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Article

Thorium(IV) and Uranium(IV) Phosphaazaallenes

by
Pokpong Rungthanaphatsophon
,
O. Jonathan Fajen
,
Steven P. Kelley
and
Justin R. Walensky
*
Department of Chemistry, University of Missouri, Columbia, MO 65211, USA
*
Author to whom correspondence should be addressed.
Inorganics 2019, 7(9), 105; https://doi.org/10.3390/inorganics7090105
Submission received: 10 July 2019 / Revised: 15 August 2019 / Accepted: 17 August 2019 / Published: 21 August 2019
(This article belongs to the Special Issue Bonding in Actinide and Lanthanide Complexes)
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Abstract

:
The synthesis of tetravalent thorium and uranium complexes with the phosphaazaallene moiety, [N(tBu)C=P(C6H5)]2−, is described. The reaction of the bis(phosphido) complexes, (C5Me5)2An[P(C6H5)(SiMe3)]2, An = Th, U, with two equivalents of tBuNC produces (C5Me5)2An(CNtBu)[η2-(N,C)-N(tBu)C=P(C6H5)] with concomitant formation of P(SiMe3)2(C6H5) via silyl migration. These complexes are characterized by NMR and IR spectroscopy, as well as structurally determined using X-ray crystallography.

Graphical Abstract

1. Introduction

The reactivity of metal–phosphido complexes is of interest for the development of hydrophosphination catalysts as well as the synthesis of phosphorus–element multiple bonds. For example, phosphaalkenes, P=C, have attracted interest for building blocks in organophosphorus chemistry [1,2,3], ligands to transition metal complexes [4,5], as well as potential applications as functional materials [6,7,8,9,10]. After nearly 20 years of dormancy [11,12,13,14,15], actinide–phosphorus has received greater attention recently [16,17,18,19] with researchers examining similarities and differences in the molecular and electronic structure of its more studied congener, nitrogen. Our interest in actinide–phosphido complexes has been on investigating small molecule reactivity. Since actinides are large, highly electropositive metals, consequently they have an affinity to coordinate to highly electronegative atoms such as oxygen and nitrogen. Thus, they are less inclined to form strong interactions with ligands bearing soft-donor atoms such as phosphorus. Therefore, the actinide–phosphido bond should, and has been demonstrated, be relatively reactive [20,21,22,23,24,25,26,27,28,29,30].
Previously, we investigated the reactivity of the primary bis(phosphido) complexes, (C5Me5)2Th[PH(R)]2, R = 2,4,6-Me3C6H2 (Mes) or 2,4,6-iPr3C6H2 (Tipp), with tBuNC [16]. This led to a proton transfer from one phosphido ligand to form the primary phosphine, and the phosphaazaallene, (C5Me5)2Th(C≡NtBu)[η2-N(tBu)C=PR], was isolated, Equation (1). To prevent this proton transfer, the bis(phosphido) complexes, (C5Me5)2An[P(C6H5)(SiMe3)]2, An = Th, U, were synthesized. However, herein, we show that instead of proton transfer, silyl migration occurs, resulting in similar phosphaazaallene moieties.
Inorganics 07 00105 i001

