Article pubs.acs.org/IC
Entangled Uranyl Organic Frameworks with (10,3)‑b Topology and Polythreading Network: Structure, Luminescence, and Computational Investigation Chao Liu,†,§ Chao-Ying Gao,†,§ Weiting Yang,† Fang-Yuan Chen,‡ Qing-Jiang Pan,*,‡ Jiyang Li,∥ and Zhong-Ming Sun*,† †
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, Jilin 130022, People’s Republic of China ‡ Key Laboratory of Functional Inorganic Material Chemistry of Education Ministry, School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080, People’s Republic of China § University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China ∥ State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, People’s Republic of China S Supporting Information *
ABSTRACT: Two 3D uranyl organic frameworks (UOFs) with entangled structures, (HPhen)2[(UO2)2L2]·4.5H2O (1) and [(UO2)3(H2O)4L2]·6H2O (2), were synthesized using a rigid tripodal linker (4,4′,4″-(phenylsilanetriyl)tribenzoic acid, H3L). Compound 1 represents a 2-fold interpenetrating UOF with the unique (10,3)-b topology. Compound 2 is composed of three interlocked sets of identical singlet networks and thus exhibits a rare 3D polythreading network with (3,4)-connected topology. These two compounds have been characterized by IR, UV−vis, and photoluminescent spectroscopy. A density functional theory (DFT) study on the model compounds of 1 and 2 shows good agreement of structural parameters and U O stretching vibrational frequencies with experimental data. The experimentally measured absorption bands were well reproduced by the time-dependent DFT calculations.
■
INTRODUCTION
abundant coordination modes and multiple spatial conformations are suited to the geometrical specifications of the uranyl unit. Up to now, some flexible and semirigid symmetrical polypodal ligands have been introduced into syntheses of uranium(VI) complexes with unusual topologies and interesting properties.14−16 For example, Xing and co-workers have utilized a flexible polypodal ligand, 1,3,5-triazine-2,4,6-triaminehexaacetic acid, to construct a series of 3D UOFs.15 The ligand features a planar triazine core with three symmetrically flexible aminodiacetate arms. Previously, we also successfully synthesized two interpenetrating 3D UOFs based on two semirigid polypodal ligands.16 Highly symmetrical rigid polypodal ligands with tetrahedral geometry are also a good choice. For example, 1,3,5,7-adamantane tetrakiscarboxylate (H4ATC),17a 4′,4″,4‴,4⁗-methanetetrayltetrabiphenyl-4-carboxylate (H4MTBC),17b tetrakis(4-carboxyphenyl)methane (H4MTB),17c and tetrakis(4-carboxyphenyl)silane (TCPS)17d were widely used to construct high-dimensional transition/
Over the past two decades, the rational design and synthesis of uranyl organic frameworks (UOFs) has attracted intense interest due to not only their fascinating architectures but also potential applications in nuclear fuel cycles as well as in other fields.1−6 One interesting aspect of coordination chemistry of uranium is the intriguing structural diversity present in the UOFs. So far, UOFs with diversified structures have been isolated such as clusters,7 chains, layers, and threedimensional (3D) frameworks.8−11 However, due to the steric hindrance of the linear uranyl unit, 3D uranyl frameworks are relatively rare but highly desirable for their superior thermal stability and porosity contrast to low-dimensional ones.12 3D UOFs usually display many outstanding properties that include nonlinear optical properties,13a selective ion exchange,13b and porous adsorption.13c One of the potentially efficient ways to synthesize 3D UOFs is to address the rational design and the selection of ligands. Among various organic bridging ligands, highly symmetrical multidentate ligands containing carboxylic acid groups have emerged as ideal linkers to build 3D UOFs because their © XXXX American Chemical Society
Received: March 8, 2016
A
DOI: 10.1021/acs.inorgchem.6b00582 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Scheme 1. Rigid Tripodal Polycarboxylate Ligand with Tetrahedral Silicon-Centered Linker H3L
identical singlet networks, which results in a rare polythreading network with (3,4)-connected topology. It also represents the first interlocked polythreading network in a uranyl organic system. They have been structurally determined by singlecrystal X-ray diffraction and characterized by IR, UV−vis, photoluminescent spectroscopy, and density functional theory (DFT) calculations.
