Pharmaceutical Analytical Chemistry - Lecture 1

Course Information

• Course title: Pharmaceutical Analytical Chemistry-l
• Course code: PA 101
• Instructor: Dr. Hany Mohamed, Ph.D.
• Course type: Pharm D-Clinical

Lecture 1: Complex Formation (Complexometric Titration)

• Topic: Complex formation titration, also known as complexometric titration
• Learning Outcomes: Students will understand complex definitions, ligand and chelating agent classifications, complex ion stability/geometry, and factors affecting complex stability.
• Interactive methods: Checkpoints, external video resources (e.g., Calcium-EDTA titration, titration of water hardness)

Complexes

• Complex definition: A species formed by the association of two or more simpler species, each capable of independent existence.
• Example: Ag+ + 2NH3 → Ag(NH3)2+

Metal Complexes

• Definition: When one of the species is a metal ion, the resulting entity is called a metal complex.
• Metal ions act as Lewis acids (electron acceptors)
• Ligands act as Lewis bases (electron donors)
• Example: Mn+ + :L → [ML]n+

Coordination Number

• Definition: The number of ligands that are bonded to each metal ion.
• Example: Ag+ + 2:NH3 → [Ag(NH3)2]+ (coordination number = 2)

Types of Ligands

• Simple (unidentate, monodentate): One site of attachment to the metal ion.
  • Examples: H₂O, :NH3, CN−, Cl−
• Chelating (multidentate): Multiple sites of attachment to the metal ion, forming a heterocyclic ring (chelating ring).
  • Classification (based on the number of attachment sites): bidentate, tridentate, tetradentate, hexadentate
  • Examples: Ethylenediamine (en), amino acids (AA), oxalate, o-phenanthroline (1,10-phenanthroline)

Chelating Ligands

• Heterocyclic ring (chelating ring): A ring formed when a chelating ligand attaches to a metal ion.
• Examples:
  • Glycine amino acid
  • Bis(glycinato)copper(II)
• Classification (based on attachment sites): bidentate, tridentate, tetradentate, hexadentate
• Product: Metal chelate

Chelating Agent

• Definition: A molecule or anion capable of forming a chelate ring with metal ions.
• Classification: bidentate, tridentate, tetradentate, hexadentate (based on the number of attachment points)

EDTA

• EDTA is a hexadentate ligand.
• It can act as a quadridentate ligand

Stability of Complex Ions

• Factors affecting complex ion stability:
  • Properties of the central metal ion (e.g., charge, ionic radius, ionic potential)
  • Properties of the ligand (e.g., basic character of the donating atom, size)
  • Stability of the chelate (number of rings, size of chelate ring)

Chelate effect

• The increasing stability of a complex when a chelating ligand forms multiple rings with a metal ion.
• Chelated complexes are more stable than non-chelated complexes

Step-wise Complex Formation

• Examples of sequential step-wise addition of ligands to a metal ion.

Polynuclear Complexes

• Definition: Metal chelates containing two or more central metal atoms, where the chelating ligand acts as a coordinating bridge.
• Examples: Ethylenediamine: Ag+, Dithiooxamide (rubeanic acid): Cu²⁺

Questions

• Short essay questions (factors affecting stability of complex ions with examples, definitions of Coordination number, requirements of a chelating agent)

This quiz covers the topic of complex formation, specifically complexometric titration. Students will explore definitions, classifications of ligands, factors affecting complex stability, and the geometry of complex ions. Utilizing interactive methods and resources, this quiz aims to enhance your understanding of metal complexes.