水力压裂将页岩暴露于酸性水力压裂流体(HFF)中,释放有毒铀(U)以及所需的石油和天然气。由于没有现有的方法来确保U保持在页岩中,这项研究试图将有机配体添加到HFF中,以探索页岩中潜在的U保留。为了测试这种可能性,培养建立了乙酸铀酰和一种有机联吡啶配体(2,2'-,2,3\'-,2,4\'-,或4,4'-联吡啶)添加到原始HFF中作为结晶介质。几个月后,所有挥发物完全蒸发,从孵育中获得大块黄色结晶材料,其中三个产生了适合单晶分析的晶体,产生两个新颖的结构和前述化合物的高质量结构。UO2VI乙酸盐络合物双(乙酸-κ2O,O\')(2,2\'-联吡啶-κ2N,N\')二氧化二(VI),[U(C2H3O2)2O2(C10H8N2)2]或[2,2'-联吡啶]UVIO2(CH3CO2)2,(I),和双(乙酸-κ2O,O\')(2,4\'-联吡啶-κN1\')二氧化二(VI),[U(C2H3O2)2O2(C10H8N2)2]或[2,4'-联吡啶]2UVIO2(CH3CO2)2,(III),在伪六边形双锥体配位几何中包含八坐标UVI,并且是分子,通过弱C-H包装..O/N交互,而catena-聚[双(2,3'-联吡啶)[二-μ-乙酸-μ3-羟基-μ-羟基-二-μ3-氧化-六氧三铀(VI)]-2,3'-联吡啶-水(1/1/1)],(C10H9N2)2[U3(C2H3O2)2O8(OH)2]·C10H8N2·H2O或{[2,3'-联吡啶]2[2,3'-联吡啶][(UVIO2)3(O)2(OH)2(CH3CO2)2·H2O]}n,(II),形成离子一维聚合物,具有七个坐标的五边形双锥体UVI中心和每个链中的氢键相互作用。这些晶体的形成可能表明联吡啶在压裂过程中与页岩中的U结合的潜力,这将在未来的研究中通过ICP-MS(电感耦合等离子体质谱)分析HFF/联吡啶/页岩孵化中的U浓度进行探索。分子结构之间的变化可能表明联吡啶异构体与U形成络合物的能力不同,这可能会影响他们在水力压裂的背景下将U保留在页岩中的能力。
Hydraulic fracking exposes shale plays to acidic hydraulic fracking fluid (HFF), releasing toxic uranium (U) along with the desired oil and gas. With no existing methods to ensure U remains sequestered in the shale, this study sought to add organic ligands to HFF to explore potential U retention in shale plays. To test this possibility, incubations were set up in which uranyl acetate and one organic bipyridine ligand (either 2,2\'-, 2,3\'-, 2,4\'-, or 4,4\'-bipyridine) were added to pristine HFF as the crystallization medium. After several months and complete evaporation of all volatiles, bulk yellow crystalline material was obtained from the incubations, three of which yielded crystals suitable for single-crystal analysis, resulting in two novel structures and a high-quality structure of a previously described compound. The UO2VI acetate complexes bis(acetato-κ2O,O\')(2,2\'-bipyridine-κ2N,N\')dioxidouranium(VI), [U(C2H3O2)2O2(C10H8N2)2] or [2,2\'-bipyridine]UVIO2(CH3CO2)2, (I), and bis(acetato-κ2O,O\')(2,4\'-bipyridine-κN1\')dioxidouranium(VI), [U(C2H3O2)2O2(C10H8N2)2] or [2,4\'-bipyridine]2UVIO2(CH3CO2)2, (III), contain eight-coordinate UVI in a pseudo-hexagonal bipyramidal coordination geometry and are molecular, packing via weak C-H...O/N interactions, whereas catena-poly[bis(2,3\'-bipyridinium) [di-μ-acetato-μ3-hydroxido-μ-hydroxido-di-μ3-oxido-hexaoxidotriuranium(VI)]-2,3\'-bipyridine-water (1/1/1)], (C10H9N2)2[U3(C2H3O2)2O8(OH)2]·C10H8N2·H2O or {[2,3\'-bipyridinium]2[2,3\'-bipyridine][(UVIO2)3(O)2(OH)2(CH3CO2)2·H2O]}n, (II), forms an ionic one-dimensional polymer with seven-coordinate pentagonal bipyramidal UVI centers and hydrogen-bonding interactions within each chain. The formation of these crystals could indicate the potential for bipyridine to bind with U in shale during fracking, which will be explored in a future study via ICP-MS (inductively coupled plasma mass spectrometry) analyses of U concentration in HFF/bipyridine/shale incubations. The variation seen here between the molecular structures may indicate variance in the ability of bipyridine isomers to form complexes with U, which could impact their ability to retain U within shale in the context of fracking.