2. Results

The secondary phosphido complexes, (C5Me5)2An[P(SiMe3)(C6H5)]2, An = Th, 1; U, 2, were synthesized from the reaction of (C5Me5)2AnCl2, An = Th, U, with two equivalents of KP(SiMe3)(C6H5), Equation (2). Complex 2 is formed in lower yields (~40%), even when three equivalents of the potassium salt are used. This is presumably due to the steric properties of the phosphido ligand with the smaller uranium(IV) ionic radii as compared to thorium(IV) as 1 has consistent yields of >80%. The major byproduct in the reaction of (C5Me5)2UCl2 with two equivalents of K[P(SiMe3)(C6H5)] is (C5Me5)2U(Cl)[P(SiMe3)(C6H5)], 2a. A similar result was observed with K[P(SiMe3)(Mes)] [31]. When one equivalent of K[P(SiMe3)(C6H5)] is reacted with (C5Me5)2UCl2, then 2a can be isolated in high yield, >90%. The 1H NMR spectrum of 1 showed resonances at 2.08 and 0.56 ppm for the (C5Me5)1− and SiMe3, respectively. In addition, the 31P NMR spectrum of 1 showed a resonance at 72.7 ppm, shifted downfield from (C5Me5)2Th[P(SiMe3)(Mes)]2 which is located at 48.5 ppm. The paramagnetic NMR spectrum of 2 showed the (C5Me5)1− resonance at 13.5 ppm, while the SiMe3 group was located at −8.94 ppm. In 2a, the (C5Me5)1− and SiMe3 resonances are observed at 13.4 ppm and −13.9 ppm, respectively. For comparison, (C5Me5)2U(PPh2)2 and (C5Me5)2U(CH3)(PPh2) have resonances for (C5Me5)1− located at 12.17 and 11.08 ppm, respectively [32].
Inorganics 07 00105 i002
The structures of 1 and 2, Figure 1, were determined by X-ray crystallographic analysis. The metal–phosphorus bond distances are 2.8243(9) Å in 1 and 2.7477(8) and 2.7478(8) Å in 2, while the P–M–P bond angles are 92.75(5) and 92.16(4)° in 1 and 2, respectively. In 1, the thorium–phosphido bond distances are similar to other metallocene thorium bis(phosphido) complexes reported and slightly shorter than the 2.855(6) and 2.938(6) Å in Th(BcMes)2[PH(Mes)]2 [33]. Complex 2 is the first structurally characterized bis(phosphido) uranium complex, however polyphosphide complexes of uranium are known from P4 activation [34,35]. The uranium–phosphido bond distances are shorter than those in U(TrenTIPS)(PH2) of 2.883(2) Å [36], but similar to the 2.789(4) Å in (C5Me5)2U[P(SiMe3)2](Cl) [14].
With 1 and 2, a proton could not be transferred to the phosphido ligand to form the phosphine as in the case for the reaction with the primary bis(phosphido) complex, so the reaction with tBuNC was attempted, Equation (3). The 31P NMR chemical shift for the thorium product, 3, was observed at 58.5 ppm, while the 13C{1H} NMR spectrum showed a resonance at 265.4 ppm. These resonances are both shifted downfield from the other phosphaazaallene complexes, (C5Me5)2Th(C≡NtBu)[η2-N(tBu)C=P(R)], R = Mes, Tipp, which have 31P NMR resonances located at −10.7 ppm and −21.3 ppm, respectively. Further, the 1H NMR and 31P NMR spectrum showed resonances for P(SiMe3)2(C6H5) [37], the byproduct of silyl-extraction from one phosphido ligand. For 4, a signal was located at 198.3 ppm in the 31P NMR spectrum. Additionally, IR stretching frequencies at 2188 and 2171 cm−1 for 3 and 4, respectively, were observed for the C≡N bond of the tBuNC adduct.
Inorganics 07 00105 i003
The structures of 3 and 4 were determined by X-ray crystallographic analysis and revealed the anticipated phosphaazaallene complexes, Figure 2. Complex 4 is the first uranium complex with the phosphaazaallene motif. The major difference between 3 and the previously reported structure, (C5Me5)2Th(CNtBu)[η2-N(tBu)C=P(Tipp)], Table 1, is the decrease in the steric properties of the phenyl versus 2,4,6-iPr3C6H2 bound to phosphorus. As a result, the phenyl bends back towards the metal center in 3 with a Th–C26–P1 bond angle of 159.7(4)° and a C26–P–C(ipso) bond angle of 102.3(4)°. These angles are 137.7(3)° and 115.8(3)°, respectively, in the tri(isopropyl)phenyl phosphaazaallene complex. The actinide–nitrogen bond distance is 2.346(6) and 2.273(2) Å in 3 and 4, respectively. The phosphaazaallene moiety in 3 has a N2–C26 bond length of 1.367(9) Å and C26-P1 distance of 1.717(9) Å. There is a slight elongation of the C26–P1 bond in 4 to 1.733(3) Å with a subsequent and nearly equivalent contraction of the N2–C26 distance to 1.343(4) Å.
Due to the large bond dissociation energies for P–H and P–Si bonds of 297.0 kJ/mol and 363.3 kJ/mol [38], respectively, the formation of the phosphaazaallene must be due to the kinetic lability of the phosphorus–element bond. Similar to the formation of the phosphaazaallene previously reported [25], no detection of a phosphinidene intermediate was observed in the 31P NMR spectrum. This result, along with others, is consistent with insertion of the incoming substrate followed by bond activation without phosphinidene formation.

