research communications
κ2O,O′)uranium(VI)
of a trigonal polymorph of aquadioxidobis(pentane-2,4-dionato-aDepartment of Chemistry and Biochemistry, Florida International University, 11200 SW 8th St., Miami, FL 33199, USA
*Correspondence e-mail: cdares@fiu.edu
The title compound, [UO2(acac)2(H2O)] consists of a uranyl(VI) unit ([O=U=O]2+) coordinated to two monoanionic acetylacetonate (acac, C5H7O2) ligands and one water molecule. The includes a one-half of a uranium atom, one oxido ion, one-half of a water molecule and one acac ligand. The coordination about the uranium atom is distorted pentagonal–bipyramidal. The acac ligands and Ow atom comprise the equatorial plane, while the uranyl O atoms occupy the axial positions. Intermolecular hydrogen bonding between complexes results in the formation of two-dimensional hexagonal void channels along the c-axis direction with a diameter of 6.7 Å. The monoclinic (P21/c space group) polymorph was reported by Alcock & Flanders [(1987). Acta Cryst. C43, 1480–1483].
Keywords: crystal structure; uranium complex; dioxo species; X-ray structure; hydrogen bonding.
CCDC reference: 2117155
1. Chemical context
Nuclear forensics applications often require the development of source materials for isotope-dilution mass-spectrometry measurements. One method for preparing actinide source materials includes the preparation of volatile compounds which can be deposited onto a conductive surface from the vapor phase. An alternative method involves electrochemical reduction to the zero-valent metal with concurrent deposition onto the electrode surface. This requires an organo-soluble actinide precursor. Hexavalent actinide complexes with β-diketonates are possibilities for either of these methods. They are neutrally charged, and with appropriate substituents on the β-diketonate may be volatile (Johnson et al., 2017). β-Diketonates also provide a platform to prepare the organosoluble precursors required for electrochemical reduction.
2. Structural commentary
The molecular structure of the title compound, [UO2(acac)2(H2O)] 1, was determined by single crystal X-ray diffraction. An ORTEP plot of the molecular structure is shown in Fig. 1 and selected geometric parameters are listed in Table 1. The complex crystallizes in the trigonal Pc1 with one-half molecule per while the other half is generated by a twofold axis running through the U and Ow atoms. In the molecular structure, the UVI center resides in a distorted pentagonal–bipyramidal coordination environment, with the equatorial positions occupied by the four O atoms of two chelating monoanionic acac ligands, and one water molecule, while the two oxido ions reside at the axial positions trans to each other. The equatorial plane composed of O1, O2 (and the two other symmetry-equivalent atoms) and O4 deviates noticeably from planarity [with a mean deviation of 0.172 (3) Å]. The two six-membered chelate rings composed of U1, O1, C1, C2, C3 and the symmetry-equivalent atoms deviate significantly from planarity [mean deviation, 0.211 (3) Å]. The dihedral angle between the two chelate best-fit planes is 26.02 (13)°.
3. Supramolecular features
Examination of the extended structure revealed a prominent intermolecular hydrogen bonding interaction (O4—H4⋯O1) involving one of the O atoms of the acac ligand and the Ow atom (Fig. 2, Table 2). This interaction results in pairing of two mononuclear units, eventually consolidating the extended structure. The packing pattern along the c-axis direction reveals an extended pattern with considerably large hexagonal void channels, each one surrounded by six other smaller void channels. The void volume was determined using contact surface maps (which offer an estimate of the volume that could be filed by guest molecules) to be 325.41 Å3, representing 13.4% of the unit-cell volume (Barbour, 2006). This interesting packing pattern is shown in Figs. 3 and 4.
