Synthesis and Structural Characterization of ... - Jacobs University

Chapter 3
Published Results
different synthetic pathways involving As 2 W 19 , but without success. We believe that the
potassium ion in the As 2 W 19 framework inhibits incorporation of an additional Yb 3+ ion. It is
interesting to note that when the same reaction was performed at pH = 2.0 in a 1M KCl
solution (instead of water), anion 13 is obtained rather than the expected
[YbAs 2 W 20 O 68 (H 2 O) 3 ] 7− , which confirms the role of potassium in mediating the reaction
pathway. We were also able to synthesize other lanthanide analogues of 13, namely
[Ln(H 2 O) 2 K(H 2 O) 2 As 2 W 19 O 67 (H 2 O)] 10− (Ln = La, Ce, Eu, Gd). The IR spectra of these
analogues are all very similar and virtually identical of 13 (see Figure 3.22).
Figure 3.22. IR spectra of KNa-13 (black line) and its four compositional analogues
[Ln(H 2 O) 2 K(H 2 O) 2 As 2 W 19 O 67 (H 2 O)] 10− (from top to bottom Ln = La, Ce, Sm, Eu, Gd).
The di-lanthanum(III) polyanion [La 2 (H 2 O) 6 As 2 W 19 O 67 (H 2 O)] 8−
(14) consists of two
AsW 9 subunits sandwiching one tungsten and two lanthanum(III) ions leading to a structure
with C 2v symmetry (see Figure 3.23). The unique tungsten atom in the central ‘belt’ is sixcoordinated,
whereas the two lanthanum ions are nine-coordinated with an average La−O
104