3. Materials and Methods

General Considerations. All syntheses were carried out under inert atmosphere of nitrogen using standard Schlenk and glove box techniques. Solvents were purified in MBRAUN solvent purification system prior to use. Tert–butyl isocyanide (Aldrich, St. Louis, MO, USA) and KN(SiMe3)2 (Aldrich) were used as received. (C5Me5)2ThCl2 [39], and (C5Me5)2UCl2 [39], were prepared according to literature procedures. KP[(C6H5)(SiMe3)] was prepared from HP[(C6H5)(SiMe3)] and KN(SiMe3)2 in toluene and collected by filtration over medium porous frit followed by washing with toluene and drying under vacuum. Elemental analyses were performed at the University of California, Berkeley Microanalytical Facility using a Perkin–Elmer Series II 2400 CHNS analyzer (Waltham, MA, USA). C6D6 (Cambridge) was dried over molecular sieves and degassed with three cycles of freeze–pump–thaw. 1H and 13C NMR experiment were performed on either Bruker Avance III 500 or 600 MHz spectrometer (Billerica, MA, USA). 1H and 13C NMR spectrum are reported in ppm referenced internally to residual proton resonances. 31P and 29Si NMR experiment were performed on Bruker AVII+ 300 MHz spectrometer (Billerica, MA, USA). 31P and 29Si NMR are reported in ppm referenced external to 85% H3PO4 and SiMe4, respectively. If coupling is not specified, then the origin is not definitively known. Infrared spectra were recorded as KBr pellets on Perkin–Elmer Spectrum One FT-IR spectrometer (Waltham, MA, USA).
Caution!Thorium-232 and depleted uranium (primarily U-238) are alpha-emitting radiometals with half-lives of 1.4 × 1010 years and 4.47 × 109 years, respectively. All work was carried out in a radiological laboratory with appropriate personal protective and counting equipment.
Synthesis of (C5Me5)2Th[P(C6H5)(SiMe3)]2. 1. Toluene (10 mL) was added to a mixture of (C5Me5)2ThCl2 (200 mg, 0.35 mmol) and KP(C6H5)(SiMe3) (154 mg, 0.7 mmol). The resulting cloudy red solution was allowed to stir overnight, then filtered through a pipette plugged with Celite. Volatiles were removed in vacuo to yield an orange solid (253 mg, 84%). X-ray quality crystals of (C5Me5)2Th[P(C6H5)(SiMe3)]2 were grown from a concentrated diethyl ether solution at −45 °C. 1H NMR (C6D6, 600 MHz, 298 K): δ 7.74 (br-t, 4H, J = 6.3 Hz, o-Ph), 7.22 (t, 4H, 3JH–H = 7.2 Hz, m-Ph), 7.12 (t, 2H, 3JH–H = 7.2 Hz, p-Ph), 2.08 (s, 30H, C5Me5), 0.56 (d, 18H, 2JH–P = 4.2 Hz, SiMe3). 13C{1H} NMR (C6D6, 150 Hz, 298 K): 140.4 (d, 1JC–P = 7.2 Hz), 140.2 (t, 2JC–P = 3.15 Hz), 128.1, 127.9, 126.6, 12.8, 3.7 (t, JC–P = 6 Hz). 31P{1H} NMR (C6D6, 120 MHz): δ 72.7. 29Si INEPT NMR (C6D6, 60 MHz): δ 5.62 (dd, 1JSi–P = 1.63 Hz, 1JSi–P = 2.18 Hz). IR (KBr, cm−1): 2951 (m), 2898 (s), 2856 (m), 1576 (w), 1472 (w), 1431 (m), 1378 (w), 1247 (s), 1098 (s), 1024 (s), 897 (w), 835 (vs), 734 (m), 697 (m), 625 (w), 579 (w), 540 (w). Anal. Calcd for C38H58P2Si2Th: C, 52.76; H, 6.76. Found: C, 52.72; H, 6.65.
