. Octa-nuclear uranyl-oxalate network reinforced by U-shaped zwitterionic dicarboxylate linkers

. Crystal structure of compound 1

. Crystal structure of compound 2

. Crystal structure of compound 3

. pH-dependent regulation of hydrothermal reactions of m-Xyl-BPy4CA linkers and uranyl

. Different optical morphologies of 1 with octa-nuclear uranyl (U8) motifs, 2 with binuclear uranyl (U2) motifs and 3 with monomeric uranyl (U1) motifs

. Experimental and simulated patterns of powder X-ray diffraction (PXRD) of compound 1

. Experimental and simulated patterns of powder X-ray diffraction (PXRD) of compound 2

. Experimental and simulated patterns of powder X-ray diffraction (PXRD) of compound 3

. (a) A nearly planar geometry of U8 motif found in this work; (b) a non-planar U8 motif with cation-cation interactions (CCIs) reported by Loiseau, et al^[1]

. (a-b) Eight-connected U8 motif with four oxalate (Ox) and four m-Xyl-BPy4CA (L) moieties extends from four directions through oxalate ligands (a), which thus connecting four adjacent ones with each oxalate ligand going together with a U-shaped bidentate m-Xyl-BPy4CA linker (b); (c) U8-based uranyl-oxalate 2D network (enlarged diagram: a minimum rhombic loop); (d) U8-based uranyl-oxalate 2D network with all the cross-linking m-Xyl-BPy4CA linkers omitted for clarity (enlarged diagram: a minimum rhombic loop in size of 1.193 nm× 1.077 nm)

. Each U8 motif displays a different overall orientation from that of its adjacent U8 with an angle of inclination of 36.6(4)° (a), resulting in a distortion of the rhombic loop (b)

. Hydrogen bonds between double loops and two nitrate anions

. Two ‘U’-shaped bidentate m-Xyl-BPy4CA ligands located in the cavity of rhombic loop crosslink all the four U8 motifs through coordination bonds and hydrogen bonds (bottom) where one m-Xyl-BPy4CA ligand points upwards (top left) and the other points downwards from the opposite direction (top right)

. Hydrogen bonds between adjacent layers of 2D sheets through U8 motifs that interact with neighboured m-Xyl-BPy4CA from another sheet or m-Xyl-BPy4CA interacting with neighboured uranyl group from another sheet

. Some examples of high-nuclear uranyl motif based on nonlinear multi-topic organic ligands, as suggested by the cases of pentanuclear (U5), hexanuclear (U6) and octanuclear (U8) uranyl motifs derived from sulfobenzoate precursors^[2], ortho-position or meta-position aromatic/heteroaromatic dicarboxylate^[3,4], calixarene ligand^[3] and U-shaped linkers used in this work

. Different molecular conformation of m-Xyl-BPy4CA linker in 1 and 2 demonstrating its flexibility in molecular conformation

. Thermogravimetric analysis (TGA) of compounds 1, where 1 starts to decompose at ~295 ℃, and finally transforms to U₃O₈ with residual weight of 69.31% (theoretical value: 70.25%)

. Thermogravimetric analysis (TGA) of compounds 2, where 2 starts to decompose at ~233 ℃, and finally transforms to U₃O₈ with residual weight of 40.95% (theoretical value: 40.20%)

. Fourier transform infrared (IR) spectra of compounds 1 (U8 motif, blue line), 2 (U2 motif, red line) and 3 (U1 motif, black line) with characteristic symmetric ν1vibrations at 915, 911 and 910 nm, respectively

. The Raman spectra of compounds s 1 (U8 motif) and 3 (U1 motif) with characteristic asymmetric ν3 vibrations (1: 833 and 863 cm^-1; 3: 829 and 860 cm^-1)

. Solid-state fluorescence spectra of compound 1 and 2 as compared to that of uranyl nitrate (UO₂(NO₃)₂): 1, a broad peak ranging from 530 to 550 nm; 2, five main emission bands located at 499, 520, 543, 568 and 596 nm; UO₂(NO₃)₂, 488, 511, 534, 561 and 589 nm

. ¹H NMR of [m-Xyl-BPy4CEt]Br₂ (500 MHz, 298 K, D₂O)