title: Structural variations within group 1 (Li-Cs)+ (2,2,6,6-tetramethyl-1-piperidinyloxy)- complexes made via metallic reduction of the nitroxyl radical.
abstract: 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.
authors.affiliation: WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1XL, UK.
authors.forename: Liam
authors.initials: L
authors.lastname: Balloch
authors.forename: Allison M
authors.initials: AM
authors.lastname: Drummond
authors.forename: Pablo
authors.initials: P
authors.lastname: García-Alvarez
authors.forename: David V
authors.initials: DV
authors.lastname: Graham
authors.forename: Alan R
authors.initials: AR
authors.lastname: Kennedy
authors.forename: Jan
authors.initials: J
authors.lastname: Klett
authors.forename: Robert E
authors.initials: RE
authors.lastname: Mulvey
authors.forename: Charles T
authors.initials: CT
authors.lastname: O'Hara
authors.forename: Philip J A
authors.initials: PJ
authors.lastname: Rodger
authors.forename: Iain D
authors.initials: ID
authors.lastname: Rushworth