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

doi:10.15541/jim20190118

Abstract

Abstract:

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.

Key words: actinide coordination polymers, octa-nuclear uranyl, U-shaped Linker, pH effect

CLC Number:

TQ174

WU Si,MEI Lei,HU Kong-Qiu,CHAI Zhi-Fang,NIE Chang-Ming,SHI Wei-Qun. pH-dependent Synthesis of Octa-nuclear Uranyl-oxalate Network Mediated by U-shaped Linkers[J]. Journal of Inorganic Materials, 2020, 35(2): 243-249.

Figures/Tables 26

Fig. 1 Octa-nuclear uranyl-oxalate network reinforced by U-shaped zwitterionic dicarboxylate linkers (a) two-dimensional coordination network; (b) octa-nuclear uranyl (U8) motif, [(UO2)8O4(μ3-OH)2(μ2-OH)2]4+; (c) U-shaped linker in a space- filling mode overlapped with its molecular structure; (d) U-shaped linker in a stick mode Color codes: uranyl polyhedra in yellow; U-shaped linkers in dark or blue

Fig. 2 Crystal structure of compound 1 (a) ORTEP view of compound 1 with the 30% probability level for thermal ellipsoids; (b) octa-nuclear uranyl (U8) motif in compound 1 showing detailed coordination spheres of all uranyl centers Color codes: uranium atoms in yellow; oxygen atoms in red; carbon atoms in dark gray; nitrogen atoms in blue; hydrogen atoms pale gray

Fig. 3 Crystal structure of compound 2 (a) ORTEP view of compound 2 with the 30% probability level for thermal ellipsoids; (b) coordination environment of each uranyl center for dimeric uranyl motif; (c-d) crystal lattice stacking for compound 2 viewed for c axis (c) and a axis (d) Color codes: uranium atoms in yellow; oxygen atoms in red; carbon atoms in dark gray; nitrogen atoms in blue; hydrogen atoms pale gray; the U-shaped linkers in green

Fig. 4 Crystal structure of compound 3 (a) ORTEP view of compound 3 with the 30% probability level for thermal ellipsoids; (b) coordination environments of uranyl center; (c-d) the extended structure based on one-dimensional oxalate-bridging monomeric uranyl chain with (c) or without (d) terminal isonicotinate ligands Color codes: uranium atoms or polyhedras in yellow; oxygen atoms in red; carbon atoms in dark gray; nitrogen atoms in blue; hydrogen atoms in pale gray

Fig. 5 pH-dependent regulation of hydrothermal reactions of m-Xyl-BPy4CA linkers and uranyl Color codes: uranium polyhedras in yellow; oxygen atoms in red; carbon atoms in gray; nitrogen atoms in blue

Fig. S1 Different optical morphologies of 1 with octa-nuclear uranyl (U8) motifs, 2 with binuclear uranyl (U2) motifs and 3 with monomeric uranyl (U1) motifs

Fig. S2 Experimental and simulated patterns of powder X-ray diffraction (PXRD) of compound 1

Fig. S3 Experimental and simulated patterns of powder X-ray diffraction (PXRD) of compound 2

Fig. S4 Experimental and simulated patterns of powder X-ray diffraction (PXRD) of compound 3

Fig. S5 (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]

Fig. S6 (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)

Fig. S7 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)

Fig. S8 Hydrogen bonds between double loops and two nitrate anions

Fig. S9 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)

Fig. S10 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

Fig. S11 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

Fig. S12 Different molecular conformation of m-Xyl-BPy4CA linker in 1 and 2 demonstrating its flexibility in molecular conformation

Fig. S13 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%)

Fig. S14 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%)

Fig. S15 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

Fig. S16 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)

Fig. S17 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

Fig. S18 1H NMR of [m-Xyl-BPy4CEt]Br2 (500 MHz, 298 K, D2O)

