Uranyl-tri-bis(silyl)amide Alkali Metal Contact and Separated Ion Pair

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Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Uranyl-tri-bis(silyl)amide Alkali Metal Contact and Separated Ion Pair Complexes Philip J. Cobb, David J. Moulding, Fabrizio Ortu, Simon Randall, Ashley J. Wooles, Louise S. Natrajan,* and Stephen T. Liddle* Centre for Radiochemistry Research, School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom S Supporting Information *

ABSTRACT: We report the preparation of a range of alkali metal uranyl(VI) tri-bis(silyl)amide complexes [{M(THF)x}{(μ-O)U(O)(N″)3}] (1M) (N″ = {N(SiMe3)2}−, M = Li, Na, x = 2; M = K, x = 3; M = K, Rb, Cs, x = 0) containing electrostatic alkali metal uranyl-oxo interactions. Reaction of 1M with 2,2,2-cryptand or 2 equiv of the appropriate crown ether resulted in the isolation of the separated ion pair species [U(O)2(N″)3][M(2,2,2-cryptand)] (3M, M = Li−Cs) and [U(O)2(N″)3][M(crown)2] (4M, M = Li, crown = 12-crown4 ether; M = Na−Cs, crown = 15-crown-5 ether). A combination of crystallographic studies and IR, Raman and UV−vis spectroscopies has revealed that the 1M series adopts contact ion pair motifs in the solid state where the alkali metal caps one of the uranyl-oxo groups. Upon dissolution in THF solution, this contact is lost, and instead, separated ion pair motifs are observed, which is confirmed by the isolation of [U(O)2(N″)3][M(THF)n] (2M) (M = Li, n = 4; M = Na, K, n = 6). The compounds have been characterized by single crystal Xray diffraction, multinuclear NMR spectroscopy, IR, Raman, and UV−vis spectroscopies, and elemental analyses.

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INTRODUCTION In recent years there has been burgeoning interest in nonaqueous uranium chemistry,1,2 and while recently reported examples of isolable uranium(II) compounds3,4 have extended the range of synthetically accessible low oxidation states for uranium, the +6 oxidation state,5 in particular the uranyl(VI) [U(O)2]2+ moiety, continues to dominate the field of uranium chemistry.6−8 In [U(O)2(X)n]2−n complexes (X = generic monoanionic ligand), the oxo-ligands are mutually trans, which contrasts to the cis-dioxo situation usually found in analogous transition metal complexes, and this is ascribed to the inverse trans-influence (ITI).8−13 This trans-dioxo arrangement leads to other ligands exclusively occupying equatorial positions. Since salt elimination is the most popular strategy for preparing uranyl complexes, halides and salts, e.g., [U(O)2(Cl)2(THF)2] and [U(O) 2(OTf) 2], are commonly employed starting materials.2,14 However, in situations where salt elimination reactions would be problematic, for example, where alkyls and amides could induce reduction at uranyl(VI) or where retention of eliminated salt is undesirable, there remains a relative dearth of alternative uranyl(VI) precursors for protonolysis reactions, namely, alkyls, alkoxides/aryloxides, and amides. The lack of uranyl(VI) alkyls available for alkane elimination strategies can be ascribed to the incompatible combination of highly oxidizing hexavalent uranium and the reducing nature of alkyls. Indeed, the only structurally characterized examples of organo-σ uranyl species are redox-robust cyanides, multidentate © XXXX American Chemical Society

pincer ligands, or poly alkylated species that saturate the coordination sphere of uranium.15−19 However, each would likely introduce synthetic complications if used as precursors to more elaborate derivatives. Uranyl alkoxides are more prevalent, and were first reported in 1959, namely, [U(O)2(OR)2] (R = Me, Et, nPr, iBu),20 along with more recent examples [U(O)2(OCHR2)2(THF)n]x (R = Ph, tBu: n = 2, x = 0; R = iPr: n = 0, x = 2), and examples of uranyl aryloxides species include [U(O)2(OR)2(THF)2] (R = 2,6-But2C6H3, 2,6Ph2C6H3), [U(O)2(OR)2(THF)2]2 (R = 2,6-Cl2C6H3, 2,6Me2C6H3), [U(O)2(O-2,6-Pri 2C6H3)2(Py)3] (Py= pyridine), and the alkali metal salt [Na(THF) 3 ] 2 [U(O) 2 (O-2,6Me2C6H3)4].21−23 However, such species, already rich in thermodynamically favorable U−O bonds, have limited practical synthetic utility, particularly if substitution with monodentate ligands is required. For amides, which would be expected to be superior to alkoxides and aryloxides in protonolysis chemistry, reduction of uranyl(VI) remains an issue due to the possibility of aminyl radical formation and so to avoid the necessity to saturate the coordination sphere of uranyl,24 cf. alkyl derivatives,19 and bulky silylamides have been investigated, though not systematically. The di-bis(silyl)amide species [U(O)2(N″)2(S)2] (N″ = N(SiMe3)2, S = THF, Py) and [U(O)2{N(SiMe2Ph)2}2(Py)2] have been reported;25,26 however, it was Received: March 16, 2018

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DOI: 10.1021/acs.inorgchem.8b00715 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Scheme 1. Synthetic Routes to Uranyl-tri-bis(silyl)amide Complexes 1M−4M

ethers and cryptands can enable the synthesis of novel actinideligand multiple bond linkages,12,32−38 SIP species of general formulas [U(O)2(N″)2}3][{M(crown)n}] and [U(O)2(N″)3][{M(2,2,2-cryptand)}] (M = Li, Na, K, Rb, Cs).

