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Questions and Answers
What is the coordination number of the metal ion in the complex ion [PtCl4]2-?
What is the coordination number of the metal ion in the complex ion [PtCl4]2-?
6
What is the coordination number of Ni in the complex [Ni(NH3)4]2+?
What is the coordination number of Ni in the complex [Ni(NH3)4]2+?
4
What is the term for the central atom/ion and the ligands attached to it?
What is the term for the central atom/ion and the ligands attached to it?
coordination sphere
Which of the following is NOT a common type of coordination polyhedron?
Which of the following is NOT a common type of coordination polyhedron?
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What type of ligand is H2NCH2CH2NH2?
What type of ligand is H2NCH2CH2NH2?
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A ligand is called ambidentate if it can bind through two different atoms.
A ligand is called ambidentate if it can bind through two different atoms.
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What is the primary function of a chelating agent?
What is the primary function of a chelating agent?
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What is EDTA's primary role as a ligand?
What is EDTA's primary role as a ligand?
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The Greek word for claw, which describes chelation, is ______.
The Greek word for claw, which describes chelation, is ______.
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How do tetracyclines affect drug absorption when forming complexes with metal ions?
How do tetracyclines affect drug absorption when forming complexes with metal ions?
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Study Notes
Coordination Number
- Defined as the number of ligand donor atoms directly bonded to a metal ion in a complex.
- For example, in [PtCl4]²⁻, the coordination number of Pt is 6; in [Ni(NH3)4]²⁺, the coordination number of Ni is 4.
Coordination Sphere
- Comprises the central atom/ion and the attached ligands, indicated within square brackets.
- Counter ions are written outside the brackets; for example, in K₄[Fe(CN)₆], the coordination sphere is [Fe(CN)₆]⁴⁻ while K⁺ serves as the counter ion.
Coordination Polyhedron
- Refers to the spatial arrangement of ligand atoms around a central atom/ion.
- Common shapes include octahedral, tetrahedral, square planar, trigonal bipyramidal, and square pyramidal.
Denticity of a Ligand
- Indicates the number of bonding sites available on a ligand.
- Unidentate: Ligands bond through a single donor atom (e.g., Cl, H₂O, NH₃).
- Bidentate: Ligands bond through two donor atoms (e.g., ethane-1,2-diamine, oxalate).
- Polydentate: Ligands with several donor atoms, like the hexadentate EDTA, which binds via two nitrogen and four oxygen atoms.
- Chelate Ligand: A type of bidentate or polydentate ligand that forms a ring with a metal ion.
Coordination Compounds
- Tend to be more stable than complexes with unidentate ligands.
- Ambidentate ligands can bond through two different atoms (e.g., NO₂⁻ and SCN⁻).
- Central atom acts as a Lewis acid; ligands function as Lewis bases, forming coordinate bonds through electron pair donation.
Chelating Agents
- Derived from kele, meaning "claw"; they facilitate complex formation with metal ions via multiple donor atoms.
- At least two donor atoms are necessary for effective binding and sterically feasible ring formation.
- Ethylenediamine exemplifies a bidentate ligand with two donor nitrogens.
Selected Examples
Tetracyclines
- Form complexes with divalent metals (e.g., calcium, magnesium) and have a stronger affinity for trivalent metals (e.g., iron, aluminum).
- Commonly result in decreased drug absorption due to complex formation (3:1 drug-metal chelates).
Ethylenediaminetetraacetic Acid (EDTA)
- An aminopolycarboxylic acid with the formula [CH₂N(CH₂CO₂H)₂]₂, known for its strong chelation properties and water solubility, widely used in medicinal applications.
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