Thorium Compounds with Bonds to Sulfur or Selenium: Synthesis

Jul 5, 2016 - Pioneers in the study of molecules with An–E bonds include Gilman,(4) who set out to make potentially volatile uranium thiolates, and ...
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Thorium Compounds with Bonds to Sulfur or Selenium: Synthesis, Structure, and Thermolysis David Rehe, Anna Y. Kornienko, Thomas J. Emge, and John G. Brennan* Department of Chemistry and Chemical Biology, Rutgers, the State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854-8087, United States S Supporting Information *

ABSTRACT: Thorium chalcogenolates Th(ER)4 (E = S, Se; R = Ph, C6F5) form pyridine complexes with a variety of coordination numbers. Four compounds, (py) 4 Th(SPh)4 , (py) 3 Th(SePh) 4 , (py)3Th(SC6F5)4, and (py)4Th(SeC6F5)4, have been isolated and characterized by spectroscopic methods and low-temperature single crystal X-ray diffraction. Two of the products, (py)4Th(SPh)4 and (py)4Th(SeC6F5)4, have classic eight coordinate A4B4 square-antiprism geometries. The SePh compound is the only seven coordinate (4Se, 3N) product, and the fluorinated thiolate is distinctive in that the structure contains two dative interactions between Th and fluoride, to give a nine coordinate (3N, 4S, 2F) structure. The EPh compounds decompose thermally to give ThE2 and EPh2, while the fluorinated compounds give primarily ThF4, E2(C6F5)2, and E(C6F5)2.

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INTRODUCTION

suggested a significant degree of covalent An−E bonding that is not present in isomorphous lanthanide compounds.9 In addition to their fundamental significance, An complexes with chalcogenolate (ER) ligands are also important because of their potential use as starting materials for the synthesis of a range of nanoscale materials, with either metathesis10 or ligand based redox chemistry11 that parallels the now well-developed chemistry of the lanthanide elements. Further, M(ER)x species are potential sources for delivering solid-state materials at relatively low temperatures, using well-established thermolysis reactions.12 While there exist U(ER)4 compounds,13 analogous thorium examples do not exist. In this work we outline the chemistry of thorium with EC6H5 and EC6F5 ligands, and explore thermal decomposition reactions that give solid-state products.

Understanding and controlling the chemistry of the actinide (An) elements remains one of the great challenges in inorganic chemistry. The complex nature of the valence 5f-orbitals, the partial shielding of these valence orbitals by filled 6s and 6p orbitals, complications associated with relativistic effects, and the small difference in energy between the 5f- and 6d-orbitals all lead to materials with enigmatic chemical and physical properties that are unique in the periodic chart. An understanding of the bonding in actinide compounds is vitally important, allowing us to interpret or predict the complex physical properties of actinide compounds or to optimize the separations processes critical to research and development or environmental waste remediation. Covalent bonding in actinide compounds is evident in a range of complex types, from organometallic compounds1 and conventional coordination complexes2 to transient matrix isolated species.3 Of the more covalent types of ligands found in actinide chemistry, the chalcogen based anions (i.e., E2−, EE2−, ER; E = S, Se, Te; R = organic) are relatively unexplored. Pioneers in the study of molecules with An−E bonds include Gilman,4 who set out to make potentially volatile uranium thiolates, and Pinkerton, who studied the spectroscopy of thiophosphonate compounds.5 More contemporary work has focused on a number of organometallic systems in attempts to understand the stability of An cations when coordinated to chalcogen based anions.6 There has been significant progress toward understanding the chemistry of dithiolene compounds of U and contrasting these with analogous Ln derivatives,7 and there exist remarkable compounds with terminal AnE bonds.8 In these molecular systems, complementary theoretical approaches have © XXXX American Chemical Society

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EXPERIMENTAL SECTION

General Methods. All syntheses were carried out under ultrapure nitrogen (Welco Praxair), using conventional drybox or Schlenk techniques. Pyridine (Aldrich) and toluene (Aldrich) were purified with a dual column Solv-Tek solvent purification system and collected immediately prior to use. Se2(C6F5)214 and S2(C6F5)215 were prepared according to literature procedures. PhSeSePh (Aldrich) was purchased and recrystallized from hexanes, PhSSPh (Acros), thorium chips (International Bioanalytical Industries Inc., 3495 North Dixie Hwy, Unit #8, Boca Raton, FL 33431), and mercury (Strem Chemicals) were purchased and used as received. Melting points were recorded in sealed capillaries and are uncorrected. IR spectra were recorded on a Thermo Nicolet Avatar 360 FTIR spectrometer from 4000 to 450 cm−1 as Nujol mulls on CsI plates. UV−vis absorption spectra were recorded on a Varian DMS 100S spectrometer with the samples dissolved in pyridine, placed in either a 1.0 mm × 1.0 cm Spectrosil Received: March 15, 2016