4. Database survey
A scrutiny of the CSD (Conquest version 2.0, 2021; Groom et al., 2016) revealed two other crystal structures of [UO2(acac)2(H2O)], 2 and 3, available for comparison [there are few others for which coordinates are not available, see: Dornberger-Schiff & Titze (1969) and Comyns et al. (1958)]. Structure 2 is a polymorph of 1, while structure 3 is a pyrazine solvate of [UO2(acac)2(H2O)]. Selected metric parameters of 1–3 are listed in Table 3. Structures 1 and 2 differ in their crystal packing arrangement. Whereas 1 crystallizes in the trigonal Pc1 with half a molecule per 2 crystallizes in the monoclinic P21/c with the consisting of the complete molecule (Alcock & Flanders, 1987). The differences in metric parameters between structures 1 and 2 are subtle (albeit with a slightly longer U—Ow distance in 2), the differences being attributed to the different crystal packing. In case of 1, classical hydrogen bonding dictates the packing pattern, while in 2, the intermolecular interactions are chemically inconsequential. Structure 3 is also quite similar to 1 and 2. However, 3 crystallizes in the triclinic P with one interstitial pyrazine molecule (the contains the full [UO2(acac)2(H2O)] molecule and two half-molecules of pyrazine). The pyrazine molecules within the structure are engaged in hydrogen bonding with the coordinated water molecule [Ow—H—-N(pyrazine), H⋯N = 1.95 (2) Å and Ow⋯N = 2.765 (5) Å; Kawasaki & Kitazawa 2008], thus preventing the supramolecular organization of the uranium complex (seen in 1). Interestingly, the lower density of 1 compared to those of 2 and 3 (1.99, 2.27 and 2.03 g cm−3 for 1, 2, and 3 respectively) is attributed to the large voids within the hexagonal channels.
5. Synthesis and crystallization
To a vial containing 377 mg (3.8 mmol) of 2,4-pentanedione (acac) in 7 mL of THF was added 20 mL of an aqueous solution containing 0.94 mmol of UO2(OAc)2(H2O)2. The reaction mixture rapidly changed color from colorless to yellow. A 10 M aqueous solution of KOH was added dropwise to the reaction mixture until the pH was approximately 9 (500 µL). The color of the solution intensified to a dark yellow concurrent with the formation of a suspension. The suspension was extracted with 50 mL of toluene, and the resultant yellow organic solution was dried over Na2SO4. After reducing the volume by 50% at reduced pressure, the remaining solution was allowed to evaporate at room temperature. Over the course of 1 week, yellow crystals were formed (150 mg, 34% yield).
6. Refinement
Crystal data, data collection and structure . The water O atom was freely refined. C-bound H atoms were positioned geometrically (C—H = 0.03–0.96) and refined as riding with Uiso(H) = 1.2–1.5Ueq(C).
details are summarized in Table 4
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Supporting information
CCDC reference: 2117155
https://doi.org/10.1107/S2056989021011063/ex2049sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989021011063/ex2049Isup2.hkl
Data collection: APEX3 (Bruker, 2016); cell
SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXT2018/2 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).[UO2(C5H7O2)2(H2O)] | Dx = 1.992 Mg m−3 |
Mr = 486.26 | Mo Kα radiation, λ = 0.71073 Å |
Trigonal, P3c1 | Cell parameters from 9890 reflections |
a = 19.5774 (9) Å | θ = 3.2–25.4° |
c = 7.3264 (5) Å | µ = 10.03 mm−1 |
