$Ln^{III}$-functionalized mono- and bi-vacant Wells-Dawson-type polyoxotungstates : discrete and extended architectures

Wang, Wenyan; Kögerler, Paul (Thesis advisor); Ullrich, Englert (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

In this work the possibilities to functionalize lacunary Wells-Dawson-type polyanions (α2-P2W17O61]10−, [α-P2W15O56]12− and [α-H2P2W12O48]12−) and Keggin-type ([α-PW11O39]7−) polyoxophosphotungstates with lanthanides and organophosphonates have been investigated.It was found that in aqueous medium self-assembly one-pot reactions of the POT precursor, LnIII salt and an organophosphonic acid do not lead to the desired bi-functionalized products but rather exclusively result in lanthanide complexes of the most stable monolacunary Wells-Dawson [α2-P2W17O61]10− and Keggin [α2-PW11O39]7−-type polyanions which do not have any organophosphonate groups, despite of large variations of pH, reaction time and temperature and the reagents ratios tested.Several novel Ln-substituted POTs with discrete and 1D and 2D polymeric structures have been isolated as the hydrated mixed alkali metal / tetramethylammonium salts and thoroughly characterized by various analytical techniques. The discrete polyanions [{(H2O)3CeIII(α2-P2W17O61)}2]14- and [{(H2O)3CeIII(α-PW11O39)}2]8- appeared to be quite stable in aqueous solu-tions and showed very interesting electrochemical behavior with several reversible processes attributed to multiple WVI / WV as well as CeIII / CeIV transitions and thus, may represent a significant interest as potential catalysts and photocatalysts for various redox processes. It was also found that the type of the product forming in the LnIII / {α2-P2W17} and LnIII / {α-PW11} is extremely sensitive to even small modifications of the synthetic conditions and, thus, de-spite of their seeming simplicity, these systems can offer an impressive flexibility, allowing for isolation of numerous structures of various unclarities, dimensionalities and topologies.In contrast, post-functionalization approach, employing reactions of the pre-functionalized with phenylphosphonate groups POT, [α2-P2W17O61(P(=O)C6H5)2]6-, with LnIII and YIII salts in aqueous medium, led to isolation of large series of discrete polyanions formula [(H2O)8LnIII2(α2,α2’-P2W16O60)(C6H5PO)2]8- (Ln = La, Ce, Pr, Sm, Gd, Tb, Dy, Ho, Er, Yb and Y) and a 1D coordination polymer [(H2O)8CeIII2(α2,α2’-P2W16O60)(C6H5PO)2]n4n−, bearing both LnIII ions as well as organophosphonate moieties in their structures. Formation of these compound occurs via so far unprecedented formation of the additional lacunary sites in al-ready pre-functionalized POTs. Moreover, these derivatives represent the first examples of the complexes based on before unknown dilacunary Wells-Dawson-type {α2,α2-P2W16O60} moie-ties. The GdIII, DyIII, HoIII and ErIII derivatives showed slow relaxation processes indicative of single molecule magnetic behavior.

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