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DOI: 10.1021/acs.inorgchem.6b00645 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. Summary of Crystallographic Details for 1−4 empirical formula fw space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z D(calcd) (g/cm−3) temp (K) λ (Å) abs coeff (mm−1) R(F)a [I > 2 σ(I)] Rw(F2)b [I > 2 σ(I)]

1

2

3

4

C44H40N4S4Th 985.08 P2/n 10.5686(5) 12.0162(6) 16.5583(8) 90 100.986(1) 90 2064.3(2) 2 1.585 100(2) 0.71073 3.850 0.0264 0.0573

C41.5H37.5N3.5Se4Th 1133.13 P21/c 19.890(3) 11.751(1) 19.668(2) 90 119.588(2) 90 3997.6(7) 4 1.883 100(2) 0.71073 7.405 0.0418 0.0934

C39H15F20N3S4Th 1265.82 C2/c 13.921(1) 16.980(1) 18.066(1) 90 103.736(2) 90 4148.1(5) 4 2.027 100(2) 0.71073 3.922 0.0349 0.0764

C51.5H27.5F20N5.5Se4Th 1651.17 P1̅ 12.433(3) 13.492(3) 18.832(4) 102.617(4) 100.856(4) 114.210(4) 2673(1) 2 2.051 100(2) 0.71073 5.625 0.0406 0.0800

R(F) = ∑||Fo| − |Fc||/∑|Fo|. bRw(F2) = {∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]}1/2. Additional crystallographic details are given in the Supporting Information.

a

1003 (m), 737 (w), 692 (m), 665 (m), 626 (m), 466 (m) cm−1. UV− vis: This compound does not show an optical absorption maximum from 400 to 1000 nm. Anal. Calcd for C24H20ThSe4: C, 33.7; H, 2.35. Found: C, 33.8; H, 2.52. 1H NMR(toluene-d8): 8.66 (d, J = 4.61 Hz, 2H, py), 7.87 (d, J = 7.36 Hz, 2H, SePh), 7.51 (m, 2H, tol), 7.46−7.35 (m, 3H, tol), 7.36 (m, H, SePh), 7.28 (m, H, py), 7.23 (m, 2H, SePh), 7.09 (m, 2H, py), 2.27 (m, 3H, tol). Synthesis of (py)3Th(SC6F5)4 (3). Th metal (0.232 g, 1.0 mmol), (SC6F5)2 (0.796 g, 2.0 mmol), and pyridine (0.317 g, 4.0 mmol) were combined in 1/1 pyridine/toluene mixture (20 mL) with a catalytic amount of Hg (0.020 g), and the mixture was stirred until Th was consumed and black powder appeared on the bottom of the flask (overnight). The pale-yellow solution was filtered away from the Hg, reduced in volume under vacuum to ca. 5 mL, and kept at room temperature for 2 days to give colorless crystals (0.99 g, 78%) that melt at 239 °C and decompose at 312 °C. IR: 2924 (w), 1627 (m), 1605 (w), 1514 (w), 1378 (m), 1261 (w), 1229 (m), 1159 (s), 1020 (w), 866 (w), 803 (w), 697 (m), 627 (s), 445 (m) cm−1. UV−vis: This compound does not show an optical absorption maximum from 400 to 1000 nm. Anal. Calcd for C24F20ThS4: C, 28.0; H, 0.00. Found: C, 27.9; H, 0.01. 1H NMR (toluene-d8): 9.22 (s, 2H, py), 7.51 (m, 2H, tol), 7.44−7.38 (m, 3H, tol), 7.32 (t, J = 7.60 Hz, 1H, py), 7.05 (m, 2H, py), 2.50 (m, 3H, tol). 19F NMR (toluene-d8): −128 (s, 2F), −157 (s, 1F), −159 (s, 2F). Synthesis of (py)4Th(SeC6F5)4·1.5py (4). Th (0.232 g, 1.0 mmol) and (SeC6F5)2 (0.984 g, 2.0 mmol) were combined in a 1/1 pyridine/ toluene mixture (20 mL) with a catalytic amount of Hg (0.020 g), and the mixture was stirred until Th was consumed and black powder appeared on the bottom of the flask (overnight). The pale-yellow solution was filtered away from the Hg, reduced in volume under vacuum to ca. 5 mL, and kept at −5 °C for a week to give colorless crystals (0.83 g, 54%) that melt at 92.5 °C and decompose at 153 °C. IR: 3852 (s), 3744 (s), 3675 (s), 3628 (s), 2923 (w), 2360 (m), 2340 (m), 1918 (m), 1899 (s), 1868 (m), 1829 (m), 1761 (m), 1717 (s), 1675 (m), 1662.45 (m), 1652 (s), 1521.0 (s), 1377 (m), 1068 (m), 812 (m), 699 (m), 625 (s) cm −1. UV−vis: This compound does not show an optical absorption maximum from 400 to 1000 nm. Anal. Calcd for C24F20ThSe4: C, 23.7; H, 0.00. Found: C, 23.9; H, 0.02. 1H NMR (toluene-d8): 9.40 (s, 2H, py), 7.51 (m, 2H, tol), 7.46−7.32 (m, 3H, tol), 7.22 (t, J = 7.80 Hz, 1H, py), 6.98 (m, 2H, py), 2.53 (m, 3H, tol). 19F NMR (toluene-d8): −125 (s, 2F), −159 (s, 1F), −163 (s, 2F), Thermolysis. Typically, a sample of 1−4 (20 mg) was placed in a quartz thermolysis tube that was sealed under vacuum, and the sample end was placed into a model 847 Lindberg tube furnace. The “cold” end of the glass tube was held at −196 °C by immersion in liquid

