Results and Discussion - New Synthetic Routes to Polyoxometalate Containing Ionic Liquids - page 81

wavenumber (cm -1 ) wavenumber (cm -1 )

Figure 44 Comparison of the IR spectra of ( 24 ) and ( 25 ). At the right side the IR-region containing
prominent cluster vibrations (encircled in red in the full spectrum at the left side) is enlarged.

The authors argued that the magnitude of this splitting can be taken as a measure of
the lack of interaction of the phosphate oxygen with the heterometal that depends on
how good the heterometal fits into the lacuna. So it can be assumed that the Fe(III) in
(Q 7 ) 4 [PW 11 O 39 Fe ( H 2 O)] shows better interaction with the phosphate oxygen than the
Cu(II) in (Q 7 ) 5 [PW 11 O 39 Cu ( H 2 O)] which also seems reasonable with respect to the
respective ionic radii (65 pm for Fe III vs. 73 pm for Cu II ) [82] . Concerning further studies of
the chemical behavior of these POM-ILs this finding may play a helpful role in
understanding their reactivity.

For synthesis of the POM-ILs containing bor-templated clusters the one step synthetic
route (II) was chosen because the monolacunary {BW 11 } is reported to be obtained only
in poor yields and as an unstable product. [77] So the complete cluster was formed in situ
by self-assembly of the WO 4 2- ; BO 3 3- and Cu 2+ /Fe 3+ building blocks. It is well known that
several factors such as the pH value, type of initial reactants and temperature have
crucial effect on the final products in the synthesis of POMs. In this case the pH is the