Synthesis of (C5Me5)2U[(P(C6H5)(SiMe3)]2, 2. (C5Me5)2U[(P(C6H5)(SiMe3)]2 was prepared in a manner similar to 1 except using (C5Me5)2UCl2 (126 mg, 0.22 mmol), KP[(C6H5)(SiMe3)] (144 mg, 0.65 mmol), and toluene (5 mL). The resulting deep brown solution was stirred overnight at room temperature, then, filtered through a pipette plugged with Celite. Volatiles were removed in vacuo to yield a dark brown solid. The residue was dissolved in pentane and filtered through Celite then isolated by concentration of the filtrate, causing crystallization of the product. The crystals were isolated and dried under vacuum (75 mg, 40%). 1H NMR (C6D6, 600 MHz, 298 K): δ 13.5 (s, 30H, C5Me5), −2.48 (s, 2H, Ph), −3.74 (s, 4H, Ph), -8.94 (s, 18H, SiMe3), −28.6 (br-s, 4H, Ph). IR (KBr, cm−1): 2955 (m), 2905 (br-s), 2859 (m), 1577 (w), 1474 (w), 1439 (br-m), 1378 (w), 1244 (m), 1137 (br-w), 1081 (w), 1064 (m), 1022 (m), 974 (w), 929 (br-w), 840 (vs), 750 (w), 727 (w), 695 (w), 630 (w). Anal. Calcd for C38H58P2Si2U: C, 52.40; H, 6.71. Found: C, 52.08; H, 6.52.
Synthesis of (C5Me5)2U[(P(C6H5)(SiMe3)](Cl), 2a. In a 20 mL scintillation vial, (C5Me5)2UCl2 (99 mg, 0.17 mmol), KP(C6H5)(SiMe3) (38 mg, 0.17 mmol), and toluene (5 mL) were combined. The resulting deep brown solution was stirred overnight at room temperature and filter over a pipette plugged with Celite. Volatiles removed in vacuo to yield a deep brownish red solid (114 mg, 92%). 1H NMR (C6D6, 600 MHz, 298 K): δ 13.4 (s, 30H, C5Me5), −5.59 (s, 2H, Ph), −5.96 (s, 1H, Ph), −13.9 (s, 9H, SiMe3), −40.8 (s, 2H, Ph). IR (KBr, cm−1): 2954 (m), 2905 (s), 2858 (m), 1579 (w), 1475 (m), 1438 (m), 1379 (m), 1259 (w), 1244 (m), 1144 (w), 1082 (s), 1066 (s), 1023 (s), 931 (m), 841 (vs), 800 (w), 751 (w), 727 (w), 694 (w), 631 (w). Anal. Calcd for C29H44Cl1P1Si1U1: C, 48.03; H, 6.12. Found: C, 48.45; H, 6.46.
Synthesis of (C5Me5)2Th(C≡NtBu)[(η2-N(tBu)C=PPh)], 3. A solution of (C5Me5)2Th[P(C6H5)(SiMe3)]2 (72 mg, 0.08 mmol) in methylcyclohexane (5 mL) was placed in a −45 °C freezer for 30 minutes prior to the next step. To this solution, an excess amount of tert-butyl isocyanide (0.15 mL, 1.3 mmol) was added dropwise. The mixture was allowed to stir at room temperature overnight, after which volatiles were removed in vacuo to yield an orange solid. An analytically pure sample of 3 was obtained after recrystallization in 1,2-dimethoxyethane (36 mg, 56%). X-ray quality crystals of 3 were grown from a concentrated 1,2-dimethoxyethane solution at −45 °C. 1H NMR (C6D6, 600 MHz, 298 K): δ 8.22 (t, 2H, 3JC–H = 6 Hz, o-Ph), 7.42 (t, 2H, 3JC–H = 7.8 Hz, m-Ph), 7.19 (t, 1H, 3JC–H = 7.2 Hz, p-Ph), 2.05 (s, 30H, C5Me5), 1.72 (d, 9H, J = 1.2 Hz, [(H3C)3C]NCPPh), 0.9 (s, 9H, (H3C)3CNC). 13C{1H} NMR (C6D6, 150 Hz, 298 K): 265.4 (d, 1JC–P = 76.8 Hz), 155.7 (d, 1JC–P = 51.6 Hz), 131.5 (d, 3JC–P = 18.6 Hz), 127.7 (d, 2JC–P = 6.3 Hz), 123.8, 122.7, 61.6, 57.2, 29.7 (d, 4JC–P = 12.8 Hz), 28.9, 12.0. 31P{1H} NMR (C6D6, 120 MHz): δ 58.5. IR (KBr, cm−1): 2966 (s), 2902 (s), 2860 (s), 2188 (vs), 1575 (m), 1470 (m), 1450 (m), 1436 (m), 1373 (m), 1355 (m), 1295 (vs), 1266 (s), 1235 (m), 1197 (s), 1086 (br-m), 1061 (m), 1023 (s), 936 (m), 838 (w), 825 (w), 802 (br-w), 749 (m), 736 (s), 698 (s), 638 (w), 590 (w), 546 (w), 525 (w). Anal. Calcd for C36H53N2PTh: C, 55.66; H, 6.88; N, 3.61. Found: C, 55.42; H, 7.01; N, 3.54.