tetrahedral center and features a tripodal geometry with a single metal-coordination-free phenyl ring, has caught our attention. H3L shows a variety of coordination modes and conformations to bind uranyl cations because of its feature of three carboxylate groups and intrinsically three-dimensional orientation. Moreover, the nonbinding phenyl ring has large steric hindrance and will alter the coordination mode of the carboxylate group. Therefore, attempts to construct UOFs based on H3L are expected to form diverse topological structures.18 Entanglement is a common natural phenomenon and has been observed in many areas of biology and chemistry.19 According to the reviews by Ciani et al.,20 entangled systems are divided into several types, including interpenetrating networks, polyknotting networks, polycatenated networks, and polythreading networks. Entangled coordination polymers have been extensively studied for transition/lanthanide metal organic species,21 but uranium-containing compounds remain relatively rare. Currently, only a few cases of interpenetrating or polycatenating UOFs have been reported.16,22−28 For example, a 2D → 2D parallel interpenetrating UOF with a honeycomb (6,3) net has been synthesized using 1,4-benzenedicarboxylate.22 Wang and co-workers reported a rare case of a 2D → 3D polycatenating uranyl network based on 3,5-di(4carboxyphenyl)benzoate.24 Another polycatenating uranyl framework was prepared by Thuėry using 4,4′-biphenyldicarboxylate.23 However, polythreading networks, as another important branch of entangled systems, are relatively sparse in relation to uranyl organic systems. Polythreading systems can be regarded as infinite periodic arrays of molecular rotaxanes or pseudo-rotaxane analogues. The basic principle for the design of those polythreading networks requires the presence of closed loops, while a rigid motif serves as the rod to penetrate through the loops. These two basic moieties may possess the same unit or have different structures. The resultant crystal structure may exhibit the same or an increased dimensionality, depending on the nature of the motif.20,29 So far, 1D and 2D uranyl polyrotaxane networks have been reported by Shi and coworkers by combining uranyl-bearing units and pseudorotaxane precusors.30,31 Current research interest will focus on the development of 3D self-assembly interlocked UOFs, which may exhibit intriguing topological structures. In this paper, we prepared two 3D UOFs based on H3L, i.e., (HPhen)2[(UO2)L2]·4.5H2O (1) and [(UO2)3(H2O)4L2]· 6H2O (2). Interestingly, these two compounds exhibit mutual entanglement with different entangled modes. Compound 1 features 2-fold parallel interpenetration with uninodal (10,3)-b topology. Compound 2 comprises three interlocked sets of
Caution! Standard procedures for handling radioactive material should be followed, although the uranyl compounds used in the lab contained depleted uranium. Materials, Syntheses, and Characterization. All chemicals were purchased commercially and used without further purification. 4,4′,4′(phenylsilanetriyl) tribenzoic acid (H3L) was synthesized according to a literature procedure.32 X-ray powder diffraction (XRD) data were collected on a D8 Focus (Bruker) diffractometer at 40 kV and 30 mA with monochromated Cu Kα radiation (λ = 1.5405 Å) with a scan speed of 5°/min and a step size of 0.02° in 2θ. Thermogravimetric (TGA) and differential thermal analysis data were recorded on a Thermal Analysis Instrument (SDT 2960, TA Instruments, New Castle, DE, USA) from room temperature to 800 °C with a heating rate of 10 °C min−1 under a nitrogen atmosphere. Solid-state UV− visible absorption measurement was performed using a Hitachi U4100 spectrophotometer. Infrared spectra were collected using a Nicolet 6700 FT-IR spectrometer with a diamond ATR objective. The photoluminescence (PL) excitation and emission spectra were recorded with a Hitachi F-7000 luminescence spectrometer equipped with a xenon lamp of 450 W as an excitation light source. Synthesis of 4,4′,4″-(Phenylsilanetriyl)tribenzoic acid. The H3L ligand was synthesized according to the method described in the literature by a two-step procedure. First, a mixture of 4-bromotoluene (5 g, 29 mmol) and butyllithium (12 mL, 2.5 mol/L) in diethyl ether was stirred at 0 °C under N2 for 4 h. Then, phenyltrichlorosilane (9.6 mmol) was added, and the mixture was stirred at room temperature overnight. The reaction mixture was quenched by water (100 mL) at 0 °C. The organic layer was washed with water three times. A white solid was obtained by evaporation, washed with water, and dried under vacuum. Yield: 75%. Then, a mixture of diphenyldi-p-tolylsilane (4.00 g, 11.0 mmol), 90 mL of pyridine, and 30 mL of water was transferred to a 1000 mL round-bottomed flask, heated, and refluxed; at the same time KMnO4 (13.9 g, 87.8 mmol) was added in portions until the dark purple solution became light yellow, and the mixture was then cooled to room temperature. MnO2 was removed by suction filtration. The filtrate was concentrated to about 15 mL, and concentrated HCl was added until the pH was 1. White solids were precipitated and collected by suction filtration, then dried at 70 °C. Synthesis of Compound 1. A mixture of H3L(30 mg, 0.064 mmol), 0.1 M UO2(NO3)2 aqueous solution (1.0 mL, 0.100 mmol) and 1,10-phenanthroline (phen) (20 mg, 0.1 mmol) was loaded into a 20 mL Teflon-lined stainless steel autoclave. The autoclave was sealed and heated at 160 °C for 2 days, and then cooled to room temperature. The solution pH was 3.0 before the reaction and 2.5 at the end. The target product, yellow single crystals, was isolated after filtration and washed thoroughly with distilled water. Yield: ca. 35% (based on uranium). Synthesis of Compound 2. A mixture of H3L (30 mg, 0.064 mmol), 0.1 M UO2(NO3)2 aqueous solution (1.0 mL, 0.100 mmol), and tetraethylammonium hydroxide (30 μL) was loaded into a 20 mL Teflon-lined stainless steel autoclave. The autoclave was sealed and heated at 160 °C for 2 days and then cooled to room temperature. The solution pH was 3.2 before the reaction and 2.7 at the end; yellow needle-like crystals of the title compound were isolated after filtration and washed thoroughly with distilled water. Yield: ca. 45% (based on uranium). X-ray Crystal Structure Determination. Suitable single crystals were selected for single-crystal X-ray diffraction analyses. Crystallographic data were collected at 298 K on a Bruker Apex II CCD diffractometer with graphite-monochromated Mo Kα radiation (λ =
lanthanide metal organic frameworks, most of which display interesting topologies and outstanding properties. In addition to the aforementioned ligands, 4,4′,4″-(phenylsilanetriyl)tribenzoic acid (H3L in Scheme 1), which possesses a
■
B
EXPERIMENTAL SECTION
DOI: 10.1021/acs.inorgchem.6b00582 Inorg. Chem. XXXX, XXX, XXX−XXX
Inorganic Chemistry
■
0.710 73 Å). Data processing was accomplished with the SAINT program. Structures were solved using direct methods (SHELXT, Olex2) and then refined using SHELXL-2014 and Olex2 to convergence,33 in which all the non-hydrogen atoms were refined anisotropically. Non-hydrogen atoms were refined with anisotropic displacement parameters during the final cycles. All hydrogen atoms of the organic molecule were placed by geometrical considerations and were added to the structure factor calculation. Hydrogen atoms residing on the oxygen atoms in water molecules were observed within difference Fourier maps and fixed at proper positions. Although most of the active hydrogen atoms could be located directly, there are still some hydrogen atoms on water molecules (O5W, O7W in compound 1, O3W in compound 2) that could not be found because of the lack of acceptors for the hydrogen bond. A summary of the crystallographic data for these two complexes is listed in Table 1. Selected bond distances and angles are given in Tables S1 and S2. CCDC 1458461− 1458462 contain the supplementary crystallographic data for this paper.