quartz cell or a 1.0 cm2 special optical glass cuvette, and scanned from 190 to 800 nm. 1H and 19F NMR spectra were obtained at 499.92 and 470.33 MHz, respectively, on a Varian VNMRS 500 spectrometer at 25 °C with the compounds dissolved in toluene-d8. LC−MS data were recorded on a Thermo Finnigan LCQ DUO system with the sample dissolved in a 10:1 MeOH/CH3COOH mixture. Mass spectra were acquired in the positive ion detection mode scanning a mass range from m/z = 150 to m/z = 1000. Powder X-ray diffraction (PXRD) data were obtained on a Bruker HiStar area detector using Cu Kα radiation from a Nonius 571 rotating-anode generator and on a Bruker SMART APEX diffractometer using Mo Kα radiation. Elemental analyses were performed by Quantitative Technologies, Inc. (Whitehouse, NJ). Because these compounds rapidly lose both lattice and coordinated pyridine within minutes of isolation, elemental analyses are time dependent. Samples were isolated and allowed to desolvate fully under vacuum prior to combustion analyses. To confirm that the single crystal data are consistent with bulk materials, samples were subjected to X-ray powder diffraction, and the profiles were compared with calculated diffraction profiles. Synthesis of (py)4Th(SPh)4 (1). Th (0.232 g, 1.0 mmol) and (SPh)2 (0.437 g, 2.0 mmol) were combined in a 1/1 pyridine/toluene mixture (20 mL) with a catalytic amount of Hg (0.020 g), and the mixture was stirred until Th was consumed and black powder appeared on the bottom of the flask (overnight). The pale-yellow solution was filtered away from the Hg, reduced in volume under vacuum to ca. 5 mL, and kept at −5 °C for a week to give colorless crystals (0.72 g, 73%) that melt at 109 °C and decompose at 152 °C. IR: 3887 (s), 3732 (s), 3664 (s), 3627 (s), 2945 (s), 2361 (s), 1966 (w), 1558 (m), 1418 (m), 1362 (s), 1224 (s), 1080 (m), 804 (w), 748 (m), 693 (m) cm−1. UV−vis: This compound does not show an optical absorption maximum from 400 to 1000 nm. Anal. Calcd for C24H20ThS4: C, 43.1; H, 3.01. Found: C, 42.8 ; H, 2.98. 1H NMR (toluene-d8): 8.89 (d, J = 4.99 Hz, 2H, py), 7.76 (d, J = 8.99 Hz, 2H, SPh), 7.51 (m, 2H, tol), 7.46−7.35 (m, 3H, tol), 7.36 (m, H, SPh), 7.32 (t, J = 9.99 Hz, 1H, py), 7.26 (m, 2H, SPh), 7.09 (m, 2H, py), 2.50 (m, 3H, tol). Synthesis of (py)3Th(SePh)4·0.5py (2). Th (0.232 g, 1.0 mmol) and (SePh)2 (0.624 g, 2.0 mmol) were combined in 1/1 pyridine/toluene mixture (20 mL) with a catalytic amount of Hg (0.020 g), and the mixture was stirred until Th was consumed and black powder appeared on the bottom of the flask (overnight). The pale-yellow solution was filtered away from the Hg, reduced in volume under vacuum to ca. 5 mL, and kept at −5 °C for a week to give colorless crystals (0.71 g, 65%) that melt at 140 °C, turn bright red at 163 °C, and decompose at 189 °C. IR: 2923 (w), 1601 (m), 1571 (s), 1442 (m), 1378 (m), 1219 (m), 1156 (s), 1064 (s), 1038 (m), 1018 (m), B

