Synthesis and Structural Characterization of ... - Jacobs University

Chapter 5
Published Results
Although we followed exactly the synthetic procedure for [TeW 9 O 33 ] 8– published by
Gaunt et al., 11
we were unable to confirm the existence of this compound. Instead, we
obtained the two novel tungstotellurate polyanions 26 and 27. In order to test whether a
mixture of the sodium salts of 26 and paradodecatungstate would react to yield POMs
containing the [TeW 9 O 33 ] 8– unit, we added such a mixture of crystals (sodium salts of 26 and
[H 2 W 12 O 42 ] 10- ) to a solution of CuCl 2·2H 2 O in sodium acetate buffer (pH 4.8). This reaction
mixture was heated to 90 ˚C for 1 h and filtered after cooling, and then a few drops of 1M
KCl solution were added. Slow evaporation at room temperature led to the formation of green
crystals of K 9 Na[Cu 3 (H 2 O) 3 (α-TeW 9 O 33 ) 2 ]. 9 We note, however, that the IR spectrum reported
by Gaunt et al. is not identical to the one we obtained; therefore, the question of whether
uncomplexed [TeW 9 O 33 ] 8– can be isolated is still an open one.
5.A.1.5. Conclusions
We have successfully synthesized and structurally characterized by IR spectroscopy, TGA
and single crystal X-ray diffraction a novel tellurium containing, polytungstate,
[H 2 Te 4 W 20 O 80 ] 22− (26). This polyanion was synthesized in aqueous sodium chloride medium
by reaction of Na 2 WO 4 with TeO 2 at pH 7.5. Polyanion 26 was isolated as a sodium salt and
crystallized in the triclinic space group P1̅. Single crystal X-ray structural analysis showed
that 26 is composed of a 20-tungsten polyanion unit {W 20 } coordinated to four tellurium ions
having coordination number four. The 20-tungstate unit {W 20 } consists of two {W 10 } subunits
which are connected by a total of four Te-O-W bridges. The decatungstate {W 10 } subunit has
not been reported before. Each {W 10 } subunit contains a pair of face-shared octahedra and
two tellurium(VI) ions having a see-saw type geometry. In addition, we have synthesized and
structurally characterized by IR spectroscopy and single crystal X-ray diffraction another
novel tellurium-containing polytungstate [NaTeW 15 O 54 ] 13− (27). Polyanion 27 could not be
obtained as a bulk pure material because it co-crystallized with two other species.
180