noted that attempts to repeat the initially reported preparation of [U(O) 2 (N″) 2 (THF) 2 ] via the reaction of [U(O)2(Cl)2(THF)2] with 2 equiv of [Na(N″)] instead led to the isolation of the contact ion pair (CIP) alkali metal complex [{U(O)2(N″)4}{Na(THF)}2].23 The preparation of [{M(THF)2}{(μ-O)U(O)(N″)3}] (M = Na or K) were subsequently reported,27 but while the potassium analogue was prepared from the reaction of [U(O)2(Cl)2(THF)2] with 3 equiv of [K(N″)], the sodium congener could not be accessed via this synthesis route. Instead, the equimolar formation of [{U(O)2(N″)4}{Na(THF)}2] and [U(O)2(N″)2(THF)2] was observed, but [{Na(THF)2}{(μ-O)U(O)(N″)3}] was successfully prepared by the more circuitous route of preparing [{U(O)2(N″)4}{Na(THF)}2] then reacting it with C5Me5H. Interestingly, the [{M(THF)2}{(μ-O)U(O)(N″)3}] complexes are notable as unusual examples of uranyl(VI) with only three equatorial ligands coordinated; however, it was reported that in THF solution an additional THF molecule appears to coordinate to the uranium center. The THF is labile and is removed in vacuo and upon recrystallization, even from THF solutions.27 In addition to sodium and potassium salts, the lithium CIP complex [{Li(Py)2}{(μ-O)U(O)(N″)3}] (1LiPy2) and cobalt and phosphonium separated ion pair (SIP) complexes [U(O)2(N″)3][Co(Cp*)2] and [U(O)2(N″)3][PPh4] complete the collection of known uranyl-bis(silyl)amide group 1 derivatives.28,29 Uranyl(VI) di-bis(silyl)amides have found synthetic utility in the preparation of alkoxide and macrocyclic derivatives,26,28,30 but despite these reports, little is known of the inherent structures of alkali metal uranyl(VI)-(N″)− derived species.27,28 Furthermore, uranyl(VI) tri-bis(silyl)amides have been barely investigated, but fascinating derivatives chemistry is hinted at by the reactivity of a related uranyl(VI) complex with a triamidoamine ligand that afforded a mixed valence diuranium(V/VI) imido-oxo complex with complete cleavage and loss of a usually very robust uranyl oxo group.31 We therefore systematically targeted a range of uranyl(VI) tri-bis(silyl)amide complexes to provide a family of precursor compounds with synthetically useful scope. Herein, we present our results, which include CIP uranyl(VI) tri-bis(silyl)amide complexes with the general formula [{M(THF)x}{(μ-O)U(O)(N″)3}] (M = Li, Na, K, Rb, Cs), and since it is increasingly clear that crown

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RESULTS Synthesis and Formulations of Uranyl-tri-bis(silyl)amides 1M−4M. Reactions of [U(O)2(Cl)2(THF)2] with 3 equiv of [M(N″)] (M = Na, K, Rb, or Cs) in THF gives the uranyl(VI) tri-bis(silyl)amide CIP complexes [{M(THF)x}{(μO)U(O)(N″)3}] (1M) (M = Na, x = 2; M = K, Rb, Cs, x = 0) in good yields (70−83%, Scheme 1). The lithium congener, [{Li(THF)2}{(μ-O)U(O)(N″)3}] (1Li), is readily prepared by a different route, where addition of [Li(N″)] to [U(O)2(N″)2(THF)2] in THF gives, as with 1Na−1Cs, 1Li in good isolated yield (76%), Scheme 1. The value of ‘x’ in the 1M series was determined by NMR spectroscopy on solids dissolved after drying. However, on drying under vacuum for the Li, Na, and K derivatives either crystallinity is lost, and/or the color of the crystalline material changes from orange to red. This suggests that the THF solvent in these complexes is labile and easily removed under vacuum. Indeed, crystallographic studies of crystals of 1Li and 1Na that have not been exposed to vacuum and instead kept in an excess of THF reveal these complexes to be the SIPs [U(O)2(N″)3][Li(THF)4] (2Li) and [U(O)2(N″)3][Na(THF)6] (2Na). However, crystallization of 1K from THF solution affords either the CIP [{K(THF)3}{(μO)U(O)(N″)3}] (1Ka) or the SIP [U(O)2(N″)3][K(THF)6] (2K), depending on the crystallization conditions. A clear trend emerges that can be linked to the diminishing metal affinity for ethers as group 1 is descended whereby 2Li and 2Na desolvate to bis(THF) derivatives where we surmise that the alkali metal is now bound to a Oyl in a CIP (see below). 2K and 1Ka completely desolvate to give [K(μ-O)U(O)(N″)3] (1K), again anticipated to be a CIP, and extending this trend further, no matter what excess of THF is present the CIP complexes [Rb(μ-O)U(O)(N″)3] (1Rb) and [Cs(μ-O)U(O)(N″)3] (1Cs) are always isolated as solvent-free polymers, consistent with the fact those two crystalline materials do not change color or form under vacuum. Interestingly, the solvent-free CIP variants are dark red, but partial or full solvation that partially or fully disrupts the M···Oyl interactions changes the color to B

DOI: 10.1021/acs.inorgchem.8b00715 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. Molecular structures of 1Ka and the repeat units of 1Rb and 1Cs at 150 K with selective labeling and displacement ellipsoids set to 25, 50, and 50%, respectively. Hydrogen atoms and minor disorder components are omitted for clarity.

Figure 2. Molecular structures of 1Rb and 1Cs with selective labeling highlighting the 1D polymeric nature of these compounds in the solid state. Displacement ellipsoids are set to 50%, and hydrogen atoms and minor disorder components are omitted for clarity.

