Collect. Czech. Chem. Commun. 2009, 74, 73-84
Published online 2009-01-27 11:30:25

Quasi-elastic neutron scattering (QENS) studies on the 1:1 tetramethylpyrazine–1,2,4,5-tetracyanobenzene complex

Jan Krawczyka, Małgorzata Nowina Konopkaa, Jerzy A. Janika, Olav Steinsvollb, Grażyna Batorc, Andrzej Pawlukojćd, Eugeniusz Greche, Joanna Nowicka-Scheibee and Lucjan Sobczykc,*

a H. Niewodniczański Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31-342 Kraków, Poland
b Institute for Energy Technology, 2007 Kjeller, Norway
c Faculty of Chemistry, University of Wrocław, Joliot-Curie 14, 50-383 Wrocław, Poland
d Joint Institute for Nuclear Research, 141980 Dubna, Russia and Institute of Nuclear Chemistry and Technology, Dorodna 16, 03-195 Warsaw, Poland
e Institute of Chemistry and Environmental Protection, Szczecin University of Technology, Piastów Al. 12, 71-065 Szczecin, Poland


The quasi-elastic neutron scattering (QENS) spectra over the temperature range 10–270 K were studied. The activation energies for the stochastic jumps of methyl groups in neat tetramethylpyrazine (TMP) and in the complex TMP·TCNB (tetracyanobenzene) were estimated to be equal to 5.0 ± 1.2 and 2.2 ± 1.1 kJ/mol, respectively, which means that the methyl groups behave in the complex more freely than in TMP. This conclusion is in good agreement with frequencies of the CH3 torsional modes recorded in the inelastic neutron scattering (INS) spectra. They are also confirmed by the DFT calculations for the crystalline state of TMP and TMP·TCNB, although the calculations overestimate the effect of the crystalline state on the CH3 torsional frequencies. The difference in the behavior of the methyl groups in neat TMP and TMP·TCNB is also reflected in the blue-shift of the ν(CH) stretching vibration modes.

Keywords: CT complex; Tetracyanobenzene; Tetramethylpyrazine; QENS; IR spectroscopy; DFT calculations; Charge-transfer complexes.

References: 21 live references.