Structural variations within group 1 (Li-Cs)+ (2,2,6,6-tetramethyl-1-piperidinyloxy)- complexes made via metallic reduction of the nitroxyl radical.

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(-)) 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(-)) 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) 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(-)) 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) 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) 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.