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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, UK.

*Email: [email protected]; [email protected]

Abstract

We report the preparation of a range of alkali-metal uranyl(VI) tri-bis(silyl)amide complexes

[{M(THF)x}{(-O)U(O)(N")3}] (1M) (N" = {N(SiMe3)2}-, M = Li, Na, x = 2; M = K, Rb, Cs, x

= 0) containing electrostatic alkali metal uranyl-oxo interactions. Reaction of 1M with 2,2,2-

cryptand or two equivalents 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-crown-4 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 X-ray diffraction, multi-nuclear

NMR spectroscopy, IR, Raman, and UV-Vis spectroscopies, and elemental analyses.

1

Introduction

In recent years there has been burgeoning interest in non-aqueous uranium chemistry,1,2 and

whilst 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- uranyl species are

redox-robust cyanides, multidentate 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,

2

x= 2) and examples of uranyl aryloxides species include [U(O)2(OR)2(THF)2] (R= 2,6-

But2C6H3, 2,6-Ph2C6H3), [U(O)2(OR)2(THF)2]2 (R= 2,6-Cl2C6H3, 2,6-Me2C6H3), [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-2,6-

Me2C6H3)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 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 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 two equivalents 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}{(-O)U(O)(N")3}] (M= Na or K) were subsequently reported,27 but whilst the

potassium analogue was prepared from the reaction of [U(O)2(Cl)2(THF)2] with three

equivalents of [K(N")], the sodium congener could not be accessed via this synthetic 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}{(-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}{(-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, but

3

the THF is labile and is removed in vacuo and also upon recrystallization, even from THF

solutions.27 In addition to sodium and potassium salts, the lithium CIP complex [{Li(Py)2}

{(-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] completes 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 uranyl(VI) tri-bis(silyl)amide with N(CH2CH2NHSiMe2But)3, which

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}{(-O)U(O)(N")3}] (M=Li,

Na, K, Rb, Cs) and, since it is increasingly clear that crown ethers and cryptands can enable

the synthesis of novel actinide-ligand multiple bond linkages,12,32–38 SIP species of general

formulae [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).

Results

Synthesis and formulations of uranyl-tri-bis(silyl)amides 1M-4M

Reactions of [U(O)2(Cl)2(THF)2] with three equivalents of [M(N")] (M = Na, K, Rb or Cs) in

THF gives the uranyl(VI) tri-bis(silyl)amide CIP complexes [{M(THF)x}{(-O)U(O)(N")3}]

4

(1M) (M = Na, x = 2; M = K, Rb, Cs, x = 0) in good yields (70-83%), Scheme 1. The lithium

congener, [{Li(THF)2}{(-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)2}

{(-O)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 desolvates to give [K(-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(-O)U(O)(N")3] (1Rb) and [Cs(-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 orange. Lastly, 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).

5

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 2,2,2-cryptand or two equivalents of size-matched crown ether afforded the SIPs

[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-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 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.

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 non-donor 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 they 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.

6

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 O yl-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 Oyl-oxo 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 so 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 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 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 the closely related SIP

7

species [U(O)2(N")3][Co(5-C5Me5)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 confirm their formulations, including the number of THF

molecules coordinated in 2M, but are otherwise structurally unremarkable.

Vibrational spectroscopic analysis of 1M-4M

The solid state ATR-IR spectroscopic data for 1M and 3M-4M are summarized in Table 1

and reveal that the total asymmetric uranyl U=O stretches range from 936-941 cm-1 for 1M

but to a higher energy range of 961-964 cm-1 for 3M-4M, indicating a weakening of the

uranyl U=O bond in 1M compared to 3M-4M. The solid state ATR-IR spectroscopic data for

2M were not obtainable, as attempts to prepare powdered samples of 2M led to desolvation

and isolation of 1M. The Raman spectra for 1M and 3M-4M follow a similar pattern to the

IR spectra, with the CIP complexes 1M exhibiting U=O symmetric stretches ranging from

795-805 cm-1 which are lower in energy than the corresponding stretches in the SIP

complexes 3M-4M (range: 805-811 cm-1), but all these values are consistent with reported

uranyl(VI) complexes.27,28,46 Solution IR spectroscopic studies of 1M in THF solvent led to an

increase in energy for the U=O bond with the antisymmetric U=O stretch increasing to 969-

973 cm-1; higher in energy than the solid state values of 1M (ca. 940 cm-1), but similar to the

separated ion pairs 3M-4M (961-964 cm-1). The stretching force constants (k1) and

interaction force constants (k12) for the U=O bonds in 1M-4M were determined using a

valence bond potential model utilising the solid state ATR-IR and Raman data for the

symmetric and asymmetric Uranyl stretches.47,48 The stretching force constant refers to the

U=O bonds of the uranyl unit while the interaction forces refers to the interaction between the

8

two oxygen atoms of the uranyl moiety. Consistent with previous reports the interaction of

the uranyl unit with the equatorial 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 the CIP

series 1M and the SIP series 3M-4M, with the former exhibiting stretching force constants of

6.63-6.72 mdyn Å-1, while the latter exhibits 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 polarising 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 <18,000 cm-1 suggesting

that no f-f transitions are observed, consistent with the assignment of a +6 oxidation state.

