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Issue 4, 2016
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Reversible quantitative guest sensing via spin crossover of an iron(ii) triazole

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Abstract

A new phenyl-triazole-pyrazine ligand, 4-p-tolyl-3-(phenyl)-5-(2-pyrazinyl)-1,2,4-triazole (tolpzph), was prepared in order to enforce pyrazine coordination of the iron(II) centre in the resulting complex, [FeII(tolpzph)2(NCS)2]·THF (1·THF). Structure determinations carried out on this discrete mononuclear complex, 1·THF, at 273 K (mostly high spin) and 100 K (mostly low spin) demonstrate this was successful, and that spin crossover (SCO) occurred on cooling. Subsequent magnetic measurements on 1·THF revealed that it shows highly sensitive and reversible solvent-dependent SCO, with T1/2(1·THF) = 255 K vs. T1/2(1) = 212 K (with SCO of 1 more abrupt and occurring with a 4 K hysteresis loop), a drop of 43 K due to THF loss. This is reversible over at least 10 cycles of re-solvating with THF followed by re-drying, so 11·THF can be considered an ‘on–off’ THF sensor, monitored by the T1/2 reversibly shifting (by 43 K). Furthermore, quantitative sensing of the fractional amount of THF present in 1·nTHF, 0 ≤ n ≤ 1, is demonstrated. Monitoring the T1/2 and using TGA to quantify n(THF) revealed a linear dependence (25 data points; Pearson r2 = 0.93): T1/2 = 41.1n(THF) + 219. Finally, 1 is also shown to take up CHCl3 [T1/2(1·CHCl3) = 248 K], with a logarithmic T1/2 dependence on the fractional amount of CHCl3 present (10 data points; Pearson r2 = 0.98): T1/2 = 27.0 log10[n(CHCl3)] + 243. This study is a proof of principle that a (multi-use) quantitative sensor material based on spin crossover is feasible.

Graphical abstract: Reversible quantitative guest sensing via spin crossover of an iron(ii) triazole

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Supplementary files

Article information


Submitted
28 Nov 2015
Accepted
09 Feb 2016
First published
09 Feb 2016

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2016,7, 2501-2505
Article type
Edge Article

Reversible quantitative guest sensing via spin crossover of an iron(II) triazole

R. G. Miller and S. Brooker, Chem. Sci., 2016, 7, 2501
DOI: 10.1039/C5SC04583E

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