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Formation of the [Ge4O16Al48(OH)108(H2O)24]20+ Tetramer from Condensation of ε-GeAl12 Keggin Polycations

submitted on 03.09.2020, 01:41 and posted on 03.09.2020, 12:46 by Mohammad Shohel, Jennifer Bjorklund, Jack Smith, Sara E. Mason, Tori Z. Forbes
Keggin-type polyaluminum cations belong to a unique class of polyoxometalates (POMs) with their large positive charge, hydroxo bridges, and divergent isomerization/oligomerization. Previously reported oligomerizations of the polyaluminum cations were driven solely by the δ-Keggin isomer, which created Al26, Al30, and Al32 dimeric species. We herein report the isolation of largest ever Keggin-type structure for this system through a unique mode of self-condensation among four ε-GeAl128+ to form [NaGe4O16Al48(OH)108(H2O)24]21+(Ge4Al48). Elemental analysis confirms the Ge4+ substitution, and dynamic light scattering experiments indicated that these larger species exist in the thermally aged solutions. DFT calculations have revealed that a single atom Ge substitution in tetrahedral site of ε-Al137+ is the key for the formation this cluster because it activates the deprotonation at certain octahedral sites to assist self-condensation in a specific mode.


National Science Foundation grant number ACI-1548562 though allocation TG-GEO160006


Email Address of Submitting Author


University of Iowa


United States

ORCID For Submitting Author


Declaration of Conflict of Interest

No conflict of interest