Formation of N, N, N′, N′-tetramethylformamidinium disulphide from the chemical and electrochemical oxidation of tetramethylthiourea: Vibrational spectra and crystal structure of the chloride dihydrate salt
The N, N, N′, N′-tetramethylformamidinium disulphide (TMFDS) was prepared from either the electro-oxidation of tetramethylthiourea (TMTU) on platinum electrodes in aqueous perchloric acid solution or the chemical oxidation of TMTU with hydrogen peroxide in hydrochloric acid-containing absolute ethan...
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Published in | Journal of molecular structure Vol. 871; no. 1; pp. 131 - 139 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier B.V
15.12.2007
|
Subjects | |
Online Access | Get full text |
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Summary: | The
N,
N,
N′,
N′-tetramethylformamidinium disulphide (TMFDS) was prepared from either the electro-oxidation of tetramethylthiourea (TMTU) on platinum electrodes in aqueous perchloric acid solution or the chemical oxidation of TMTU with hydrogen peroxide in hydrochloric acid-containing absolute ethanol. The electrochemical formation of TMFDS at different potentials was followed by
in situ FTIRRAS spectroscopy. The IR and Raman spectra of TMFDS chemically formed as a chloride dihydrate were determined and compared to the product produced electrochemically. The crystal structure of the chloride salt [N(CH
3)
2]
2C
S
S
C [N(CH
3)
2]
2Cl
2·2H
2O, as determined by X-ray diffraction, crystallises in the monoclinic
C2/
c space group with
a
=
23.267(1),
b
=
10.824(1),
c
=
17.774(1)
Å,
β
=
126.91(1)°, and
Z
=
8. The structure was solved from 2489 reflections with
I
>
2
σ(
I) and refined to an agreement
R1-factor of 0.0405. The two molecular halves of the dimeric
[
N
(
CH
3
)
2
]
2
C
S
S
C
[
N
(
CH
3
)
2
]
2
2
+
ion are linked by a disulphide single bond [
d(S
S)
=
2.0454(9)
Å] and related to each other by a non-crystallographic pseudo two-fold axis. DFT structure optimisation and normal mode frequencies were calculated using the 6-311G(d,f) basis set at DFT theory level. An estimation of the free energy for the dimer formation and rate ratio for the homogeneous and heterogeneous processes are presented. These data are consistent with the electrochemical mechanism of the anodic formation of TMFDS
2+ from TMTU electro-oxidation in acid solutions. |
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ISSN: | 0022-2860 1872-8014 |
DOI: | 10.1016/j.molstruc.2007.02.004 |