Hexahalometallate salts of trivalent scandium, yttrium and lanthanum: Cation-anion association in the solid state and in solution

Article abstract of DOI:10.1039/c6nj01068g

The hexahalide salts, [NⁿBu₄]₃[LaCl₆], [BMPYRR]₃[LaCl₆] (BMPYRR = 1-butyl-1-methylpyrrolidinium), [EMIM]₃[MX₆] (EMIM = 1-ethyl-3-methylimidazolium; M = La, X = Cl, Br, I; M = Sc, Y, Ce, X = Cl) and [EDMIM]₃[MX₆] (EDMIM = 1-ethyl-2,3-dimethylimidazolium; M = Y, X = Cl; M = La, X = Cl, I) have been prepared and X-ray crystal structures determined for several of them, with a view to probing the effect of varying the trivalent metal ion, the halide and the counter-cation on the structures adopted in the solid state. The crystal structures of the EMIM and EDMIM salts show extensive H-bonding between the halide ligands and organic cations; based upon the H-bonding distances, this appears to be strongest for the [EMIM]₃[MCl₆] salts, becoming progressively weaker for heavier metal ion or halide. In terms of the cations, changing from EMIM to EDMIM also reduces the strength of the H-bonding. The strength of the cation-anion pairing in solution has also been probed in solution via NMR spectroscopy where possible (⁴⁵Sc, ⁸⁹Y and ¹⁸⁹La) and, for the EMIM salts, via the shift of δ(H2) relative to [EMIM]Cl at a standard concentration. The trends observed in solution mirror those determined in the solid state.

Full text of DOI:10.1039/c6nj01068g

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Hexahalometallate salts of trivalent scandium,
yttrium and lanthanum: cation–anion association
in the solid state and in solution†
Cite this:DOI: 10.1039/c6nj01068g
Martin J. D. Champion, William Levason, David Pugh and Gillian Reid*
The hexahalide salts, [NnBu4]3[LaCl6], [BMPYRR]3[LaCl6] (BMPYRR = 1-butyl-1-methylpyrrolidinium), [EMIM]3[MX6]
(EMIM = 1-ethyl-3-methylimidazolium; M = La, X = Cl, Br, I; M = Sc, Y, Ce, X = Cl) and [EDMIM]3[MX6]
(EDMIM = 1-ethyl-2,3-dimethylimidazolium; M = Y, X = Cl; M = La, X = Cl, I) have been prepared and
X-ray crystal structures determined for several of them, with a view to probing the effect of varying
the trivalent metal ion, the halide and the counter-cation on the structures adopted in the solid state.
The crystal structures of the EMIM and EDMIM salts show extensive H-bonding between the halide
ligands and organic cations; based upon the H-bonding distances, this appears to be strongest for
the [EMIM]3[MCl6] salts, becoming progressively weaker for heavier metal ion or halide. In terms of the
cations, changing from EMIM to EDMIM also reduces the strength of the H-bonding. The strength of the
cation–anion pairing in solution has also been probed in solution via NMR spectroscopy where possible
Received (in Victoria, Australia)
6th April 2016,
Accepted 20th June 2016
DOI: 10.1039/c6nj01068g
(
45Sc, 89Y and 189La) and, for the EMIM salts, via the shift of d(H2) relative to [EMIM]Cl at a standard
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concentration. The trends observed in solution mirror those determined in the solid state.
the [MX6]3À trianions incorporating a range of trivalent metal
ions from group 3 and the lanthanides, in the anticipation that
Introduction
In the course of our work on electrodeposition of metals and the trianionic charge would give rise to significant cation–anion
1
semiconductors from unusual low polarity solvents, such as CH2Cl2
association both in the solid state and in low polarity solvents.
and supercritical CH2F2,2 we have established that halometallates We report the synthesis of a series of halometallate anion salts
can often offer both the solubility and extent of dissociation into of scandium, yttrium and several lanthanides. All complexes
discrete cations and anions to be highly effective as reagents for have been characterised by NMR spectroscopy (1H, 45Sc, 89Y and
delivering the elements of choice. Taking germanium as an example, 139La as appropriate), IR spectroscopy, elemental analysis and,
we have shown that the cation, halide and anion charge all play an in several cases, single-crystal X-ray diffraction. To gain further
important role in determining the extent of cation–halogermanate insight into the cation–anion pairing in these species, we have
anion association both in the solids and in solution.3 While we have explored the effects that systematic changes in the counter-
often used quaternary ammonium salts for this purpose, recent work cation, metal ion and halide co-ligands have on the solid-state
on the electrodeposition of elemental germanium from supercritical structures adopted and the spectroscopic behaviour of these
CH2F2 has established that using the 1-ethyl-3-methylimidazolium halometallate salts in MeCN (and where possible, CH2Cl2)
(EMIM) cation leads to improved quality of the electrodeposited solution.
