Coordination Chemistry and Transition Metals


        



Coordination Chemistry and Transition Metals

Coordination chemistry is a branch of inorganic chemistry that focuses on the study of coordination compounds, which involve metal atoms or ions bonded to surrounding molecules or ions (ligands). Transition metals play a significant role in coordination chemistry due to their ability to form complex compounds with various ligands.

1. Transition Metals in Coordination Chemistry

  • Definition: Transition metals are elements found in groups 3-12 of the periodic table. They have partially filled d-orbitals, allowing them to form various oxidation states and complex compounds.
  • Common Transition Metals in Coordination Chemistry: Iron (Fe), Copper (Cu), Cobalt (Co), Nickel (Ni), Chromium (Cr), Manganese (Mn), Platinum (Pt).

2. Coordination Compounds

  • Definition: Molecules or ionic compounds in which a central metal ion is bonded to surrounding ligands.
  • Coordination Number: The number of ligands attached to the central metal ion. Common coordination numbers include 2, 4, and 6.

Common Geometries Based on Coordination Number

Coordination NumberGeometryExample
2Linear[Ag(NH₃)₂]⁺
4Tetrahedral[NiCl₄]²⁻
4Square Planar[Pt(NH₃)₂Cl₂]
6Octahedral[Fe(CN)₆]³⁻

3. Ligands

  • Definition: Molecules or ions that donate electron pairs to the metal center.
  • Types of Ligands:
    • Monodentate (one donor atom): H₂O, NH₃, Cl⁻
    • Bidentate (two donor atoms): Ethylenediamine (en), oxalate (C₂O₄²⁻)
    • Polydentate (multiple donor atoms): EDTA (hexadentate)

4. Naming of Coordination Compounds (IUPAC Rules)

  1. Name the ligands first (alphabetical order) and then the metal.
  2. Use prefixes for multiple ligands: di-, tri-, tetra-, etc.
  3. If the complex is an anion, the metal name ends in "-ate" (e.g., Ferrate for Fe, Cuprate for Cu).
  4. Oxidation state of the metal is shown in Roman numerals.

Example:

  • [Cu(NH₃)₄]²⁺ → Tetraamminecopper(II) ion
  • [Fe(CN)₆]³⁻ → Hexacyanoferrate(III) ion

5. Isomerism in Coordination Compounds

  • Structural Isomerism
    • Linkage Isomerism: Different donor atoms in ligands (e.g., NO₂⁻ vs. ONO⁻).
    • Ionization Isomerism: Different ions inside vs. outside the coordination sphere.
  • Stereoisomerism
    • Geometrical Isomerism: Cis-trans (e.g., [Pt(NH₃)₂Cl₂]).
    • Optical Isomerism: Mirror image isomers (chiral complexes).

6. Crystal Field Theory (CFT)

  • Explains the splitting of d-orbitals in a metal complex due to ligand interactions.
  • Octahedral Field Splitting: d-orbitals split into higher-energy 
    ege_g and lower-energy t2gt_{2g} levels.
  • Tetrahedral Field Splitting: Inverse of octahedral splitting.

7. Applications of Coordination Compounds

  • Biological Systems: Hemoglobin (Fe complex), Vitamin B12 (Co complex), Chlorophyll (Mg complex).
  • Medicinal Chemistry: Cisplatin ([Pt(NH₃)₂Cl₂]) used in cancer treatment.
  • Industrial Uses: Catalysis (Wilkinson’s catalyst, Zeigler-Natta catalyst).

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