Coordination Compounds
Easy Overview
Ever wondered why chlorophyll is green or why hemoglobin carries oxygen? Both are coordination compounds. They're like molecular LEGOs — a central metal atom surrounded by other molecules or ions (ligands). This chapter explains how these complexes work.
What are coordination compounds?
A coordination compound has a central metal ion bonded to surrounding ligands. Ligands are molecules or ions that donate electron pairs. NH3 and H2O are common ligands. The number of ligands attached is the coordination number. It's like a metal king sitting on a throne with advisors (ligands) around him.
Nomenclature
Naming these compounds follows strict rules. Cation named first, anion last. Ligands come before the metal name. If the complex is an anion, the metal gets an '-ate' ending. K3[Fe(CN)6] = potassium hexacyanoferrate(III). It looks intimidating but once you break it down, it's logical.
Isomerism in coordination compounds
Two compounds with the same formula but different arrangement. Structural isomers have different connectivity. Geometrical isomers (cis-trans) have same bonds but different spatial arrangement. Optical isomers are mirror images that can't be overlapped — like your left and right hands.
Crystal Field Theory (CFT)
CFT explains why coordination compounds are colored and magnetic. The ligands create an electric field that splits the d-orbitals into different energy levels. Some d-orbitals get pushed higher, some stay lower. Electrons fill these split orbitals, and the pattern determines the color and magnetic behavior.
Applications in real life
Hemoglobin is an iron coordination compound that carries oxygen. Chlorophyll has magnesium at its center — that's why plants are green. Vitamin B12 has cobalt. Coordination compounds are also used in chemotherapy (cisplatin), water purification, and as catalysts in industry.
Key Points
- •Coordination compound = central metal + ligands
- •Coordination number = number of ligand donor atoms bonded
- •Chelate: ligand that forms a ring with the metal
- •IUPAC naming: ligands alphabetical, metal with oxidation state in roman numerals
- •CFT: ligand field splits d-orbitals into t2g and eg sets
- •Cisplatin is used in cancer treatment
- •EDTA is a hexadentate ligand — grabs metals tightly
Practice Questions
- Explain Crystal Field Theory. Draw the splitting of d-orbitals in an octahedral field.
- Write the IUPAC name of [Co(NH3)5Cl]Cl2 and K3[Fe(CN)6].
- Differentiate between geometrical and optical isomerism in coordination compounds.
- What is a chelate? Give an example.