The absorption spectra of all fourteen complexes follow a similar profile with a maximum

absorption at ca. 20,160 cm-1, commensurate with the yellow color of these species in

solution. The absorption bands in the region 18,000-25,000 cm-1 are characteristic ligand to

metal charge transfer bands (with molar absorption extinction coefficients, ɛ, in the expected

range, ca. 400 mol-1 cm-1), which are commonly observed in uranyl(VI) complexes.49,50

9

Discussion

The preparation of 1Na, and possibly 1Li, is notable and surprising. This is because it has

been previously reported that addition of three equivalents of [Na(N")] to [U(O)2(Cl)2(THF)2]

results in the formation of an equimolar mixture of [U(O)2(N")2(THF)2] and [{U(O)2(N")4}

{Na(THF)}2] with only trace quantities of 1Na detected.27 The entirely reasonable rationale

that had been advanced to explain this is that the lighter alkali metals produce uranyl(VI)-

diamide derivatives that are more soluble than heavier alkali metal ones and thus remain

available for further reaction in solution; for example for potassium, which readily affords 1K

from [U(O)2(Cl)2(THF)2] with three equivalents of [K(N")], it is proposed that the lower

solubility of 1K effectively removes it from further reaction in solution. Thus, the reasons for

these different outcomes from different laboratories is currently not clear, and there are

multiple variables to consider, but we note that where we have isolated 1Na directly the

reaction stir time was nearly twice as long as previous studies. We suggest that perhaps

longer stirring times enables the di-/tetraamide mixture to equilibrate to the triamide average

over time, but if halted ‘prematurely’ the di- and tetraamide formulations are still dominant

after being initially established rapidly.

Our attempts to structurally characterize the entire 1M series were thwarted by the

combination of low solubility in non-donor solvent, and the coordination of donor solvent to

the Li, Na and K centers upon dissolution in donor solvents such as THF. This is in contrast

to the reports of [{Li(Py)2}{(-O)U(O)(N")3}] (1LiPy2) which was soluble in benzene and

was isolated as a crystalline material with only two donor solvents coordinated to Li. This

variation in solubility and crystallinity is perhaps surprising, with the nature of the donor

solvent having a large influence on the properties of the compound and may be due to the

aromatic pyridines increasing solubility in aromatic solvents. Gratifyingly, even though we

10

were unable to structurally characterize 1Li, the report of 1LiPy2 allowed for a direct

comparison of the entire CIP series, both spectroscopically and structurally.

The variation of number of THF molecules coordinated to the alkali metal in the crystalline

and post-vacuum-dried powdered samples of 1M-2M for Li, Na and K suggest that the THF

molecules are labile and it is likely crystallization effects and rates of cooling that are

influencing which THF adduct is isolated in each case. For the monomeric examples in the

1M series, namely 1LiPy2, 1Na and 1Ka we observed a lengthening of the U=O bond that is

capped by the respective alkali metal. This lengthening of the U=O bond by coordination of

the alkali metal could be considered as an alkali metal-mediated push-pull effect, in which

case the U-N bond distance would shorten.51,52 However, there appears to be no statistically

distinguishable shortening of the U-N bond distances in 1M in comparison to the SIP species

2M-4M so this is likely not present. However, this would be in-line with the more

electrostatic nature of the bonding of uranyl(VI) generally in the equatorial plane compared

to the axial oxo groups and electrostatic bonding might be expected to be a poor reporter of

electronic effects.

Weakening of the U=O bond in 1M compared to 2M-4M is confirmed by ATR-IR and

Raman spectroscopy with 1M exhibiting lower energy U=O stretches than the 3M-4M series,

and is also indicated by inspection of the calculated force constants for each series, with the

1M series exhibiting decreased stretching force constants (6.63-6.72 mdyn Å-1) compared to

3M-4M (6.91-6.95 mdyn Å-1). Indeed, whilst differences between different series of

compounds are significant, there is little variation of the data for compounds within a series.

Solution IR studies suggest that the variation in U=O stretching frequencies observed in 1M

11

and 3M-4M is due to the alkali metal coordinating to the uranyl group. When 1M is

dissolved in THF, the IR stretch increases in energy by ca. 30 cm-1, akin to 3M-4M, and we

reason that this is due to THF coordinating to the alkali metals forming SIP motifs rather than

CIP, as in the solid state. Interestingly, in the solid state the 1M compounds are dark red, but

they each turn yellow upon dissolution in THF solution, which we again ascribe is due to the

coordination of THF to the alkali metal center leading to a SIP motif. This is also supported

by the fact that 3M-4M are yellow in both the solid and solution states. Indeed, the optical

spectra for each complex in the 1M, 3M-4M series appears to be very similar suggesting the

uranyl(VI) centers are equivalent in each complex in solution.