[U(O)2(N″)3][M(crown)2] (4M, M = Li, crown = 12-crown-4 ether; M = Na−Cs, crown = 15-crown-5 ether), respectively (Scheme 1). The reactions to make these derivatives are largely quantitative, as adjudged by NMR spectroscopy, but crystalline yields vary appreciably, spanning the ranges of 31−83 and 29− 82% for these two series, respectively. Other than confirming amide/THF/cryptand/crown ether ratios, the NMR spectra of these complexes are not particularly informative. Bulk identities were confirmed by elemental analyses, and IR, Raman, and electronic absorption spectroscopic analyses are presented below.

orange. Last, 1M complexes only dissolve in donor solvents such as THF, DME, or pyridine, which suggests that in solution the donor solvents cleave those compounds into SIPs which is also suggested by UV/vis/NIR spectroscopic data (see below). Since there could be situations where it would be synthetically desirable to have uranyl(VI)-triamide complexes with formulations that are free of THF-loss complications, we prepared well-defined separated ion pair derivatives. Accordingly, treatment of complexes 1M (M = Li−Cs) with 2,2,2cryptand or 2 equiv of size-matched crown ether afforded the SIPs [U(O)2(N″)3][M(2,2,2-cryptand)] (3M, M = Li−Cs) and C

DOI: 10.1021/acs.inorgchem.8b00715 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 3. Molecular structures of 2Li, 2Na, and 2K with selective labeling and displacement ellipsoids set to 25%. Hydrogen atoms and minor disorder components are omitted for clarity.

Solid State Structural Analysis of Uranyl-triamides 1M−4M. The formulations of 1Ka, 1Rb, 1Cs, and 2M−4M were confirmed by single crystal X-ray diffraction and the solid state structures are shown in Figures 1−5 with selected bond lengths and angles compiled in Table 1. The solid state structure for 1Na has been reported previously;27 however, in our hands we find that following the same crystallization conditions as previously reported we obtain crystals of 2Na rather than 1Na. It was not possible to isolate crystalline samples of 1Li and 1K, as these were insoluble in nondonor solvents, and upon dissolution in donor solvents, solvated structures such as 2Li, 1Ka, and 2K were observed. The solid state structures of complexes 1Rb and 1Cs were determined and are always found to crystallize solvent-free, so conversely, the 2Rb and 2Cs analogues are not available, as is the case with 1Li, 1Na, and 1K. The solid state structures of 2Li, 2Na, 2K contain alkali metal cations coordinated to four (Li) and six (Na, K) molecules of THF, which are lost when crystalline samples are

placed under vacuum. Complexes 1M and 2M−4M form two distinct classes of structure, the former being contact ion pairs (CIP), where the alkali metal is bound to the Oyl-group, and the latter adopting separated ion pair motifs (SIP), where each alkali metal is fully encapsulated with THF, crown, or cryptand. In all cases, the data confirm a trigonal bipyramidal geometry about uranium with three amide ligands occupying the equatorial positions (N−U−N angles: ca. 120°, N−UO: ca. 90°) and the two oxo groups occupying the axial positions in a trans manner [range OUO: 178.0(2) to 180(0)°].8 In the CIP 1M series, each alkali metal is coordinated to an Oyloxo group, with the M-O distances increasing from Li [1.83(3) Å] to Cs [2.926(13) Å] in line with the increased radii of the alkali metal on descending Group 1.39 In 1LiPy2, 1Na, and 1K, each alkali metal is coordinated by donor solvent leading to mononuclear units, whereas in 1Rb and 1Cs, there is no donor solvent present. Thus, an infinite polymeric chain is observed. For the monomers, the UO bond distances appear to vary, with the bridging UO distances [1.880(11), 1.810(5), and D

DOI: 10.1021/acs.inorgchem.8b00715 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 5. Molecular structures of the 4M series with selective labeling and displacement ellipsoids set to 25% for 4Na and 4K and 40% for 4Li, 4Rb, and 4Cs. Hydrogen atoms and minor disorder components are omitted for clarity.

Figure 4. Molecular structures of the 3M series with selective labeling and displacement ellipsoids set to 25% except for 3Li which is set at 50%. Hydrogen atoms and minor disorder components are omitted for clarity.

spanning the narrow ranges 1.784(4)−1.802(14) Å and 2.308(18)−2.330(4) Å, respectively, confirming that similar structures are obtained independent of the alkali metal used. The UO distances are typical for uranyl(VI) species,40 and the U−N distances compare well to those of the closely related SIP species [U(O) 2 (N″) 3 ][Co(η 5 -C 5 Me 5 ) 2 ] and [U(O)2(N″)3][PPh4] (mean U−N: 2.318 Å),29,41 but are longer than reported uranium(V) mono-oxo (N″)3 complexes (mean U−N: 2.264 Å)28,42,43 and the neutral uranium(VI) series [U(O)(N″)3(X)] (X = F, Cl, Br, or Me) (mean U−N: 2.206 Å),44,45 likely due to the uranyl centers in 2M−4M being anionic rather than neutral. The cation components of 2M−4M

1.804(3) Å, respectively] being longer than the terminal UO bond distances [1.810(11), 1.781(5), and 1.776(3) Å, respectively] which is likely due to the alkali metal drawing charge away from the UO unit leading to a weakening of the UO bond. This effect is greatest in 1LiPy2, as expected due to the lithium metal being the hardest electropositive metal in the series. In polymeric 1Rb and 1Cs, no UO bond variation is observed as each UO bond is coordinated to an alkali metal, and they are in fact identical as they are related by symmetry. As expected, the uranyl anions in 2M−4M are essentially identical, with UO and U−N bond distances E