V = 2431.8 (3) Å3 | T = 298 K |
Z = 6 | Needle, yellow |
F(000) = 1344 | 0.30 × 0.15 × 0.05 mm |
Bruker D8 Quest PHOTON II diffractometer | 1426 reflections with I > 2σ(I) |
ω–scan | Rint = 0.027 |
Absorption correction: multi-scan (SADABS; Krause et al., 2015) | θmax = 25.4°, θmin = 3.5° |
Tmin = 0.457, Tmax = 0.745 | h = −23→23 |
26571 measured reflections | k = −23→23 |
1493 independent reflections | l = −8→8 |
Refinement on F2 | Primary atom site location: dual |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.016 | Hydrogen site location: mixed |
wR(F2) = 0.042 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.13 | w = 1/[σ2(Fo2) + (0.0203P)2 + 3.5627P] where P = (Fo2 + 2Fc2)/3 |
1493 reflections | (Δ/σ)max < 0.001 |
89 parameters | Δρmax = 0.51 e Å−3 |
0 restraints | Δρmin = −1.06 e Å−3 |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. A suitable crystal of [UO2(acac)2(H2O)] was selected and mounted on a Bruker D8 Quest diffractometer. The crystal was kept at 298.0?K during data collection. Using Olex2 (Dolomanov, 2009) the structure was solved with the SHELXT (Sheldrick 2015) structure solution program using Intrinsic Phasing and refined with the SHELXL (Sheldrick 2015) refinement package using Least Squares minimisation. |
x | y | z | Uiso*/Ueq | ||
U1 | 0.38611 (2) | 0.000000 | 0.750000 | 0.03158 (8) | |
O4 | 0.5083 (2) | 0.000000 | 0.750000 | 0.0415 (8) | |
O1 | 0.45776 (16) | 0.08101 (15) | 0.4979 (3) | 0.0442 (6) | |
O2 | 0.31937 (16) | 0.06227 (16) | 0.6287 (4) | 0.0525 (7) | |
O3 | 0.42991 (16) | 0.08004 (14) | 0.9047 (3) | 0.0453 (6) | |
C1 | 0.4697 (2) | 0.1489 (2) | 0.4498 (5) | 0.0437 (9) | |
C2 | 0.4199 (3) | 0.1769 (2) | 0.4902 (6) | 0.0524 (10) | |
H2 | 0.436802 | 0.229520 | 0.464721 | 0.063* | |
C3 | 0.3450 (3) | 0.1311 (3) | 0.5675 (5) | 0.0503 (9) | |
C4 | 0.5432 (3) | 0.1979 (3) | 0.3397 (7) | 0.0674 (13) | |
H4A | 0.588238 | 0.204246 | 0.406406 | 0.101* | |
H4B | 0.548844 | 0.248675 | 0.316338 | 0.101* | |
H4C | 0.539460 | 0.171870 | 0.225884 | 0.101* | |
C5 | 0.2896 (3) | 0.1632 (4) | 0.5750 (7) | 0.0742 (15) | |
H5A | 0.249096 | 0.134214 | 0.663397 | 0.111* | |
H5B | 0.266109 | 0.158127 | 0.457143 | 0.111* | |
H5C | 0.318349 | 0.217860 | 0.609141 | 0.111* | |
H4 | 0.525 (3) | −0.018 (3) | 0.694 (7) | 0.073 (17)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
U1 | 0.03345 (9) | 0.02596 (10) | 0.03283 (11) | 0.01298 (5) | 0.00110 (3) | 0.00219 (6) |
O4 | 0.0423 (15) | 0.044 (2) | 0.0383 (19) | 0.0222 (10) | −0.0026 (8) | −0.0052 (16) |
O1 | 0.0552 (16) | 0.0402 (14) | 0.0435 (13) | 0.0286 (12) | 0.0131 (12) | 0.0121 (11) |
O2 | 0.0516 (16) | 0.0580 (17) | 0.0576 (18) | 0.0345 (15) | 0.0090 (13) | 0.0207 (13) |
O3 | 0.0560 (16) | 0.0355 (13) | 0.0447 (14) | 0.0231 (12) | −0.0011 (12) | −0.0068 (11) |
C1 | 0.054 (2) | 0.0369 (19) | 0.0394 (19) | 0.0223 (18) | 0.0035 (16) | 0.0077 (15) |
C2 | 0.068 (3) | 0.041 (2) | 0.054 (2) | 0.032 (2) | 0.011 (2) | 0.0157 (18) |
C3 | 0.071 (3) | 0.061 (3) | 0.0364 (19) | 0.046 (2) | 0.0031 (18) | 0.0109 (18) |
C4 | 0.062 (3) | 0.054 (3) | 0.082 (3) | 0.025 (2) | 0.022 (2) | 0.027 (2) |
C5 | 0.097 (4) | 0.101 (4) | 0.065 (3) | 0.080 (3) | 0.024 (3) | 0.031 (3) |
U1—O4 | 2.392 (4) | C1—C2 | 1.369 (6) |
U1—O1 | 2.381 (2) | C1—C4 | 1.504 (5) |
U1—O1i | 2.381 (2) | C2—H2 | 0.9300 |
U1—O2 | 2.361 (3) | C2—C3 | 1.400 (6) |
U1—O2i | 2.361 (3) | C3—C5 | 1.502 (5) |
