Cation‐Directed Dimeric versus Tetrameric Assemblies of Lanthanide‐Stabilized Dilacunary Keggin Tungstogermanates

Abstract

Reaction of mid- to late lanthanide ions with GeO2 and Na2WO4 in NaOAc buffer results in a library of [Ln2 (GeW10O38)](6-) clusters (Ln2), which consist of dilacunary Keggin fragments stabilized by the insertion of 4f atoms in the vacant sites and show the ability to undergo cation-directed self-assembly processes. In the presence of Na(+), two β-Ln2 subunits assemble by means of Ln-O(WO5)-Ln bridges to form the chiral [Ln4(H2O)6(β-GeW10O38)2](12-) dimeric anions (ββ-Ln4, Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). When Cs(+) is present, two Ln4-like dimers further assemble into the [{Ln4(H2O)5(GeW10O38)2}2](24-) species (Ln8, Ln = Ho, Er, Tm, Yb, Lu). Two types of tetramers coexist in the solid state: One shows a full ββ-Ln8 architecture, whereas the other one is a mixed αβ-Ln8 assembly in which each β-subunit is linked to its corresponding α-Ln2 derivative. Regardless of differences in isomeric forms and the relative arrangement of Ln2 subunits, all anions display virtually identical {Ln4} cores as a common structural feature. A combination of ESI mass spectrometry and (183)W NMR spectroscopy experiments indicates that Ln8 tetramers fragment into Ln4 dimers upon dissolution, which undergo partial dissociation into Ln2 monomers and slow dimer/monomer equilibration. This is most likely followed by β-to-α isomerization of Ln2 clusters with consequent reassembly, as indicated by isolation of three additional αα-Ln4 derivatives. Magnetic and photoluminescence properties in the Na-ββ-Ln4 series are also discussed.

Ln12‐Containing 60‐Tungstogermanates: Synthesis, Structure, Luminescence, and Magnetic Studies

“…showed that {GeW 10 } fragments can also be formed in situ by direct reaction of Na 2 WO 4 , GeO 2 , and lanthanide sources in acetate buffer 6d. g, 10j…”

Crown‐Shaped Tungstogermanates as Solvent‐Controlled Dual Systems in the Formation of Vesicle‐Like Assemblies

“…Analogous studies carried out for mid-to-late lanthanides showed that dimerica nions based on similar Ln 2 subunits were obtained for Ln = Gd to Lu in the presence of exclusively Na + ,w hereas tetrameric speciesw ere isolated for Ln = Ho to Lu when Cs + wasa dded. [15] NeitherK + nor [Ni(H 2 O) 6 ] 2 + played any structuralroleinthis case. The variety of POM frameworks afforded by this approach led us to extend our work to the whole group of early lanthanides (Ln = La to Sm) to explore whether additional Ln 2 -based POM aggregates exist.…”

“…[14] The use of mid-to-late lanthanides insteado fC e III led to the isolation of smaller dimeric or tetrameric species. [15] These POMa ggregates are all based on different but closely related[ Ln 2 GeW 10 O 38 ] 6À (Ln 2 ) subunits and they show complex behavior in aqueous solution that originates from partial fragmentation upon dissolution with consequent dissociation into oligomers and/ori ndividual Ln 2 clusters.…”

A Nanosized Gly‐Decorated Praseodymium‐Stabilized Selenotungstate Cluster: Synthesis, Structure, and Oxidation Catalysis

“…Although Pr1 exhibits distortedm onocapped square-antiprismatic geometry and Pr2 adopts at ricapped triangular prism geometry,t hey are both nine-coordinated andt heir coordination environment is very similar (Figure 2b) (19) ), and one m 3oxo atom (O89/O93;P r1ÀO: 2.604 (14) ;P r2ÀO: 2.592 (15) ), which is coordinated to one Se atom and one Wa tom from the {Se 2 W 7 O 30 H 2 }u nit and one Pr1/Pr2 atom simultaneously (Figure 2a). In contrast, Pr3 is eight-coordinated in ab icapped triangularp rism geometry,w hich is coordinated to twoa vailable terminal oxygen atoms from the {Se 2 (2) ), and one m 3 -oxo atom (O84;P r3ÀO: 2.561 (15) ), which is coordinatedt oo ne Se atom and one Wa tomf rom the {Se 2 W 7 O 30 H 2 }u nit and one Pr3 atom (Figure 2b).…”

“…The diversity of polyoxometalates (POMs) has never ceasedt o amaze us with their aesthetically pleasing structures and their potentiala pplicationsi nm any areas, such as catalysis, medicine, magnetism, andm aterials science. [1][2][3][4][5][6] In the context of designing and synthesizing polynuclear clusters, of particular interestt os cientific researchers is the fact that polynuclear anionic metal-oxo clusters can be formed throught he assembly of small oxometalate units (traditionally W, Mo, or V) by controlling flexible reaction parameters (e.g.,p H, temperature, molar ratio of the reactants, reactions olvents). [7][8][9] Perhaps based on this concept, an especially enlightening versatile one-pot self-assembly synthesis remains an important synthetic strategy to construct high-nuclearity polyoxotungstates (POTs), particularly POTst hat contain nonconventional heteroatoms Se IV and Te IV ,w hichm ainly result from the difficulty of separating as table synthetic Se IV or Te IV precursor.…”