Coordinate Compounds - Naming Coordination Compounds

  • Introduction to coordination compounds
  • What are coordination compounds?
  • Coordination sphere and central metal ion
  • Ligands and their types
  • Naming coordination compounds

Introduction to Coordination Compounds

  • Definition of coordination compounds
    • Special class of compounds with a central metal ion or atom
    • Surrounded by a fixed number of ions or molecules (ligands)
  • Also known as complex compounds
  • Importance of coordination compounds
    • Used in many biological processes
    • Medicinal applications
    • Industrial applications
    • Catalysis

What are Coordination Compounds?

  • Coordination compounds are formed when a Lewis base (ligand) donates a pair of electrons to a Lewis acid (metal ion/atom).
  • The central metal ion or atom forms coordinate bonds with the ligands.
  • The coordination number of the metal ion is the number of coordinate bonds formed.
  • Examples:
    • [Fe(H2O)6]2+ - Hexaaquairon(II) ion
    • [CuCl4]2- - Tetrachlorocuprate(II) ion

Coordination Sphere and Central Metal Ion

  • Coordination sphere: The central metal ion or atom and the ligands bonded to it.
  • Square brackets [] indicate the coordination sphere. Example 1:
  • [Co(NH3)4Cl2]Cl - Coordination sphere: [Co(NH3)4Cl2]
  • Central metal ion: Cobalt (Co) Example 2:
  • [Cu(NH3)4(H2O)2]SO4 - Coordination sphere: [Cu(NH3)4(H2O)2]
  • Central metal ion: Copper (Cu)
  • The coordination number of the central metal ion determines the shape and properties of the coordination compound.

Ligands and their Types

  • Ligands: Ions or molecules that donate electrons to the metal ion and form coordinate bonds.
  • Types of Ligands:
    1. Monodentate ligands: Donate only one electron pair
      • Example: H2O, NH3, Cl-
    2. Bidentate ligands: Donate two electron pairs
      • Example: ethylenediamine (en), oxalate ion (C2O4 2-)
    3. Polydentate ligands: Donate multiple electron pairs (more than two)
      • Example: EDTA (ethylenediaminetetraacetate), porphyrins (hemoglobin)

