2,2,6,6-Tetramethyl-1-oxopiperidinetribromide and two forms of 1-hydroxy-2,2,6,6-tetramethylpiperidinium bromide salt: Syntheses, crystal structures and theoretical calculations
Abstract
The reaction of the nitroxy radical 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) with Br2 has been investigated with CCl4 and hexane to obtain TEMPO-Br salts: 2,2,6,6-tetramethylpiperidine-1-oxopiperidine tribromide [TEMPO] [Br3- ] (I), and the 1-hydroxy-2,2,6,6-tetramethylpiperidinium bromide salts [TEMPH+OHBr-] (II and III). The salt I was isolated in crystalline form directly from the synthesis and II and III by only changing the solvent. The crystals of I belong to the orthorhombic crystal systems with space group Cmc21, a = 10.5596(4) Å, b = 14.0464(4) Å, c = 9.4202(5), and with asymmetric unit of Z = 4. Crystals II belong to Pnna a = 11.9860(3) Å, b = 23.6720(9) Å, c = 7.7051(3) Å while III belongs to Cmc21 with a = 10.2686(3) Å, b = 10.7661(3) Å, c = 10.0274(2) Å; the asymmetric unit of II and III was Z = 8 and Z = 4, respectively. The crystal structure of I shows the Br3- ion as [Br-Br-Br]- for each molecule of TEMPO. The crystal structure of II shows a weak intermolecular hydrogen bond between -N-H⋯Br(1) and O(1)H⋯Br(2) due to the presence of the -N+HOH- moiety. In contrast, crystal III shows intermolecular hydrogen bonding between O(1)H⋯Br(1)⋯HN(1) due to the -N+HOH- moiety. The resulting compounds were characterized by FT-IR and UV-vis spectroscopy. The structural parameters have been compared with the related hydroxylaminotrichlorosilane known from the literature and with results of DFT calculations.
- Publication:
-
Journal of Molecular Structure
- Pub Date:
- January 2016
- DOI:
- 10.1016/j.molstruc.2015.09.020
- Bibcode:
- 2016JMoSt1103..254J
- Keywords:
-
- Radicals;
- Br<SUB>3</SUB><SUP>-</SUP> ion;
- TEMPO;
- X-ray diffraction;
- Reaction mechanisms;
- Bromide 1-hydroxy-2;
- 2;
- 6;
- 6-tetramethyl-1-piperidinium salt;
- Computational chemistry