germanium,4 and hence this and other substituted imidazolium
A small number of earlier studies report structural data on
cation salts, which are also used extensively for electrodeposition halometallate salts of the Ln(III) ions. The examples most pertinent
from ionic liquids,5 have become of greater importance in this area to the present study are [EMIM]3[LnCl6] (Ln = La, Pr, Nd,
of work.
Sm, Eu) grown from hydrated LnCl3 in [EMIM]Cl at 110 1C,6,7
In order to gain a better understanding of the cation–anion [MPPYRR]3[NdI6] (MPPYRR = 1-methyl-1-propylpyrrolidinium),8
association in halometallate salts, we describe here a study of and [SEt3]3[LnI6] (Ln = Nd, Sm), obtained from reaction of LnI2
with the ionic liquid [SEt3][NTf2] (NTf2 = bis-(trifluoromethane-
sulfonyl)imide).9 A very recent study has described the structures
of a series of [BMIM]3[CeX6] salts (BMIM = 1-butyl-3-methylimid-
School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
E-mail: G.Reid@soton.ac.uk
† CCDC 1472564 ([EMIM]3[ScCl6]), 1472565 ([EMIM]3[YCl6]), 1472566 ([EMIM]3[CeCl6]),
azolium), also obtained directly from CeX3 in the [BMIM]X ionic
1472567 ([EMIM]3[LaBr6]), 1472568 ([EMIM]3[LaI6]), 1472569 ([EDMIM]3[YCl6]), 1472570
liquids, which are reported to exhibit intense Ce3+ based 5d–4f-
([EDMIM]3[LaCl6]) and 1472571 ([EDMIM]3[LaI6]). For crystallographic data in CIF
or other electronic format see DOI: 10.1039/c6nj01068g
centred emission.10
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Results and discussion
Preparations
anions were observed in the solid state with different arrange-
ments of hydrogen bonding cations, including bifurcated
hydrogen bonding, accounting for the difference. Most of the
hydrogen bonding occurs through the acidic NCN proton of the
imidazolium ring but interactions through the NCCN backbone
protons (which are less acidic) were also observed, resulting in
an extended structure in the solid state (Fig. 2(b)).
The hexahalide salts, [NnBu4]3[LaCl6], [BMPYRR]3[LaCl6] (BMPYRR =
1-butyl-1-methylpyrrolidinium, [EMIM]3[MX6] (M = La, X = Cl, Br, I;
M = Sc, Y, Ce, X = Cl) and [EDMIM]3[MX6] (EDMIM = 1-ethyl-2,3-
dimethylimidazolium; M = Y, X = Cl; M = La, X = Cl, I), were selected
for study on the basis that they would allow us to probe the effects
that the cation (extent of H-bonding or not), the metal ion size and
the halide type have upon the solid state and solution properties.
The salts were readily prepared as powdered solids in good yield by
treatment of anhydrous MX3 with three (or slightly greater) molar
equivalents of the appropriate halide salt of the organic cation,
[NnBu4]+, [BMPYRR]+, [EMIM]+ or [EDMIM]+) in MeCN, acetone or
CH2Cl2 solution, and their formulations were confirmed by micro-
analyses. The isolated salts are moderately soluble in MeCN and, in
some cases, in CH2Cl2 solution. Crystals of several examples with
EMIM and EDMIM cations were obtained by vapour diffusion of
Et2O into a concentrated MeCN solution of the relevant salt.
Here it should be noted that in our experience, the criteria
used for assigning the strength of hydrogen bonds13 are not
always applicable where metal complexes with heavy halogens
are acting as acceptors. Other important factors such as crystal
packing effects and p-bonding interactions can have a significant
effect on the donor–acceptor distances and donor–hydrogen–
acceptor (DHA) angles which are used to classify ‘strong’,
‘moderate’ or ‘weak’ hydrogen bonds. Typically, these DHA
interactions are quantified via the crystallographically deter-
mined DÁ Á ÁA (CÁ Á ÁX) distances. The radii of BrÀ and especially
IÀ also have an effect on the CÁ Á ÁX bond lengths. Nonetheless,
for a given halide, the shortest CÁ Á ÁX distances for the [EMIM]3-
[LaX6] series of complexes (Table 1) occur where the NCN proton
(H2) acts as the donor, consistent with it being the most acidic
proton on the imidazolium ring. The CÁ Á ÁX distances where
the backbone NCCN protons (H4/H5) act as donors are typically
0.1–0.2 Å longer, implying weaker hydrogen bonding. In all cases
the DHA angles are also generally greater than 1301, hence we
assign these as ‘moderate’ hydrogen bonds.