Naming Coordination Compounds

  • IUPAC rules are followed for naming coordination compounds.
  1. Naming the ligands:
    • Common ligands have specific names (e.g., H2O = aqua, NH3 = ammine).
    • For anionic ligands, replace the suffix with -o (e.g., Cl- = chloro).
  1. Determining the oxidation state of the central metal ion.
    • This is done by considering the charges of ligands and any known charge of the compound.
  1. Naming the central metal ion:
    • Cations: Name of metal followed by its oxidation state in Roman numerals in parentheses.
    • Anions: Name of metal followed by -ate or -ite if metal has more than one oxidation state.
  1. Writing the name of the ligands in alphabetical order and indicating their number using prefixes (e.g., di-, tri-).
  1. If necessary, use prefixes bis-, tris-, tetrakis-, etc., to indicate multiple numbers of identical ligands.
  1. If there are multiple types of ligands, separate their names with commas.
  1. If the compound is a complex ion, the name ends in -ate or -ium.
  1. Naming Coordination Compounds (Continued)
  • If there are multiple central atoms or ions, use a prefix to indicate the number of each.
    • Example: [Co(NH3)4Cr(CN)6] - Tetraamminecobalt(III) hexacyanochromate(III)
  • When there are polyatomic anions in the coordination sphere, use special names.
    • Example: [Ni(NH3)6][Ni(CN)4] - Nickel(II) hexaamminenickelate(II)
  • If the complex ion is negatively charged, use the suffix -ate.
    • Example: [Fe(CN)6]4- - Hexacyanoferrate(II) ion
  1. Isomerism in Coordination Compounds
  • Isomers: Different compounds with the same chemical formula but different arrangements of atoms or ions.
  • Types of Isomerism:
    1. Structural Isomerism: Different connectivity of atoms in the complex.
    2. Stereoisomerism: Same connectivity of atoms but different spatial arrangement of ligands.
  • Geometric (cis-trans) isomerism:
    • Occurs when two ligands are attached to the central atom in a square planar or octahedral complex.
  • Optical isomerism:
    • Occurs in complexes with asymmetric carbon atoms or chiral ligands.
  1. Color in Coordination Compounds
  • Coordination compounds often exhibit vibrant colors.
  • Color arises due to electronic transitions in the d-orbitals of the central metal ion.
  • Factors influencing color:
    1. Nature of ligands
    2. Oxidation state of the central metal ion
    3. Coordination number of the metal ion
  • Example: [Cu(H2O)6]2+ is blue, while [CuCl4]2- is yellow.
  1. Stability of Coordination Compounds
  • Stability in coordination compounds is influenced by various factors:
    1. Nature of the central metal ion
    2. Charge density on the metal ion
    3. Nature and charge of the ligands
    4. Chelation effect (chelate ligands form more stable complexes)
  • Stability constants (formation constants) are used to measure the stability of coordination compounds.
  • Higher stability constants indicate more stable complexes.
  1. Isolobal Analogy
  • Isolobal analogy is used to compare the electronic configurations of main group atoms and central metal ions.
  • Main group atom and central metal ion are considered isolobal if they have similar numbers of valence electrons and similar orbital energy levels.
  • This analogy helps in understanding the bonding and reactivity of coordination compounds.
  1. Spectrochemical Series
  • The spectrochemical series ranks ligands based on their ability to split d-orbitals of the central metal ion in octahedral complexes.
  • Strong-field ligands cause a larger energy difference (Δ) between the d-orbitals.
  • The series ranges from strong-field ligands (high Δ) to weak-field ligands (low Δ).
  • Example: I- < Br- < SCN- < Cl- < F- < OH- < H2O < en < NO2- < CN-
  1. Coordination Chemistry in Biology
  • Coordination compounds play essential roles in biological processes.
  • Hemoglobin: Iron coordination complex responsible for oxygen transport in blood.
  • Chlorophyll: Magnesium coordination complex involved in photosynthesis.
  • Vitamin B12: Cobalt coordination complex necessary for red blood cell production.
  • Many enzymes used in biological reactions contain coordination complexes.
  1. Industrial Applications of Coordination Compounds
  • Coordination compounds have various industrial applications:
    • Catalysts in chemical reactions
    • Extraction and purification of metals
    • Pigments in paints and dyes
    • Medicinal applications (chemotherapy drugs)
    • Electroplating and corrosion prevention
  1. Medicinal Applications of Coordination Compounds
  • Many coordination compounds are used in medicinal applications.
  • Chemotherapy drugs like cisplatin (Pt(NH3)2Cl2) are used in cancer treatment.
  • Platinum-based coordination complexes inhibit DNA replication in cancer cells.
  • Other coordination compounds show antimicrobial properties or are used as MRI contrast agents.
  1. Review Questions
  • What is the coordination number of a metal ion?
  • Give examples of monodentate, bidentate, and polydentate ligands.
  • How do you name coordination compounds following IUPAC rules?
  • What is the difference between structural and stereoisomerism in coordination compounds?
  • Explain why coordination compounds exhibit different colors.
  • What factors influence the stability of coordination compounds?
  • What is the isolobal analogy?
  • What is the spectrochemical series and how is it helpful?
  • Give examples of coordination compounds used in biology and industry.
  • How are coordination compounds used in medicinal applications?

Slide 21: Types of Isomerism in Coordination Compounds

  • Structural Isomerism:
    • Different connectivity of atoms in the complex.
    • Examples: Linkage isomerism, coordination isomerism.
  • Stereoisomerism:
    • Same connectivity of atoms but different spatial arrangement of ligands.
    • Geometric isomerism: cis-trans isomerism.
    • Optical isomerism: chirality and enantiomers. Examples:
  • [Co(NH3)4Cl2]+
    • Structural isomer: [Co(NH3)4(Cl)2]+
    • Geometric isomer: [Co(NH3)4(Cl)(H2O)]2+
  • [Pt(en)2Cl2]
    • Structural isomer: [Pt(en)(H2O)Cl2]
    • Optical isomer: [Pt(en)2Cl2] (R) and [Pt(en)2Cl2] (S)

Slide 22: Color in Coordination Compounds

  • The colors of coordination compounds arise due to electronic transitions within the d-orbitals of the central metal ion.
  • Factors influencing color:
    • Nature of ligands: Different ligands may cause different energy splitting of d-orbitals.
    • Oxidation state of the central metal ion: Different oxidation states may result in different electronic configurations and energy levels of d-orbitals.
    • Coordination number of the metal ion: Different coordination numbers may lead to different energy splitting.
  • Example:
    • [Fe(H2O)6]2+ is pale green.
    • [Fe(CN)6]4- is deep violet.
  • The observed colors can be used to identify unknown coordination compounds.

