keep in mind when naming coordination complexes:

Ligands are listed alphabetically first.

The metal’s name is the next item on the list.

The metal’s oxidation state is indicated by a Roman numeral.

Anionic Ligands (Rule 1)

Neutral Ligands (Rule 2)

Multiplicity of Ligands (Rule 3)

The Metals (Rule 4)

Formulas for coordination complexes

Formulas for coordination complexes can be written in a variety of ways.

Although chemistry generally follows nomenclature rules for naming complexes and compounds, the principles for building formulas for inorganic complexes are disputed. Different conventions have been used to determine the order of ligand names in their formula (charged vs neutral, number of each ligand, etc.). In 2005, the International Union of Pure and Applied Chemistry (IUPAC) recommended that all ligand names in formulations be given alphabetically (as in the naming convention), regardless of the charge or quantity of each ligand type.

Coordination complex importance

The coordination compounds are commonly used as catalysts, substances that change the pace of chemical reactions. For example, in the synthesis of polyethylene and polypropylene, complex metal catalysts play an important role.

Transition metals absorption and storage

In order of increasing concentration in the diet, there are three conceivable dietary levels for any necessary element: insufficient, optimum, and poisonous. An organism must be able to extract and concentrate a necessary ingredient from the environment if its concentration in the food is too low. An organism must be able to limit its intake of an essential element if the concentration in the food is too high to avoid harmful effects. Furthermore, organisms must be able to quickly turn off the absorption process if dietary levels abruptly surge and store vital nutrients for later use.

There are three steps involved in transition metal uptake.

First step: the metal is captured from the environment and converted into a form that can be absorbed by a cell. 

Second step: the metal is transported across the cell membrane into the cell. 

Third step: the element is transported to its point of utilisation within a cell or to other cells within the organism.

Metalloproteins and metalloenzymes 

Metalloproteins and metalloenzymes are metal proteins and enzymes, respectively.

A metalloprotein is a protein that contains one or more metal ions strongly linked to amino acid side chains; these are some of the most typical ligands formed by amino acids. A metalloenzyme is a metalloprotein that catalyses a chemical reaction. As a result, all metalloenzymes are metalloproteins, but not the other way around. According to recent estimations, nearly all enzymes involved in the manufacture, duplication, and repair of DNA (deoxyribonucleic acid) and RNA require at least one metal ion for action (ribonucleic acid).

Blue copper proteins 

In the 1950s, blue copper proteins were obtained from bacteria, and in the early 1960s, they were isolated from plant tissues. A high absorption band at a wavelength of about 600 nm is responsible for the bright blue colour of these proteins. Although simple Cu2+ complexes like [Cu(H2O)6]2+ and [Cu(NH3)4]2+ have a 600 nm absorption band, the strength of the absorption band is around 100 times less than that of a blue copper protein. Furthermore, the Cu2+/Cu+ couple in a blue copper protein has a reduction potential of +0.3 to +0.5 V, which is significantly higher than that of the aqueous Cu2+/Cu+ couple (+0.15 V).

Conclusion

Coordination complexes are a very important part of inorganic chemistry. Understanding the structures of the complexes, we can design new reactions that can be used for many applications.