DOI: 10.1021/acs.inorgchem.6b00645 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry nitrogen. The sample was heated to 850 °C at a ramp rate of 10 °C/ min and then held at 850 °C for 6 h, at which time it was cooled to 25 °C at a rate of 3.5 °C/min. For 1, the black powder that was formed at the sample end of the quartz tube was identified by PXRD as ThS2;16 2 gave ThSe2;17 3 and 4 gave ThF4.18 LC−MS analysis of the volatile products identified py, EPh2, (SC6F5)2, and Se(C6F5)2. X-ray Structure Determination. Data for 1−4 were collected on a Bruker Smart APEX CCD diffractometer with graphite monochromatized Mo Kα radiation (λ = 0.710 73 Å) at 100 K.19 Crystals were immersed in a Paratone/mineral oil mixture and examined at low temperatures. The data were corrected for Lorenz effects, polarization, and absorption, the last by a multiscan method.19 The structures were solved by direct methods.20 All non-hydrogen atoms were refined20 based upon Fobs2. All hydrogen atom coordinates were calculated with idealized geometries. Crystallographic data and final R indices for 1−4 are given in Table 1. Thermal ellipsoid diagrams for 1−4 are shown in Figures 1−4, respectively. Complete crystallographic details are given in the Supporting Information.

Figure 2. ORTEP diagram of (py)3Th(SePh)4, 2, with the H atoms removed for clarity and ellipsoids at the 50% probability level. Significant bond lengths [Å] and angles [deg] for 2: Th(1)−N(2), 2.626(4); Th(1)−N(3), 2.642(4); Th(1)−N(1), 2.657(4); Th(1)− Se(4), 2.9039(6); Th(1)−Se(2), 2.9116(6); Th(1)−Se(1), 2.9235(6); Th(1)−Se(3), 2.9465(6); N(2)−Th(1)−N(3), 143.53(13); N(2)− Th(1)−N(1), 69.20(14); N(3)−Th(1)−N(1), 146.87(14); N(2)− Th(1)−Se(4), 97.80(10); N(3)−Th(1)−Se(4), 91.58(9); N(1)− Th(1)−Se(4), 86.50(10); N(2)−Th(1)−Se(2), 79.35(9); N(3)− Th(1)−Se(2), 64.76(9); N(1)−Th(1)−Se(2), 148.37(10); Se(4)− Th(1)−Se(2), 94.658(16); N(2)−Th(1)−Se(1), 149.38(9); N(3)− Th(1)−Se(1), 66.80(9); N(1)−Th(1)−Se(1), 80.23(10); Se(4)− Th(1)−Se(1), 81.525(18); Se(2)−Th(1)−Se(1), 131.267(16); N(2)−Th(1)−Se(3), 94.62(10); N(3)−Th(1)−Se(3), 85.92(9); N(1)−Th(1)−Se(3), 86.03(11); Se(4)−Th(1)−Se(3), 162.186(17); Se(2)−Th(1)−Se(3), 100.164(17); Se(1)−Th(1)−Se(3), 81.281(18); C(1)−Se(1)−Th(1), 112.34(15); C(7)−Se(2)−Th(1), 114.18(16); C(13)−Se(3)−Th(1), 105.51(15); C(19)−Se(4)− Th(1), 108.92(15).

Figure 1. ORTEP diagram of (py)4Th(SPh)4, 1, with the H atoms removed for clarity and ellipsoids at the 50% probability level. Significant bond lengths [Å] and angles [deg] for 1: Th(1)−N(2)′, 2.6909(19); Th(1)−N(2), 2.6909(19); Th(1)−N(1), 2.6949(19); Th(1)−N(1)′, 2.6950(19); Th(1)−S(1)′, 2.8451(6); Th(1)−S(1), 2.8451(6); Th(1)−S(2)′, 2.8481(6); Th(1)−S(2), 2.8481(6); N(2)′− Th(1)−N(2), 69.46(9); N(2)′−Th(1)−N(1), 125.02(6); N(2)− Th(1)−N(1), 141.72(6); N(2)′−Th(1)−N(1)′, 141.72(6); N(2)− Th(1)−N(1)′, 125.02(6); N(1)−Th(1)−N(1)′, 68.48(9); N(2)′− Th(1)−S(1)′, 79.65(4); N(2)−Th(1)−S(1)′, 70.22(4); N(1)− Th(1)−S(1)′, 141.73(5); N(1)′−Th(1)−S(1)′, 74.70(5); N(2)′− Th(1)−S(1), 70.22(4); N(2)−Th(1)−S(1), 79.65(4); N(1)−Th(1)− S(1), 74.70(5); N(1)′−Th(1)−S(1), 141.73(5); S(1)′−Th(1)−S(1), 143.25(2); N(2)′−Th(1)−S(2)′, 74.14(4); N(2)−Th(1)−S(2)′, 141.70(4); N(1)−Th(1)−S(2)′, 71.23(4); N(1)′−Th(1)−S(2)′, 78.89(4); S(1)′−Th(1)−S(2)′, 92.145(17); S(1)−Th(1)−S(2)′, 99.135(17); N(2)′−Th(1)−S(2), 141.70(4); N(2)−Th(1)−S(2), 74.14(4); N(1)−Th(1)−S(2), 78.89(4); N(1)′−Th(1)−S(2), 71.23(4); S(1)′−Th(1)−S(2), 99.135(17); S(1)−Th(1)−S(2), 92.145(17); S(2)′−Th(1)−S(2), 143.74(2); C(1)−S(1)−Th(1), 120.59(8); C(7)−S(2)−Th(1), 120.62(8). Symmetry transformations used to generate equivalent atoms (A or ′): x + 1/2, y, −z + 1/2.