Slide 23: Stability of Coordination Compounds

  • Stability in coordination compounds depends on several factors:
    • Nature of the central metal ion: Some metal ions form more stable complexes.
    • Charge density on the metal ion: Higher charge density favors the formation of stable complexes.
    • Nature and charge of the ligands: Chelating ligands and negatively charged ligands tend to form more stable complexes.
    • Chelation effect: The formation of a multi-dentate chelate ligand increases the stability.
  • Stability constants (formation constants) are used to measure the stability of coordination compounds.
    • High stability constants indicate more stable complexes.
  • For example, the complex [Cu(NH3)4]2+ is more stable than [Fe(NH3)6]3+ due to the stability of the Cu-N bond.

Slide 24: Isolobal Analogy

  • Isolobal analogy is used to compare the electronic configurations of main group atoms and central metal ions.
  • Main group atom and central metal ion are considered isolobal if they have similar numbers of valence electrons and similar orbital energy levels.
  • This analogy helps in understanding the bonding and reactivity of coordination compounds.
  • Example:
    • PCl3 and [Co(NH3)3Cl3] can be considered isolobal because they both have an octahedral arrangement and occupied 3d orbitals.

Slide 25: Spectrochemical Series

  • The spectrochemical series ranks ligands based on their ability to split d-orbitals of the central metal ion in octahedral complexes.
  • Strong-field ligands cause a larger energy difference (Δ) between the d orbitals.
  • The series ranges from strong-field ligands (high Δ) to weak-field ligands (low Δ).
    • Example: I- < Br- < SCN- < Cl- < F- < OH- < H2O < en < NO2- < CN-
  • The position in the spectrochemical series determines the color of the complex and its stability.
  • Example: Complexes with ligands from the lower part of the series show stronger absorption in the visible region and exhibit intense colors.

Slide 26: Coordination Chemistry in Biology

  • Coordination compounds play essential roles in biological processes.
  • Hemoglobin: Iron coordination complex responsible for oxygen transport in blood.
  • Chlorophyll: Magnesium coordination complex involved in photosynthesis.
  • Vitamin B12: Cobalt coordination complex necessary for red blood cell production.
  • Many enzymes used in biological reactions contain coordination complexes.
  • Coordination chemistry helps in understanding and designing drugs for specific biological targets.

Slide 27: Industrial Applications of Coordination Compounds

  • Coordination compounds find various industrial applications:
    • Catalysts in chemical reactions: Transition metal complexes can act as catalysts in many important industrial processes.
    • Extraction and purification of metals: Complexation is used to extract metals from ores and purify them.
    • Pigments in paints and dyes: Coordination compounds provide vibrant colors in paints and dyes.
    • Medicinal applications: Some coordination compounds are used as drugs or in medical diagnostics.
    • Electroplating and corrosion prevention: Coordination compounds are used to create protective coatings on metal surfaces.

Slide 28: Medicinal Applications of Coordination Compounds

  • Many coordination compounds are used in medicinal applications.
  • Chemotherapy drugs like cisplatin (Pt(NH3)2Cl2) are used in cancer treatment.
  • Platinum-based coordination complexes inhibit DNA replication in cancer cells.
  • Other coordination compounds show antimicrobial properties or are used as MRI contrast agents.
  • Coordination compounds can target specific cells or receptors in the body for treatment.
  • Research in coordination chemistry is ongoing for developing new therapeutic agents.

Slide 29: Review Questions

  1. What is the difference between structural and stereoisomerism in coordination compounds?
  1. Give examples of geometric and optical isomerism in coordination compounds.
  1. How does color arise in coordination compounds?
  1. What factors influence the stability of coordination compounds?
  1. Explain the isolobal analogy in coordination chemistry.
  1. What is the significance of the spectrochemical series?
  1. Give examples of coordination compounds used in biology and industry.
  1. How are coordination compounds used in medicinal applications?
  1. How can coordination compounds be used for catalysis?
  1. What are the applications of coordination compounds in electroplating and corrosion prevention?