Synthesis and Structural Characterization of ... - Jacobs University

Chapter 1
Introduction
P 2 W 16 O 56 ] 12− which have an ability to coordinate transition metal and lanthanide ions. 54
Mialane’s group synthesized polyanions containing Cu(II) and Ln(III) cations by reaction of
the [A-α-SiW 9 O 34 ] 10− unit with the Cu(II) acetate and Ln(NO 3 ) 3 . 55 As well, Wang et al. have
been synthesizing several polyanions containing 3d-transition metal centers and having
lanthanide cations as linkers between the different POM units. 56 They also reported the
synthesis of a polyanion based 3d-4f heterometallic aggregate, constructed from three {α-
AsW 9 O 38 } fragments bridged by three {Fe-(μ 3- O) 3 -Ce} heterometalic clusters. 56c Reinoso et al.
reported [{Ce(H 2 O) 2 } 2 Mn 2 (B-α-GeW 9 O 34 ) 2 ] 8- polyanion constituting the first example of a
heterometallic 3d-4f cluster related to the Weakley-type dimeric structure, and it contains
Ce III 2Mn III 2O 20 rhomblike moiety. 57
The aforementioned three subclasses of this subfield in POM chemistry will be our
interests in this work. Firstly, the area of lanthanide-containing polyanions based on
isopolytungstate fragments has a lack of discovering of new units (rather than the
monolacunary Lindqvist [W 5 O 18 ] 6− anion) that can be stabilized by lanthanide ions. Hence,
the production of novel isopolytungstate based lanthanides represents a challenge in POM
syntheses and applications, especially with the labile coordination environment of the
lanthanides. This provides an impetus to prepare other, novel isopolyanion structures
coordinated to lanthanide ions. Secondly, it is more likely that the bulk of novel
lanthanide-containing polyoxotungstates will be based on heteropoly rather than isopoly
fragments. This is due to the fact that a large number of lacunary, stable heteropolytungstates
are known. Nevertheless, it becomes apparent that several lacunary heteropolytungstates have
not yet been reacted systematically with lanthanide ions. Trilacunary POM precursors and in a
particular lacunary POM precursors containing a hetero group with a lone pair of electrons
(e.g. As III , Sb III ) might result in unusual compounds. Thirdly, a paramagnetic 3d metal oxocluster
interacting with paramagnetic lanthanide centers is an interesting combination for
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