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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
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
Cryst size, mm 0.757 x 0.415 x 0.23 0.394 x 0.258 x 0.144 0.422 x 0.333 x 0.317 0.798 x 0.399 x 0.171
Crystal system orthorhombic orthorhombic monoclinic triclinic
Space group Pccn Pccn P21/c P-1
38
Collection Temperature (K) 150(2) 120(2) 100(2) 100(2)
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
No. of reflections measuredd 57741 33146 47913 175350
No. of unique reflections, Rint 16407, 0.0591 13203, 0.0385 24728, 0.0340 29814, 0.0638
No. of reflections with F2 > 2s(F2) 10464 11685 17128 18462
Transmission coefficient range 0.869-0.944 0.041-0.238 0.361-0.454 0.116-0.544
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
Parameters, Restraints 703, 750 843, 1815 1063, 435 1771, 7099
39
Max.,min. difference map, e Å-3 0.914, -0.653 2.003, -1.404 1.977, -1.788 2.511, -5.762
3K 3Rb 3Cs 4Li
Formula C40H98KN5O9Si6U C48H114N5O11RbSi6U C48H114CsN5O11Si6U C34H86LiN3O10Si6U
Fw, g mol-1 1238.9 1429.48 1476.92 1110.56
Cryst size, mm 0.295 x 0.143 x 0.124 0.188 x 0.128 x 0.067 0.335 x 0.240 x 0.200 0.289 x 0.257 x 0.156
Crystal system monoclinic trigonal trigonal triclinic
Space group P21/c R-3m R3m P-1
Collection Temperature (K) 125(2) 120(2) 120(2) 150(2)
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
No. of reflections measuredd 61788 8395 11127 27411
No. of unique reflections, Rint 20039, 0.0375 1364, 0.0908 2724, 0.0819 12340, 0.0472
No. of reflections with F2 > 2s(F2) 16564 1355 2677 11173
Transmission coefficient range 0.839-0.927 0.750-0.885 0.038-0.188 0.525-0.696
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
Parameters, Restraints 577, 0 111, 149 196, 367 514, 1
Max.,min. difference map, e Å-3 3.669, -1.792 3.057, -1.930 2.323, -2.613 2.785, -0.932
4Na 4K 4Rb 4Cs
Formula C38H94N3NaO12Si6U C38H94KN3O12Si6U C38H94N3O12RbSi6U C38H94CsN3O12Si6U
Fw, g mol-1 1214.72 1230.83 1277.2 1324.64
Cryst size, mm 0.379 x 0.198 x 0.149 0.616 x 0.303 x 0.218 0.412 x 0.245 x 0.100 0.184 x 0.113 x 0.056
Crystal system monoclinic trigonal monoclinic monoclinic
Space group Pn R-3c C2/c I2/a
Collection Temperature (K) 150(2) 150(2) 150(2) 150(2)
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
No. of reflections measuredd 48796 22650 14454 25178
No. of unique reflections, Rint 32299, 0.0554 2372, 0.0597 6996, 0.0395 7363, 0.0843
No. of reflections with F2 > 2s(F2) 23880 1642 4678 4320
Transmission coefficient range 0.499-0.711 0.151-0.359 0.434-0.776 0.705-0.876
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
Parameters, Restraints 2448, 4630 228, 511 423, 304 423, 753
42
Max.,min. difference map, e Å-3 2.270, -1.633 1.680, -1.829 0.838, -0.641 1.117, -1.080
ToC Entry
43
A range of contact and separated ion pair complexes of a uranyl triamide are reported.
44