Related Experiment Video
Updated: May 13, 2026
Design, Synthesis, and Photochemical Properties of Clickable Caged Compounds
Published on: October 15, 2019
Aperture-Controlled Cs+ Uptake/Release Kinetics and Extremely Short Cs+-π Contact in Open-Cage Cobalt(III)
Shigehisa Akine1,2, Sachiko Yano1
1Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kanazawa, Japan.
Abstract:
Cage-shaped molecules with an internal cavity provide platforms for molecular recognition. However, systematic control over guest exchange kinetics remains limited. Here, we report a series of cobalt(III) metallocryptands in which guest uptake/release rates are tuned by steric modulation of the cage apertures. The open-cage metallocryptands LCo3A6, bearing monoamine ligands (A = MeNH2, EtNH2, PrNH2) of different steric bulk, were synthesized and their Cs+ uptake/release behavior was investigated. The guest exchange rates depend strongly on the coordinated amine ligands, spanning timescales from 6.5 s to 24 min, which are significantly faster than those of the corresponding closed-cage analogue, LCo3(hda)3 (hda = 1,6-hexanediamine). X-ray crystallographic analyses confirmed that the Cs+ ion is completely encapsulated within the cavity to form robust cation-in-cation structures, despite the tricationic nature of the cryptand host. These analyses further revealed unusually short Cs+-π distances in the range of 2.98-3.04 Å, significantly shorter than the previously reported range of 3.3-3.6 Å, due to geometrical constraints imposed by the rigid metallocryptand framework with a 6.0 Å π-π spacing. Structural comparisons demonstrated that the steric bulk of the amine ligands modulates the cage aperture sizes, accounting for the observed kinetic trends.
More Related Videos
Related Concept Videos
03:02Colors and Magnetism
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.
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:42Valence Bond Theory
03:45Formation of Complex Ions
01:19Complexation Equilibria: The Chelate Effect
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...