Ligands and complexes
Introduced| English | Meaning |
|---|---|
| ligand/ˈlɪɡænd/ | An ion or molecule that binds to another species at a specific site, such as a metal centre or a receptor. |
| complex/ˈkɒmpleks/ | complex |
| dative bond/ˈdætɪv bɒnd/ | dative bond |
| coordination number/kəʊˈɔːdɪneɪʃn ˈnʌmbə/ | The number of nearest neighbours around a particle, or of donor atoms directly bonded to the central atom in a complex. |
| monodentate/ˈmɒnəʊdenteɪt/ | Describes a ligand forming one dative bond to the central metal ion, as water does. |
| bidentate/baɪˈdenteɪt/ | Describing a ligand that forms two coordinate bonds to the same central metal ion. |
| octahedral/ˌɒktəˈhiːdrəl/ | Describing six positions arranged towards the vertices of an octahedron around a central point. |
Surrounding the metal
- A transition ion can be surrounded by ligands 配体 to form a complex 配合物.
- A ligand donates a lone pair in a dative bond 配位键.
- The shape follows the coordination number 配位数.
Ligand and complex lab
Identify the part of a complex ion that controls its structure.
A molecule or ion that donates a lone pair to a central metal ion is a ______.
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It forms a coordinate bond to the metal.
Ligands and denticity
- a ligand has a lone pair that forms a dative covalent bond to the metal.
- monodentate 单齿 (one bond): $\text{H}_2\text{O}$, $\text{NH}_3$, $\text{Cl}^-$, $\text{CN}^-$.
- bidentate 双齿 (two): "en", ethanedioate $\text{C}_2\text{O}_4^{2-}$.
- polydentate (many): $\text{EDTA}^{4-}$ (six).
Monodentate, bidentate and polydentate ligands
A ligand bonds to a metal ion by:
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A ligand donates a lone pair to the metal's vacant orbital — a dative (coordinate) bond.
A bidentate ligand forms:
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Bidentate ligands (e.g. "en", ethanedioate) form two dative bonds each.
Match each complex-chemistry term.
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Each item links the term to its correct meaning.
Shape and coordination number
- The coordination number = number of dative bonds to the metal:
- 2 → linear; 4 → tetrahedral or square planar; 6 → octahedral 八面体形.
- Most complexes are 6-coordinate octahedral (small ligands) or 4-coordinate (bulky ligands like Cl⁻).
A complex with coordination number 6 is:
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6 → octahedral; 4 → tetrahedral or square planar; 2 → linear.
The overall charge on a complex ion is found by:
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Sum the central metal charge with the charges of all the ligands.
Working out the charge
- The complex's overall charge = the metal's charge + the sum of the ligand charges.
- [Cu(H₂O)₆]²⁺: Cu²⁺ + 6 neutral H₂O → charge = +2.
- [CuCl₄]²⁻: Cu²⁺ + 4 × Cl⁻ → +2 + (−4) = −2.
- [Fe(CN)₆]³⁻: Fe³⁺ + 6 × CN⁻ → +3 + (−6) = −3.
Neutral ligands (H₂O, NH₃) add nothing; charged ligands (Cl⁻, CN⁻, OH⁻) shift the total.
You've got it
- a ligand donates a lone pair (dative bond); mono-/bi-/poly-dentate = 1/2/many bonds
- coordination number: 2 → linear, 4 → tetrahedral/square planar, 6 → octahedral
- complex charge = metal charge + ligand charges (e.g. [CuCl₄]²⁻ = +2 − 4 = −2)