Varying the halide
In order to assess the effect of varying the halide on the nature
of the hydrogen bonding interactions, the [EMIM]3[LaX6] system
(X = Cl, Br, I) was chosen. [EMIM]3[LaCl6] had previously been
synthesised and crystallographically characterised.6,7 Crystals of the
bromide (Fig. 1) and iodide (Fig. 2) analogues were obtained by slow
diffusion of Et2O into an MeCN solution. Surprisingly these are
rare examples of discrete [LaX6]3À anions with organic cations:
Varying the metal
[2,4,6-trimethylpyridinium]4[LaCl6]Cl11 and [BMPYRR]4[LaI6][NTf2]12 Another variable to assess in this series of complexes is the
are the only other structurally authenticated complexes. nature of the metal ion. By choosing a range of trivalent metals
[EMIM]3[LaCl6] and [EMIM]3[LaBr6] are isomorphous and for [EMIM]3[MCl6] (M = Sc, Y, La, Ce) it is possible to vary the
isostructural, whereas [EMIM]3[LaI6] crystallises with a different unit ionic radius, and hence the charge : radius ratio, and observe
cell, presumably reflecting the increased steric requirements of the effect on the hydrogen bonding. Addition of [EMIM]Cl to
IÀ over BrÀ and ClÀ. Nonetheless, in each case the [LaX6]3À anion MCl3 led to the formation of crystalline samples of [EMIM]3-
is octahedrally coordinated with six halides comprising the primary [ScCl6] (Fig. 3), [EMIM]3[YCl6] (Fig. 4) and [EMIM]3[CeCl6]
coordination sphere. Two crystallographically independent [LaX6]3À (Fig. 5).
Fig. 1 ORTEP representation of [EMIM]3[LaBr6] showing the hydrogen bonding (dotted lines) surrounding the La1-centred cation (left) and the La2-
centred cation (right). Displacement ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å): La1–Br1 2.9371(13), La1–Br2 2.9296(16),
La1–Br3 2.9534(13), La2–Br4 2.9477(15), La2–Br5 2.9484(14), La2–Br6 2.9524(13). Symmetry codes: (i) 2 À x, 1 À y, 1 À z; (ii) 1 À x, 1 À y, Àz.
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Fig. 2 (a) ORTEP representation of [EMIM]3[LaI6] showing the hydrogen bonding (dotted lines) surrounding the La1-centred cation (left) and the La2-
centred cation (right). Displacement ellipsoids are drawn at the 50% probability level and H atoms not involved in hydrogen bonding are omitted for
clarity. Selected bond lengths (Å): La1–I1 3.1557(5), La1–I2 3.1448(4), La1–I3 3.1930(8), La2–I4 3.1988(5), La2–I5 3.1663(5), La2–I6 3.1733(10). Symmetry
codes: (i) 1 À x, 3 À y, 1 À z; (ii) Àx, 2 À y, 1 À z; (iii) x, 2.5 À y, 1.5 À z; (iv) 1 À x, 0.5 À y, 1 À z; (v) 1 À x, 0.5 À y, 1.5 À z. (b) Representation of [EMIM]3[LaI6]
showing the extended structure generated by the hydrogen bonding (dotted lines).
The Sc and Y complexes are isostructural and isomorphous, However, there is a small increase in the hydrogen bond lengths
with a slight increase in cell parameters owing to the increase involving H2 for [EMIM]3[YCl6] compared to [EMIM]3[ScCl6].
in metal ionic radius (Sc = 0.745 Å, Y = 0.90 Å for 6-coordinate These are notably shorter than the equivalent bonds in [EMIM]3-
complexes).14 The known lanthanide examples are structurally [LaCl6], continuing the same trend. Trifurcated hydrogen bonding
different, but within the series (including La, Eu, Gd, Nd, Pr and is present in [EMIM]3[CeCl6] through C13 (Fig. 5).
Sm analogues) they are all isomorphous and isostructural7 and the
Varying the cation
cell parameters for [EMIM]3[CeCl6] fit well with this trend.
