PCH

Questions and Answers

What is the coordination number of the metal ion in the complex ion [PtCl4]2-?

What is the coordination number of Ni in the complex [Ni(NH3)4]2+?

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?

Hexagonal Signup and view all the answers

What type of ligand is H2NCH2CH2NH2?

Bidentate Signup and view all the answers

A ligand is called ambidentate if it can bind through two different atoms.

True Signup and view all the answers

What is the primary function of a chelating agent?

All of the above Signup and view all the answers

What is EDTA's primary role as a ligand?

It acts as a hexadentate ligand. Signup and view all the answers

The Greek word for claw, which describes chelation, is ______.

kele Signup and view all the answers

How do tetracyclines affect drug absorption when forming complexes with metal ions?

They can lead to decreased drug absorption. Signup and view all the answers

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.

PCH