Summary of Inorganic Chemistry: Spectra and Complexes
Inorganic Chemistry: Spectra & Complexes - Student Guide
Introduction
Coordination chemistry studies compounds in which a central metal atom or ion binds to surrounding molecules or ions called ligands. These complexes determine many properties of transition-metal chemistry, influence catalysis, bioinorganic function, and materials design.
Definition: A complex is a central metal atom or ion bonded to a group of molecules or ions called ligands. The coordination number (CN) is the number of donor atoms directly bonded to the metal.
Fundamental concepts
Coordination number (CN)
- CN is the count of ligand donor atoms bound to the metal center.
- Factors determining CN:
- Size of the central metal ion (larger ions accommodate higher CN).
- Steric bulk of ligands (bulky ligands lower CN).
- Electronic factors (early transition metals with few d-electrons often have higher CN; ligands that form multiple bonds reduce effective CN).
Typical coordination numbers and geometries
| Coordination number | Common geometries | Typical examples and notes |
|---|---|---|
| CN = 2 | Linear | ce{[Au(CN)2]-}, ce{Hg(CH3)2} |
| CN = 3 | Trigonal planar | Sterically demanding ligands or d^{10} metals |
| CN = 4 | Tetrahedral or square planar | Small metal + large ligands → tetrahedral; d^{8} with strong field → square planar |
| CN = 5 | Trigonal bipyramidal (TBP) or square pyramidal (SPY) | Steric/chelate effects decide; TBP often fluxional (Berry pseudorotation) |
| CN = 6 | Octahedral (most common) | ce{[Fe(CN)6]^{3-}}, Jahn–Teller distortions possible |
| CN > 6 | 7–12 (seen in 4d/5d and f-block) | f-block often CN = 9,10,12; some 3d reach 7 |
💡 Věděli jste?Did you know that many 4d and 5d metal ions frequently show coordination numbers of 7, 8, or 9 because their larger radii allow more ligand donor atoms to fit around the metal center?
Geometric preferences and examples
- CN = 4:
- Tetrahedral: favored by smaller metal ions with large ligands (heavier halides, oxo). Examples: ce{[FeCl4]^{2-}}, ce{[MnO4]-}.
- Square planar: common for d^{8} metal ions (e.g. Ni^{2+}, Pd^{2+}, Pt^{2+}, Rh^{+}, Ir^{+}, Au^{3+}). Examples: ce{[Pt(NH3)4]^{2+}}, ce{[PdCl4]^{2-}}. Note: 3d d^{8} ions like Ni^{2+} adopt square planar geometry only with strong pi-acceptor ligands (e.g. ce{[Ni(CN)4]^{2-}} is square planar while ce{[NiBr4]^{2-}} is tetrahedral).
- CN = 5:
- Two isomers: TBP and SPY. TBP ↔ SPY interconversion can occur via Berry pseudorotation, which exchanges axial and equatorial positions and leads to ligand equivalence in NMR for identical ligands (but IR can distinguish positions).
- Steric constraints (tripodal or porphyrin ligands) can fix geometry; heme proteins use a roughly square-pyramidal/planar coordination around Fe in porphyrin.
- CN = 6:
- Octahedral: highest symmetry and common CN for transition metals. Examples: ce{[Sc(H2O)6]^{3+}}, ce{[Cr(NH3)6]^{3+}}, ce{[Fe(CN)6]^{3-}}.
- Distortions often arise from electronic effects such as the Jahn–Teller effect.
- CN > 6:
- More common for 4d/5d and especially f-block metals. Examples: ce{[V(CN)7]^{4-}}, ce{[Mo(Me)7]-}, ce{[Eu(H2O)9]^{3+}}, cerium complexes with CN = 10 or 12.
Ligands and bonding
Definition: A ligand is an atom, ion, or molecule that donates a lone pair of electrons to a metal center (acts as a Lewis base). The metal that accepts electron pairs is a Lewis acid.
Ligand classification
- By charge:
- Neutral ligands (L-type): have a lone pair available without formal electron addition. Examples: NH3 (ammine), H2O (aqua), PPh3.
- Anionic ligands (X-type): require addition of electron(s) to the donor atom in Lewis structures; examples: Cl^{-} (chlorido), O^{2-} (oxide), R2N^{-}.
- By denticity:
- Monodentate: one donor atom (e.g. Cl^{-}, NH3).
- Bidentate, tridentate, tetradentate, hexadentate: two or more donor atoms from same ligand. Example: ethylenediamine (en) is bidentate; EDTA^{4-} is hexadentate.
