How Ions Arrange in Solution: Detailed Insight from NMR Spectroscopy of Paramagnetic Ion Pairs

Marko Damjanović; Takaumi Morita; Yoji Horii; Keiichi Katoh; Masahiro Yamashita; Markus Enders

doi:10.1002/cphc.201600804

How Ions Arrange in Solution: Detailed Insight from NMR Spectroscopy of Paramagnetic Ion Pairs

Chemphyschem. 2016 Nov 4;17(21):3423-3429. doi: 10.1002/cphc.201600804. Epub 2016 Sep 1.

Authors

Marko Damjanović¹, Takaumi Morita², Yoji Horii², Keiichi Katoh², Masahiro Yamashita², Markus Enders¹

Affiliations

¹ Institute of Inorganic Chemistry, Heidelberg University, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany), Tel: +49-6221-54-6247, Fax: +49-6221-54-161-6247.
² Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Sendai, 980-8578, Japan.

PMID: 27584046
DOI: 10.1002/cphc.201600804

Abstract

Ion pairing between the paramagnetic anion [Tb(obPc)₂ ]^- (obPc=2,3,9,10,16,17,23,24-octabutoxyphthalocyaninato), which has a very large magnetic anisotropy, with various diamagnetic counterions [P(Ph)₄ ]⁺ (1 a), [As(Ph)₄ ]⁺ (1 b), bis(triphenylphosphine)iminium ([PPN]⁺ , 1 c) and tetra-n-butylammonium ([TBA]⁺ , 1 d) was studied by means of ¹ H, ¹³ C, ¹⁴ N, and ³¹ P NMR spectroscopy in solution at various temperatures. The influence of the paramagnetic anion on the NMR spectroscopy properties of the diamagnetic cations allowed a detailed insight into the distances and relative orientations of the paired ions. Isotropic tumbling models for the description of the quaternary cations are inaccurate, particularly for [TBA]⁺ with its flexible butyl chains. The effects of temperature and concentration were also assessed. The advantage of this technique is that relatively large distances and the orientation between molecules or ions in solution can be studied.

Keywords: NMR spectroscopy; ion pairs; magnetic anisotropy; magnetic properties; pseudo-contact shifts.