Treatment of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) with a group 1 metal (Li, Na, K, Rb, or Cs), resulted in the reduction of this important radical to the TEMPO(-) anion--the first examples of elemental-metal single electron reduction of the radical to its anionic form. The synthesis and characterization of seven alkali metal TEMPO(-) complexes are reported. A variety of structural motifs are encountered depending on the choice of metal and/or solvent. (THF)(2) x [Li(+)(TEMPO(-))](4) 1 crystallized from THF as a cyclic (Li(4)O(4)) molecule. Two Li centers are stabilized by coordination to a THF molecule; the others by intramolecular coordination to N(TEMPO) atoms. [(THF) x Na(+)(TEMPO(-))](4) 2 exists as a distorted cubane where each Na center is coordinated to a THF molecule. No appreciable Na-N(TEMPO) coordination is observed. [(THF)(2) x Na(+)(3)(TEMPO(-))(2)(OH)](2) 3 was serendipitously prepared and exists as a distorted bis(cubane). It is envisaged that 3 is formed from 2 by insertion of a (Na-OH)(2) double bridge into its framework. [Na(+)(4)(mu(3)-TEMPO(-))(2)(mu(2)-TEMPO(-))(2)(TMEDA)(2)] 4, adopts a four-runged ladder structure, whereby the two outer Na centers are coordinated to TMEDA, in addition to two mu(2)-O and a N atom. The inner metal atoms are bound to three mu(3)-O atoms and a N atom. [(THF) x K(+)(TEMPO(-))](4) 5 resembles the motif found for 2; however, presumably because of the larger size of the metal, K-N(TEMPO) interactions are present in 5. The asymmetric unit of [(TMEDA) x Rb(+)(2)(TEMPO(-))(2)](2) 6 comprises a Rb(4)O(4) cubane with half a molecule of TMEDA coordinated to each metal. From a supramolecular perspective, 6 exists as a polymeric array of cubane units connected by TMEDA bridges. Completing the series, [Cs(+)(TEMPO)](infinity) 7 crystallizes from hexane to form a donor-free polymeric complex. Complexes 1, 2, and 4-7 are soluble in D(8)-THF solution, and their NMR spectra are reported. The solution structures in donor solvent appear virtually identical.
Background: This paper describes the development of a novel non-invasive sampling and analysis method that can be used to assess the presence of volatile pesticides on objects held in heritage collections. Vapour phase sampling was conducted using sampling tubes loaded with Tenax-TA™ and trapped analytes were determined using thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). The results of this study are presented in a simple 'decision tree' diagram to provide the heritage sector with the best methods to identify the presence of pesticides in collections. To illustrate the use of the methodology developed, the results from two case studies in heritage institutions are presented.
A collection of 1980s Mexican rubberised cotton garments was investigated in order to assess conservation treatment options, to improve their long term storage conditions and to investigate the origin of the strong odour associated with the garments. Chemical and mechanical deterioration of the rubber was confirmed by FTIR and SEM analyses. Recommendations for remedial conservation were made after trials to re-shape a garment by the application of gentle heat. Passive diffusion tube sampling was carried out to assess the levels of acids, aldehydes and VOCs emitted from the garments. Very high concentrations of acetic acid off-gassing were confirmed and deemed a risk to the cotton fabric. Test set-ups in sealed ambient and anoxic conditions with and without the inclusion of MicroChamber® paper showed the effectiveness of this pollutant sorbent in reducing acetic acid levels as well as general odour emitted by the garments
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