DOI: 10.1021/acs.inorgchem.8b00715 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Table 1. Selected Bond Distances, Vibrational Absorption Data (Symmetric: ν1, Asymmetric: ν3), Calculated Stretching Force Constants (k1), and Interaction Force Constants (k12) for the UO2 Linkages in 1M−4Ma entry 1LiPy2 1Li 1Na 1Ka 1Rb 1Cs 2Li 2Na 2K 2Rb 2Cs 3Li 3Na 3K 3Rb 3Cs 4Li 4Na 4K 4Rb 4Cs

UO (Å)

U−N (mean) (Å)

OUO (deg)

Oyl−M (mean) (Å)

ATR-IR (cm−1) (ν3)

solution IR (cm−1)

Raman (cm−1) (ν1)

k1 (mdyn A−1)

k12 (mdyn A−1)

1.810(11), 1.880(11)

2.285(13)

178.2(5)

1.83(3)

936 (935)

969

799

6.65

−0.63

1.7.81(5), 1.810(5) 1.776(3), 1.804(3) 1.80(3) 1.792(13) 1.784(4) 1.791(3) 1.786(3)

2.310(4)

179.31(18)

2.201(6)

943 938(928)

969 973

798 795(805)

6.69 6.63

−0.69 −0.68

2.312(4)

179.43(15)

2.669(3)

940

973

799

6.68

−0.66

2.28(3) 2.293(19) 2.321(5) 2.330(4) 2.323(3)

180(0) 180(0) 179.77(19) 179.79(14) 179.56(13)

2.74(3) 2.926(13)

940 941

973 971 969 973 973 973 971

804 804

6.72 6.72

−0.62 −0.63

1.797(3) 1.772(8) 1.8010(18) 1.802(14) 1.792(19) 1.787(4) 1.785(15) 1.786(12) 1.788(2) 1.789(3)

2.325(4) 2.329(10) 2.322(2) 2.308(18) 2.308(19) 2.319(5) 2.320(19) 2.318(19) 2.320(4) 2.314(6)

178.96(16) 179.8(4) 178.58(9) 180(0) 180(0) 178.8(2) 178.0(8) 180(0) 178.71(15) 178.0(2)

809 811 809 810 809 808 810 811 805 805

6.94 6.95 6.94 6.95 6.92 6.92 6.92 6.96 6.91 6.91

−0.78 −0.75 −0.77 −0.77 −0.75 −0.77 −0.74 −0.76 −0.81 −0.81

964 963 963 964 961 962 960 964 964 964

a

Data for 1LiPy2 and 1Na is taken from independently prepared samples. Previously reported IR (nujol mull) and Raman data for 1LiPy2 and 1Na is included in parentheses. No Raman data for 1LiPy2 has been previously reported.27,28

ligands is ignored, and the uranyl moiety is treated as a linear triatomic molecule.47,48 As shown in Table 1 there is a clear difference between CIP series 1M and SIP series 3M−4M, the former with stretching force constants of 6.63−6.72 mdyn Å−1 and the latter with a larger stretching force constant of 6.91− 6.95 mdyn Å−1. Within the 1M series, the heavier group 1 metals exhibit a larger stretching force constant (1Rb and 1Cs: 6.72 mdyn Å−1) than the lighter alkali metals (1Li: 6.69, 1Na: 6.63, 1Ka: 6.68 mdyn Å−1) consistent with the increased polarizing nature of the lighter group 1 metals weakening the UO bond to a greater extent than the heavier congeners. As 3M and 4M are all SIP complexes with no interaction with the alkali metal, there is no such pattern observed in these series. The interaction force constants are also distinct for each series (1M: − 0.62 to −0.69; 3M−4M: − 0.74 to −0.81), due to a weakening of the UO bonds in the 1M series, but there are no patterns observed within each series. UV/Vis Spectroscopic Studies of 1M−4M. The UV/vis spectra of complexes 1M and 3M-4M in THF can be found in the Supporting Information. In each case, there are no absorption bands observed 2s(F2) transmission coefficient range R, Rwa (F2 > 2s(F2)) R, Rwa (all data) Sa parameters, restraints max, min difference map (e Å−3)

C30H78KN3O5Si6U 1006.62 0.519 × 0.310 × 0.243 triclinic P1̅ 150(2) 11.7320(8) 11.8934(7) 18.0043(9) 88.667(4) 76.677(5) 89.377(5) 2443.9(2) 2 1.368 3.586 15443 8874, 0.0361 7224 0.580−1.000 0.0399, 0.0623 0.0597, 0.0686 1.003 480, 403 1.171, −1.170 2Na

C18H54N3ORbSi6U 820.68 0.243 × 0.081 × 0.054 trigonal R3̅c 120(2) 18.6372(5) 18.6372(5) 17.5257(5) 90 90 120 5271.9(3) 6 1.551 6.213 3582 1045, 0.0354 928 0.224−0.595 0.0821, 0.1937 0.0882, 0.1963 1.183 102, 156 5.983, −1.820 2K

C18H54CsN3O2Si6U 884.12 0.186 × 0.100 × 0.081 trigonal R3̅c 120(2) 18.5482(5) 18.5482(5) 17.9573(7) 90 90 120 5350.2(4) 6 1.646 5.776 3798 1395, 0.0361 1115 0.977−0.987 0.0701, 0.1695 0.0835, 0.1751 1.238 102, 117 1.426, −1.461 3Li

C42H102LiN3O8Si6U 1190.77 0.209 × 0.134 × 0.109 monoclinic P21/n 150(2) 17.1131(9) 16.1172(9) 23.6514(12) 90 107.815(5) 90 6210.6(6) 4 1.274 2.771 28693 12680, 0.0593 8736 0.899−0.937 0.0556, 0.0994 0.0961, 0.1162 1.005 880, 1536 0.670, −0.675 3Na

formula fw (g mol−1) cryst size, mm crystal system space group collection temperature (K) a (Å) b (Å) c (Å) α, (deg) β (deg) γ (deg) V (Å3) Z ρcalc (g cm−3) μ (mm−1) no. of reflections measured no. of unique reflections, Rint no. of reflections with F2 > 2s(F2) transmission coefficient range R, Rwa (F2 > 2s(F2)) R, Rwa (all data) Sa parameters, restraints max, min difference map (e Å−3)