In the solid state all the metal centres are six-coordinate Altering the nature of the cation can have a marked effect on the
regular octahedra. There is only one metal environment in the structural properties of the complexes. In order to probe this effect
asymmetric unit of [EMIM]3[ScCl6] and [EMIM]3[YCl6] and the the [CATION]3[LaCl6] system was initially chosen (CATION = EMIM,
hydrogen bonding interactions are very similar (Table 2). Despite EDMIM, NnBu4 and BMPYRR). Complexes were prepared by adding
the decreased charge:radius ratio for Y over Sc, the hydrogen a slight excess of [CATION]Cl to LaCl3 in MeCN, resulting in a series
bonds through H4/5 are identical within experimental error. of compounds where the hydrogen bonding interactions should be
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Table 1 Hydrogen bond data for the [EMIM]3[LaX6] series of compounds
[EMIM]3[LaCl6]a
[EMIM]3[LaBr6]
[EMIM]3[LaI6]
Angle
Length
(Å)
Angle Length Angle Length
(1) (Å) (1) (Å)
(1)
CÁ Á ÁX (H2)
3.557(8) 152.2
3.479(6) 131.6
3.393(4) 120.2
3.612(4) 150.2
3.579(12) 134.2 3.942(5) 139.8
3.659(10) 153.8 3.758(5) 134.0
3.765(17) 134.7 3.864(5) 134.9
3.825(5) 160.4
CÁ Á ÁX (H4/5) 3.635(5) 150.3
3.614(6) 148.4
3.723(12) 121.6 3.974(5) 136.7
3.683(11) 139.8 3.972(5) 113.5
3.744(12) 118.3 3.796(5) 143.2
3.755(11) 146.8 3.894(5) 119.0
3.708(12) 145.1 3.830(5) 124.0
3.693(12) 153.7 4.210(5) 172.5
3.708(16) 143.9
3.692(5) 146.7
3.632(5) 145.9
3.564(6) 137.5
a
Data from ref. 7.
Fig. 4 ORTEP representation of [EMIM]3[YCl6] showing the hydrogen
bonding (dotted lines). Displacement ellipsoids are drawn at the 50%
probability level and hydrogen atoms not involved in hydrogen bonding
are omitted for clarity. Selected bond lengths (Å): Y–Cl1 2.6541(12),
Y–Cl2 2.614(1), Y–Cl3 2.6185(12), Y–Cl4 2.640(1), Y–Cl5 2.6515(14),
Y–Cl6 2.6524(14). Symmetry codes: (i) 1 À x, 1 À y, z À 0.5; (ii) 0.5 À x,
y À 0.5, z À 0.5; (iii) x, y À 1, z; (iv) x, y, z À 1.
A comparison between the [EMIM]+ and [EDMIM]+ cations can
also be drawn for the [YCl6]3À and [LaI6]3À salts. The structures of
[EDMIM]3[YCl6] and [EDMIM]3[LaI6] are shown in Fig. 7 and 8,
respectively.
[EDMIM]3[YCl6] and [EDMIM]3[LaCl6] are isomorphous and
isostructural, whereas [EMIM]3[YCl6] and [EMIM]3[LaCl6] crystallise
in different space groups. This suggests that the hydrogen bonding
interactions play a greater role in the crystal packing arrangements
for the [EMIM]+ salts. The CÁÁÁCl (H4/H5) distances (Table 3) are
not notably different between [EMIM]3[YCl6] and [EDMIM]3[YCl6].
For [EDMIM]3[LaI6] two different [LaX6]3À environments are
apparent, with one iodine acting as an acceptor to five different
donor hydrogens. However, the CÁ Á ÁI distances (Table 3) are not
notably different between the EMIM and EDMIM compounds.
Fig. 3 ORTEP representation of [EMIM]3[ScCl6] showing the hydrogen
bonding (dotted lines). Displacement ellipsoids are drawn at the 50%
probability level and hydrogen atoms not involved in hydrogen bonding
are omitted for clarity. Selected bond lengths (Å): Sc–Cl2 2.479(1),
Sc–Cl3 2.513(1), Sc–Cl4 2.5066(7), Sc–Cl5 2.520(1), Sc–Cl6 2.4735(8),
Sc–Cl7 2.522(1). Symmetry codes: (i) 1 À x, Ày, z À 0.5; (ii) x À 0.5, 0.5 À y, z;
(iii) x, y À 1, z.
moderate (EMIM), weak (EDMIM) and non-existent (NnBu4,
Spectroscopic characterisation and comparisons
BMPYRR). The difference between the [EDMIM]+ cation and In keeping with our previous observations for [GeCl6]2À anions,3
the [EMIM]+ cation is the presence of a methyl group at the C2 the chemical shift of the H2 proton in the 1H NMR spectrum was
position, thus the most acidic protons are now on the backbone used to indicate the strength of the hydrogen bonding in solution
of the imidazolium ring. This was expected to significantly influence (Table 4).
the hydrogen bonding. The structure of [EDMIM]3[LaCl6] is
shown in Fig. 6.