- Ambidentate ligands: can bind through d
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Coordination Chemistry Essentials
Klíčové pojmy: Coordination number (CN) counts donor atoms directly attached to the metal, CN depends on metal size, ligand sterics, and electronic factors, CN = 4 can be tetrahedral or square planar; d^{8} metals favor square planar with strong-field ligands, CN = 5 yields TBP or SPY; TBP often undergoes Berry pseudorotation, CN = 6 is most common: octahedral geometry with possible Jahn–Teller distortion, Ligands classified by charge (L vs X), denticity, and ambidentate/chelating behavior, Naming: ligands alphabetically; metal oxidation state in parentheses; anionic complexes end with -ate, Isomerism includes ionization, hydration, coordination, linkage, geometric and optical isomers, Chelate rings (5- or 6-membered) stabilize complexes (chelate effect), Δ/Λ and C/A descriptors specify handedness for chiral complexes, Ligand choice influences reactivity, catalysis, and biological activity, Berry pseudorotation makes certain TBP ligands equivalent in NMR
## Introduction
Coordination chemistry studies compounds in which a central metal atom or ion binds to surrounding molecules or ions called ligands. These complexes determine many properties of transition-metal chemistry, influence catalysis, bioinorganic function, and materials design.
> Definition: A complex is a central metal atom or ion bonded to a group of molecules or ions called ligands. The coordination number (CN) is the number of donor atoms directly bonded to the metal.
## Fundamental concepts
### Coordination number (CN)
- **CN** is the count of ligand donor atoms bound to the metal center.
- Factors determining CN:
- Size of the central metal ion (larger ions accommodate higher CN).
- Steric bulk of ligands (bulky ligands lower CN).
- Electronic factors (early transition metals with few d-electrons often have higher CN; ligands that form multiple bonds reduce effective CN).
### Typical coordination numbers and geometries
| Coordination number | Common geometries | Typical examples and notes |
|---|---:|---|
| CN = 2 | Linear | ce{[Au(CN)2]-}, ce{Hg(CH3)2} |
| CN = 3 | Trigonal planar | Sterically demanding ligands or d^{10} metals |
| CN = 4 | Tetrahedral or square planar | Small metal + large ligands → tetrahedral; d^{8} with strong field → square planar |
| CN = 5 | Trigonal bipyramidal (TBP) or square pyramidal (SPY) | Steric/chelate effects decide; TBP often fluxional (Berry pseudorotation) |
| CN = 6 | Octahedral (most common) | ce{[Fe(CN)6]^{3-}}, Jahn–Teller distortions possible |
| CN > 6 | 7–12 (seen in 4d/5d and f-block) | f-block often CN = 9,10,12; some 3d reach 7 |
> Did you know that many 4d and 5d metal ions frequently show coordination numbers of 7, 8, or 9 because their larger radii allow more ligand donor atoms to fit around the metal center?
### Geometric preferences and examples
- CN = 4:
- **Tetrahedral**: favored by smaller metal ions with large ligands (heavier halides, oxo). Examples: ce{[FeCl4]^{2-}}, ce{[MnO4]-}.
- **Square planar**: common for d^{8} metal ions (e.g. Ni^{2+}, Pd^{2+}, Pt^{2+}, Rh^{+}, Ir^{+}, Au^{3+}). Examples: ce{[Pt(NH3)4]^{2+}}, ce{[PdCl4]^{2-}}. Note: 3d d^{8} ions like Ni^{2+} adopt square planar geometry only with strong pi-acceptor ligands (e.g. ce{[Ni(CN)4]^{2-}} is square planar while ce{[NiBr4]^{2-}} is tetrahedral).
- CN = 5:
- Two isomers: TBP and SPY. TBP ↔ SPY interconversion can occur via **Berry pseudorotation**, which exchanges axial and equatorial positions and leads to ligand equivalence in NMR for identical ligands (but IR can distinguish positions).
- Steric constraints (tripodal or porphyrin ligands) can fix geometry; heme proteins use a roughly square-pyramidal/planar coordination around Fe in porphyrin.
- CN = 6:
- **Octahedral**: highest symmetry and common CN for transition metals. Examples: ce{[Sc(H2O)6]^{3+}}, ce{[Cr(NH3)6]^{3+}}, ce{[Fe(CN)6]^{3-}}.
- Distortions often arise from electronic effects such as the Jahn–Teller effect.
- CN > 6:
- More common for 4d/5d and especially f-block metals. Examples: ce{[V(CN)7]^{4-}}, ce{[Mo(Me)7]-}, ce{[Eu(H2O)9]^{3+}}, cerium complexes with CN = 10 or 12.
## Ligands and bonding
> Definition: A ligand is an atom, ion, or molecule that donates a lone pair of electrons to a metal center (acts as a Lewis base). The metal that accepts electron pairs is a Lewis acid.
### Ligand classification
- By charge:
- **Neutral ligands (L-type)**: have a lone pair available without formal electron addition. Examples: NH3 (ammine), H2O (aqua), PPh3.
- **Anionic ligands (X-type)**: require addition of electron(s) to the donor atom in Lewis structures; examples: Cl^{-} (chlorido), O^{2-} (oxide), R2N^{-}.
- By denticity:
- **Monodentate**: one donor atom (e.g. Cl^{-}, NH3).
- **Bidentate, tridentate, tetradentate, hexadentate**: two or more donor atoms from same ligand. Example: ethylenediamine (en) is bidentate; EDTA^{4-} is hexadentate.
- **Ambidentate** ligands: can bind through d