Inorganic Chemistry Communications 9 (2006) 397–399 www.elsevier.com/locate/inoche
A uranium–potassium-organic framework solids: Hydrothermal synthesis, structure, and property of K[(UO2)3 (l3-OH)3(l2-OH) (C7H4O4N)2]OH Weihai Zhang, Jianshe Zhao
Shaanxi Key Laboratory of Physico-Inorganic Chemistry, Department of Chemistry, Northwest University, Xi’an, Shaanxi 710069, China Received 6 October 2005; accepted 5 January 2006 Available online 13 March 2006
Abstract A novel 3D uranyl complex is reported as synthesized via hydrothermal treatment of uranium oxynitrate and p-nitrobenzoic acid. The structure of the complex is quite unusual. It consists of one-dimensional [(UO2)3(l3-OH)3(l2-OH) (C7H4O4N)2] ribbons along the b-axis. These ribbons are linked to form a two-dimensional layer structure by the potassium ion that serves to bridge between the two adjacent ribbons. p-Nitrobenzoic acids make the layers a three-dimensional architecture. The complex is studied by DSC-TGA in order to get more information about its thermal stability. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Simulation; Uranyl complex; Hydrothermal synthesis; Coordination polymer
The family of uranium compounds with fascinating structural topologies is currently gaining considerable attention due to their physical–chemical properties and their behavior in the nuclear industry, mineralogy and natural environment [1–6]. Some recent studies in this area have focused on the use of hydrothermal synthetic condition, in both the mild (<250 °C) and supercritical (>374 °C) regimes, for preparing new phases, as well as attempting to reproduce the conditions under which uranium-bearing minerals may form . In order to gain a better understanding of the intrinsic interactions between uranyl ion and humic substance in the process of uranium deposit, we have designed a series of experiments to simulate this course. We chose some organic acid and synthetic HAs as model substance to react with dioxouranium(VI), respectively. Here, we report the synthesis, structure and characterization of dioxouranium(VI) complex K[(UO2)3(l3-OH)3(l2-OH) (C7H4O4N)2]OH.
Corresponding author. E-mail address: [email protected]
1387-7003/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2006.01.016
The complex is synthesized in a one-step process by the reaction of UO2(NO3)2 Æ 6H2O with p-nitrobenzoic acid in the presence of potassium hydroxide and 10 mL H2O under hydrothermal conditions at 180 °C. The resulting product is isolated as yellow crystal that is stable to air and suitable for X-ray crystallography . Fig. 1 shows the coordination environment of U(1), U(2) and U(3) atoms in the complex. The atoms U(1) and U(2), which are identic, are seven-coordinated, including a couple of uranyl oxygen atoms, three l3-OH, one p-nitrobenzoic acid group and a l2-OH, which makes the coordination environment of U(1) and U(2) adopt a pentagonal bipyramids conﬁguration. As for U(3), it is also seven-coordinated, but its coordination environment, which is composed of a couple of uranyl oxygen atoms, three l3-OH and two p-nitrobenzoic acid groups, is diﬀerent from U(1) and U(2). The ﬁve donor atoms around U(3) ˚ , the U(3) deﬁne a plane with mean deviation of 0.0367 A ˚ atom being separated by 0.0344 A from this plane. The bond lengths in the pentagonal bipyramids of UO7, which ˚ for the axial [email protected]
bonds range from 1.766(5) to 1.786(5) A ˚ and 2.209(5) to 2.566(5) A for the equatorial U–O bonds,
W. Zhang, J. Zhao / Inorganic Chemistry Communications 9 (2006) 397–399
Fig. 1. Ellipsoid representation of the part structure of K[(UO2)3(l3OH)3(l2-OH) (C7H4O4N)2]OH. It show the inﬁnite one-dimensional [(UO2)3(l3-OH)3(l2-OH) (C7H4O4N)2] ribbons that run down the b-axis.
are comparable to the values in similar cases . The U–U distances among the U(1), U(2) and U(3) vary from 3.8579 ˚ , which are larger than the sum of the covalent to 3.9776 A radii, hence no metal-metal bonds are evident. U(1), U(2), U(3), O(12) and O(13) deﬁne a plane with a mean deviation ˚. of 0.0250 A The uranium polyhedron forms an inﬁnite one-dimensional ribbon along the b-axis, which is constructed by numerous edge-sharing uranium pentagonal bipyramids. The edge of the ribbon is terminated by p-nitrobenzoic acid and l2-OH that arrange in AABAAB fashion along the ribbon. These ribbons are linked to form a two-dimensional layer structure by the potassium ion that serves to bridge between the two adjacent ribbons as shown in Fig. 2. Each potassium ion resides in a distorted tetradecahedral environment and is bonded by four uranyl oxygen atoms, four nitryl oxygen atoms and one dissociative hydroxyl. The K–O distance, which ranges from 2.681(6) ˚ , mean value 2.903(6) A ˚ , is well in agreement to 3.339(8) A with the values in similar cases . Up to now, such uranium–potassium–oxygen layer is rarely observed in either
Fig. 3. A view of the 3D network from b-axis direction. All the hydrogen atoms are omitted for clarity of presentation.
naturally occurring or synthetic systems. p-Nitrobenzoic acids arrange crosswise between the two adjacent layers as shown in Fig. 3. Its carboxyl oxygen atoms join the uranyl ions that belong to one of the layer, while its nitryl oxygen atoms link the potassium ions remaining with another layer. Thus, p-nitrobenzoic acids make the layers a threedimensional architecture. In order to get more information about the thermal stability of the complex, DSC-TGA has been performed. The thermal decomposition takes place in two stages. Initially, in the temperature range from 100 to 480 °C, one point ﬁve units of p-nitrobenzoic acid are removed which is followed by an exothermic maximum at 409 °C. The experimental mass loss in this stage is 19.80% that is in good agreement with the theoretical value calculated for the loss of one point ﬁve units of p-nitrobenzoic acid (19.71%). It decomposes in the second stage of thermal decomposition to K2O and U3O8, in the temperature range from 480 to 599 °C, which is manifested by an exothermic peak with maximum at 599 °C. The experimental value for mass loss in this stage is 11.30%, while the calculated one is 10.13%. Bond valence sum (BVS) analysis is also undertaken, a procedure that has found widespread utility in assigning ambiguous oxidation states in metal cluster . The BVS analysis gives an average valence of 5.979 for U(1), 5.990 for U(2) and 6.095 for U(3), which are consistent with the formula provided for this compound. Acknowledgements
Fig. 2. A view of the uranium–potassium–oxygen layer. It shows the arrangement of the uranyl ion and potassium ion.
We are grateful to the National Basic Research Program (the 973 Program, No. 2003CB214600), the Natural Science Foundation of China (No. 20371039), the Key Laboratory Research and Establishment Program of Shaanxi Education Section (No. 03JS006), and the Natural Science Foundation of Shaanxi Education Section (No. 04JK143) for ﬁnancial support.
W. Zhang, J. Zhao / Inorganic Chemistry Communications 9 (2006) 397–399
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