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2016
ACL
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Sahnun Mohamud, Vinh Ta Phuoc, Leire del Campo, Néstor E.Massa, Silvina Pagola, 'TTF-DDQ: Two “green” synthetic routes, crystal structure and band gap from FT-IR spectroscopy', Synth. Met. 214 71-75 (2016) doi:10.1016/j.synthmet.2016.01.016
TTF-DDQ (DDQ = 2,3-dichloro-5,6-dicyano-p-benzoquinone) is an ionic and diamagnetic charge transfer
salt. Polycrystalline powders of TTF-DDQ were obtained by three synthetic methods: solvent evaporation
from MeCN solution (1), MeCN vapor digestion (2), and mechanochemistry (liquid assisted grinding with
DMSO) (3). The analysis of the synchrotron X-ray powder diffraction data of 1 afforded the crystal
structure, which is isomorphous to that of the black polymorph of TTF-CA (CA = chloranil). TTF-DDQ is
composed of (TTF+)2 and (DDQ)2 dimeric radical ions arranged in segregated columnar stacks, linked
by weak hydrogen bonds. The
Cl and
CN substituents in DDQ are disordered, and this was modeled
by Rietveld analysis.
The FT-IR absorption spectra as a function of the temperature in the 300–10 K interval showed an
absorption edge, indicating that TTF-DDQ is a semiconductor with a small band gap of (0.21
0.01) eV.
The monotonous evolution of the FT-IR spectra denotes the absence of crystallographic phase transitions
in the temperature interval studied, likely due to the thermodynamic stability of this packing motif
compared to the less stable donor-acceptor alternating stacks; or the segregated, potentially conducting
stacks.
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