Alkali metal complexes of a pendant arm tetraaza macrocycle. Equilibrium, inter- and intramolecular exchange process
Date
1996
Authors
Lincoln, S.
Whitbread, S.
Politis, S.
Stephens, A.
Lucas, J.
Dhillon, R.
Wainwright, K.
Editors
Advisors
Journal Title
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Volume Title
Type:
Journal article
Citation
Journal- Chemical Society Dalton Transactions, 1996; 7(7):1379-1384
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Abstract
The stabilities log(K/dm<sup>3</sup> mol<sup>-1</sup>) of [ML<sup>1</sup>]<sup>+</sup> formed by 1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane (L<sup>1</sup>) were found to vary with M<sup>+</sup> in the sequence Li<sup>+</sup> (8.07 ± 0.05 and 8.90 ± 0.05), Na<sup>+</sup> (6.66 ± 0.05 and 7.49 ± 0.05), K<sup>+</sup> (3.40 ± 0.05 and 5.91 ± 0.05), Rb<sup>+</sup> (3.00 ± 0.05 and 4.23 ± 0.05), Cs<sup>+</sup> (2.90 ± 0.05 and 4.04 ± 0.05) and Ag<sup>+</sup> (9.35 ± 0.04 and 14.00 ± 0.05), in acetonitrile and propylene carbonate, respectively, determined by potentiometric titration at 298.2 K and I = 0.05 mol dm<sup>-3</sup> (NEt<inf>4</inf>ClO<inf>4</inf>). Complexes of the parent macrocycle 1,4,7,10-tetraazacyclododecane (L<sup>2</sup>) are less stable. For the monomolecular decomplexation of [NaL<sup>1</sup>]<sup>+</sup> in acetonitrile and propylene carbonate the values k<inf>d</inf> (298.2 K) = 78.5 ± 1.0 and 26.1 ± 0.6 s<sup>-1</sup>, ΔH<inf>d</inf><sup>‡</sup> = 49.2 ± 0.3 and 57.7 ± 0.4 kJ mol<sup>-1</sup>, and ΔS<inf>d</inf>‡ = -43.7 ± 0.9 and -24.0 ± 1.0 J K<sup>-1</sup> mol<sup>-1</sup>, respectively, were determined by <sup>23</sup>Na NMR spectroscopy. Carbon-13 NMR spectroscopy showed that for the enantiomerisation of square-antiprismatic [LiL<sup>1</sup>]<sup>+</sup>, [NaL<sup>1</sup>]<sup>+</sup> and [KL<sup>1</sup>]<sup>+</sup> in methanol, k<inf>e</inf> (298.2 K) = 18 300 ± 3100, 7100 ± 220 and 7010 ± 200 s<sup>-1</sup>, ΔH<inf>e</inf><sup>‡</sup> = 41.3 ± 1.3, 24.6 ± 0.5 and 53.7 ± 0.6 kJ mol<sup>-1</sup>, and ΔS<inf>e</inf>‡ = -24.8 ± 5.9, -88.6 ± 1.8 and 8.8 ± 2.3 J K<sup>-1</sup> mol<sup>-1</sup>, respectively. For [LiL<sup>1</sup>]<sup>+</sup> and [NaL<sup>1</sup>]<sup>+</sup> enantiomerisation occurs much more rapidly than intermolecular exchange of L<sup>1</sup>, but for [KL<sup>1</sup>]<sup>+</sup> enantiomerisation occurs predominantly through intermolecular exchange of L<sup>1</sup>.