Conclusion

We have prepared the uranyl(VI)-tri-bis(silyl)amide CIP complexes [{M(THF)x}{(-O)U(O)

(N")3}] (1M) along with the SIP complexes [U(O)2(N")3][M(2,2,2-cryptand)] (3M) and

[U(O)2(N")3][M(crown)2] (4M) for the full Group 1 series. The combination of

crystallographic studies and IR, Raman and UV/Vis spectroscopic studies reveal that in 1M,

the alkali metal coordinates to the uranyl-oxo unit in the solid state leading to a weakening of

the U=O bond being observed. When 1M are dissolved in THF, or additionally in the case of

1Li-1K when samples are crystallized from THF solution, rather than being prepared as

powdered samples, the alkali metal is encapsulated by the THF molecules leading to a SIP

motif (2Li-2K), analogous to 3M-4M. Previous preparations of the 1M series have reported

difficulties in controlling the ratio of amide:uranyl:THF ratio, however our investigation has

revealed the optimum methods for isolating 1M and have elucidated their structures and

exact formulations, which will ensure accurate stoichiometries for future reactions where 1M

is a synthetic precursor. Additionally the conversion of 1M to the SIP species 3M-4M will

allow additional synthetic options where the alkali metal is preinstalled and encapsulated,

12

thus not hindering or adversely affecting the installation of new ligand linkages at the

uranyl(VI) center.

Experimental Section

General

All manipulations were carried out under a dry nitrogen or argon atmosphere, using standard

Schlenk techniques or in an MBraun UniLab or Innovative Technologies System Two

glovebox. Solvents were dried by passage though activated alumnia towers and degassed

prior to use. All solvents were stored over either 3Å or 4Å activated sieves except hexane and

toluene, which were stored over potassium mirrors. The deuterated solvents d5-pyridine and

d6-benzene were distilled from CaH2 or potassium respectively and degassed by three freeze-

pump-thaw cycles and stored under a nitrogen or argon atmosphere. Compounds

[U(O)2(Cl)2(THF)2],53 [U(O)2(N")2(THF)2],23 [Li(N")],54 [K(N")],55 [Rb(N")],56 [Cs(N")],56

were synthesized via published procedures. [Na(N")] was purchased from commercial

sources and used as received.

1H, 7Li, 13C, 23Na and 29Si NMR spectra were recorded on a Bruker 400 spectrometer

operating at 400.2, 155.5, 100.6, 105.8 and 79.5 MHz respectively; chemical shifts are quoted

in ppm and are relative to tetramethylsilane (1H, 13C,

29Si), 1M LiCl (7Li) and 1M NaCl (23Na).

Attenuated total reflectance infrared spectra were recorded on a Bruker Alpha spectrometer

with Platinum-ATR module. Raman spectra were recorded on a Horiba XploRA Plus Raman

microscope with a 638 nm laser with a power of ≤150 mW. The power was adjusted using a

power filter for each complex to inhibit sample decomposition. UV/Vis/NIR spectra were

recorded on a Perkin Elmer Lambda 750 spectrometer. Data were collected in 1mm path

length cuvettes loaded in an MBraun UniLab glovebox and were run versus the appropriate

13

THF reference solvent. Elemental analyses were carried out on an EAI CE-400 Elemental

Analyser or a Thermo Scientific Flash 2000 Organic Elemental Analyser. Satisfactory

elemental analyses for 3Li, 3Na, 3Rb, 3Cs, 4Li, 4Na and 4Cs were unobtainable despite

multiple attempts. The consistent low carbon values in these compounds is ascribed to

carbide formation causing incomplete combustion during analysis.57 Due to the preparations

of a) 1Na – 1Cs, b) 3Li – 3Cs and c) 4Li – 4Cs being very similar, only the preparations of

1Na, 3Li and 4Li are given in detail.

Preparation of [{Li(Py)2}{(-O)U(O)(N")3}] (1LiPy2)

1LiPy2 was synthesized via a previously published procedure; NMR spectroscopic data and

elemental analyses match previous reports.28 FTIR v/cm-1 (Neat): 2946 (w), 2894 (w), 1602

(w), 1492 (w), 1444 (w), 1238 (m), 1154 (w), 1070 (w), 1039 (w), 1008 (w), 936 (s), 857

(m), 823 (s), 751 (m), 898 (m), 683 (m), 659 (s), 608 (s), 455 (w); Raman v/cm-1 (Neat,

≤15mW ): 3071 (w), 2954 (w), 2900 (m), 1595 (w), 1238 (w), 1035 (w), 1008 (m), 856 (m),

859 (m), 799 (s), 798 (m), 758 (m), 679 (m), 614 (s), 376 (s), 247 (w), 196 (m), 183 (w), 118

(w), 104 (w), 54 (s).