Synthesis of (C5Me5)2U(C≡NtBu)[(η2-N(tBu)C=PPh)], 4. Complex 4 was prepared in a manner similar to 3 using (C5Me5)2U[(P(C6H5)(SiMe3)]2 (241 mg, 0.28 mmol), tert-butyl isocyanide (0.1 mL, 0.88 mmol), and pentane (5 mL). The solution turned instantly from dark brown to black. An analytically pure sample of 4 was obtained after recrystallization in diethyl ether (87 mg, 40%). X-ray quality crystals of 4 were grown from a concentrated pentane solution at −45 °C. 1H NMR (C6D6, 500 MHz, 298 K): δ 28.5 (s, 9H, tBu), 4.10 (s, 2H, Ph), 1.50 (s, 30H, C5Me5), −1.50 (s, 1H, Ph), −14.7 (s, 9H, tBu), −46.5 (s, 2H, Ph). 31P{1H} NMR (C6D6, 120 MHz): δ 198.3. IR (KBr, cm−1): 2967 (s), 2912 (s), 2171 (vs), 1438 (m), 1375 (m), 1262 (m), 1205 (br-m), 1082 (br-m), 1023 (m), 903 (w), 884 (w), 803 (br-m), 751 (w), 694 (w), 676 (w), 577 (w). Satisfactory elemental analysis could not be obtained after multiple attempts.
Crystallographic Data Collection and Structure Determination. The selected single crystals were mounted on Kapton cryoloops using viscous hydrocarbon oil. X-ray data collection was performed at 100(2) K. The X-ray data were collected on a Bruker D8 Venture diffractometer (Madison, WI, USA) equipped with a Photon 100 CMOS area detector using Mo-Kα radiation from a microfocus source (λ = 0.71073 Å). The data collection and processing utilized Bruker Apex2 suite of programs [40]. The structures were solved using an iterative dual space approach as implemented in SHELXT [41] and refined by full-matrix least-squares methods on F2 using Bruker SHELX-2014/7 program. All non-hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms were placed at calculated positions and included in the refinement using a riding model. Thermal ellipsoid plots were prepared by using Olex2 [42] with 50% of probability displacements for non-hydrogen atoms. Crystal data and detail for data collection for complexes 1–4 are provided in Table 2, and Crystallographic Information Files (CIFs) are included in the Supplementary Materials.
Although the structure of 3 refined with satisfactory geometrical parameters, the model contained errors including anomalously large difference map holes, prolate/oblate thermal ellipsoids, and a high goodness of fit. Inspection of synthesized precession images from the diffraction photographs revealed the presence of at least one additional domain rotated slightly and largely overlapping with the first, suggesting a split crystal. The unit cell was re-determined with the program CELL_NOW using 1740 reflections with a signal-to-noise greater than 20 taken from 420 diffraction photographs. Of these, 1422 (82.1%) could be given hkl indices within +/− 0.20 of integer values to a single domain. Including a second domain rotated by 1° with respect to the first increased this value to 1664 reflections (95.6%). Contribution from the additional crystallites was incorporated into the model using the SHELX TWIN command with the twin matrix output by CELL_NOW. The minor domain fraction refined to 9.43(3)%. Inclusion of the TWIN command improved but did not eliminate the problems with difference map and GooF, likely because there are additional unrefined domains.