C46H110N3NaO9Si6U 1278.92 0.757 × 0.415 × 0.23 orthorhombic Pccn 150(2) 25.3118(11) 24.2190(10) 21.5295(8) 90 90 90 13198.1(9) 8 1.287 2.62 57741 16407, 0.0591 10464 0.869−0.944 0.0455, 0.0851 0.0947, 0.1005 1.049 703, 750 0.914, −0.653 3K

formula fw (g mol−1) cryst size (mm) crystal system space group collection temperature (K) a (Å) b (Å)

C40H98KN5O9Si6U 1238.9 0.295 × 0.143 × 0.124 monoclinic P21/c 125(2) 12.7132(3) 31.7536(6)

C46H110KN3O9Si6U 1295.03 0.394 × 0.258 × 0.144 orthorhombic Pccn 120(2) 25.4608(4) 24.1287(4) 21.5883(3) 90 90 90 13262.5(3) 8 1.297 8.848 33146 13203, 0.0385 11685 0.041−0.238 0.0399, 0.1085 0.0445, 0.1129 1.017 843, 1815 2.003, −1.404 3Rb C48H114N5O11RbSi6U 1429.48 0.188 × 0.128 × 0.067 trigonal R3̅m 120(2) 18.8256(5) 18.8256(5) I

C36H90LiN5O8Si6U 1134.63 0.422 × 0.333 × 0.317 monoclinic P21/c 100(2) 23.0245(9) 16.2392(7) 30.9335(11) 90 110.086(4) 90 10862.5(8) 8 1.388 3.166 47913 24728, 0.0340 17128 0.361−0.454 0.0464, 0.0846 0.0841, 0.0986 1.033 1063, 435 1.977, −1.788 3Cs C48H114CsN5O11Si6U 1476.92 0.335 × 0.240 × 0.200 trigonal R3m 120(2) 18.8360(4) 18.8360(4)

C74H184N10Na2O16.50Si12U2 2337.42 0.798 × 0.399 × 0.171 triclinic P1̅ 100(2) 15.7127(3) 16.4229(3) 23.2039(4) 87.8864(14) 72.9160(15) 88.9040(14) 5719.42(17) 2 1.357 3.016 175350 29814, 0.0638 18462 0.116−0.544 0.0813, 0.1604 0.1417, 0.1901 1.098 1771, 7099 2.511, −5.762 4Li C34H86LiN3O10Si6U 1110.56 0.289 × 0.257 × 0.156 triclinic P1̅ 150(2) 11.3846(3) 15.3547(4) DOI: 10.1021/acs.inorgchem.8b00715 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 2. continued 3K

3Rb

3Cs

4Li

c (Å) α, (deg) β (deg) γ (deg) V (Å3) Z ρcalc (g cm−3) μ (mm−1) no. of reflections measured no. of unique reflections, Rint no. of reflections with F2 > 2s(F2) transmission coefficient range R, Rwa (F2 > 2s(F2)) R, Rwa (all data) Sa parameters, restraints max, min difference map (e Å−3)

16.2067(3) 90 111.979(2) 90 6067.0(2) 4 1.356 2.909 61788 20039, 0.0375 16564 0.839−0.927 0.0389, 0.0761 0.0542, 0.0802 1.122 577, 0 3.669, −1.792 4Na

18.1448(5) 90 90 120 5569.0(3) 3 1.279 8.254 8395 1364, 0.0908 1355 0.750−0.885 0.0668, 0.1757 0.0672, 0.1762 1.102 111, 149 3.057, −1.930 4K

18.1445(4) 90 90 120 5575.1(3) 3 1.32 11.215 11127 2724, 0.0819 2677 0.038−0.188 0.0601, 0.1661 0.0610, 0.1679 1.044 196, 367 2.323, −2.613 4Rb

16.3194(3) 89.581(2) 70.881(2) 89.837(2) 2695.32(12) 2 1.368 3.19 27411 12340, 0.0472 11173 0.525−0.696 0.0513, 0.1374 0.0577, 0.1416 1.116 514, 1 2.785, −0.932 4Cs

formula fw (g mol−1) cryst size (mm) crystal system space group collection temperature (K) a (Å) b (Å) c (Å) α, (deg) β (deg) γ (deg) V (Å3) Z ρcalc (g cm−3) μ (mm−1) no. of reflections measured no. of unique reflections, Rint no. of reflections with F2 > 2s(F2) transmission coefficient range R, Rwa (F2 > 2s(F2)) R, Rwa (all data) Sa parameters, restraints max, min difference map (e Å−3)

C38H94N3NaO12Si6U 1214.72 0.379 × 0.198 × 0.149 monoclinic Pn 150(2) 16.6244(5) 35.3160(10) 20.8018(7) 90 104.813(4) 90 11807.0(7) 8 1.367 2.928 48796 32299, 0.0554 23880 0.499−0.711 0.0780, 0.1654 0.1085, 0.1890 0.953 2448, 4630 2.270, −1.633

C38H94KN3O12Si6U 1230.83 0.616 × 0.303 × 0.218 trigonal R3̅c 150(2) 16.9231(5) 16.9231(5) 36.4058(9) 90 90 120 9029.4(6) 6 1.358 2.934 22650 2372, 0.0597 1642 0.151−0.359 0.0882, 0.2159 0.1199, 0.2300 1.231 228, 511 1.680, −1.829