U1—O3 | 1.769 (2) | C4—H4A | 0.9600 |
U1—O3i | 1.769 (2) | C4—H4B | 0.9600 |
O4—H4 | 0.71 (4) | C4—H4C | 0.9600 |
O4—H4i | 0.71 (4) | C5—H5A | 0.9600 |
O1—C1 | 1.279 (4) | C5—H5B | 0.9600 |
O2—C3 | 1.261 (5) | C5—H5C | 0.9600 |
O1i—U1—O4 | 75.17 (6) | C1—O1—U1 | 130.3 (2) |
O1—U1—O4 | 75.17 (6) | C3—O2—U1 | 131.1 (3) |
O1i—U1—O1 | 150.33 (12) | O1—C1—C2 | 124.0 (3) |
O2—U1—O4 | 144.24 (7) | O1—C1—C4 | 115.4 (4) |
O2i—U1—O4 | 144.24 (6) | C2—C1—C4 | 120.5 (3) |
O2i—U1—O1 | 139.25 (9) | C1—C2—H2 | 118.0 |
O2—U1—O1i | 139.25 (9) | C1—C2—C3 | 124.0 (4) |
O2i—U1—O1i | 70.00 (9) | C3—C2—H2 | 118.0 |
O2—U1—O1 | 70.00 (9) | O2—C3—C2 | 124.0 (4) |
O2i—U1—O2 | 71.52 (13) | O2—C3—C5 | 116.7 (4) |
O3—U1—O4 | 87.61 (9) | C2—C3—C5 | 119.3 (4) |
O3i—U1—O4 | 87.61 (9) | C1—C4—H4A | 109.5 |
O3i—U1—O1i | 92.50 (11) | C1—C4—H4B | 109.5 |
O3—U1—O1i | 86.27 (10) | C1—C4—H4C | 109.5 |
O3—U1—O1 | 92.50 (11) | H4A—C4—H4B | 109.5 |
O3i—U1—O1 | 86.27 (10) | H4A—C4—H4C | 109.5 |
O3—U1—O2i | 97.81 (12) | H4B—C4—H4C | 109.5 |
O3—U1—O2 | 86.10 (11) | C3—C5—H5A | 109.5 |
O3i—U1—O2 | 97.81 (12) | C3—C5—H5B | 109.5 |
O3i—U1—O2i | 86.10 (11) | C3—C5—H5C | 109.5 |
O3—U1—O3i | 175.21 (17) | H5A—C5—H5B | 109.5 |
U1—O4—H4i | 134 (4) | H5A—C5—H5C | 109.5 |
U1—O4—H4 | 134 (4) | H5B—C5—H5C | 109.5 |
H4—O4—H4i | 92 (8) | ||
U1—O1—C1—C2 | −26.9 (6) | O1—C1—C2—C3 | −8.8 (7) |
U1—O1—C1—C4 | 154.2 (3) | C1—C2—C3—O2 | 9.1 (7) |
U1—O2—C3—C2 | 27.1 (6) | C1—C2—C3—C5 | −169.0 (4) |
U1—O2—C3—C5 | −154.8 (3) | C4—C1—C2—C3 | 170.0 (4) |
Symmetry code: (i) x−y, −y, −z+3/2. |
D—H···A | D—H | H···A | D···A | D—H···A |
O4—H4···O1ii | 0.72 (6) | 2.01 (5) | 2.704 (3) | 164 (7) |
Symmetry code: (ii) −x+1, −y, −z+1. |
1a | 2b | 3c | |
U—O(H2O) | 2.392 (4) | 2.489 (8) | 2.409 (4) |
U═(oxo) | 1.769 (2) | 1.743 (6) | 1.776 (3) |
U—O(acac) | 2.371 (3) | 2.339 (6) | 2.354 (4) |
Notes: (a) this work; (b) Alcock & Flanders (1987); (c) Kawasaki & Kitazawa (2008). |
Funding information
Funding for this research was provided by: Idaho National Laboratory (contract No. 18A12-107); U.S. Nuclear Regulatory Commission (grant No. 31310018M0012).
References
Alcock, N. W. & Flanders, D. J. (1987). Acta Cryst. C43, 1480–1483. CSD CrossRef CAS Web of Science IUCr Journals Google Scholar
Barbour, L. J. (2006). Chem. Commun. pp. 1163–1168. Web of Science CrossRef Google Scholar
Bruker (2016). APEX3 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Comyns, A. E., Gatehouse, B. M. & Wait, E. (1958). J. Chem. Soc. 4655–4665. Google Scholar
Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339–341. Web of Science CrossRef CAS IUCr Journals Google Scholar
Dornberger-Schiff, K. & Titze, H. (1969). Acta Chem. Scand. 23, 1685–1694. CAS Google Scholar
Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171–179. Web of Science CrossRef IUCr Journals Google Scholar
Johnson, A. T., Parker, T. G., Dickens, S. M., Pfeiffer, J. K., Oliver, A. G., Wall, D., Wall, N. A., Finck, M. R. & Carney, K. P. (2017). Inorg. Chem. 56, 13553–13561. CrossRef CAS PubMed Google Scholar
Kawasaki, T. & Kitazawa, T. (2008). Acta Cryst. E64, m673–m674. Web of Science CSD CrossRef IUCr Journals Google Scholar
Krause, L., Herbst-Irmer, R., Sheldrick, G. M. & Stalke, D. (2015). J. Appl. Cryst. 48, 3–10. Web of Science CSD CrossRef ICSD CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
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