Related Concept Videos
01:18Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Removing one hydrogen from the intervening CH2 group with both...
03:02Colors and Magnetism
Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
02:42Valence Bond Theory
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
00:43Complexometric Titration: Ligands
Different monodentate and polydentate ligands are used as complexing agents in complexometric titration reactions. The formation of complexes by mono- and bidentate ligands involves two or more intermediate steps, limiting their use as complexing agents. In comparison, polydentate ligands can form complexes with metal ions in a single-step process, facilitating sharper end points. This means polydentate ligands, such as amino carboxylic acid derivatives, are most commonly employed in...
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Dynamic topomerization of Cu(I)-complexed pseudorotaxanes.
Meera Mohankumar1, Michel Holler, Michel Schmitt
1Laboratoire de Chimie des Matériaux Moléculaires, Université de Strasbourg et CNRS (UMR 7509), Ecole Européenne de Chimie, Polyméres et Matériaux, 25 rue Becquerel, 67087 Strasbourg Cedex 2, France.
Chemical Communications (Cambridge, England)
|December 13, 2012
Summary
Dynamic molecular motions in a copper(I)-complexed pseudorotaxane were observed. These movements arise from the folding of a flexible macrocyclic component, confirmed by NMR, X-ray crystallography, and computational analysis.
Area of Science:
- Supramolecular Chemistry
- Coordination Chemistry
- Molecular Dynamics
Background:
- Pseudorotaxanes are mechanically interlocked molecules with potential applications in nanotechnology.
- Understanding the dynamic behavior of macrocyclic components is crucial for designing functional supramolecular systems.
- Copper(I) complexes offer unique electronic and coordination properties relevant to molecular machines.
Purpose of the Study:
- To investigate the dynamic molecular motions within a Cu(I)-complexed pseudorotaxane.
- To elucidate the conformational changes associated with the folding of the macrocyclic component.
- To provide structural and computational evidence for observed molecular dynamics.
Main Methods:
- Variable temperature Nuclear Magnetic Resonance (NMR) spectroscopy to probe molecular motion.
- X-ray crystallography to determine static structures and conformational states.
- Computational studies (e.g., molecular modeling, DFT) to support experimental findings.
Main Results:
- Evidence of dynamic molecular motions was observed in the Cu(I)-complexed pseudorotaxane.
- Conformational changes were identified, linked to the folding of the flexible macrocyclic component.
- Variable temperature NMR data correlated with structural and computational results.
Conclusions:
- The study successfully evidenced dynamic molecular motions in the pseudorotaxane system.
- The folding of the macrocyclic component drives observed conformational changes.
- A combination of experimental and computational techniques provides a comprehensive understanding of the system's dynamics.