Preparation of [{Li(THF)2}{(-O)U(O)(N")3}] (1Li)

THF (15 ml) was added to a mixture of [U(O)2(N")2(THF)2] (0.735 g, 1.00 mmol) and

[Li(N")] (0.182 g, 1.1 mmol) and allowed to stir for 18 hours. 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 orange crystals, which turned red when dried in vacuo

to yield 1Li as a red power. Yield 0.66 g, 76%. 1H NMR (d5-Pyr, 294K): δ 0.78 (s, 54H,

CH3), 1.63 (m, 8H, OCH2CH2), 3.67 (m, 8H, OCH2CH2). 13C{1H} NMR (d5-Pyr, 294K): δ

6.78 (CH3), 26.18 (OCH2CH2), 68.20 (OCH2CH2). 7Li{1H} NMR (d5-Pyr, 294K): δ 4.86.

14

29Si{1H} NMR (d5-Pyr, 294K): δ -7.03 (Si(CH3)3). FTIR v/cm-1 (Neat): 2946 (w), 2892 (w),

1237 (m), 1036 (w), 943 (s), 857 (m), 823 (s), 770 (m), 755 (m), 684 (m), 661 (s), 609 (s),

448 (w). Raman v/cm-1 (Neat, ≤15mW ): 2954 (w), 2893 (m), 1396 (w), 1259 (w), 1251 (w),

1027 (w), 898 (w), 858 (m), 798 (s), 763 (s), 684 (m), 613 (m), 377 (s), 244 (w), 169 (m),

171 (m), 110 (m). Anal. Calc. for C26H70LiN3O4Si6U: C 34.61, H 7.82, N 4.66%; Found: C

34.79, H 8.01, N 4.53%. UV/Vis (25 mM, THF) λmax (/ mol-1 cm-1): 497 (412).

Preparation of [{Na(THF)2}{(-O)U(O)(N")3}] (1Na)

[Na(N")] (0.858 g, 4.68 mmol) in THF (40 ml) was added dropwise to a stirring solution of

[U(O)2(Cl)2(THF)2] (1.51 g, 1.56 mmol) in THF (60 ml) and the resulting mixture was stirred

for 48 hr at R.T. The resulting red suspension was filtered through a celite padded fritted

Schlenk and reduced in volume under reduced pressure to ca. 10 ml. Storage of this solution

at -30 °C yielded 1Na as a red crystalline powder. Yield: 1.39 g, 48%. NMR spectroscopic

data and elemental analysis match previous reports.27 FTIR v/cm-1 (Neat): 2948 (w), 2891

(w), 1407 (w), 1241 (m), 1051 (w), 938 (s), 831 (s), 768 (m), 682 (m), 612 (s); Raman ν/cm-1

(Neat, ≤15mW ): 2954 (w), 2908 (w), 895 (w), 854 (w), 795 (s), 753 (s), 675 (m), 615 (w),

373 (s), 182 (w), 116 (w).

Preparation of [K(-O)U(O)(N")3] (1K) and [{K(THF)3}{(-O)U(O)(N")3}] (1Ka)

[K(N")] (5.99 g, 30.0 mmol) and [U(O)2(Cl)2(THF)2] (4.86 g, 10.0 mmol) gave 1K as a red

crystalline powder. Yield: 6.59 g, 83%. 1H NMR (d5-Pyr, 298 K): δ 0.78 (s, 54H, CH3).

13C{1H} NMR (d5-Pyr, 298 K): δ 7.02 (CH3). 29Si{1H} NMR (d5-Pyr, 298 K): -7.05

(Si(CH3)3). FTIR v/cm-1 (Neat): 2947 (w), 2895 (w), 1239 (m), 940 (s), 823 (s), 768 (m), 753

(m), 682 (m), 660 (m), 610 (s). Raman ν/cm-1 (Neat, ≤15mW): 2954 (w), 2896 (w), 1260 (w),

898 (w), 853 (w), 799 (s), 761 (m), 678 (m), 616 (w), 374 (s), 233 (w), 200 (w), 175 (m), 108

15

(m), 54 (m). Anal. Calc. for C18H54N3Si6O2KU: C 27.35, H 6.90, N 5.32%; Found: C 27.08, H

6.76, N 4.93%. UV/Vis (25 mM, THF) λmax (ɛ/mol-1 cm-1): 496 (425) nm. A concentrated THF

solution of 1K, layered with toluene, afforded crystals of 1Ka suitable for single crystal X-

ray diffraction studies upon storage at -30 °C.

Preparation of [Rb][UO2(N{SiMe3}2)2] (1Rb)

[Rb(N")] (3.69 g, 15.00 mmol) and [U(O)2(Cl)2(THF)2] (2.43 g, 5.0 mmol) gave 1Rb as red

crystals. Yield: 2.94 g, 70%. Crystals suitable for X-ray diffraction were obtained from slow

evaporation of a Et2O/toluene mix. 1H NMR (d5-Pyr, 298 K): δ 0.79 (s, 54H, CH3). 13C{1H}

NMR (d5-Pyr, 298 K): δ 6.88 (CH3). 29Si{1H} NMR (d5-Pyr, 298 K): -7.02 (Si(CH3)3). FTIR

v/cm-1 (Neat): 2947 (w), 2895 (w), 1238 (m), 940 (s), 822 (s), 768 (m), 753 (m), 660 (m), 609

(s). Raman ν/cm-1 (Neat, ≤15mW): 2954 (w), 2898 (w), 1260 (w), 1237 (w), 901 (w), 854 (w)

804 (s), 765 (m), 681 (m), 619 (w), 376 (s), 234 (w), 202 (m), 176 (m), 111 (m), 59 (m).

