Chemistry · MU Sofia

6.1 Complex compounds

Explains what complex compounds are, covering the central ion, ligands that donate electron pairs, and coordination number, with examples. Goes on to dative bonds, ligand denticity including chelating agents, and the charge types of complex ions. Also covers naming rules, geometric and optical isomerism, and the role of haemoglobin, antidotes and chelation therapy in medicine.

Inside: 7 sections · 5 labelled pictures · 20 flashcards · 6 min

Topic 18 of 42 in the MU Sofia syllabus for Chemistry (Medicine, Year 1). The free AceMed note covers it in 7 sections, about 784 words (6 min of reading), with 20 flashcards.

In this note

  1. Complex (coordination) compounds.
  2. Coordinate covalent bond (Dative bonds).
  3. Types of ligands - denticity.
  4. Chelate complexes.
  5. Positively charged, negatively charged and neutral complex ions.
  6. Nomenclature, structure and stability of complex compounds.
  7. Biological significance / Application in medicine.

Complex (coordination) compounds.

  • Complex (Coordination) Compound: A molecule formed by the association of a central metal atom or ion and surrounding molecules or ions (ligands).

Central ion, ligands and coordinative number.

  • Central Ion and Ligands:
  • Central Ion (Metal Center): The core of the complex, often a metal atom or metal ion, but can also be a non-metallic element in specific cases (e.g., N in NH4+).
  • Ligands: Molecules or ions surrounding the central ion, donating electron pairs to form bonds.
  • Electron Donation: They form dative covalent bonds with the central ion by donating lone pairs of electrons.
  • Types of Ligands:
  • Monodentate: Ligands that bind to the central metal ion through one donor atom (e.g., Cl- in FeCl3, NH3 in [Co(NH3)6]Cl3).
  • Bidentate: Ligands that bind to the central metal ion through two donor atoms (e.g., ethylenediamine (en) in [Pt(en)2]Cl2).
  • Polydentate: Ligands with more than two donor atoms, also called chelating agents (e.g., EDTA).
  • Coordination Number is
  • The number of ligands directly attached to the central atom/ion.
  • Represented in the formula, like [Pt(NH3)2Cl4] (coordination number 6 for Pt).
  • Examples:
  • [Pt(NH3)2Cl4] (coordination number 6 for Pt, monodentate NH3 ligands)
  • [Co(NH3)6]Cl3 (coordination number 6 for Co, monodentate NH3 ligands)
  • Additional Notes:
  • Ligands are Lewis bases due to their electron-donating ability.
  • Chelating agents form stable complexes with metals due to their multiple coordination points.

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