are no solid-state byproducts. Addition of catalytic mercury reduces the amount of time required for all the Th metal to be consumed. Compounds with R = Ph. With PhEEPh, reduction over a period of days followed by saturation of the solution once the Th is consumed (reaction 1) leads to the isolation of (py)4Th(SPh)4 (1) and (py)3Th(SePh)4 (2) as colorless crystalline solids in high yield. Both compounds were characterized by conventional spectroscopic methods and low-temperature single crystal X-ray diffraction. The molecular structures of 1 and 2 are shown in Figures 1 and 2, respectively, with significant bond geometries given in the figure captions. py/Hg

Th + 2PhE−EPh ⎯⎯⎯⎯⎯⎯→ (py)x Th(EPh)4 (E = S, x = 4; E = Se, x = 3)

(1)

Both compounds are molecular, with the eight coordinate thiolate derivative crystallizing in a classic A4B4 arrangement of two interpenetrating A4 and B4 tetrahedra, adopting Kepert’s square-antiprismatic geometry isomer I.21 In 1, the unique Th− S bond length is 2.844(2) Å, and the unique Th−N distance is 2.676(6) Å. These values are consistent with the range of Th−S bond lengths in the literature, i.e., 2.747 Å in (C5Me5)2Th(SPh)2,6b 2.895 Å in Th[S2P(4-MeOC6H4)(OMe)]4,22 or 2.898 Å in Th[S2PiPr2]4,23 and statistically equivalent to previously reported Th−N(pyridine) bond lengths, i.e., 2.662(8), 2.696(8) Å in cis-Th(OC6H3Me2-2,6)4(Py)224 and 2.609(5) Å in [η5-1,2,4-(Me3C)3C5H2]Th(SePh)3(bipy).25 The

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RESULTS AND DISCUSSION Reactions of Th with RE−ER (E = S, Se; R = Ph, C6F5) in a toluene/pyridine mixture lead to the reductive cleavage of the E−E bond and the formation of Th(IV) chalcogenolate compounds that crystallize as pyridine adducts. This is a particularly attractive synthetic approach because of the minimal number of reagents involved, the relatively high yields, and the ease with which product can be isolated, because there C

DOI: 10.1021/acs.inorgchem.6b00645 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 4. ORTEP diagram of (py)4Th(SeC6F5)4, 4, with the H atoms removed for clarity and ellipsoids at the 30% probability level. Selected bond lengths [Å] and angles [deg] for 4: Th(1)−N(1), 2.635(4); Th(1)−N(2), 2.642(4); Th(1)−N(3), 2.653(4); Th(1)−N(4), 2.685(4); Th(1)−Se(3), 2.9519(7); Th(1)−Se(4), 2.9961(7); Th(1)−Se(1), 3.0137(7); Th(1)−Se(2), 3.0183(7); Se(1)−C(1), 1.906(5); Se(2)−C(7), 1.905(5); Se(3)−C(13), 1.916(4); Se(4)− C(19), 1.909(5); N(1)−Th(1)−N(2), 96.78(12); N(1)−Th(1)− N(3), 134.92(12); N(2)−Th(1)−N(3), 77.09(11); N(1)−Th(1)− N(4), 75.15(12); N(2)−Th(1)−N(4), 134.97(11); N(3)−Th(1)− N(4), 138.85(11); N(1)−Th(1)−Se(3), 149.96(9); N(2)−Th(1)− Se(3), 85.99(9); N(3)−Th(1)−Se(3), 74.93(8); N(4)−Th(1)−Se(3), 81.79(8); N(1)−Th(1)−Se(4), 87.08(8); N(2)−Th(1)−Se(4), 150.61(8); N(3)−Th(1)−Se(4), 79.65(8); N(4)−Th(1)−Se(4), 74.21(7); Se(3)−Th(1)−Se(4), 105.05(2); N(1)−Th(1)−Se(1), 72.82(9); N(2)−Th(1)−Se(1), 79.79(9); N(3)−Th(1)−Se(1), 62.11(8); N(4)−Th(1)−Se(1), 135.10(8); Se(3)−Th(1)−Se(1), 136.71(2); Se(4)−Th(1)−Se(1), 73.55(2); N(1)−Th(1)−Se(2), 79.77(8); N(2)−Th(1)−Se(2), 73.55(8); N(3)−Th(1)−Se(2), 136.98(8); N(4)−Th(1)−Se(2), 61.44(7); Se(3)−Th(1)−Se(2), 72.32(2); Se(4)−Th(1)−Se(2), 135.58(2); Se(1)−Th(1)−Se(2), 138.85(2); C(1)−Se(1)−Th(1), 118.39(14); C(7)−Se(2)−Th(1), 115.05(14); C(13)−Se(3)−Th(1), 115.43(13); C(19)−Se(4)− Th(1), 113.65(12).

