38 Questions
Who first introduced the concept and term 'supramolecular chemistry'?
J.M. Lehn
Which of the following interactions is not typically considered an intermolecular force in supramolecular chemistry?
Covalent bonding
What is a key characteristic of supramolecular species compared to molecules?
More flexible dynamics
Which of the following best describes the idea behind supramolecular chemistry according to Lehn?
Chemistry beyond the molecule
Which intermolecular force involves π-π stacking interactions?
Van der Waals interactions
Which of the following is a true statement about intermolecular forces in supramolecular chemistry?
They provide supramolecular species with dynamic flexibility
Which interaction has the highest bond energy?
Triple bond
What is a characteristic of molecular recognition?
Host binding sites attract different parts of the guest molecule
Which category of molecular receptors is responsible for binding cations via electrostatic ion-dipole interactions?
Cation binding hosts
Which substance incorporates softer atoms like N, S, P to bind strongly with transition metal ions?
Heterocrowns
Which type of host is specifically designed to remove Li+?
Spherands
Which molecule shows greater selectivity for K+ among alkali and alkaline-earth cations?
Cryptands
What advantage do lariat ethers have over crown ethers?
Ability to transport cations across lipophilic membranes
Which interaction type has the weakest bond energy?
Dispersion forces
What affects the selectivity of cation binding?
Cation binding kinetics
What is a characteristic feature of cyclodextrins?
Hydrophilic due to -OH groups in the faces
Which of these is not a factor affecting cation binding?
Host molecule size
What type of interaction is observed in calixarenes?
π-cation interaction
Which host molecules are used for anion recognition?
Polycyclic amide ligands
Which type of host molecules are cavitands?
Molecules with an intrinsic cavity present in both solid-state and solution
Which of the following is an example of a macrocyclic polyamide anion receptor?
Positively charged hosts binding to [PdCl4]2-
Why are anions generally large, and what does this imply for their receptors?
Anions are large, so their receptors need to be large as well
What term is used for components that undergo self-assembly?
Tectons
Which type of self-assembly is characterized by dynamic and reversible interactions?
Supramolecular self-assembly
Who introduced the concept of metallosupramolecular chemistry?
E.C. Constable
In the context of metallosupramolecular chemistry, what do metal ions provide?
Set of coordination geometries
What type of helicates was introduced by Lehn in 1987?
Cyclic
What is the structural characteristic of a rotaxane?
A stoppered filamentous molecule threaded through a cyclic one
Which type of coordination geometry is not associated with double stranded helicates?
Triclinic
Who introduced the concept of catenanes, and what do they involve?
Sauvage; Interlocking of two cyclic structures
What common attributes are shared by components in molecular devices?
They are photochemically, redox, or chemically active molecules
What is the coordination number (CN) and shape for Cu(I)?
CN = 4, tetrahedral
Which year was the Nobel Prize in Chemistry awarded for the design and synthesis of molecular machines?
2016
In molecular machines, what input is required for them to perform a task?
Energy
What motion is observed with an electric car powered by nanoscale molecules?
Rotational motion
Which of the following molecules have a coordination number (CN) of 6 and exhibit octahedral symmetry plus Jahn-Teller distortion?
Cu(II)
What kind of motion does the term 'pirouetting' describe in the context of molecular devices?
Spinning rotation
What are some potential applications of molecular machines as speculated by researchers?
