Synthesis and Structural Characterization of ... - Jacobs University

Chapter 2
Experimental
2.2.3 Thermogravimetry
Thermogravimetric (TGA) analyses were performed using a TA Instruments SDT Q600
thermobalance from room temperature to 900 ºC with a heating rate of 5°/min for 10-30 mg
of sample in alumina pans under 100 mL/min flow of nitrogen.
2.2.4 Multinuclear magnetic resonance spectroscopy
NMR spectra were recorded on a JEOL 400 ECX spectrometer operating at 9.39 T (400 MHz
for proton) magnetic field. Chemical shifts were given relative to external standards, 2 M
solution of Na 2 WO 4 for 183 W in D 2 O, Si(CH 3 ) 4 in CDCl 3 for 1 H- and 13 C-NMR and YCl 3 in
D 2 O for 89 Y-NMR. The resonance frequency employed was 16.656 MHz for 183 W. All
aqueous 183 W-NMR spectra were collected on highly concentrated solution.
2.3 Preparation of starting materials
Synthetic procedures of starting materials (lacunary POM precursors) that served as building
blocks for all the heteropolyoxotungstates presented in this work are detailed in the following
sections.
2.3.1 Synthesis of K14[As2W19O67(H2O)]
0.89 g (4.5 mmol) of As 2 O 3 , 18.8 g (57.0 mmol) of Na 2 WO 4·2H 2 O, and 0.67 g (9.0 mmol) of
KCl were added to 50 mL H 2 O at 80˚ C with stirring. After dissolution, the pH was adjusted
to 6.3 by adding 12 M HCl dropwise. The solution was kept at 80˚ C for 10 min and then
filtered. Finally 15 g KCl was added and the solution stirred for 15 minutes. The white
precipitate formed was isolated by filtration and dried at 80˚ C. 4
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