Anal. Calc. for H54C18N3Si6O2RbU: C 25.84, H 6.51, N 5.02%; Found: C 26.23, H 6.38, N

4.64%. UV/Vis (25 mM, THF) λmax (ɛ/mol-1 cm-1): 496 (294) nm.

Preparation of [Cs][UO2(N{SiMe3}2)2] (1Cs)

[Cs(N")] (4.40 g, 15.00 mmol) and [U(O)2(Cl)2(THF)2] (2.43 g, 5.0 mmol) gave 1Cs as red

crystals. Yield: 3.26 g, 74%. Crystals suitable for X-ray diffraction studies were obtained

from slow evaporation of a Et2O/toluene mix. 1H NMR (d5-Pyr, 298 K): δ 0.78 (s, 54H, CH3).

13C{1H} NMR (d5-Pyr, 298 K): δ 6.57 (CH3). 29Si{1H} NMR (d5-Pyr, 298 K): -7.39

(Si(CH3)3). FTIR v/cm-1 (Neat): 2946 (w), 2895 (w), 1398 (w), 1237 (m), 1091 (w), 1018 (w),

941 (s), 819 (s), 767 (m), 751 (m), 682 (m), 659 (m), 607 (s). Raman ν/cm-1 (Neat, ≤15mW):

2951 (w), 2896 (w), 1260 (w), 1236 (w), 900 (w), 857 (w), 804 (s), 765 (m), 682 (s), 619 (m),

376 (s), 235 (w), 201 (m), 172 (m), 108 (m), 61 (w). Anal. Calc. for C18H54N3Si6O2CsU: C

16

24.45, H 6.16, N 4.75%; Found: C 24.58, H 6.02, N 4.55%. UV/Vis (25 mM, THF) λmax

(ɛ/mol-1 cm-1): 496 (366) nm.

Preparation of [UO2(N")3][Li(THF)4] (2Li) and [UO2(N")3][M(THF)6] (M= Na, 2Na; M=

K, 2K)

Concentrated THF solutions of 1Li, 1Na and 1K afforded crystals suitable for single crystal

X-ray studies of 2Li, 2Na and 2K, respectively, upon cooling to 30 °C.

Preparation of [UO2(N")3][Li(2,2,2-cryptand)] (3Li)

THF (4 ml) was added to a pre cooled (-78 °C) mixture of 1Li (0.450 g, 0.50 mmol) and

2,2,2-cryptand (0.188 g, 0.50 mmol) and the resulting mixture was stirred for 12 hr at R.T.

Toluene (6 ml) was added and the volume of the resulting solution was reduced in volume

under reduced pressure to ca. 2 ml, which afforded yellow crystals of 3Li. Yield: 0.39 g,

68%. Crystals suitable for X-ray diffraction were obtained from a THF/toluene mix. 1H NMR

(d5-Pyr, 298 K): δ 0.78 (s, 54H, CH3), 2.56 (br, 12H, CH2), 3.52 (br, 12H, CH2), 3.60 (br,

12H, CH2). 13C{1H} NMR (d5-Pyr, 298 K): δ 6.58 (CH3), 54.11 (CH2), 68.96 (br, CH2).

29Si{1H} NMR (d5-Pyr, 298 K): -8.56 (Si(CH3)3). 7Li{1H} NMR (d5-Pyr, 298 K): -1.05 (Li).

FTIR v/cm-1 (Neat): 2944 (w), 2884 (w), 1449 (w), 1356 (w), 1302 (w), 1233 (m), 1128 (w),

1093 (m), 964 (s), 860 (m), 824 (s), 770 (m), 689 (m), 659 (s), 607 (s). Raman ν/cm-1 (Neat,

≤37.5mW): 2946 (m), 2891 (s), 1455 (w), 1404 (w), 1252 (w), 1233 (w), 859 (w), 809 (s),

773 (w), 689 (m), 665 (m), 612 (s), 373 (m), 199 (m), 108 (w), 58 (m). Anal. Calc. for

C36H90N5O8Si6ULi: C, 38.11 H, 7.99 N 6.17%; Found C, 34.74 H, 7.33 N 5.90%. UV/Vis (25

mM, THF) λmax (ɛ/mol-1 cm-1): 496 (384) nm.