From the NMR data it is apparent that the chemical shift of
the signal associated with the H2 proton shifts to low frequency
Structural characterisation of [EDMIM]3[LaCl6] revealed that for the heavier halides. This correlates with decreasing strength
the [LaCl6]3À trianion was stabilised by hydrogen bonding of the solution phase hydrogen bonding interactions upon
through five associated [EDMIM]+ cations. The CÁ Á ÁCl distances changing from Cl to I. The chemical shifts of the less acidic
were slightly shorter than the corresponding CÁ Á ÁCl distances H4/5 protons are not affected by changing the halide, suggesting
for [EMIM]3[LaCl6], suggesting that hydrogen bonding through that the salts are completely dissociated in solution. This is con-
the backbone protons may be slightly stronger when no H2 sistent with the trend observed for [EMIM][GeX3] (X = Cl, Br, I).3
proton is present. However, 1H NMR data (below) show that the
For the [MX6]3À salts, 45Sc, 89Y and 139La NMR spectra were
chemical shifts for H4/5 are consistent with complete dissociation also obtained (Table 5). All complexes were soluble in MeCN at
of the molecule in CD3CN solution. The La–Cl bond lengths are approximate 10–15 mM concentration. The [NnBu4]+ salt was
comparable to those observed for [EMIM]3[LaCl6].
soluble at a similar concentration in CH2Cl2, whereas the
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Fig. 5 ORTEP representation of [EMIM]3[CeCl6] showing the hydrogen bonding (dotted lines) surrounding the Ce1-centred cation (left) and the Ce2-
centred cation (right). Displacement ellipsoids are drawn at the 50% probability level and H atoms not involved in hydrogen bonding are omitted for
clarity. Selected bond lengths (Å): Ce1–Cl1 2.7872(16), Ce1–Cl2 2.7514(17), Ce1–Cl3 2.7738(16), Ce2–Cl4 2.7755(17), Ce2–Cl5 2.7752(17), Ce2–
Cl6 2.7722(17). Symmetry codes: (i) Àx, Ày, Àz; (ii) À1 À x, Ày, 1 À z; (iii) Àx, 0.5 + y, 0.5 À z; (iv) x, À0.5 À y, 0.5 + z; (v) Àx, y À 0.5, 0.5 À z.
Table 2 Hydrogen bond data for the [EMIM]3[MCl6] series of compounds
prepared in this study
[EMIM]3[ScCl6]
[EMIM]3[YCl6]
[EMIM]3[CeCl6]
Angle
Length
(Å)
Angle Length Angle Length
(1) (Å) (1) (Å)
(1)
CÁ Á ÁX (H2)
3.506(3) 149.5 3.547(4) 146.6 3.547(7) 150.8
3.496(3) 131.3 3.531(5) 130.0 3.425(7) 132.4
3.407(3) 138.1 3.422(5) 135.9 3.333(7) 117.1
3.604(3) 135.2 3.650(4) 134.6 3.569(8) 141.9
3.548(3) 146.8 3.588(5) 145.0
CÁ Á ÁX (H4/5) 3.586(3) 166.7 3.584(5) 165.0 3.568(7) 150.4
3.692(3) 152.5 3.695(4) 153.1 3.583(7) 143.2
3.604(3) 135.6 3.604(5) 135.8 3.622(8) 142.7
3.434(3) 131.7 3.459(4) 128.6 3.542(8) 147.2
3.383(3) 135.1 3.365(5) 136.2 3.512(7) 139.7
Fig. 6 ORTEP representation of [EDMIM]3[LaCl6] showing the hydrogen
bonding (dotted lines). Displacement ellipsoids are drawn at the 50%
probability level. Selected bond lengths (Å): La–Cl1 2.7963(7), La–Cl2 2.7582(6),
La–Cl3 2.8029(6), La–Cl4 2.7950(7), La–Cl5 2.8262(6), La–Cl6 2.7742(5).
Symmetry codes: (i) 1 À x, 1 À y, 1 À z; (ii) x À 1, y, z.