Computing, novel materials, and energy storage
Study Notes
Bond Energies
- Single bond energy: 350 KJ/mol
- Triple bond energy (N2): 942 KJ/mol
- Ion-ion interactions: 250 KJ/mol
- Hydrogen bonding: 20 KJ/mol
- Dispersion forces: 2 KJ/mol
Host-Guest Chemistry
- Early example: selective binding of alkali metal cations in crown ethers and cryptands
- Molecular recognition: selective binding of a specific substrate to a receptor
- Self-assembly process: self-organization of molecular system via molecular recognition
Molecular Recognition
- Geometrical preorganization and interaction complementarity
- Preorganization: construction of host that exactly matches with guest (both sterically and electronically)
- Complementarity: host must have binding sites that attract binding sites of guests
- Interactions are relatively weaker than covalent bonds, but multiple site interactions yield strong selective complexation
Molecular Receptors (Hosts)
- Cation binding hosts
- Anion binding hosts
- Neutral molecule binding hosts (inorganic, organic, or biological)
Cation Binding Sites
- Bind via electrostatic ion-dipole interaction
- Examples: crown ethers, lariat crown ethers, heterocrown, spherands, cryptands, calixarene
Cation Binding Hosts
- Binding by electrostatic ion-dipole interaction
- Better the fit of the cation into the crown, the stronger the complex: optimal spatial fit
Lariat Ethers
- Designed to carry and transport cations across lipophilic membranes
- Higher binding constants than crown ethers
Heterocrowns
- Incorporation of softer atoms: N, S, P
- Binding to Ag+ and transition metal ions
- Strong complexation of toxic Cd2+, Pb2+, Hg2+ ions
Spherands
- Macrocyclic host with rigid cavity
- High stability Li+ complex (size fit)
- Used for removal of Li+
Cryptands
- Macrocyclic ligands that form a 3-dimensional cage to encapsulate (hide) the metal ion
- Special recognition for alkali and alkaline-earth cations
- Selectivity of K+ is observed for [2.2.2] 104 times stronger than its crown analog
Supramolecular Chemistry
- Definitions:
- Chemistry beyond the molecule, bearing organized entities of higher complexity that result from the association of two or more chemical species held together by intermolecular forces
- Chemistry of species made of two or more molecular components
- Introduced by Lehn in 1978
- DNA backbone: example of supramolecular chemistry
Intermolecular Bonds
- Hydrogen bonding
- Electrostatic forces
- Van der Waals interactions
- Donor-acceptor interactions
- π-π stacking interactions
- Metal ion coordination
- Bond energy comparison: intermolecular forces are generally weaker than covalent bonds
Calixarenes
- Act as host for cations, anions, and neutral molecules depending on the degree of functionalization
- π-cation interaction also observed
Selectivity of Cation Binding
- Several factors:
- Size match between cation and host cavity
- Electrostatic charge
- Solvent (polarity, hydrogen bonding, coordination stability)
- Degree of host preorganization
- Enthalpy and entropy contribution
- Cation and host free energies of solvation
- Nature of counter-anion
- Interaction of counter-anion with solvent and the cation
- Cation binding kinetics
- Chelate ring size
Anionic Recognition
- Simple inorganic anions occur in a range of shapes and geometries (spherical, linear, planar, tetrahedral, octahedral)
- Positively charged hosts:
- Polycyclic-amide ligands
- Macrocyclic tetraamide
- Katapinands (swallow up)
Neutral Molecules Recognition
- Cavitands: host molecules with intrinsic cavity present in both solid-state and solution
- Examples: calixarene, cyclodextrines, cucurbituril
Supramolecular Chemistry, Metallosupramolecular Chemistry, and Molecular Architecture
- Definitions
- Molecular recognition
- Self-assembly
- Metallosupramolecular chemistry
- Encapsulated guests in metallonanostructures
- Molecular devices and machines
Metallosupramolecular Chemistry
- Introduced by E.C. Constable
- Non-covalent interaction: coordinative bonds
- Metal ions provide:
- Set of coordination geometries
- Range of binding strengths (from weak to strong)
- Range of formation and dissociation kinetics (from labile to inert)
Helicates
- Introduced by Lehn (1987)
- Tetrahedral versus octahedral coordination in double-stranded helicates
- Triple-stranded helicates
- Cyclic helicates
- Grid-type metal ion architectures
- Polygons
- Polyhedra
Supramolecular Devices and Machines
- Defined as complex systems made up of molecular components with definite individual properties
- Common components in molecular devices are photochemically, redox, or chemically active molecules
- Examples:
- Pirouetting of ring in a catenate
- Translation in rotaxanes
- Contracting and stretching motion
- World’s smallest electric car (animation)
- Electrically driven directional motion of a four-wheeled molecule on a metal surface
Test your knowledge of supramolecular chemistry, including definitions, molecular recognition, self-assembly, and metallosupramolecular chemistry. Learn about encapsulated guests in metallonanostructures and molecular devices and machines.
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