Issue 6, 1987

A quantitative approach to host–guest interactions for matrix-isolated alkali-metal salts of hexafluoroanions and perchlorates

Abstract

From matrix-isolation i.r. studies it is demonstrated that heavier alkali-metal salts of a number of hexafluoroanions can be vaporised as molecular species. In all cases there is some decomposition and this is particularly serious for the non-transition elements. The i.r. spectrum of CsNbF6 in a range of matrix gases is reported in the Nb–F stretching region. It is found that for matrices where the host–guest interaction is expected to be weak (Ne, Ar) a characteristic doubling of ν3 of the NbF6 ion is observed. This is interpreted as due to the presence of a tridentate (facial) interaction between the caesium ion and the NbF6 anion. For matrices where the host-guest interaction is expected to be stronger (CO, N2) a characteristic triplet is observed and this is interpreted as due to a bidentate (edge) interaction between the caesium ion and the NbF6 ion. In an attempt to calibrate the host–guest interaction CsClO4 is studied in a range of matrix gases. The separation between the ‘terminal’ stretching frequency and the ‘bridge’ stretching frequency is taken as a measure of the interaction between the CsClO4 and the matrix. This leads to the following sequence in order of decreasing frequency separation: Ne > Ar > 02≈ F2 > Kr > Xe > N2 > CO. (Neon showing the greatest separation is assumed to have the smallest host-guest interaction.) When the above frequency separations for CsClO4 are plotted against those for CsNbF6 in the same matrix gases there is a close correlation between the two. Further, those matrices in which a doublet behaviour is observed for CsNbF6are precisely the ones which interact weakly in terms of the above sequence (Ne, Ar, O2, F2, Kr); a triplet is found for matrices showing a stronger interaction(CO, N2) For xenon (and to a lesser extent krypton) both doublet and triplet forms are present. The spectrum of CsNbF6 in a 1:1 mixture of argon and nitrogen is strikingly similar to that in xenon.

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1987, 1521-1527

A quantitative approach to host–guest interactions for matrix-isolated alkali-metal salts of hexafluoroanions and perchlorates

I. R. Beattie and K. R. Millington, J. Chem. Soc., Dalton Trans., 1987, 1521 DOI: 10.1039/DT9870001521

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Spotlight

Advertisements