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Cation‐Directed Dimeric versus Tetrameric Assemblies of Lanthanide‐Stabilized Dilacunary Keggin Tungstogermanates
Author(s) -
Artetxe Beñat,
Reinoso Santiago,
San Felices Leire,
Lezama Luis,
GutiérrezZorrilla Juan M.,
García José A.,
GalánMascarós José Ramón,
Haider Ali,
Kortz Ulrich,
Vicent Cristian
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201403028
Subject(s) - dimer , lanthanide , crystallography , monomer , chemistry , isomerization , dissociation (chemistry) , ion , nuclear magnetic resonance spectroscopy , stereochemistry , catalysis , polymer , biochemistry , organic chemistry
Reaction of mid‐ to late lanthanide ions with GeO 2 and Na 2 WO 4 in NaOAc buffer results in a library of [Ln 2 (GeW 10 O 38 )] 6− clusters ( Ln 2 ), 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‐ Ln 2 subunits assemble by means of Ln‐O(WO 5 )‐Ln bridges to form the chiral [Ln 4 (H 2 O) 6 (β‐GeW 10 O 38 ) 2 ] 12− dimeric anions (ββ‐ Ln 4 , Ln=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). When Cs + is present, two Ln 4 ‐like dimers further assemble into the [{Ln 4 (H 2 O) 5 (GeW 10 O 38 ) 2 } 2 ] 24− species ( Ln 8 , Ln=Ho, Er, Tm, Yb, Lu). Two types of tetramers coexist in the solid state: One shows a full ββ‐ Ln 8 architecture, whereas the other one is a mixed αβ‐ Ln 8 assembly in which each β‐subunit is linked to its corresponding α‐ Ln 2 derivative. Regardless of differences in isomeric forms and the relative arrangement of Ln 2 subunits, all anions display virtually identical {Ln 4 } cores as a common structural feature. A combination of ESI mass spectrometry and 183 W NMR spectroscopy experiments indicates that Ln 8 tetramers fragment into Ln 4 dimers upon dissolution, which undergo partial dissociation into Ln 2 monomers and slow dimer/monomer equilibration. This is most likely followed by β‐to‐α isomerization of Ln 2 clusters with consequent reassembly, as indicated by isolation of three additional αα‐ Ln 4 derivatives. Magnetic and photoluminescence properties in the Na ‐ββ‐ Ln 4 series are also discussed.