Synthesis of Gold Nanosheets through Thermolysis of Mixtures of ...

Fabrication of Gold Nanosheets through Thermolysis J. Chin. Chem. Soc., Vol. 56, No. 1, 2009 103
8a and 8b respectively. On the other hand, ionic [C 18 -
imH]Cl and [C 18 -imH][AuCl 4 ] possessed N(sp 2 )-H bonds,
therefore N-H bands were expected. Indeed [C 18 -imH]Cl
and [C 18 -imH][AuCl 4 ] showed strong N-H at 3417 (Fig.
8c) and 3293 (Fig. 8d) cm -1 respectively. The difference
in these two N-H positions is likely caused by the difference
between the hydrogen bonding interactions of NH
ClAuCl 3 and NH Cl; the latter has a stronger hydrogen
bonding interaction. The sample prepared by mixing a 1:1
molarof[C 18 -im]/[HAuCl 4 ] showed N-H at 3296 cm -1 (Fig.
8e), suggesting the presence of [C 18 -imH][AuCl 4 ]. At the
ratio of 4:1 a broad N-H band at 3417 cm -1 was observed,
indicating the presence of [C 18 -imH]Cl. This observation
can be reasoned that at 4:1 molar ratio, C 18 -im may have
better chance to react with AuCl 4 - to form neutral (C 18 -
im)AuCl 3 (eq. 2), therefore more [C 18 -imH]Cl may be
formed.
The 1 H-NMR spectra of C 18 -im (Fig. 9a), (C 18 -
im)AuCl 3 (Fig. 9b), [C 18 -imH]Cl (Fig. 9c), [C 18 -imH]
[AuCl 4 ] (Fig. 9d), [C 18 -im]/[HAuCl 4 ] (1:1) (Fig. 9e), and
[C 18 -im]/[HAuCl 4 ] (4:1) (Fig. 9f) in d 6 -DMSO were examined.
Because the chemical shifts of C 2,4,5 -H protons are
sensitive to the surrounding environment, they were used
to monitor the formation of each individual species. The
neutral C 18 -im and (C 18 -im)AuCl 3 and the ionic [C 18 -
imH]Cl and [C 18 -imH][AuCl 4 ]hadC 2,4,5 protons at 7.58,
7.12, 6.85; 9.08, 7.75, 7.65; 9.21, 7.79, 7.67, and 9.11,
7.75, 7.67 ppm, respectively. For the 1:1 mixture the corresponding
chemical shifts were at 9.11, 7.77, and 7.68 ppm.
These values were close to that of the ionic [C 18 -imH]
[AuCl 4 ], consistent with the results from IR studies. For the
4 to 1 mixture, the values at 8.65, 7.56, and 7.40 ppm could
not be assigned to any of the species mentioned. An exchange
of imidazole among C 18 -im, (C 18 -im)AuCl 3 ,[C 18 -
imH][AuCl 4 ]and[C 18 -imH]Cl may however explain the
results.
Diffractograms of C 18 -im (Fig. 10a), (C 18 -im)AuCl 3
(Fig. 10b), [C 18 -imH]Cl (Fig. 10c), [C 18 -imH][AuCl 4 ](Fig.
10d), [C 18 -imH]/[AuCl 4 ] (1:1) (Fig. 10e), and [C 18 -im]/
[HAuCl 4 ] (4:1) (Fig. 10f) are given and compared. Diffractogram
of the 1:1 mixture (Fig. 10e) showed patterns
corresponding to that of [C 18 imH][AuCl 4 ] and (C 18 -
im)AuCl 3 ; the former had a much higher (001) peak intensity
than that of the latter (around 3:2). Diffractogram for
the sample with molar ratio of 4:1 is complicated. Although
we were unable to identify the species in the 4:1 mixture
from the diffractogram, the observation of reflections with
corresponding d-spacings of 28.0, 14.0, and 9.3 Å suggests
the formation of lamellar structure.
Fig. 8. Infrared spectra of (a) C 18 -im, (b) (C 18 -
im)AuCl 3 , (c) [C 18 -imH]Cl, (d) [C 18 -imH]
[AuCl 4 ], (e) [C 18 -im]/[HAuCl 4 ] (1:1), and (f)
[C 18 -im]/[HAuCl 4 ] (4:1). All spectra were obtained
in KBr pellets.
Fig. 9. The 1 H-NMR of (a) C 18 -im, (b) (C 18 im)AuCl 3 ,
(c) [C 18 -imH]Cl, (d) [C 18 -imH][AuCl 4 ], (e)
C 18 im/HAuCl 4 (1:1), and (f) C 18 im/HAuCl 4
(4:1) in d 6 -DMSO.