Controlling the extent of spin exchange coupling in 2,2,6,6- tetramethylpiperidine-1-oxyl (TEMPO) biradicals via molecular recognition with cucurbit[ n ]uril hosts

Song Yi, Burjor Captain, M. Francesca Ottaviani, Angel Kaifer

Research output: Contribution to journalArticle

36 Citations (Scopus)

Abstract

The binding interactions between two paramagnetic cobaltocenium guests and the hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated using a combination of electronic absorption, NMR, and electron paramagnetic resonance (EPR) spectroscopies, mass spectrometry, and X-ray crystallography. Guest 1, (4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl)cobaltocenium, forms very stable inclusion complexes with CB7 and CB8. However, CB7 interacts with 1 by including the organometallic cobaltocenium unit, while CB8 engulfs the TEMPO residue. The corresponding equilibrium association constant (K) values are 2.8 ± 0.3 × 106 M-1 for CB7•1 and 2.1 ± 1.0 × 108 M-1 for CB8•1. Biradical guest 2, 1,1′-bis(4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl) cobaltocenium, forms a very stable ternary complex with two CB8 hosts, in which each 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) residue is encircled by a host molecule. The structure of this ternary complex was confirmed in the solid state using single-crystal X-ray diffraction. Binding of the TEMPO side arms by the CB8 hosts gradually decreases the observed level of spin exchange coupling between the two nitroxide groups. In the final 2:1 complex, no spin exchange coupling was observed, but the initial levels of spin exchange coupling could be regenerated in a reversible fashion by adding a competing guest, adamantyltrimethylammonium (AdTMA), to the solution. The binding interactions between 2 and CB7 are similar but the stabilities of the 1:1 and 2:1 complexes are much lower than those of the corresponding CB8 complexes.

Original languageEnglish
Pages (from-to)5624-5632
Number of pages9
JournalLangmuir
Volume27
Issue number9
DOIs
StatePublished - May 3 2011

Fingerprint

Molecular recognition
Exchange coupling
spin exchange
X ray crystallography
Organometallics
crystallography
Mass spectrometry
Paramagnetic resonance
electron paramagnetic resonance
x rays
mass spectroscopy
Nuclear magnetic resonance
Association reactions
Single crystals
interactions
Spectroscopy
inclusions
solid state
X ray diffraction
nuclear magnetic resonance

ASJC Scopus subject areas

  • Electrochemistry
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Materials Science(all)
  • Spectroscopy

Cite this

Controlling the extent of spin exchange coupling in 2,2,6,6- tetramethylpiperidine-1-oxyl (TEMPO) biradicals via molecular recognition with cucurbit[ n ]uril hosts. / Yi, Song; Captain, Burjor; Ottaviani, M. Francesca; Kaifer, Angel.

In: Langmuir, Vol. 27, No. 9, 03.05.2011, p. 5624-5632.

Research output: Contribution to journalArticle

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abstract = "The binding interactions between two paramagnetic cobaltocenium guests and the hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated using a combination of electronic absorption, NMR, and electron paramagnetic resonance (EPR) spectroscopies, mass spectrometry, and X-ray crystallography. Guest 1, (4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl)cobaltocenium, forms very stable inclusion complexes with CB7 and CB8. However, CB7 interacts with 1 by including the organometallic cobaltocenium unit, while CB8 engulfs the TEMPO residue. The corresponding equilibrium association constant (K) values are 2.8 ± 0.3 × 106 M-1 for CB7•1 and 2.1 ± 1.0 × 108 M-1 for CB8•1. Biradical guest 2, 1,1′-bis(4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl) cobaltocenium, forms a very stable ternary complex with two CB8 hosts, in which each 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) residue is encircled by a host molecule. The structure of this ternary complex was confirmed in the solid state using single-crystal X-ray diffraction. Binding of the TEMPO side arms by the CB8 hosts gradually decreases the observed level of spin exchange coupling between the two nitroxide groups. In the final 2:1 complex, no spin exchange coupling was observed, but the initial levels of spin exchange coupling could be regenerated in a reversible fashion by adding a competing guest, adamantyltrimethylammonium (AdTMA), to the solution. The binding interactions between 2 and CB7 are similar but the stabilities of the 1:1 and 2:1 complexes are much lower than those of the corresponding CB8 complexes.",
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