RESULT AND DISCUSSION Both UOFs were prepared by the reaction of a moderate amount of UO2(NO3)2·6H2O with H3L under hydrothermal conditions. As shown in the Experimental Section, the organic template phen directed the synthesis of compound 1. The pH values (3.2−2.7) are crucial for the crystallization of compound 2, which was synthesized in the presence of traces of tetraethylammonium hydroxide. In addition, the reaction temperature also plays a key role for the morphology of the compounds. Heating at 180 °C also resulted in these two compounds but with lower crystallinity. The phase purities of both compounds were confirmed using powder XRD (Figures S3 and S4). The TG curve for compound 1 indicated that the first weight loss of 4.4% from 30 to 112 °C corresponds to the lattice water molecules (calcd 4.2%, Figure S5). The framework then began to become unstable for the removal of protonated phen molecules and started to decompose at 429 °C. For compound 2, the lattice water molecules were lost between 30 and 110 °C (obsd, 3.2%; calcd, 2.8%), and the solvent-free 2 is stable until 350 °C and started to decompose. Structure Description. Compound 1 crystallizes in the centrosymmetric triclinic space group P1̅. The asymmetric unit contains two crystallographically unique uranium atoms and two L ligands (Figure 1a). Both uranium ions are in the
Table 1. Crystallographic Data and Structure Refinement Parameters for Compounds 1 and 2 empirical formula fw cryst syst space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z F(000) ρcalcd /g cm−3 μ(Mo Kα)/mm−1 R1/wR2 (I > 2σ(I))a R1, wR2 (all data)
compound 1
compound 2
C78H61N4O20.5Si2U2 1923.57 triclinic P1̅ 10.4237(13) 14.7281(17) 25.599(3) 81.665(2) 82.260(3) 71.667(3) 3674.5(8) 2 1858 1.727 4.512 0.0544/0.1390 0.0774/0.1568
C54H54O28Si2U3 1921.25 monoclinic P21/c 7.263(3) 24.540(10) 17.718(7) 90 90.726(9) 90 3158(2) 2 1792 2.004 7.794 0.0400/0.0965 0.0504/0.1027
Article
R1 = ∑(ΔF/∑(Fo)); wR2 = (∑[w(Fo2 − Fc2)])/∑[w(Fo2)2]1/2, w = 1/σ2(Fo2). a
Computational Details. The model complexes were fully optimized in the gas phase without any symmetry constraints using the Priroda code (version 6).34,35 These calculations were carried out with the PBE functional36 of the generalized gradient approximation (GGA) and an all-electron correlation-consistent Gaussian basis set of double-ς polarized quality (labeled as B-I). Relativistic effects were implemented using a scalar relativistic four-component all-electron (AE) approach.35 Frequency calculations were used to confirm the local minima nature of the stationary points on the potential energy surface. The vibrational spectra were theoretically simulated by using Lorentzian broadening. Population-based (Mayer)37 bond orders were calculated. With the ADF 2014 code,38−40 electronic spectroscopy in THF solution was calculated using time-dependent density functional theory (TD-DFT). Two functionals, GGA-PBE and hybrid B3LYP, were used. The ZORA scalar relativistic approach of van Lenthe et al.41 was employed, associated with the all-electron Slater-type TZP basis sets (B-II). The solvent effects of THF were taken into account with the COSMO model as implemented in ADF.42 Klamt radii were used for the main group atoms (H = 1.30 Å, C = 2.00 Å, N = 1.83 Å, O = 1.72 Å, and Si = 2.40 Å)43 and for the uranium atom (1.70 Å).44 An integration parameter of 6.0 was applied.