Figure 3. ORTEP diagram of (py)3Th(SC6F5)4, 3, with the H atoms removed for clarity and ellipsoids at the 50% probability level. Significant bond lengths [Å] and angles [deg] for 3: Th(1)−N(1)′, 2.634(4); Th(1)−N(1), 2.634(4); Th(1)−N(2), 2.718(5); Th(1)− S(1), 2.8111(11); Th(1)−S(1)′, 2.8111(11); Th(1)−S(2)′, 2.8252(10); Th(1)−S(2), 2.8253(10); Th(1)−F(1), 3.129(3); N(1)′−Th(1)−N(1), 140.26(15); N(1)′−Th(1)−N(2), 70.13(7); N(1)−Th(1)−N(2), 70.13(7); N(1)′−Th(1)−S(1), 129.66(8); N(1)−Th(1)−S(1), 82.62(8); N(2)−Th(1)−S(1), 138.58(2); N(1)′−Th(1)−S(1)′, 82.62(8); N(1)−Th(1)−S(1)′, 129.66(8); N(2)−Th(1)−S(1)′, 138.58(2); S(1)−Th(1)−S(1)′, 82.83(4); N(1)′−Th(1)−S(2)′, 84.63(8); N(1)−Th(1)−S(2)′, 83.18(8); N(2)−Th(1)−S(2)′, 71.79(2); S(1)−Th(1)−S(2)′, 136.36(3); S(1)′−Th(1)−S(2)′, 75.22(3); N(1)′−Th(1)−S(2), 83.18(8); N(1)−Th(1)−S(2), 84.63(8); N(2)−Th(1)−S(2), 71.79(2); S(1)− Th(1)−S(2), 75.22(3); S(1)′−Th(1)−S(2), 136.36(3); S(2)′− Th(1)−S(2), 143.59(4); N(1)′−Th(1)−F(1), 147.20(9); N(1)− Th(1)−F(1), 63.94(9); N(2)−Th(1)−F(1), 126.19(5); S(1)− Th(1)−F(1), 60.39(5); S(1)′−Th(1)−F(1), 66.95(5); S(2)′− Th(1)−F(1), 76.30(5); S(2)−Th(1)−F(1), 127.29(5); C(1)−S(1)− Th(1), 108.22(14); C(7)−S(2)−Th(1), 112.27(14); C(2)−F(1)− Th(1), 111.6(2). Symmetry transformations used to generate equivalent atoms (A or ′): −x, y, −z + 1/2.

additional pyridine ligand in 1, and the difference can be rationalized by assuming that the four larger Se atoms in the primary coordination sphere effectively crowd out coordination of a fourth pyridine ligand. This distorted pentagonal bipyramidal structure, where the central plane contains 3 N atoms and 2 Se atoms, has approximate D2h symmetry. There is one very wide, one wide, two intermediate, and two narrow Se−Th−Se angles (162° vs 131° and 100°, 95° and 82°, 81°), and nearly trigonally placed py with two wide versus one narrow N−Th−N (147°, 144° vs 69°); in this case, the lonepair electrons for pairs of Se atoms are all approximately “cis”. There are two intramolecular π···π interactions between one py and one SePh ligand, namely, the ligands containing N(1) and Se(1) and those with N(2) and Se(2). As will be seen again in monomer 4, only compounds with Se-containing ligands appear to have the flexibility to yield intramolecular π···π interactions of the type py···chalcogenolate. Compounds with R = C6F5. Fluorinated chalcogenolate are relatively unexplored throughout the periodic chart when compared with hydrocarbon analogues, with syntheses often motivated by the tendency of ring fluorination to form compounds with unusual physical properties,28 i.e., stability of high oxidation states or compound volatility. Fluorinated

