pH-dependent Synthesis of Octa-nuclear Uranyl-Oxalate Network Mediated by U-shaped Linkers

In this work, we report a novel octa-nuclear uranyl (U8) motif [(UO2)8O4(μ3-OH)2(μ2-OH)2] 4+ embedded in a uranyl-oxalate coordination polymer (compound 1) based on a U-shaped linker with extra-long xylylene chains for stabilizing the resulting high-nuclear motif through additional cross-linking connectivity. A comparison with dimeric and monomeric uranyl compounds obtained at different pH value from the same hydrothermal system reveals that, solution pH plays a vital role in formation of this octa-nuclear uranyl motif by promoting hydrolysis of uranyl source. Since high similarity of eight uranium centers in this nearly planar U8 motif here, overlapping and broadening of signals in fluorescence, infra-red (IR) and Raman spectra can be found.