Figure 1. ORTEP representation of the asymmetric units of compounds 1 (a) and 2 (b). Thermal ellipsoids are drawn at the 50% probability level; phen molecules in (a) are omitted for clarity. Symmetry codes for compound 1: A, x, 1+y, z; B, x+1, y−1, z; C, x+1, y, z−1; Symmetry codes for compound 2: A, x, −y+3/2, z−1/2; B, −x +3, y−1/2, 1/2−z; C, x, −y+2, −z. C
DOI: 10.1021/acs.inorgchem.6b00582 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry hexagonal bipyramidal coordination environment with the uranyl (UO22+) oxygen atoms at the apex and six oxygen atoms in the equatorial plane from three sets of carboxylate groups from three L ligands. Each carboxylate group adopts a bidentate coordination mode chelating one uranyl unit. The lengths of the U−Oyl bonds are 1.752(8) and 1.767(8) Å for U1 and 1.719(10) and 1.744(9) Å for U2. The bond distances in the equatorial plane range from 2.435(7) to 2.503(6) Å for U1 and 2.420(9) to 2.507(7) Å for U2, all in good agreement with the typical bond length report for uranium-containing materials.45 It is worth mentioning that the uranyl units, all in a slightly distorted environment with the oxygen donors from the carboxylate group, slightly depart from the uranyl equatorial plane. The angles between the uranyl axis and the equatorial plane oxygen range from 85.8(3)° to 93.5(3)° for U1 and 86.9(3)° to 94.6(3)° for U2. As described above, the carboxylate group adopts a chelating coordination mode in compound 1. The ligand can be considered as a 3-connected node to link three UVI centers. Because of the tripodal configuration of the ligand, three of the aromatic rings feature a large degree of rotation and point in different directions. Consequently, the dihedral angles among the three of the equatorial planes of uranyl units also span a wide range. As illustrated in Figure 2, two equatorial planes are
Figure 3. (a) Singlet network of compound 1 viewed along the a axis. (b) Twofold 3D interpenetrating network of compound 1 viewed along the a axis. (c) Topology representation of a single network of compound 1 viewed along the a axis. (d) Topology representation of the 2-fold interpenetrating network viewed along the a axis.
In the absence of an organic template, and using tetraethylammonium hydroxide to regulate the basicity of the system, the other 3D entangled framework was formed. As shown in Figure 1b, there are two crystallographically inequivalent uranium sites and one L ligand in an asymmetric unit. The uranium atoms exhibit two different coordination environments. The U1 atom exists in the form of a UO7 pentagonal bipyramid, including two linear uranyl oxygen atoms, four planar oxygen atoms from three L ligands, and one aqua ligand. The U2 atom is in the inversion center of a hexagonal bipyramid defined by four O atoms from two carboxylate groups, two aqua ligands in the equatorial plane, and two symmetrical “yl” oxo atoms, while the carboxylate groups display two coordination modes in compound 2. Two carboxylate groups bond two uranium atoms in a chelating fashion, and the third carboxylate arm connects two uranium atoms in a dimonodentate mode. Thus, the ligand acts as a μ4bridge to link four uranyl units. The lengths of the U−Oyl bond are 1.771(5) and 1.773(5) Å for U1 and 1.795(5) Å for U2. The bond distances in the equatorial plane range from 2.310(5) to 2.484(5) Å for U1 and 2.441(5) to 2.475(6) Å for U2. Compound 2 has a 3-fold interlocked polythreading framework. In order to have a clear understanding of the 3fold polythreading structure, we analyze the singlet network of the framework in detail. As shown in Figure 4a, there exists a quadrangle-like channel along the c axis. The vertex of the quadrangle is occupied by the silicon-centered polycarboxylate ligand, and the edges of the quadrangle are formed by the uranium oxide polyhedron, including a dimeric UO7 pentagonal bipyramid on one edge and a UO8 hexagonal bipyramid on the other edge. The effective size of the quadrangle channel is ca.
Figure 2. Coordination configurations of H3L in compound 1.
in a parallel position. The dihedral angle between the two planes is close to zero. However, the third plane crosses these two planes with a dihedral angle of 59.167(2)°, which is 58.225(2)° in the other crystallographically unique L ligand. In this way, the spatial structure extends and stretches in different directions around the core of silicon-centered tripodal links and an intriguing 3D porous framework is generated. As shown in Figure 3a, a large hexagonal channel was observed along the a axis in the singlet network. The effective size of the channel is ca. 9 × 9 Å2. Two crystallographically equivalent networks interpenetrate each other, leading to a 2-fold interpenetrating structure and further strengthening the stability of the skeleton (as shown in Figure 3b). Topological analyses indicate that compound 1 features 3-connected nets with a (10,3)-b topology (sometimes referred to as the ThSi2-related net)18 (Figure 3c and d). This type of topology is common in transition metal systems, but to the best of our knowledge, it has never been reported in uranyl organic materials. Compound 1 also represents the first case of 2-fold interpenetrating UOFs with a 3D singlet network. The solvent-accessible volume is estimated by the PLATON program to be about 21.9% of the total crystal volume, and large hexagon-shaped channels are observed along the a axis, which are occupied by partially protonated phen molecules. D
DOI: 10.1021/acs.inorgchem.6b00582 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Figure 4. (a) Singlet network of compound 2 viewed along the a axis. (b) Threefold 3D interlocked polythreading network of compound 2 viewed along the a axis.
13 × 13 Å2. As described above, the single network has a large void volume, which allows triple equivalent networks to become entangled with each other and thus keeps the stability of the whole framework (Figure 4b). A better understanding of the structure of compound 2 can be achieved from viewing the topology. Two U1 atoms connect to each other by two carboxyl groups, which adopt the bidentate bridging mode to form a dimeric unit. The dinuclear SBU is surrounded by four carboxylate groups from four distinct L ligands, which can be considered as a 4-connected node. Each L ligand connects two dimer units directly and links another L through a U2 hexagonal bipyramid, which can be regarded as a 3-connected node. Topological analysis indicates that compound 2 can be simplified to a binodal (3,4)connected 3-fold interpenetrating net with the Schläfli symbol {83}2{85.10} (Figure 5).
(10,3)-b net. The minimal close loop consists of five uranyl units and five L ligands. As shown in Figure 6a, two sets of
Figure 5. (a) Topological structure corresponding to the single network of compound 2. (b) Topological structure corresponding to the 3-fold interlocked polythreading network of compound 2.