smaller coordination number in the related uranium compound13c (py)3U(SPh)4 can presumably be attributed to the smaller ionic radius of U.26 The coordination sphere can best be described as a distorted square antiprism with two S atoms and two N atoms on each square facet, with distortions such that wide versus narrow S−Th−S (144°, 143° vs two each of 99°, 92°) or N−Th−N (142°, 125° vs two each of 69°, 68°) angles alternate for adjacent facets. It is worth noting that the two wide S−Th−S angles have lone-pair vectors approximately “cis” (e.g., the lone-pair is approximately perpendicular to the adjacent S−Th−S plane in all four instances in 1 and 3, see below). The fact that adjacent py and SPh ligands are far from coplanar may affect the occurrence or strength of possible intramolecular π···π interactions in this compound. In contrast, the selenolate 2 crystallizes with one less pyridine donor, as proposed for the related uranium derivative (py)3U(SePh)4 on the basis of spectroscopic data.13c An average of the Th−Se bond lengths is 2.92(1) Å, which is in agreement with previously reported 2.938(8) Å in [η5-1,2,4(Me3C)3C5H2]Th(SePh)3(bipy)25 and 2.918(1) Å in {[η51,2,4-(Me3C)3C5H2]Th(SePh)}2[μ-N(p-tolyl)]227 values. The seven coordinate structure of 2 is surprising given the D

DOI: 10.1021/acs.inorgchem.6b00645 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry thiolates have been examined with the s-,29 p-,30 and d-block31 metals, as well as a number of highly NIR emissive lanthanide32 compounds, while analogous selenolates are thus far limited to a handful of main group examples12d,33 and a single example from the lanthanide34 series. Fluorinated chalcogenolates of thorium can also be prepared by direct reduction of RE−ER to give (py)3Th(SC6F5)4 (3) and (py)4Th(SeC6F5)4 (4), as given in reaction 2. As with the EPh products, the fluorinated thiolate and selenolate adopt different structures, although here it is the thiolate 3 that coordinates three pyridine ligands, with the primary coordination sphere saturated by two additional dative Th−F bonds to give a nine coordinate degraded capped trigonal prism (C2v), with the N(2) pyridine as the ligand on the side of the prism and two S atoms and one N atom comprising each trigonal face. Two narrow N−Th−N, both at 70°, result, as do three wide (one 144° and two 136°) and three narrow (one 83° and two 75°) S−Th−S angles; this arrangement also allows lonepair vectors to be “cis” to each other for all pairs of coordinated S atoms; there is one instance of intramolecular π···π interaction between the two SC6F5 ligands containing atoms S(1) and S(1′).

ligand−ligand repulsions. Although significant intermolecular π···π interactions are expected for all four compounds here, they are surprisingly not present. Instead, they are replaced by perhaps weaker and certainly less directed H···π or F···π, such that the packing schemes in all four cases appear to be shape based. Chemical differences are also evident: whereas most d-block chalcogenolates are air and moisture stable, these actinide derivatives react immediately with both water and oxygen. Further, unlike 3, there are no examples within the transition metal literature where a fluorinated chalcogenolate ligand forms a dative M−F interaction. Comparison with the lanthanide (Ln) series is also warranted, but in this case there are clear similarities. As with 1−4, the lanthanide chalcogenolates adopt a range of coordination numbers for a given Lnn+, but there has always been a tendency for Ln(EPh)x, to crystallize as oligiomeric, or even polymeric, structures. Two variables appear to favor oligiomerization: first, lower oxidation states, where coordination polymers were more frequently observed in divalent Ln(EPh)2 compounds,36 and second, ionic radius, where the larger, early lanthanides also had a propensity to form extended structures, i.e., [(py)2Sm(SPh)3]436c versus (py)3Yb(SPh)3).12b The same tendencies were observed in Ln(SC6F5)n compounds.37 Both lower oxidation states and larger ionic radii reduce electrostatic interactions, presumably to the extent that the entropy gained by forming oligomers and displacing neutral donors from a primary coordination sphere becomes a significant factor influencing structure. In the present work, the observation of only molecular species is consistent with the lanthanide chemistry, given both the tetravalent Th(IV) oxidation state and the fact that the ionic radius of Th(IV) (0.94 Å, CN = 6) matches Gd(III) (1.05, CN = 8) in the middle of the lanthanide series.26 Not much can be inferred from direct comparisons of EPh and EC6F5 given that neither pair has an identical pair of coordination numbers: in lanthanides, ring fluorination polarizes electron density away from the chalcogen atom, and M− S(Ph) bonds are typically shorter than M−S(C6F5) bonds. However, it is interesting to note that ionic radius summations are inconsistent when we compare lanthanides with actinides. For example, if we compare the bond lengths in 1 with the related bond lengths in Sm−N(py) and terminal Sm−S bonds in [(py)2Sm(SPh)3]4 (Th−S = 2.84 Å, terminal Sm−S = 2.75 Å, difference = 0.09 Å; Th−N = 2.69 Å, Sm−N = 2.52 Å, difference = 0.17 Å), it is clear that simple electrostatic models do not accurately predict these metal−ligand bond lengths.26 Thermolysis. Thermal conversion of molecular precursors to solid-state materials is a well-developed synthetic approach to the preparation of materials at relatively low temperatures. Molecular approaches to actinide solids are relatively unexplored, having focused exclusively on the delivery of oxide materials as particles, films, or solids. A limited range of precursor ligand systems have been examined, including nitrates,38 oxalates,39 alkoxides,40 amides,40 and croconates.41 Interestingly, volatile compounds prepared with fluorinated βdiketonates have been shown to give oxide films for uranium, but fluoride materials with americium.42 There exists an extensive literature describing the use of metal chalcogenolate molecules (M(ER)x) from every part of the periodic chart to deliver chalcogenide materials. R-group migration in thermal conversions of M(ER)x to give MEx/2 and ER2 is a well-established reactivity pathway,12b,d,43 and the

