Class 12 Chemistry: Coordination Compounds

परिचय

• Coordination compounds में atoms और ions के बीच अच्छा coordination होता है।
• Complex molecules होते हैं जिनमें metal atom, neutral molecules या negative charge ions के साथ बंध होते हैं।
• उदाहरण: Chlorophyll (Magnesium का coordination compound), Hemoglobin (Iron का coordination compound), Vitamin B12 आदि।
• Coordination compounds की applications कई क्षेत्रों में हैं जैसे प्लांट्स, मेडिसिन आदि।

Theories of Coordination Compounds

• Werner's Theory: Coordination compounds के बारे में पहली theory।
  • Primary Valency: Oxidation number, ionizable, जैसे K4Fe(CN)6 में K+ ionizes outside the bracket.
  • Secondary Valency: Non-ionizable, coordination number, जैसे Fe(CN)6, coordination number 6.
  • Coordination Polyhedra: Specific spatial arrangement जैसे tetrahedral, square planar, octahedral.

Coordination Compounds के Components

• Coordination Entity: Central metal atom और surrounding ions/molecules का समूह।
• Central Metal Atom/Ion: वह atom/ion जिसे ligands surround करते हैं।
  • Coordinate Bond: एक प्रकार का covalent bond जहां central atom electrons नहीं contribute करता।
• Ligands: Ions/molecules जो central atom से जुड़े होते हैं।
  • Types:
    • Uni/Monodentate: एक donor atom (e.g., Cl-, NH3)
    • Bidentate: दो donor atoms (e.g., Oxalate ion)
    • Polydentate: अनेक donor atoms (e.g., EDTA)
    • Ambidentate: Multiple different donor atoms (e.g., SCN-)

Naming of Coordination Compounds (IUPAC Rules)

1. Cation first, Anion second
2. Ligands before Central Metal Atom
3. Order of ligands: Anionic ligands end with 'o' (e.g., chloro, nitro), followed by neutral ligands.
4. Prefix for multiple same ligands: Di, Tri, Tetra, etc.
5. Central Metal Atom Naming: Includes oxidation state in Roman numerals.

Bonding Theories

• Valence Bond Theory (VBT): Bond formation involves hybrid orbitals; central atom accepts electrons from ligands.
  • Example: Co(NH3)6 with hybridization D2SP3 forms octahedral geometry.
• Crystal Field Theory (CFT): Ligands create an electric field that causes D-orbitals to split.
  • Splitting in Octahedral Field: Dxy, Dyz, Dxz remain lower energy (T2g); Dx2-y2, Dz2 higher energy (Eg).
  • Splitting in Tetrahedral Field: Inverted splitting; E lower, T2 higher without 'g' (gerade symmetry absent).
  • Color: Arises from D-D transitions, depends on absorbed wavelength and complementary color.

Applications and Limitations

• Uses in biological systems, industrial catalysts, and photographic processes.
• Limitations in explaining covalent character in bonding and thermodynamic stability.

Summary

• Coordination compounds are complex and useful due to their unique properties and applications.
• Theories like Werner, VBT, and CFT help explain their structure, bonding, and color.
• Naming and understanding their components is crucial for studying their chemistry.