Figure 6. Schematic representation of different entangled modes for compounds 1 (a) and 2 (b).
loops are entangled together to constitute the minimum entangled unit, then extend to a 3D 2-fold interpenetrating framework. In comparison to that of compound 1, a big loop was also observed in compound 2, which is constituted by four dimer uranyl units and four L ligands. The loops are linked via sharing two dimer uranyl units and an L ligand to generate a layered arrangement parallel to the bc plane, which is further connected by a linear UO2(COOR)2(H2O)2 unit to form a 3D
The difference in the coordination modes of the carboxylate groups in H3L results in different spatial structures and topologies in compounds 1 and 2. The most amazing structural difference between compounds 1 and 2 is the distinct entangled mode they adopt, which can be described in detail from their minimum entangled motif. According to the above description, compound 1 can be topologically described as the 3-connected E
DOI: 10.1021/acs.inorgchem.6b00582 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Scheme 2. Comparison of Coordination Modes and Crystal Structures between the Entangled UOFs Based on a Rigid Tripodal Polycarboxylate with a Tetrahedral Center in This Work (Left) and Those Built from a Rigid Polycarboxylate with an Aromatic Center Previously Reported (Right)
polycarboxylate ligands reveal that H3L is a reasonable choice for the syntheses of uranyl organic materials with intriguing topologies. Our work presented here could provide a new strategy for the design and construction of more complicated UOFs. IR, UV−vis−NIR, and Luminescent Spectroscopy. Infrared spectra of two compounds as well as the H3L ligand were recorded (Figure S6). The peaks around 3072 and 3020 cm−1 are attributed to the phenyl C−H stretching mode. The carbonyl CO stretching vibration band is observed around 1690 cm−1 in H3L, which nearly disappears completely in compounds 1 and 2, indicating the coordination between the carboxylate group and the uranyl unit. The bands at 1601, 1554, 1502, and 1419 cm−1 are assigned to benzene skeleton vibrations. The absorption bands located at 1096 and 697 cm−1 are dominated by the Si−C characteristics. Compared to those of the ligand, additional vibrational peaks around 905 and 852 cm−1 in 1 and 937, 910, and 858 cm−1 in 2 are observed, which are attributed to the asymmetric and symmetric UO vibrations, respectively.46 These stretches will be addressed in the following theoretical computations. The UV−vis absorption spectra of both compounds are studied (Figure S7). One can see that the spectra of both compounds 1 and 2 are dominated by vibronically coupled charge transfer bands in the region of 385−490 nm due to the uranyl unit. The adsorption spectrum of 1 splits into five peaks, situated at 407, 418, 432, 449, and 463 nm, while three split and resolved peaks of 2 at 415, 432, and 474 nm are observed. Moreover, additional absorption bands are also observed around 330 nm due to the ligand-to-metal charge transfer in the spectra of compounds 1 and 2. In addition, the other four peaks determined at 243 and 293 nm for 1 and 234 and 280 nm for 2 are related to the ligand transition, which are in accordance with the spectrum of the H3L ligand. A detailed discussion is shown in the next section. Emission spectra under excitation at a wavelength of 420 nm were recorded for the two compounds. As shown in Figure 7,
framework (Figure S1). The linear UO2(COOR)2(H2O)2 unit consisting of a UO8 hexagonal bipyramid and two L can be simplified as a rod. To our surprise, the 3D network does not penetrate through the others from the loop. As shown in Figure 6b, three sets of identical networks are entangled together by a rod from one network threading through two loops from other two networks, resulting in a rare triple interlocked framework. Considering the rotaxane-like mechanical links present in compound 2 (Figure S2), we therefore describe the structure of compound 2 as a polythreading framework. This type of entanglement first appears in a uranyl organic system and is also rare in metal coordination polymers. As indicated in the Introduction, rigid polycarboxylate ligands easily form chains or layers with uranyl cations. One of the most widely studied structure types is the graphene-like (6,3) net topology, which is easily formed when the carboxylate group adopts a chelating mode. Insight into the entangled UOFs, which are synthesized based on rigid polycarboxylate ligands with an aromatic center, such as terephthalic acid,22 4,4′-biphenyldicarboxylic acid,23 and 3,5-di(4-carboxyphenyl)benzoate,24 reveals that those structures all possess a (6,3) net topology singlet network. As summarized in Scheme 2, particularly worth mentioning is that the rare case of a 2D → 3D inclined polycatenation uranyl network constructed by 3,5di(4-carboxyphenyl)benzoate, a rigid conjugated tricarboxylate ligand, which is an analogue of H3L but possesses a conjugate structure, also results in a (6,3) net singlet network. However, when a tripodal polycarboxylate ligand with tetrahedral center replaces those aromatic polycarboxylate ligands, such layer structure did not occur in compound 1. Although the coordination environment of the uranyl unit is similar, a novel 3D 3-connected 2-fold interpenetrating (10,3)-b net was present. In addition, with a small change in the experimental conditions, a 3D triple interlocked polythreading uranyl organic network with the Schläfli symbol {83}2{85.10} appeared. Significant differences between structures constructed by aromatic polycarboxylate ligands and those based on tripodal F