py/Hg

Th + 2C6F5E−EC6F5 ⎯⎯⎯⎯⎯⎯→ (py)x Th(EC6F5)4 (E = S, x = 3; E = Se, x = 4)

(2)

Selenolate 4 is a distorted square antiprism similar to 1, adopting Keppert’s isomer II arrangement.21 The structure contains four wide and two narrow angles for both Se−Th−Se (139°, 137°, 136°, 105° and 74°, 72°) and N−Th−N (139°, 135°, 135°, 97° and 77°, 75°); the wider (versus 75−77°) N− Th−N angle of 97° for N(1) and N(3) py ligands appears to be due to intramolecular π···π interactions with SeC6F5 ligands containing Se(2) and Se(1), respectively, at the expense of more H···F crystal packing contacts (which are likely unfavorable) within the space between these pairs of py, although the latter situation is possible. Fluorinated arenes typically exhibit π−π stacking interactions more frequently than their hydrocarbon analogues because of the greater polarity of the C−F bond relative to C−H. Likewise, the intramolecular π···π interaction of ligands containing N(4) and Se(3) and the above-mentioned N(1) and Se(2) intraligand π···π interaction result in the wide 135° N(4)−Th(1)−N(1) angle. In fact, all four SeC6F5 ligands are involved in intramolecular π···π interactions with nearly coplanar py and rings from chalcogenolate ligands, and this situation may help to stabilize the present version of the square-antiprism coordination, which allows pairs of Se lone-pair vectors (e.g., those with widest Se− Th−Se angles) to be positioned “trans” to each other. It is frustrating to note that the effect of fluorination on the Th−E bond length is not readily assessed, given that neither pair of ER complexes have structures with identical coordination numbers that would invite such a comparison. As expected, there are clear differences between these actinide chalcogenolates and the more developed chalcogenolates of the d-block metals. Most obvious is the difference between the seemingly random coordination numbers of the actinides and the more predictable geometries of the covalent metals, where covalent forces favor directional bonding.35 With characteristically shallow potential energy surfaces defining actinide coordination chemistry, coordination numbers and geometries are often impacted by variables other than metal valence requirements, i.e., lattice effects and intermolecular E

DOI: 10.1021/acs.inorgchem.6b00645 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

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thorium chalcogenolate compounds reported here are no exception. For both 1 and 2, thermolysis (reaction 3) leads to the formation of ThE2, with the volatile products of the reactions identified by LC−MS as pyridine and EPh2. (py)x Th(EPh)4 → ThE 2 + EPh 2 + py (E = S, n = 4; E = Se, n = 3)

(3)

Thermolysis of molecules with fluorinated ligands is potentially more complicated. More covalent metals with fluorinated chalcogenolate ligands tend to form metal chalcogenide phases upon heating, but the more electropositive metals, i.e., the lanthanides, react by abstraction of fluoride from the arene ring to give metal fluorides and a range of organic products. Thorium follows the path typically taken by electropositive metals: when heated, both Th(EC 6 F 5 ) 4 complexes react to eventually form ThF4. This is not straightforward, however, with low temperatures (≤650 °C) leading to the formation of what appears to be nitrides, oxyfluoride, and fluoride phases. At 850 °C, these nonfluoride phases have reacted further either with trapped SeC6F5 or with volatile Se(C6F5)2 to give ThF4 as main crystalline product.

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CONCLUSIONS Molecular thorium chalcogenolate complexes can be prepared in high yield by direct reduction of RE−ER with elemental Th. As pyridine complexes they adopt a variety of structures and coordination numbers, with both fluorinated compounds exhibiting π−π stacking interactions, and dative Th−F bonds in the thiolate compound that are not found in the selenolate. The fluorinated compounds decompose to give ThF4, while the benzenechalcogenolates can be used as a source of solid-state ThE2.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00645. X-ray crystallographic files for the crystal structures of 1− 4 (CIF) Calculated and observed XRPD profiles for 1−4 (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Author Contributions

The manuscript was written through contributions of all authors. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the support of the American Chemical Society (ACS PRF 52382-ND3). D.R. received support from the Rutgers Aresty Chemistry Scholars Program.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.6b00645 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.6b00645 Inorg. Chem. XXXX, XXX, XXX−XXX