Coordination Compounds Notes (1)

Chapter 22: Coordination Chemistry

Sections 1 – 3 & 5 - 7

Section 22.1: Review of Using Oxidation States in Naming Compounds

  • Oxidation States are crucial for naming transition metal compounds.

    • Transition metals can exhibit multiple oxidation states, e.g., Cu has +1 and +2.

Section 22.2: The Properties of Transition Metals

  • General Characteristics:

    • All transition elements are metals.

    • Many transition metal complexes are highly colored due to d-d electronic transitions.

    • Paramagnetic properties result from unpaired electrons.

Electron Configurations

  • Periods 4 & 5 Transition Metals:

    • Configuration: [noble gas] ns² (n-1)d^x

      • Example: Fe: [Ar] 4s² 3d⁶

      • Exceptions: Cr: [Ar] 4s¹ 3d⁵, Cu: [Ar] 4s¹ 3d¹⁰

  • Periods 6 & 7 Transition Metals:

    • Configuration: [noble gas] ns² (n-2)f¹⁴ (n-1)d^x

      • Example: W: [Xe] 6s² 4f¹⁴ 5d^4

      • Exception: Au: [Xe] 6s¹ 4f¹⁴ 5d¹⁰

Ion Formation

  • Electrons are lost from the ns level first.

    • Example: Fe → Fe²⁺: [Ar] 3d⁶

    • Example: Cu → Cu²⁺: [Ar] 3d⁹

Oxidation States of Transition Metals

  • Transition metals can have multiple oxidation states:

    • Examples: Mn²⁺, MnO₄⁻, MnO₄²⁻

  • For elements in groups 3B through 7B, the highest oxidation state equals the group number.

  • For groups 8B through 2B, the highest oxidation state is less than the group number.

Section 22.3: Introduction to Coordination Compounds

  • Coordination Compound:

    • Contains at least one complex ion and counter ions.

    • Example: [Cu(NH₃)₄]Cl₂

  • Complex Ion:

    • Consists of a central metal cation bonded to ligands (molecules/ions).

    • Example: Complex ion [Cu(NH₃)₄]²⁺, counter ion Cl⁻, central metal cation Cu²⁺.

Lewis Acids and Bases

  • Lewis Acid: Accepts an electron pair; usually less than 4 outer atoms (not sp³).

  • Lewis Base: Donates an electron pair; contains lone pairs.

  • Acid-Base Reaction: Occurs when a base shares its electron pair with an acid.

Complex Ion Formation

  • Water forms covalent bonds to metal ions; stronger Lewis bases can displace water.

  • Example Reaction: Cu(H₂O)₄²⁺ + 4NH₃ → Cu(NH₃)₄²⁺ + 4H₂O

Behavior of Coordination Compounds in Solution

  • Example: Dissociation of [Co(NH₃)₆]Cl₃ in solution:

    • Produces [Co(NH₃)₆]³⁺ and 3Cl⁻ ions.

Writing Formulas for Coordination Compounds

  • The cation appears before the anion in the formula.

  • Charge balance between cation(s) and anion(s).

  • The metal in the complex ion is written first, followed by neutral ligands before anionic ligands in square brackets.

    • Example: 2K⁺ + [Mn(NH₃)₂Br₄]²⁻ → K₂[Mn(NH₃)₂Br₄]

Coordination Number and Geometry

  • Coordination Number (CN): Number of atoms directly bonded to the metal.

    • CN = 2: Linear

    • CN = 6: Octahedral

    • CN = 4: Depends on metal type (d⁸: square planar, d¹⁰: tetrahedral).

Donor Atoms Per Ligand

  • The nature of donor atoms affects structure and bonding in complex ions.

    • Example: Ethylenediamine (en) can be bidentate (2 bonds).

Isomerism in Coordination Compounds (Section 22.5)

  • Isomers: Compounds with same formula but different structures/properties.

    • Structural Isomers: Different atom connectivities.

    • Coordination Isomers: Swapped ligands/counter ions.

    • Linkage Isomers: Different donor atoms in ligands.

    • Geometric and Optical Isomers: Arrangements around metal ions are different, influencing spatial configurations and chiral properties.

Crystal Field Theory (Section 22.6)

  • Examines effects of ligands on metal d-orbital energies as they approach.

    • Crystal Field Splitting (Δ): Energy differences between d-orbitals influenced by ligand positioning.

  • High-spin vs. Low-spin: Depends on the interaction of electrons with crystal field splitting.

    • High-spin: Electrons remain unpaired (E_pairing > Δ).

    • Low-spin: Electrons pair up (E_pairing < Δ).

The Spectrochemical Series, Color, and Magnetism (Section 22.7)

  • Many transition metal complexes display vibrant colors due to partially filled d orbitals.

  • Crystal Field Splitting Energy: Influences light absorption and observed color.

    • Changing ligands or metal ions alters Δ, thus changing the color observed in solution.

  • Example: Ni(H₂O)₆²⁺ in varying complexes shows color shifts due to changes in Δ.

Biological Significance of Heme

  • Heme composition: Fe²⁺ complexed with porphyrin.

  • Alteration of geometry/signaling in oxygenated versus deoxygenated states is crucial for biological function.