DOI: 10.1021/acs.inorgchem.6b00582 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Å, close to the experimental value of 2.84 Å. The uranyl ion remains linear with OUO angles of 180° (expt = 179.4° for 1 and 179.5° for 2). The calculated UO bond order is 2.37, suggesting partial triple-bonding character, as is normally found for uranyl(VI) complexes. The dative bond from the equatorial carboxylate to the uranium center is found to be very weak, reflected by the calculated U−Qeq bond order of 0.48. The infrared vibrational spectra of 3a and 3b have been theoretically simulated in Figure 8. The absorption bands of 3a at 819/906 cm−1 and 3b at 817/905 cm−1 are attributed to the symmetric/asymmetric UO stretching vibrational modes.50 This agrees with the experimentally obtained 852/905 cm−1 (1) and 858/910 cm−1 (2) stretches. Besides the UO vibrations, calculated characteristic peaks around 3125−3127 cm−1 are assigned to the phenyl C−H stretching vibrational mode, which are comparable to 3072 and 3020 cm−1 of 1 and 2. As 3a and 3b were calculated to show close geometry parameters and IR spectra, we will focus on 3a to unravel electronic properties of experimental compounds 1 and 2. In Figure 9, we present diagrams of characteristic orbitals from the PBE/B-II/ZORA/COSMO calculation. Four lowlying unoccupied orbitals are of f(U) in character. One fϕ(U) orbital forms the LUMO, and the other fϕ(U) is greatly destabilized by the antibonding interaction of fϕ(U) and π(Oeq), orbital 103; the two fδ(U) orbitals (101 and 102) are energetically degenerate. Orbitals 104−106 are π*(L) in character. Above them are two π*(UO) orbitals. The π(Ph)-based HOMO (orbital 100) is observed, mixed with some σ(UO). The orbitals 92−96 are also primarily of π(Ph) character. The π∥(Oeq) forms two orbitals of 97 and 98, where the notation “∥” denotes that they are parallel to the equatorial plane of the uranyl ion. Accordingly, π⊥(Oeq) character contributes to orbital 90 at a relatively low energy region. The σ(U−Oeq) bond is formed in orbital 97. Pure σ(UO) bonding orbital 87 occurs at −6.83 eV, which derives from the interaction of fz3(U) and pz(O). We also observed the σ(Si− C)-character orbitals (82 and 83). The electronic absorption spectra of 3a were calculated with two functionals, PBE and B3LYP. Four characteristic absorption bands were experimentally measured, for instance, peaks at 407−449, 330, 293, and 353 nm for 1. The calculated absorption spectra (Figure S8) illustrate that the PBE functional yields good agreement. Combining Table S4 and Figure 9, band I at 443 nm is primarily of π(Ph) → fδ(U) character. The peak around 354 nm (labeled band II) is the admixture of π∥(Oeq) → fϕ(U) and σ(UO) → fδ(U) character.50 The absorption band at 309 nm (band III) is related to the electronic promotion from
Figure 7. Emission spectra of compounds 1, 2, and UO2(NO3)2· 6H2O.
both the compounds display prototypical “five-finger” peaks of uranyl materials (471, 488, 507, 530, and 553 nm for 1; 478, 495, 515, 538, and 563 nm for 2). This characteristic emission is generally assigned to the symmetric and antisymmetric vibrational modes of the uranyl group.47 It finds a 8 nm redshift of emission peaks of 2 compared to those of benchmark compound UO2(NO3)2·6H2O, while the emission peaks of compound 1 and UO2(NO3)2·6H2O are almost in the same position. This may be attributed to various surrounding factors such as a distorted coordination environment of the uranyl unit or different uranyl coordination modes, etc.48 Density Functional Theory Calculation. In this work, two model compounds, [UO2{(OOC)(C6H4) (SiR3)}3]− (R = H (3a) and Me (3b)), were investigated using the DFT approach.34−36 They can represent the core of experimentally synthesized 1 and 2, which exhibit similar IR and absorption spectra and luminescence as mentioned above. Good overall agreement has been achieved between the calculated and experimental data, within 0.04 Å and 3° (Table S3). The UO bond lengths were calculated to be 1.81 Å for 3a and 3b, which is slightly longer than experimental values of 1.76−1.78 Å for 1 and 2. The difference mainly originates from the GGA functional overestimating the bond lengths.49 The calculated U−Oeq bond lengths (2.50 Å) are longer than the experimental ones (2.46 Å). The U−C separation was calculated to be 2.86
Figure 8. Simulated vibrational spectra of model complexes 3a (left) and 3b (right), where the UO stretches (red number) are addressed at the bottom. G
DOI: 10.1021/acs.inorgchem.6b00582 Inorg. Chem. XXXX, XXX, XXX−XXX
Inorganic Chemistry
■
Article
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00582. X-ray crystallographic cif files, selected bond lengths and angles, PXRD pattern, TG, IR, UV−vis−NIR, and luminescent spectroscopy, and simulated spectra of 3a and 3b (PDF) (CIF)
■
AUTHOR INFORMATION
Corresponding Authors
*E-mail (Q.-J. Pan):
[email protected]. *E-mail (Z.-M. Sun):
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS We thank the National Nature Science Foundation of China (Nos. 21171162, 21301168, 21273063, U1407101) for support of this work.
■
Figure 9. Energy levels and diagrams of orbitals for 3a from the TDPBE/TZP/ZORA/COSMO calculation.
σ(Si−C) to fϕ(U). The strong peak (band IV) occurs in the high-energy region, composed of two transitions (272 and 267 nm). The latter transition is mainly of σ(UO) → π*(Ph) character mixed with some minor π(Ph) → π*(Ph), while the former has π∥(Oeq) → π*(UO) charge transfer character.
