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.