C38H94N3O12RbSi6U 1277.2 0.412 × 0.245 × 0.100 monoclinic C2/c 150(2) 29.048(3) 17.2018(7) 15.3135(13) 90 127.610(13) 90 6061.7(12) 4 1.4 3.643 14454 6996, 0.0395 4678 0.434−0.776 0.0409, 0.0692 0.0758, 0.0795 1.049 423, 304 0.838, −0.641

C38H94CsN3O12Si6U 1324.64 0.184 × 0.113 × 0.056 monoclinic I2/a 150(2) 15.2644(4) 17.2395(8) 23.3984(10) 90 95.541(3) 90 6128.5(4) 4 1.436 3.399 25178 7363, 0.0843 4320 0.705−0.876 0.0543, 0.0786 0.1125, 0.0961 1.009 423, 753 1.117, −1.080

Preparation of [UO2(N″)3][Rb(2,2,2-cryptand)] (3Rb). 1Rb (0.837 g, 1 mmol) and 2,2,2-cryptand (0.376 g, 1 mmol) gave 3Rb as yellow crystals. Yield: 0.89 g, 73%. Crystals suitable for X-ray diffraction studies were obtained from a concentrated THF solution layered with toluene. 1H NMR (d5-Pyr, 298 K): δ 0.78 (s, 54H, CH3), 2.37 (br, 12H, CH2), 3.46 (br, 12H, CH2), 3.41 (br, 12H, CH2). 13 C{1H} NMR (d5-Pyr, 298 K): δ 6.57 (CH3), 54.47 (CH2), 69.92 (CH2), 70.76 (CH2). 29Si{1H} NMR (d5-Pyr, 298 K): −7.40 (Si(CH3)3). FTIR v/cm−1 (Neat): 2944 (w), 2883 (w), 2821 (w), 1476 (w), 1445 (w), 1352 (w), 1297 (w), 1234 (m), 1130 (w), 1102 (m), 1072 (w), 961 (s), 880 (w), 826 (s), 771 (m), 752 (m), 688 (m), 661 (s), 607 (s), 518 (w). Raman ν/cm−1 (Neat, ≤37.5 mW): 2956 (m), 2890 (s), 2841 (w), 1477 (w), 1443 (w), 1408 (w), 1294 (w), 1254 (w), 1237 (w), 1132 (w), 1071 (w), 852 (w), 810 (s), 773 (w), 687 (m), 666 (m), 612 (s), 374 (m), 258 (w), 200 (m), 102 (w), 56 (m). Anal. Calcd for C36H90N5O8Si6URb: C 35.64, H 7.48, N 5.77%; Found: C 33.95, H 7.27, N 5.44%. UV/vis (25 mM, THF) λmax (ε/ mol−1 cm−1): 495 (367) nm.

Preparation of [UO2(N″)3][K(2,2,2-cryptand)] (3K). 1K (1.58 g, 2.00 mmol) and 2,2,2-cryptand (0.75 g, 2.00 mmol) gave 3K as yellow crystals. Yield: 1.96 g, 84%. Crystals suitable for X-ray diffraction were obtained from slow evaporation of a THF/toluene mix. 1H NMR (d5Pyr, 298 K): δ 0.78 (s, 54H, CH3), 2.36 (br, 12H, CH2), 3.37 (br, 12H, CH2), 3.42 (br, 12H, CH2). 13C{1H} NMR (d5-Pyr, 298 K): δ 6.83 (CH3), 54.38 (CH2), 68.12 (CH2), 70.88 (CH2). 29Si{1H} NMR (d5Pyr, 298 K): −7.02 (Si(CH3)2). FTIR v/cm−1 (Neat): 2945 (w), 2885 (w), 2824 (w), 1446 (w), 1354 (w), 1296 (w), 1234 (m), 1133 (m), 1103 (s), 1076 (m), 963 (s), 880 (m), 826 (s), 771 (m), 753 (m), 688 (m), 660 (s), 606 (m), 523 (w). Raman ν/cm−1 (Neat, ≤37.5 mW): 2957 (m), 2889 (s), 2842 (w), 1476 (w), 1443 (w), 1403 (w), 1296 (w), 1254 (w), 1234 (w), 1114 (w), 1070 (w), 857 (w), 809 (s), 773 (w), 689 (m), 667 (m), 612 (s), 374 (m), 260 (w), 198 (m), 105 (w), 58 (m). Anal. Calcd for C36H90N5O8Si6UK: C 37.05, H 7.79, N 6.00%; Found: C 36.49, H 7.63, N 5.66%. UV/vis (25 mM, THF) λmax (ε/ mol−1 cm−1): 496 (408) nm. J

DOI: 10.1021/acs.inorgchem.8b00715 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