■
REFERENCES
(1) Natrajan, L. S. Coord. Chem. Rev. 2012, 256, 1583−1603. (2) Andrews, M. B.; Cahill, C. L. Chem. Rev. 2013, 113, 1121−1136. (3) Yang, W. T.; Parker, G. T.; Sun, Z. M. Coord. Chem. Rev. 2015, 303, 86−109. (4) Adelani, P. O.; Albrecht-Schmitt, T. E. Angew. Chem., Int. Ed. 2010, 49, 8909−8911. (5) Thuery, P. Inorg. Chem. 2013, 52, 435−447. (6) Wang, K. X.; Chen, J. S. Acc. Chem. Res. 2011, 44, 531−540. (7) (a) Burns, P. C. Can. Mineral. 2005, 43, 1839−1894. (b) Qiu, J.; Vlaisavljevich, B.; Jouffret, L.; Nguyen, K.; Szymanowski, J. E. S.; Gagliardi, L.; Burns, P. C. Inorg. Chem. 2015, 54, 4445−4455. (8) Parker, T. G.; Cross, J. N.; Polinski, M. J.; Lin, J.; AlbrechtSchmitt, T. E. Cryst. Growth Des. 2014, 14, 228−235. (9) Zheng, T.; Wu, Q. Y.; Gao, Y.; Gui, D. X.; Qiu, S. W.; Chen, L. H.; Sheng, D. P.; Wu, J. D.; Shi, W. Q.; Chai, Z. F.; Albrecht-Schmitt, T. E.; Wang, S. A. Inorg. Chem. 2015, 54, 3864−3874. (10) An, S. W.; Mei, L.; Wang, C. Z.; Xia, C. Q.; Chai, Z. F.; Shi, W. Q. Chem. Commun. 2015, 51, 8978−8981. (11) Thangavelu, S. G.; Cahill, C. L. Cryst. Growth Des. 2016, 16, 42− 50. (12) (a) Liao, Z. L.; Li, G. D.; Wei, X.; Yu, Y.; Chen, J. S. Eur. J. Inorg. Chem. 2010, 2010, 3780−3788. (13) (a) Wang, S.; Alekseev, E. V.; Ling, J.; Liu, G.; Depmeier, W.; Albrecht-Schmitt, T. E. Chem. Mater. 2010, 22, 2155−2163. (b) Shvareva, T. Y.; Skanthkumar, S.; Soderholm, L.; Clearfield, A.; Albrecht-Schmitt, T. E. Chem. Mater. 2007, 19, 132−134. (c) Alsobrook, A. N.; Hauser, B. G.; Hupp, J. T.; Alekseev, E. V.; Depmeier, W.; Albrecht-Schmitt, T. E. Chem. Commun. 2010, 46, 9167−9169. (14) Bao, S. S.; Chen, G. S.; Wang, Y.; Li, Y. Z.; Zheng, L. M.; Luo, Q. H. Inorg. Chem. 2006, 45, 1124−1129. (15) Song, J.; Gao, X.; Wang, Z. N.; Li, C. R.; Xu, Q.; Bai, F. Y.; Shi, Z. F.; Xing, Y. H. Inorg. Chem. 2015, 54, 9046−9059. (16) Wu, H. Y.; Wang, R. X.; Yang, W.; Chen, J.; Sun, Z. M.; Li, J.; Zhang, H. J. Inorg. Chem. 2012, 51, 3103−3107. (17) (a) Chen, B. L.; Eddaoudi, M.; Reineke, T. M.; Kampf, J. W.; O’Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2000, 122, 11559−11560. (b) Zhang, M. W.; Chen, Y. P.; Bosch, M.; Wang, K. H.; Feng, D. W.; Wang, Z. U.; Zhou, H. C. Angew. Chem., Int. Ed. 2014, 53, 815−818. (c) Furukawa, H.; Gandara, F.; Zhang, Y. B.; Jiang, J. C.; Queen, W. L.; Hudson, M. R.; Yaghi, O. M. J. Am. Chem. Soc. 2014, 136, 4369−4381.
CONCLUSION
Via introducing a rigid tripodal polycarboxylate ligand with a tetrahedral center into a uranyl organic system, two 3D entangled uranyl organic compounds have been successfully synthesized by a facile hydrothermal method. Due to the diverse coordination from the ligand to the uranium center, these two compounds possess different topological structures. Compound 1 features 2-fold interpenetration with (10,3)-b topology. Compound 2 exhibits a rare 3,4-connected 3-fold interlocked polythreading framework. Notably, compound 2 represents the first interlocked polythreading network in UOFs. The preparation of compounds 1 and 2 further demonstrates a promising route that rational selection of organic ligands with certain geometry and functionality can fabricate new UOFs with intriguing structures. Good agreement between computation and experiment has been achieved for geometry parameters and UO vibrational stretches. The experimental low-energy absorption bands are assigned as electronic promotion from the ligand to the uranium center, while the intense high-energy peak has mixed σ(UO)/π(Ph) → π*(Ph) character. Further work will focus on preparing more UOFs with interesting topologies based on the tetrahedral ligand via introducing secondary ligands. H
DOI: 10.1021/acs.inorgchem.6b00582 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
(49) (a) Shamov, G. A.; Schreckenbach, G.; Vo, T. N. Chem. - Eur. J. 2007, 13, 4932−4947. (b) Shamov, G. A.; Schreckenbach, G. J. Phys. Chem. A 2005, 109, 10961−10974. (50) Pan, Q. J.; Wang, Y. M.; Wang, R. X.; Wu, H. Y.; Yang, W. T.; Sun, Z. M.; Zhang, H. X. RSC Adv. 2013, 3, 1572−1582.