[EMIM]+, [BMPYRR]+ and [EDMIM]+ salts were poorly soluble in
CH2Cl2. For the [LaCl6]3À salts a small high frequency shift in
d139La occurs as the cation changes along the series: [NnBu4]+ -
[BMPYRR]+ - [EDMIM]+ - [EMIM]+ in both MeCN and CH2Cl2
solution, but given the large 139La NMR chemical shift range,
these differences may not be significant. The 139La NMR resonance
shifts to high frequency as the halide becomes heavier; the
[LaI6]3À system showing a very broad resonance at B1400 ppm
(W1/2 B 12 000 Hz). The yttrium salts show no 89Y NMR
resonance at room temperature in MeCN, presumably due to
chloride exchange. However, cooling to 233 K reveals a sharp
singlet for each compound.
The shortest CÁÁÁX distances for the [EMIM]3[MX6] series involve
the NCN (H2) proton, with much weaker interactions to the H4/H5
protons. Despite the decreased charge : radius ratio along the series
from Sc to Y to La, the hydrogen bonds through H4/5 are
unaffected. However, there is a small increase in the hydrogen
bond lengths involving H2 along the same series.
Substitution of the H2 proton with a Me group in the
EDMIM cation has a significant influence on the cation–anion
interactions in the solid state. The structure of [EDMIM]3[LaCl6]
revealed five associated [EDMIM]+ cations and the CÁ Á ÁCl
Conclusions
All of the salts are based upon six-coordinate [MX6]3À units, and distances involving H4/H5 were shorter than those for
for those containing EMIM and EDMIM cations, significant [EMIM]3[LaCl6].
C–HÁ Á ÁX hydrogen-bonding interactions to the substituted
imidazolium cations are evident from crystallographic studies. bonding to the EMIM (H2) cations becomes weaker as the
The solution 1H NMR trends indicate that the hydrogen
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dried in vacuo at 100 1C for 4 hours and stored in a glove box.
[EDMIM]I was prepared by stirring a solution of [EDMIM]Cl and
NaI in water for 4 hours, then extracting into CH2Cl2 followed by
drying in vacuo at 100 1C for 4 hours. MeCN and CH2Cl2 were
dried prior to use from CaH2. Infrared spectra were recorded as
Nujol mulls between CsI plates using a Perkin-Elmer Spectrum
100 spectrometer over the range 4000–200 cmÀ1. Raman spectra
were recorded from powdered solid samples using a Perkin-
1
Elmer FT-Raman 2000R with a Nd:YAG laser. H NMR spectra
were recorded in CD2Cl2 and CD3CN using a Bruker DPX400
spectrometer and are referenced to the residual protio solvent.
45Sc, 89Y and 139La NMR spectra were also recorded in CD2Cl2 or
CD3CN on a Bruker DPX400 spectrometer and are referenced
to 0.1 mol dmÀ3 solutions of the chlorides in D2O solutions at
pH = 1. For yttrium-89 NMR spectra a 3 s pulse delay was used
and TEMPO (2,2,6,6-tetramethylpiperidine-oxyl) was added as
relaxation agent. Microanalyses were undertaken by Medac Ltd
or London Metropolitan University.
Fig. 7 ORTEP representation of [EDMIM]3[YCl6] showing the hydrogen
bonding (dotted lines). Displacement ellipsoids are drawn at the 50%
probability level and hydrogen atoms not involved in hydrogen bonding
are omitted for clarity. Selected bond lengths (Å): Y–Cl1 2.6580(5),
Y–Cl2 2.6398(5), Y–Cl3 2.6496(5), Y–Cl4 2.6800(5), Y–Cl5 2.6464(5),
Y–Cl6 2.6167(5). Symmetry codes: (i) Àx, 2 À y, Àz; (ii) x + 0.5, 1.5 À y,
z À 0.5; (iii) Àx, 1 À y, Àz; (iv) 1 À x, 1 À y, Àz.
Preparations
[NnBu4]3[LaCl6]. LaCl3 (100 mg, 0.408 mmol) was suspended
in dichloromethane (10 mL) in a Schlenk flask and a solution of
[NnBu4]Cl (396 mg, 1.43 mmol) in acetone (10 mL) added. The
mixture was stirred until all the solids had dissolved. Diethyl ether
(20 mL) was added slowly and a white solid precipitated which was
filtered and dried under vacuum. Yield: 345 mg, 79%. Raman
(solid): 262 cmÀ1 (A1g [LaCl6]3À). 1H NMR (CD3CN, 300 K): d =
3.08–3.14 (m, [2H]), 1.55–1.66 (m, [2H]), 1.30–1.42 (m, [2H]), 0.97
(t, J = 7.35 Hz, [3H]). 139La NMR (CH3CN/CD3CN, 300 K): d = 846
halide becomes heavier, while the EDMIM salts appear to be
completely dissociated in solution.