−7.01 (Si(CH3)3). FTIR v/cm−1 (Neat): 2945 (br, w), 2885 (br, w), 1446 (w), 1354 (w), 1236 (sh, m), 1119 (sh, s), 1091 (w), 1040 (w), 964 (sh, s), 940 (w), 826 (br, s), 768 (w), 666 (w), 660 (m), 605 (sh, m). Raman v/cm−1 (Neat, ≤75 mW): 2955 (br, w), 2895 (br, m), 1443 (w), 852 (w), 808 (sh, s), 789 (w), 687 (m), 663 (m), 607 (sh, s), 374 (sh, s), 256 (w), 203 (w), 109 (w). Anal. Calcd for C38H94N3Si6O12RbU: C 35.74, H 7.42, N 3.29%; Found C 35.52, H 7.45, N 3.34%. UV/vis (5 mM, THF) λmax (ε/mol−1 cm−1): 495 (398) nm. Preparation of [UO2(N″)3][Cs(15-crown-5)2] (4Cs). 1Cs (0.884 g, 1 mmol) and 15-crown-5 (0.40 mL, 2 mmol) gave 4Cs as orange crystals. Yield: (0.382 g, 29%). 1H NMR (d5-Pyr, 294 K): δ 0.79 (s, 54H, CH3), 3.57 (s, 40H, CH2). 13C {1H} NMR (d5-Pyr, 294 K): δ 6.79 (CH3), 69.85 (CH2). 29Si{1H} NMR (d5-Pyr, 294 K): δ −7.00 (Si(CH3)3). FTIR v/cm−1 (Neat): 2947 (br, w), 2865 (br, w), 1448 (w), 1356 (w), 1240 (sh, m), 1117 (sh, m), 1091 (w), 962 (br s), 936 (br, s), 83 (br, s), 662 (w). Raman v/cm−1 (Neat, ≤75 mW): 2952 (br, m), 2894 (br, m), 1446 (w), 1269 (w), 856 (sh, m), 805 (sh, s), 767 (sh, m), 685 (m), 662 (m), 607 (sh, s), 369 (sh, s), 251 (br, m), 196 (br, m), 106 (w). Anal. Calcd for C38H94N3Si6O12CsU: C 34.46, H 7.15, N 3.17%; Found C 33.56, H 7.03, N 3.10%. UV/vis (5 mM, THF) λmax (ε/mol−1 cm−1): 495 (253) nm. Single Crystal X-ray Crystallography (CCDC Numbers 1827552−1827567). Crystallographic data for 1M−4M is compiled in Table 2. Data for 1M−4M were recorded on (a) an Agilent Supernova diffractometer, equipped with either an Atlas/AtlasS2 or TitanS2 CCD area detector with mirror-monochromated CuKα radiation (λ = 1.5418 Å), (b) an Agilent Supernova diffractometer, equipped with an Eos CCD area detector with a Microfocus source with Mo Kα radiation (λ = 0.71073 Å), or (c) a Rigaku Xcalibur2 diffractometer, equipped with an Atlas CCD area detector and a sealed tube source with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Intensities were integrated from data recorded on narrow (0.5 or 1.0°) frames by ω rotation. Cell parameters were refined from the observed positions of all strong reflections in each data set. Either Gaussian grid face-indexed or multiscan absorption corrections with a beam profile correction were applied. The structures were solved by direct methods using either SHELXS or SHELXT,58,59 and the data sets were refined by full-matrix least-squares on all unique F2 values, with anisotropic displacement parameters for all non-hydrogen atoms, and with constrained riding hydrogen geometries; Uiso(H) was set at 1.2 (1.5 for methyl groups) times Ueq of the parent atom. The largest features in final difference syntheses were close to heavy atoms and were of no chemical significance. CrysAlisPro60 was used for control and integration, and SHELXL61 and OLEX262 were employed for structure refinement. ORTEP-363 and POV-Ray64 were employed for molecular graphics.