(d) Xue, Y. S.; Zhou, L.; Liu, M. P.; Liu, S. M.; Yan Xu, Y.; Du, H. B.; You, X. Z. CrystEngComm 2013, 15, 6229−6236. (18) Liu, Z. Q.; Stern, C. L.; Lambert, J. B. Organometallics 2009, 28, 84−93. (19) (a) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460−1494. (b) Yang, G. P.; Hou, L.; Ma, L. F.; Wang, Y. Y. CrystEngComm 2013, 15, 2561. (20) (a) Carlucci, L.; Ciani, G.; Proserpio, D. M. Coord. Chem. Rev. 2003, 246, 247−289. (b) Carlucci, L.; Ciani, G.; Proserpio, D. M.; Mitina, T. G. Chem. Rev. 2014, 114, 7557−7580. (21) Wu, H.; Yang, J.; Su, Z. M.; Batten, S. R.; Ma, J. F. J. Am. Chem. Soc. 2011, 133, 11406−11409. (22) Go, Y. B.; Wang, X.; Jacobson, A. J. Inorg. Chem. 2007, 46, 6594−6600. (23) Thuery, P.; Harrowfield, J. Inorg. Chem. 2015, 54, 8093−8102. (24) Wang, Y.; Liu, Z.; Li, Y.; Bai, Z.; Liu, W.; Wang, Y.; Xu, X.; Xiao, C.; Sheng, D.; Diwu, J.; Su, J.; Chai, Z. F.; Albrecht-Schmitt, T. E.; Wang, S. J. Am. Chem. Soc. 2015, 137, 6144−6147. (25) Chen, F.; Wang, C. Z.; Li, Z. J.; Lan, J. H.; Ji, Y. Q.; Chai, Z. F. Inorg. Chem. 2015, 54, 3829−3834. (26) Mei, L.; Wu, Q. Y.; An, S. W.; Gao, Z. Q.; Chai, Z. F.; Shi, W. Q. Inorg. Chem. 2015, 54, 10934−10945. (27) An, S. W.; Mei, L.; Hu, K. Q.; Xia, C. Q.; Chai, Z. F.; Shi, W. Q. Chem. Commun. 2016, 52, 1641−1644. (28) Borkowski, L. A.; Cahill, C. L. Cryst. Growth Des. 2006, 6, 2248− 2259. (29) Wang, G. H.; Li, Z. G.; Jia, H. Q.; Hu, N. H.; Xu, J. W. Cryst. Growth Des. 2008, 8, 1932−1939. (30) Mei, L.; Wu, Q. Y.; Liu, C. M.; Zhao, Y. L.; Chai, Z. F.; Shi, W. Q. Chem. Commun. 2014, 50, 3612−3615. (31) Mei, L.; Wang, L.; Yuan, L. Y.; An, S. W.; Zhao, Y. L.; Chai, Z. F.; Burns, P. C.; Shi, W. Q. Chem. Commun. 2015, 51, 11990−11993. (32) Davies, R. P.; Less, R. J.; Lickiss, P. D.; Robertson, K.; White, A. J. P. Inorg. Chem. 2008, 47, 9958−9964. (33) (a) Sheldrick, G. M. Acta Crystallogr. 2015, C71, 3−8. (b) Dolomnov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. J. Appl. Crystallogr. 2009, 42, 329−341. (34) Laikov, D. N. Chem. Phys. Lett. 1997, 281, 151−156. (35) Laikov, D. N.; Ustynyuk, Y. A. Russ. Chem. Bull. 2005, 54, 820− 826. (36) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865−3868. (37) Mayer, I. Simple Theorems, Proof and Derivations in Quantum Chemistry; Kluwer Academic /Plenum Publishers: New York, 2003. (38) te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; Fonseca Guerra, C.; Van Gisbergen, S. J. A.; Snijders, J. G.; Ziegler, T. J. Comput. Chem. 2001, 22, 931−967. (39) Fonseca Guerra, C.; Snijders, J. G.; te Velde, G.; Baerends, E. J. Theor. Chem. Acc. 1998, 99, 391−403. (40) Baerends, E. J.; Ziegler, T.; Autschbach, J.; et al. ADF, ADF2014.06; SCM, Theoretical Chemistry; Vrije Universiteit: Amsterdam, The Netherlands, 2014. (41) van Lenthe, E.; Ehlers, A.; Baerends, E. J. J. Chem. Phys. 1999, 110, 8943−8953. (42) Pye, C. C.; Ziegler, T. Theor. Chem. Acc. 1999, 101, 396−408. (43) Klamt, A.; Jonas, V.; Burger, T.; Lohrenz, J. C. W. J. Phys. Chem. A 1998, 102, 5074−5085. (44) Pan, Q. J.; Schreckenbach, G. Inorg. Chem. 2010, 49, 6509− 6517. (45) Masci, B.; Thuéry, P. Cryst. Growth Des. 2008, 8, 1689−1696. (46) Poojary, D. M.; Cabeza, A.; Aranda, M. A. G.; Bruque, S.; Clearfield, A. Inorg. Chem. 1996, 35, 1468−1473. (47) Liu, G.; Beitz, J. V. In The Chemistry of the Actinide and Transactinide Elements; Morss, L. R., Edelstein, N. M., Fuger, J., Eds.; Springer: Heidelberg, 2006; p 2088. (48) Leung, A. F.; Hayashibara, L.; Spadaro, J. J. Phys. Chem. Solids 1999, 60, 299−304. I
DOI: 10.1021/acs.inorgchem.6b00582 Inorg. Chem. XXXX, XXX, XXX−XXX