Experimental
All preparations were carried out using standard Schlenk (s, W1/2 = 800 Hz). Anal. required for C48H108Cl6LaN3: C, 53.43;
techniques under a N2 atmosphere. Anhydrous MCl3 (M = La, Ce) H, 10.09; N, 3.89%. Found: C, 53.29; H, 9.92; N, 4.04%.
were obtained by reacting hydrated MCl3 (Sigma) with excess SOCl2,
[EDMIM]3[LaCl6]. Synthesised in an analogous way, using
then drying in vacuo. Anhydrous ScCl3, YCl3, LaBr3 and LaI3 were LaCl3 (100 mg, 0.408 mmol) and [EDMIM]Cl (197 mg, 1.22 mmol).
obtained from Alfa and used as received. [EMIM]X (X = Cl, Br, I), White crystalline product. Yield: 213 mg, 72%. Raman (solid):
[EDMIM]Cl, [NnBu4]Cl and [BMPYRR]Cl were obtained from Sigma, 244 cmÀ1 (A1g [LaCl6]3À).1H NMR (CD3CN, 300 K): d = 7.36
Fig. 8 ORTEP representation of [EDMIM]3[LaI6] showing the hydrogen bonding (dotted lines) surrounding the La1-centred cation (left) and the La2-
centred cation (right). Displacement ellipsoids are drawn at the 50% probability level and H atoms not involved in hydrogen bonding are omitted for
clarity. Selected bond lengths (Å): La1–I1 3.1800(7), La1–I2 3.1545(6), La1–I3 3.1903(7), La2–I4 3.1779(5), La2–I5 3.1566(5), La2–I6 3.1870(5). Symmetry
codes: (i) 1 À x, Ày, 1 À z; (ii) Àx, À1 À y, Àz; (iii) x, y À 1, z; (iv) Àx, À1 À y, 1 À z; (v) 1 À x, À1 À y, 1 À z; (vi) x, y, 1 + z; (vii) x, 1 + y, z.
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Yield: 245 mg, 77%. Raman (solid): 240 cmÀ1 (A1g [LaCl6]3À).
1H NMR (CD3CN, 300 K): d = 3.44–3.59 (m, [4H]), 3.30–3.35
(m, [2H]), 3.03 (s, [3H]), 2.18 (br. s, [4H]), 1.68–1.78 (m, [2H]),
1.32–1.45 (m, [2H]), 0.96 (t, J = 7.35 Hz, [3H]). 139La NMR
(CH3CN/CD3CN): d = 855 (s, W1/2 = 500 Hz). Anal. required for
Table 3 Hydrogen bond data for [EDMIM]3[YCl6], [EDMIM]3[LaCl6] and
[EDMIM]3[LaI6]
[EDMIM]3[YCl6]
[EDMIM]3[LaCl6]
[EDMIM]3[LaI6]
Length
(Å)
Angle Length Angle Length
(1) (Å) (1) (Å)
Angle
(1)
C
27H60Cl6LaN3: C, 41.66; H, 7.77; N, 5.40%. Found: C, 41.81;
CÁ Á ÁX (H4/5) 3.542(2) 142.4 3.580(2) 149.6
3.693(2) 123.8 3.515(2) 136.6
3.388(2) 129.8 3.521(2) 148.9
3.482(2) 145.1 3.686(2) 122.5
3.520(2) 149.9 3.455(2) 125.8
3.544(2) 150.2 3.601(2) 112.0
3.577(2) 122.6 3.524(2) 143.0
3.948(3) 118.8
3.956(3) 118.5
3.933(3) 139.2
3.775(3) 125.2
3.883(3) 124.3
3.892(3) 124.8
3.883(3) 115.3
H, 7.63; N, 5.50%.