Preparation of [UO2(N")3][Na(2,2,2-cryptand)] (3Na)

17

1Na (0.459 g, 0.50 mmol) and 2,2,2-cryptand (0.188 g, 0.50 mmol) gave 3Na as yellow

crystals. Yield: 0.18 g, 31%. 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), 2.43 (br, 12H, CH2), 3.42 (br, 12H, CH2), 3.47 (br, 12H, CH2). 13C{1H} NMR (d5-

Pyr, 298 K): δ 6.82 (CH3), 53.23 (CH2), 68.13 (CH2), 68.95 (CH2). 29Si{1H} NMR (d5-Pyr,

298 K): -8.55 (Si(CH3)3). 23Na{1H} NMR (d5-Pyr, 298 K): -9.42 (Na). FTIR v/cm-1 (Neat):

477 (w), 607 (m), 660 (m), 689 (m), 797 (s), 860 (m), 880 (w), 963 (s), 1017 (m), 1082 (s),

1234 (m), 1258 (m), 1356 (w), 1448 (w), 2890 (w), 2961 (w). Raman ν/cm-1 (Neat, ≤15mW):

2946 (m), 2892 (s), 1459 (w), 1404 (w), 1278 (w), 1231 (w), 1134 (w), 1041 (w), 906 (w),

811 (s), 772 (w), 741 (w), 668 (m), 612 (s), 374 (m), 198 (s), 56 (s). Anal. Calc. for

C36H90N5O8Si6UNa: C 37.58, H 7.88, N 6.09%; Found: C 36.65, H 7.88, N 5.94%. UV/Vis

(25 mM, THF) λmax (ɛ/mol-1 cm-1): 496 (298) 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 (d5-Pyr, 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 (d5-Pyr, 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, ≤37.5mW): 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).

18

Anal. Calc. 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 (ɛ/mol-1 cm-1): 496 (408) nm.

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). 13C{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, ≤37.5mW): 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. Calc. 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 (ɛ/mol-1 cm-1): 495 (367) nm.

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). 13C{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

19

(m), 660 (s), 606 (s), 508 (w). Raman ν/cm-1 (Neat, ≤37.5mW): 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.

Calc. 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 (ɛ/mol-1 cm-1): 496 (370) nm.

Preparation of [UO2(N")3][Li(12-crown-4)2] (4Li)

THF (15ml) was added to a mixture of 1Li (0.771 g, 0.89 mmol) and 12-crown-4 (0.288 ml,

1.78 mmol) and allowed to stir for 18 hours. The resulting solution was filtered and reduced

in volume under reduced pressure to ca. 8 ml, then layered with hexane and stored at 5oC for

2 days to afford 4Li as orange crystals. Yield: 0.545 g, 55 %. 1H NMR (d5-Pyr, 294K): δ 0.78

(s, 54H, CH3), 3.66 (s, 32H, CH2). 13C {1H} NMR (d5-Pyr, 294K): δ 6.18 (CH3), 70.47 (CH2).

7Li NMR {1H} (d5-Pyr, 294K): δ 4.40 (Li). 29Si {1H} NMR (d5-Pyr, 294K): 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, ≤37.5mW): 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. Calc. 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 (ɛ/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, 294K): δ 0.79 (s, 54H, CH3), 3.65 (s, 40H, CH2).

13C{1H} NMR (d5-Pyr, 294K): δ 6.50 (CH3), 70.25(CH2). 23Na {1H} NMR (d5-Pyr, 294K): δ

20

0.52. 29Si {1H} NMR (d5-Pyr, 294K): 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, ≤15mW): 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. Calc. 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(ɛ/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, 294K): δ 0.79 (s, 54H, CH3), 3.55 (s, 40H, CH2).

13C{1H} NMR (d5-Pyr, 294K): δ 6.80 (CH3), 69.44 (CH2). 29Si{1H} NMR (d5- Pyr, 294K): 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, ≤75mW): 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. Calc. 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 (/ 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, 294K): δ 0.79 (s, 54H, CH3), 3.55 (s, 40H,

CH2). 13C {1H} NMR (d5-Pyr, 294K): δ 6.79 (CH3), 69.92 (CH2). 29Si{1H} NMR (d5-Pyr,

294K): δ -7.01 (Si(CH3)3). FTIR v/cm-1 (Neat): 2945 (br, w), 2885 (br, w), 1446 (w), 1354

21

(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, ≤75mW): 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. Calc. 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 (ɛ/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, 2mmol) gave 4Cs as orange crystals. Yield:

(0.382 g, 29 %). 1H NMR (d5-Pyr, 294K): δ 0.79 (s, 54H, CH3), 3.57 (s, 40H, CH2). 13C {1H}

NMR (d5-Pyr, 294K): δ 6.79 (CH3), 69.85 (CH2). 29Si{1H} NMR (d5-Pyr, 294K): 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,

≤75mW): 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. Calc.

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 (ɛ/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

either 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 MoKα 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

22

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 multi-scan 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 datasets 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.

References

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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.

Associated Content

Crystallographic details for 1Ka, 1Rb, 1Cs, 2Li, 2Na, 2K, 3M and 4M. This material is

30

available free of charge via the internet at http://pubs.acs.org. The X-ray crystallographic

information files (cif) for all the single crystal X-ray structures reported herein have been

deposited with the Cambridge Crystallographic Database (CCDC), numbers: 1827552-

1827567. These data are available free of charge at www.ccdc.cam.ac.uk. All other data are

available from the authors on request.

