10.1021/cm011524g.s002
Kyle L. Fujdala
Kyle L.
Fujdala
T. Don Tilley
T. Don
Tilley
New Vanadium Tris(<i>tert</i>-butoxy)siloxy Complexes and
Their Thermolytic Conversions to Vanadia−Silica
Materials
American Chemical Society
2002
VOSi 2 ss
VOSi 1 ss
material
OV
t BuO
IV
VOSi 3 xg
precursor
V 2 O 5 crystallite formation
calcination
VOSi 1 xg
TEM
PXRD
V 2 O 5 crystallites
O 2
transmission electron microscopy
VOSi 2 xg
V 2 O 5
New Vanadium Tris
Crystalline V 2 O 5
70 m 2 g
2002-02-13 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/New_Vanadium_Tris_i_tert_i_-butoxy_siloxy_Complexes_and_Their_Thermolytic_Conversions_to_Vanadia_Silica_Materials/3593439
The V(IV) alkoxysiloxy complexes (<i><sup>t</sup></i><sup></sup>BuO)<sub>3</sub>VOSi(O<i><sup>t</sup></i><sup></sup>Bu)<sub>3</sub> (<b>1</b>) and (<i><sup>t</sup></i><sup></sup>BuO)<sub>2</sub>V[OSi(O<i><sup>t</sup></i><sup></sup>Bu)<sub>3</sub>]<sub>2</sub> (<b>2</b>)
were synthesized via the silanolysis of V(O<i><sup>t</sup></i><sup></sup>Bu)<sub>4</sub> with 1 and 2 equiv of HOSi(O<i><sup>t</sup></i><sup></sup>Bu)<sub>3</sub>,
respectively. Complexes <b>1</b> and <b>2</b> are efficient single-source molecular precursors to
homogeneous V/Si/O materials via the <i>thermolytic molecular </i><i>precursor </i>method. The thermal
transformations of these complexes occurred at low temperatures (≤160 °C), via the
elimination of isobutene as the major carbon-containing product. Thermolyses of <b>1</b> in the
solid state and in solution (forming a xerogel in the latter case) yielded V/Si/O materials
(<b>VOSi1</b><b><sub>ss</sub></b> and <b>VOSi1</b><b><sub>xg</sub></b>, respectively) with low surface areas (30−40 m<sup>2</sup> g<sup>-1</sup>). After calcination
at 400 °C in O<sub>2</sub>, these materials exhibited powder X-ray diffraction (PXRD) patterns
consistent with the presence of V<sub>2</sub>O<sub>5</sub>. Similar thermolyses of <b>2</b> yielded V/Si/O materials
(<b>VOSi2</b><b><sub>ss</sub></b> and <b>VOSi2</b><b><sub>xg</sub></b>) that exhibited higher surface areas (up to 170 and 70 m<sup>2</sup> g<sup>-1</sup>,
respectively) and V<sub>2</sub>O<sub>5</sub> crystallite formation after calcination at 400 °C. Comparisons of
<b>VOSi1</b><b><sub>xg</sub></b> and <b>VOSi2</b><b><sub>xg</sub></b> with a previously reported V/Si/O xerogel (<b>VOSi3</b><b><sub>xg</sub></b>), generated from
the V(V) precursor OV[OSi(O<i><sup>t</sup></i><sup></sup>Bu)<sub>3</sub>]<sub>3</sub>, revealed interesting differences. Crystalline V<sub>2</sub>O<sub>5</sub> was
first observed in <b>VOSi3</b><b><sub>xg</sub></b> after calcination at only 300 °C in O<sub>2</sub>. Transmission electron
microscopy (TEM) and PXRD were used to determine that the average size of the V<sub>2</sub>O<sub>5</sub>
crystallites in the V/Si/O xerogels, after calcination at a given temperature, increased with
increasing silicon content of the precursor and was highest for the V(V) tris(siloxide). The
precursors containing vanadium in the lower oxidation state (IV) appear to initially provide
more homogeneous V/Si/O materials. Higher Si content for the precursor leads to a greater
surface area for the resultant material, but also to earlier phase separation during the
calcination process.