Compound 1
Bond	Distance/nm	Bond	Distance/nm
U(1)-O(1)	0.1748(17)	U(2)-O(3)	0.1752(15)
U(1)-O(2)	0.1770(2)	U(2)-O(4)	0.1751(15)
U(1)-O(9)	0.2208(13)	U(2)-O(9)	0.2275(12)
U(1)-O(12)	0.2327(15)	U(2)-O(10)	0.2193(14)
U(1)-O(13)	0.2506(14)	U(2)-O(15)	0.2466(14)
U(1)-O(14)	0.2440(18)	U(2)-O(16)	0.2578(14)
U(1)-O(18)	0.2426(16)	U(2)-O(17)	0.2380(17)
U(3)-O(5)	0.1746(17)	U(4)-O(7)	0.165(3)
U(3)-O(6)	0.178(2)	U(4)-O(8)	0.171(2)
U(3)-O(9)	0.2344(14)	U(4)-O(10)	0.2200(14)
U(3)-O(10)	0.2237(14)	U(4)-O(11)	0.242(2)
U(3)-O(11c)	0.248(2)	U(4)-O(11c)	0.2461(14)
U(3)-O(12)	0.2349(17)	U(4)-O(16)	0.249(2)
U(3)-O(19a)	0.2439(16)	U(4)-O(20d)	0.2399(16)
Compound 2
Bond	Distance/nm	Bond	Distance/nm
U(1)-O(1)	0.1776(2)	U(1)-O(4)	0.2364(2)
U(1)-O(2)	0.1784(2)	U(1)-O(5a)	0.2358(2)
U(1)-O(7)	0.2325(2)	U(1)-O(7a)	0.2339(2)
U(1)-O(1W)	0.2576(2)
Compound 3
Bond	Distance/nm	Bond	Distance/nm
U(1)-O(1)	0.182(3)	U(1)-O(4b)	0.244(2)
U(1)-O(1a)	0.182(3)	U(1)-O(5)	0.237(2)
U(1)-O(2)	0.240(2)	U(1)-O(6)	0.2307(18)
U(1)-O(3)	0.2397(19)

Compound 1
Hydrogen bond	D-H/nm	H··A/nm	D··A/nm	Angle/(°)
C6-H6···O6	0.093	0.215	0.305	165
C17-H17···O1	0.093	0.243	0.316	135
C18-H18···O13	0.093	0.242	0.330	159
C15-H15···O5	0.093	0.245	0.322	141
C16-H16A···O3	0.097	0.242	0.321	138
Compound 2
Hydrogen bond	D-H/nm	H···A/nm	D···A/nm	Angle/(°)
O7-H7···O10	0.073	0.216	0.285	161
C16-H16···O10	0.093	0.258	0.324	128
C15-H16···O9	0.093	0.298	0.358	123

	Compound 1	Compound 2	Compound 3
Formula	C₂₂H₁₆N₂O₂₀U₄	C₄₀H₃₈N₆O₂₂U₂	C₈H₅NO₈U
Formula weight	1580.49	1430.82	481.16
Crystal system	monoclinic	triclinic	orthorhombic
Space group	P2₁/c	P-1	Ibam
a/nm	1.15944(14)	0.98277(3)	2.6039(4)
b/nm	1.9854(3)	1.05830(4)	1.17462(13)
c/nm	1.5002(2)	1.15097(4)	0.91646(17)
α/(º)	90	82.951(2)	90
β/(º)	105.390(3)	88.168(2)	90
γ/(º)	90	66.735(2)	90
V/nm³	3.3296(8)	1.09126(7)	2.8031(7)
Z	4	1	8
T/K	296	297	293
F(000)	2760	680	1728
D_c/(g·cm^-3)	3.153	2.177	2.280
μ/mm^-1	^a19.480	^b 7.507	^c32.914
R_int	0.073	0.028	0.088
R₁, wR₂ (all data)	0.0646, 0.1536	0.0227, 0.0491	0.0755, 0.2833

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