Figures and Schemes

Scheme 1. Synthetic routes to uranyl-tri-bis(silyl)amide complexes 1M-4M.

Figure 1. Molecular structures of 1Ka and the repeat units of 1Rb, and 1Cs at 150 K with

selective labelling and displacement ellipsoids are set to 25, 50, and 50%, respectively.

Hydrogen atoms and minor disorder components are omitted for clarity.

31

http://www.ccdc.cam.ac.uk/

http://pubs.acs.org/

Figure 2. Molecular structures of 1Rb and 1Cs with selective labelling highlighting the 1D-

polymeric nature of these compounds in the solid state. Displacement ellipsoids set to 50%

and hydrogen atoms and minor disorder components are omitted for clarity.

32

Figure 3. Molecular structures of 2Li, 2Na, and 2K with selective labelling and displacement

ellipsoids set to 25%. Hydrogen atoms and minor disorder components are omitted for

clarity.

33

Figure 4. Molecular structures of the 3M series with selective labelling and displacement

ellipsoids set to 25% except for 3Li which is set at 50%. Hydrogen atoms and minor disorder

components are omitted for clarity.

34

Figure 5. Molecular structures of the 4M series with selective labelling 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.

35

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-4M. 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

Entry U=O / Å U-N (mean) / Å O=U=O / ° 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

1LiPy21.810(11), 1.880(11) 2.285(13) 178.2(5) 1.83(3) 936

(935) 969 799 6.65 0.63

1Li - - - - 943 969 798 6.69 0.69

1Na 1.7.81(5), 1.810(5) 2.310(4) 179.31(18) 2.201(6) 938(928) 973 795(805) 6.63 0.68

1Ka 1.776(3), 1.804(3) 2.312(4) 179.43(15) 2.669(3) 940 973 799 6.68 0.66

1Rb 1.80(3) 2.28(3) 180(0) 2.74(3) 940 973 804 6.72 0.621Cs 1.792(13) 2.293(19) 180(0) 2.926(13) 941 971 804 6.72 0.632Li 1.784(4) 2.321(5) 179.77(19) - - 969 - - -2Na 1.791(3) 2.330(4) 179.79(14) - - 973 - - -2K 1.786(3) 2.323(3) 179.56(13) - - 973 - - -2Rb - - - - - 973 - - -2Cs - - - - - 971 - - -3Li 1.797(3) 2.325(4) 178.96(16) - 964 - 809 6.94 0.783Na 1.772(8) 2.329(10) 179.8(4) - 963 - 811 6.95 0.753K 1.8010(18) 2.322(2) 178.58(9) - 963 - 809 6.94 0.773Rb 1.802(14) 2.308(18) 180(0) - 964 - 810 6.95 0.773Cs 1.792(19) 2.308(19) 180(0) - 961 - 809 6.92 0.75

36

4Li 1.787(4) 2.319(5) 178.8(2) - 962 - 808 6.92 0.774Na 1.785(15) 2.320(19) 178.0(8) - 960 - 810 6.92 0.744K 1.786(12) 2.318(19) 180(0) - 964 - 811 6.96 0.764Rb 1.788(2) 2.320(4) 178.71(15) - 964 - 805 6.91 0.814Cs 1.789(3) 2.314(6) 178.0(2) - 964 - 805 6.91 0.81

Table 2. Experimental X-ray crystallographic details.

1Ka 1Rb 1Cs 2Li

Formula C30H78KN3O5Si6U C18H54N3ORbSi6U C18H54CsN3O2Si6U C42H102LiN3O8Si6U

Fw, g mol-1 1006.62 820.68 884.12 1190.77

Cryst size, mm 0.519 x 0.310 x 0.243 0.243 x 0.081 x 0.054 0.186 x 0.100 x 0.081 0.209 x 0.134 x 0.109

Crystal system triclinic trigonal trigonal monoclinic

Space group P-1 R-3c R-3c P21/n

Collection Temperature (K) 150(2) 120(2) 120(2) 150(2)

a, (Å) 11.7320(8) 18.6372(5) 18.5482(5) 17.1131(9)

b, (Å) 11.8934(7) 18.6372(5) 18.5482(5) 16.1172(9)

c, (Å) 18.0043(9) 17.5257(5) 17.9573(7) 23.6514(12)

α, (°) 88.667(4) 90 90 90

β, (°) 76.677(5) 90 90 107.815(5)

γ, (°) 89.377(5) 120 120 90

37

V, (Å3) 2443.9(2) 5271.9(3) 5350.2(4) 6210.6(6)

Z 2 6 6 4

ρcalc g cm-3 1.368 1.551 1.646 1.274

μ, mm-1 3.586 6.213 5.776 2.771

No. of reflections measuredd 15443 3582 3798 28693

No. of unique reflections, Rint 8874, 0.0361 1045, 0.0354 1395, 0.0361 12680, 0.0593