Preparation of [UO2(N″)3][Cs(2,2,2-cryptand)] (3Cs). 1Cs (0.884 g, 1 mmol) and 2,2,2-cryptand (0.376 g, 1 mmol) gave 3Cs as yellow crystals. Yield: 1.00 g, 83%. Crystals suitable for X-ray diffraction studies were obtained from a concentrated THF solution layered with toluene. 1H NMR (d5-Pyr, 298 K): δ 0.81 (s, 54H, CH3), 2.45 (br, 12H, CH2), 3.42 (br, 12H, CH2), 3.49 (br, 12H, CH2). 13 C{1H} NMR (d5-Pyr, 298 K): δ 6.61 (CH3), 53.45 (CH2), 68.71 (CH2), 70.98 (CH2). 29Si{1H} NMR (d5-Pyr, 298 K): −7.37 (Si(CH3)3). FTIR v/cm−1 (Neat): 2946 (w), 2882 (w), 2817 (w), 1475 (w), 1444 (w), 1297 (w), 1232 (s), 1183 (m), 1123 (m), 1106 (m), 1064 (m), 961 (s), 826 (m), 771 (m), 746 (m), 660 (s), 606 (s), 508 (w). Raman ν/cm−1 (Neat, ≤37.5 mW): 2952 (m), 2893 (s), 1836 (w), 1474 (w), 1443 (w), 1407 (w), 1296 (w), 1253 (w), 1134 (w), 1126 (w), 1062 (w), 858 (w), 809 (s), 777 (w), 688 (m), 663 (w), 611 (s), 374 (s), 257 (w), 199 (m), 107 (m), 59 (m). Anal. Calcd for C36H90N5O8Si6UCs: C 34.29, H 7.21, N 5.56%; Found: C 32.30, H 6.82, N 5.39%. UV/vis (25 mM, THF) λmax (ε/mol−1 cm−1): 496 (370) nm. Preparation of [UO2(N″)3][Li(12-crown-4)2] (4Li). THF (15 mL) was added to a mixture of 1Li (0.771 g, 0.89 mmol) and 12crown-4 (0.288 mL, 1.78 mmol) and allowed to stir for 18 h. The resulting solution was filtered and reduced in volume under reduced pressure to ca. 8 mL, then layered with hexane and stored at 5 °C for 2 days to afford 4Li as orange crystals. Yield: 0.545 g, 55%. 1H NMR (d5Pyr, 294 K): δ 0.78 (s, 54H, CH3), 3.66 (s, 32H, CH2). 13C {1H} NMR (d5-Pyr, 294 K): δ 6.18 (CH3), 70.47 (CH2). 7Li NMR {1H} (d5-Pyr, 294 K): δ 4.40 (Li). 29Si {1H} NMR (d5-Pyr, 294 K): δ −7.00 (Si(CH3)3). FTIR v/cm−1 (Neat): 2940 (br, w), 2904 (br, w), 2871 (br, w) 1446 (w), 1364 (w), 1288 (w), 1233 (m), 1133 (m), 1095 (m), 1025 (m), 962 (s), 921 (w), 821 (br, s) 768 (br w), 752 (br, w), 689 (sh, m), 658 (sh, s) 605 (sh, s) and 554(w). Raman v/cm−1 (Neat, ≤37.5 mW): 2944 (w), 2896 (br, s), 1484 (w), 1448 (w), 1412 (w), 1356 (w), 1302 (w), 1299 (w), 1258 (w), 1236 (w), 1031 (w), 859 (w), 808 (sh, s), 773 (w), 692 (w), 671 (w), 611 (sh, s), 375 (m), 201 (br, m), 110 (w), 62 (w). Anal. Calcd for C34H86N3Si6O10LiU: C, 36.77 H, 7.81 N 3.78%; Found C, 35.30 H, 7.58 N 3.23%. UV/vis (25 mM, THF) λmax (ε/mol−1 cm−1):497 nm (465). Preparation of [UO2(N″)3][Na(15-crown-5)2] (4Na). 1Na (0.713 g, 0.78 mmol) and 15-crown-5 (0.35 mL, 1.75 mmol) gave 4Na as orange crystals. Yield: 0.775 g, 82%. 1H NMR (d5-Pyr, 294 K): δ 0.79 (s, 54H, CH3), 3.65 (s, 40H, CH2). 13C{1H} NMR (d5-Pyr, 294 K): δ 6.50 (CH3), 70.25(CH2). 23Na {1H} NMR (d5-Pyr, 294 K): δ 0.52. 29 Si {1H} NMR (d5-Pyr, 294 K): δ −8.55 (Si(CH3)3). FTIR v/cm−1 (Neat): 2943 (br, w), 2869 (br, w), 1448 (w), 1354 (sh, w), 1235 (sh, m), 1117 (br, s), 1091 (br, s), 1029 (br, w), 960 (s), 819 (br, s), 770 (w), 752 (w), 687(sh, m), 658 (sh, m) and 605 (sh, m). Raman v/ cm−1 (Neat, ≤15 mW): 2951 (w), 2899 (br, m), 1455 (w), 1255 (br, w), 863 (w), 812 (sh, s), 777 (w), 692 (w), 669 (w), 612 (sh, s), 493 (w), 376 (m), 202 (br, w). Anal. Calcd for C38H94N3Si6O12NaU: C 37.57, H 7.80, N 3.46%; Found C 37.00, H 7.76, N 3.47%; UV/vis (5 mM, THF) λmax(ε/mol−1 cm−1): 496 (548) nm. Preparation of [UO2(N″)3][K(15-crown-5)2] (4K). 1K (1.185 g, 1.5 mmol) and 15-crown-5 (0.56 mL, 2.9 mmol) gave 4K as orange crystals. Yield: 0.856 g, 47%. 1H NMR (d5-Pyr, 294 K): δ 0.79 (s, 54H, CH3), 3.55 (s, 40H, CH2). 13C{1H} NMR (d5-Pyr, 294 K): δ 6.80 (CH3), 69.44 (CH2). 29Si{1H} NMR (d5-Pyr, 294 K): δ −7.04 (Si(CH3)3). FTIR v/cm−1 (Neat): 2947 (br, w), 2887 (br, w) 1443 (w), 1354 (w), 1236 (m), 1121 (s), 1091 (s), 1042 (w), 964 (s)821 (br, s), 768 (w), 685 (w), 658 (sh, m), 605 (sh, m). Raman v/cm−1 (Neat, ≤75 mW): 2958 (br, m), 2900 (br, s), 1476 (w), 1477 (w),1278 (w), 1258 (br, w), 1152 (w), 858 (sh, m), 811 (sh, s), 773 (w), 692 (w, 669 (m), 611 (sh, s), 374 (sh, m), 209 (br, m), 113 (w), 64 (m). Anal. Calcd for C38H94N3Si6O12KU: C 37.08, H 7.70, N 3.41%; Found C 36.76, H 7.78, N 3.66%. UV/vis (5 mM, THF) λmax (ε/ mol−1 cm−1): 496 (571) nm Preparation of [UO2(N″)3][Rb(15-crown-5)2] (4Rb). 1Rb (0.376 g, 0.45 mmol) and 15-crown-5 (0.18 mL, 0.93 mmol) gave 4Rb as orange crystals. Yield: (0.243 g, 44%). 1H NMR (d5-Pyr, 294 K): δ 0.79 (s, 54H, CH3), 3.55 (s, 40H, CH2). 13C {1H} NMR (d5-Pyr, 294 K): δ 6.79 (CH3), 69.92 (CH2). 29Si{1H} NMR (d5-Pyr, 294 K): δ

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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.8b00715. Crystallographic details for 1Ka, 1Rb, 1Cs, 2Li, 2Na, 2K, 3M, and 4M (PDF) Accession Codes

CCDC 1827552−1827567 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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*E-mail: [email protected]. *E-mail: [email protected]. K

DOI: 10.1021/acs.inorgchem.8b00715 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry ORCID

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Ashley J. Wooles: 0000-0001-7411-9627 Louise S. Natrajan: 0000-0002-9451-3557 Stephen T. Liddle: 0000-0001-9911-8778 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the EPSRC (grants EP/M027015/1, EP/P001386/1, EP/G004846/1, and EP/K039547/1), ERC (grant CoG612724), Royal Society (grant UF110005), Leverhulme Trust (grant RL-2012-072), and the University of Manchester for generous funding and support.

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DOI: 10.1021/acs.inorgchem.8b00715 Inorg. Chem. XXXX, XXX, XXX−XXX