4. Conclusions

In summary, the synthesis and characterization of two new actinide bis(phosphido) complexes and their reactivity with tBuNC has been investigated. Despite being secondary phosphido complexes, silyl migration from one phosphido to the other to form the parent phosphine and phosphaazaallene moieties was observed in analogy to the reactivity observed previously with primary phosphido complexes.

Supplementary Materials

The following are available online at https://www.mdpi.com/2304-6740/7/9/105/s1: The CIFs and CheckCIFs.

Author Contributions

P.R., O.J.F., J.R.W. and S.P.K. worked together to conceive experimental design and write the manuscript. P.R. and O.J.F. executed the experimental work, while J.R.W. obtained funding. All authors contributed to writing of the manuscript.

Funding

We gratefully acknowledge support for this work from the U.S. Department of Energy, Office of Science, Early Career Research Program under Award DE-SC-0014174. We also thank the MU Honors College Discovery Fellows Program for partial support of O.J.F.

Conflicts of Interest

The authors declare no conflict of interest.

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Inorganics 07 00105 g001 550
Figure 1. Thermal ellipsoid plots of 1 (left) and 2 (right) shown at the 50% probability level. Hydrogen atoms have been omitted and silyl groups shown in wireframe for clarity.
Figure 1. Thermal ellipsoid plots of 1 (left) and 2 (right) shown at the 50% probability level. Hydrogen atoms have been omitted and silyl groups shown in wireframe for clarity.
Inorganics 07 00105 g001
Inorganics 07 00105 g002 550
Figure 2. Thermal ellipsoid plots of 3 (left) and 4 (right) shown at the 50% probability level. Hydrogen atoms have been omitted for clarity.
Figure 2. Thermal ellipsoid plots of 3 (left) and 4 (right) shown at the 50% probability level. Hydrogen atoms have been omitted for clarity.
Inorganics 07 00105 g002
Table
Table 1. Selected bond distances (Å) and angles in 3 and 4 with comparison to the previously reported, (C5Me5)2Th(CNtBu)[tBuNC=PTipp], Tipp = 2,4,6-iPr3C6H2 [25].
Table 1. Selected bond distances (Å) and angles in 3 and 4 with comparison to the previously reported, (C5Me5)2Th(CNtBu)[tBuNC=PTipp], Tipp = 2,4,6-iPr3C6H2 [25].
Bond Distance (Å)/Angle (deg)3, An = Th4, An = U(C5Me5)2Th(CNtBu)[N(tBu)C=PTipp]
An–N22.346(6)2.273(2)2.346(5)
An–C262.458(7)2.383(3)2.430(6)
N2–C261.367(9)1.343(4)1.348(8)
C26–P11.714(7)1.733(3)1.691(6)
An–C212.650(8)2.568(3)2.643(6)
N2–C26–P1130.9(6)130.4(2)152.1(5)
Table
Table 2. Crystallography parameters for complexes 1–4.
Table 2. Crystallography parameters for complexes 1–4.
1234
CCDC deposit number1826995182699618269991827000
Empirical formulaC38H58P2Si2ThC38H58P2Si2UC36H53N2PThC36H53N2PU
Formula weight (g/mol)865.00870.99776.81782.80
Crystal habit, colorprism, redplate, brownprism, yellowplate, brown
Temperature (K)100(2)100(2)100(2)100(2)
Space groupP 43 21 2P 43 21 2P21/cP21/c
Crystal systemTetragonalTetragonalMonoclinicMonoclinic
Volume (Å3)3988.1(9)3927.8(8)3516.2(6)3469.4(2)
a (Å)12.1642(12)12.0767(11)10.0829(10)10.0337(4)
b (Å)12.1642(12)12.0767(11)33.981(3)33.6762(14)
c (Å)26.953(3)26.931(3)10.7807(11)10.7644(4)
α (°)90909090
β (°)9090107.8389(17)107.477(1)
γ (°)90909090
Z4444
Calculated density (mg/m3)1.4411.4731.4671.499
Absorption coefficient (mm−1)3.9034.2994.3114.750
Final R indices [I > 2σ(I)]R = 0.0203;
wR2 = 0.0424		R = 0.0166;
wR2 = 0.0330		R = 0.0594;
wR2 = 0.1147		R = 0.0264;
wR2 = 0.0459

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Rungthanaphatsophon, P.; Fajen, O.J.; Kelley, S.P.; Walensky, J.R. Thorium(IV) and Uranium(IV) Phosphaazaallenes. Inorganics 2019, 7, 105. https://doi.org/10.3390/inorganics7090105

AMA Style

Rungthanaphatsophon P, Fajen OJ, Kelley SP, Walensky JR. Thorium(IV) and Uranium(IV) Phosphaazaallenes. Inorganics. 2019; 7(9):105. https://doi.org/10.3390/inorganics7090105

Chicago/Turabian Style

Rungthanaphatsophon, Pokpong, O. Jonathan Fajen, Steven P. Kelley, and Justin R. Walensky. 2019. "Thorium(IV) and Uranium(IV) Phosphaazaallenes" Inorganics 7, no. 9: 105. https://doi.org/10.3390/inorganics7090105

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