No. of reflections with F2 > 2s(F2) 7224 928 1115 8736

Transmission coefficient range 0.580-1.000 0.224-0.595 0.977-0.987 0.899-0.937

R, Rwa (F2 > 2s(F2)) 0.0399, 0.0623 0.0821, 0.1937 0.0701, 0.1695 0.0556, 0.0994

R, Rwa (all data) 0.0597, 0.0686 0.0882, 0.1963 0.0835, 0.1751 0.0961, 0.1162

Sa 1.003 1.183 1.238 1.005

Parameters, Restraints 480, 403 102, 156 102, 117 880, 1536

Max.,min. difference map, e Å-3 1.171, -1.170 5.983, -1.820 1.426, -1.461 0.670, -0.675

2Na 2K 3Li 3Na

Formula C46H110N3NaO9Si6U C46H110KN3O9Si6U C36H90LiN5O8Si6U C74H184N10Na2O16.50Si12U2

Fw, g mol-1 1278.92 1295.03 1134.63 2337.42


Crystal system orthorhombic orthorhombic monoclinic triclinic

Space group Pccn Pccn P21/c P-1

38


a, (Å) 25.3118(11) 25.4608(4) 23.0245(9) 15.7127(3)

b, (Å) 24.2190(10) 24.1287(4) 16.2392(7) 16.4229(3)

c, (Å) 21.5295(8) 21.5883(3) 30.9335(11) 23.2039(4)

α, (°) 90 90 90 87.8864(14)

β, (°) 90 90 110.086(4) 72.9160(15)

γ, (°) 90 90 90 88.9040(14)

V, (Å3) 13198.1(9) 13262.5(3) 10862.5(8) 5719.42(17)

Z 8 8 8 2

ρcalc g cm-3 1.287 1.297 1.388 1.357

μ, mm-1 2.62 8.848 3.166 3.016





R, Rwa (F2 > 2s(F2)) 0.0455, 0.0851 0.0399, 0.1085 0.0464, 0.0846 0.0813, 0.1604

R, Rwa (all data) 0.0947, 0.1005 0.0445, 0.1129 0.0841, 0.0986 0.1417, 0.1901

Sa 1.049 1.017 1.033 1.098


39


3K 3Rb 3Cs 4Li

Formula C40H98KN5O9Si6U C48H114N5O11RbSi6U C48H114CsN5O11Si6U C34H86LiN3O10Si6U

Fw, g mol-1 1238.9 1429.48 1476.92 1110.56


Crystal system monoclinic trigonal trigonal triclinic

Space group P21/c R-3m R3m P-1


a, (Å) 12.7132(3) 18.8256(5) 18.8360(4) 11.3846(3)

b, (Å) 31.7536(6) 18.8256(5) 18.8360(4) 15.3547(4)

c, (Å) 16.2067(3) 18.1448(5) 18.1445(4) 16.3194(3)

α, (°) 90 90 90 89.581(2)

β, (°) 111.979(2) 90 90 70.881(2)

γ, (°) 90 120 120 89.837(2)

V, (Å3) 6067.0(2) 5569.0(3) 5575.1(3) 2695.32(12)

Z 4 3 3 2

ρcalc g cm-3 1.356 1.279 1.32 1.368

μ, mm-1 2.909 8.254 11.215 3.19

40





R, Rwa (F2 > 2s(F2)) 0.0389, 0.0761 0.0668, 0.1757 0.0601, 0.1661 0.0513, 0.1374

R, Rwa (all data) 0.0542, 0.0802 0.0672, 0.1762 0.0610, 0.1679 0.0577, 0.1416

Sa 1.122 1.102 1.044 1.116



4Na 4K 4Rb 4Cs

Formula C38H94N3NaO12Si6U C38H94KN3O12Si6U C38H94N3O12RbSi6U C38H94CsN3O12Si6U

Fw, g mol-1 1214.72 1230.83 1277.2 1324.64


Crystal system monoclinic trigonal monoclinic monoclinic

Space group Pn R-3c C2/c I2/a


41

a, (Å) 16.6244(5) 16.9231(5) 29.048(3) 15.2644(4)

b, (Å) 35.3160(10) 16.9231(5) 17.2018(7) 17.2395(8)

c, (Å) 20.8018(7) 36.4058(9) 15.3135(13) 23.3984(10)

α, (°) 90 90 90 90

β, (°) 104.813(4) 90 127.610(13) 95.541(3)

γ, (°) 90 120 90 90

V, (Å3) 11807.0(7) 9029.4(6) 6061.7(12) 6128.5(4)

Z 8 6 4 4

ρcalc g cm-3 1.367 1.358 1.4 1.436

μ, mm-1 2.928 2.934 3.643 3.399





R, Rwa (F2 > 2s(F2)) 0.0780, 0.1654 0.0882, 0.2159 0.0409, 0.0692 0.0543, 0.0786

R, Rwa (all data) 0.1085, 0.1890 0.1199, 0.2300 0.0758, 0.0795 0.1125, 0.0961

Sa 0.953 1.231 1.049 1.009


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ToC Entry

43

A range of contact and separated ion pair complexes of a uranyl triamide are reported.

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research explorer | the university of manchester€¦ · web viewand whilst recently reported...

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