Coordination compounds are formed by the combination of transition metals with anions or neutral molecules through electron sharing. Alfred Werner, a Swiss chemist, proposed the first systematic theory of coordination compounds. He introduced the concepts of primary and secondary valences to explain their properties. Key points include:
Coordination compounds are crucial in various fields, including biological systems, industrial processes, and analytical chemistry. Examples include chlorophyll, hemoglobin, and vitamin B12, which are coordination compounds of magnesium, iron, and cobalt, respectively.
A coordination entity consists of a central metal atom or ion bonded to a fixed number of ions or molecules. For example, [CoCl3(NH3)3] is a coordination entity where cobalt is surrounded by three ammonia molecules and three chloride ions.
Ligands are ions or molecules that bind to the central atom/ion in a coordination entity. They can be:
Mnemonic:
To remember ligand types, think "Uni-Di-Poly": Unidentate (one), Didentate (two), Polydentate (many).
The coordination number is the number of ligand donor atoms directly bonded to the central atom/ion. For instance, in [PtCl6]2–, the coordination number of Pt is 6.
Common Misconception:
Coordination number is not the total number of ligands but the number of donor atoms bound to the central metal ion.
NEET Tip:
Practice writing and naming coordination compounds to avoid losing marks on nomenclature-related questions.
Occurs in complexes with different spatial arrangements of ligands. Common in square planar and octahedral complexes.
Occurs in chiral complexes that have non-superimposable mirror images, known as enantiomers.
Real-life Application:
Optical isomers are significant in pharmaceuticals where different isomers can have different biological activities.
VBT explains the bonding in coordination compounds using hybridization. It accounts for the geometry and magnetic properties of complexes.
CFT explains the color, magnetic properties, and stability of coordination compounds based on the electrostatic interactions between the central metal ion and ligands. It introduces the concept of crystal field splitting, where d-orbitals split into different energy levels.
Did You Know?
The color of coordination compounds arises from the d-d electronic transitions, which are influenced by the crystal field splitting.
Link to Biology:
Coordination compounds play a vital role in biological systems. For example, the structure and function of hemoglobin and chlorophyll are directly related to their coordination chemistry.
Describe Werner’s theory of coordination compounds. Answer: Werner’s theory explains the formation and properties of coordination compounds using the concepts of primary and secondary valences. Primary valences are ionizable and satisfied by negative ions, while secondary valences are non-ionizable and satisfied by neutral molecules or negative ions.
Write the formula and name for the following coordination compound: Tetraamminediaquacobalt(III) chloride. Answer: Formula: [Co(NH3)4(H2O)2]Cl3 Name: Tetraamminediaquacobalt(III) chloride.
Explain the difference between geometrical and optical isomerism with examples. Answer: Geometrical isomerism arises from different spatial arrangements of ligands (e.g., cis- and trans-[Pt(NH3)2Cl2]). Optical isomerism occurs in chiral complexes that have non-superimposable mirror images (e.g., [Co(en)3]3+).
Using Crystal Field Theory, explain why [Ni(CN)4]2– is diamagnetic while [NiCl4]2– is paramagnetic. Answer: In [Ni(CN)4]2–, the strong field ligand CN– causes pairing of electrons, leading to a diamagnetic complex. In [NiCl4]2–, the weak field ligand Cl– does not cause pairing, resulting in a paramagnetic complex.
List three applications of coordination compounds in industry. Answer:
Did You Know?
The blue color of copper sulfate solution is due to the [Cu(H2O)4]2+ complex, while the colorless solution of anhydrous copper sulfate indicates the absence of coordinated water molecules.
What is the coordination number and oxidation state of the central metal ion in [Cr(NH3)3Cl3]? Answer: Coordination number: 6 Oxidation state: +3