[EMIM]3[LaCl6]. LaCl3 (100 mg, 0.408 mmol) was suspended
in MeCN (5 mL) and a solution of [EMIM]Cl, (210 mg,
1.43 mmol) in MeCN (5 mL) was added. The mixture was
heated briefly and then stirred for 1 hour. The resulting
suspension was filtered and diethyl ether (10 mL) was added
to the filtrate, leading to the precipitation of a white crystalline
product. This was allowed to settle, the solvent removed via
cannula and the solid was then dried under vacuum. Yield:
185 mg, 66%. Raman: 240 cmÀ1 (A1g [LaCl6]3À). 1H NMR
(CD3CN, 300 K): d = 9.27 (s, [H]), 7.39 (s, [H]), 7.34 (s, [H]),
4.33 (q, J = 7.16 Hz, [2H]), 3.96 (s, [3H]), 1.46 (t, J = 7.16 Hz,
[3H]). 139La NMR (CH3CN/CD3CN): d = 867 (s, W1/2 = 400 Hz).
Anal. required for C18H33Cl6LaN6: C, 31.56; H, 4.85; N, 12.27%.
Found: C, 31.31; H, 4.67; N, 12.07%.
[EMIM]3[LaBr6]. Synthesised in an analogous way, using
LaBr3 (100 mg, 0.264 mmol) and [EMIM]Br (151 mg, 0.792 mmol).
White solid. Yield: 143 mg, 57%. H NMR (CD3CN, 300 K): 8.93
(s, [H]), 7.42 (s, [H]), 7.37 (s, [H]) 4.27 (q, J = 7.34 Hz, [2H]), 3.91
(s, [3H]), 1.47 (t, J = 7.34 Hz, [3H]). 139La NMR (CH3CN/CD3CN,
300 K): d = 1095 (s, W1/2 = 1200 Hz). Anal. required for
C18H33Br6LaN6:C, 22.71; H, 3.49; N, 8.83%. Found: C, 22.57; H,
3.39; N, 8.74%.
Table 4 Effect of [MX6]3À on the N–CH–N 1H NMR shift in CD3CN
solution
d(1H)a/ppm
Compound
N–CH–N
Db
[EMIM]3[LaCl6]
[EMIM]3[LaBr6]
[EMIM]3[LaI6]
[EMIM]3[CeCl6]
[EMIM]3[YCl6]
[EMIM]3[ScCl6]
[EMIM]Cl
9.27
8.93
8.61
9.77
9.26
9.41
8.82
8.84
+0.45
+0.11
À0.21
+0.95
+0.44
+0.59
—
[EMIM]Br
—
1
a
b
6.8 mM solutions in CD3CN. Change in shift compared with
[EMIM]Cl at the same concentration in CD3CN.
Table 5 Selected NMR spectroscopic data for [CATION]3[MX6]
d (ppm)
W1/2 (Hz)
d (ppm)
W1/2 (Hz)
[EMIM]3[LaI6]. Synthesised in an analogous way, using LaI3
(150 mg, 0.289 mmol) and [EMIM]I (240 mg, 1.01 mmol). After
filtering, the solvent volume was reduced to approximately 25%
and diethyl ether was added. Large colourless crystals suitable
for X-ray diffraction were grown overnight. Yield: 180 mg, 46%.
1H NMR (CD3CN, 300 K): d = 8.61 (s, [H]), 7.41 (s, [H]) 7.36
(s, [H]) 4.19 (q, J = 7.16 Hz, [2H]), 3.84 (s, [3H]), 1.46 (t, J =
7.35 Hz, [3H]). Raman: 110 cmÀ1 (A1g [LaI6]3À). Anal. required
for C18H33I6LaN6: C, 17.52; H, 2.70; N, 6.81%. Found: C, 17.38;
H, 2.65; N, 6.94%.
MeCN
CH2Cl2
Salt
[NnBu4]3[LaCl6]
[BMPYRR]3[LaCl6]
[EDMIM]3[LaCl6]
[EMIM]3[LaCl6]
[EMIM]3[LaBr6]
[EMIM]3[LaI6]
846
855
864
800
500
600
872
880
n.o.b
892
n.o.b
n.o.b
—
1200
300
—
300
—
—
—
867
400
1095
B1400
407
1200
12 000
—
[EMIM]3[YCl6]a
[EDMIM]3[YCl6]a
[EMIM]3[ScCl6]
401
254
—
—
—
—
—
170
a
b
Spectrum recorded at 233 K. n.o. = not observed due to low
solubility.
[EDMIM]3[LaI6]. Synthesised in an analogous way. Yield:
55%. White crystalline solid. 1H NMR (CD3CN, 300 K): d =
7.36 (d, [2H], J = 1.96 Hz), 4.08 (q, J = 7.34 Hz, [2H]), 3.70
(s, [2H]), 4.12 (q, J = 7.16 Hz, [2H]), 3.75 (s, [3H]), 2.54 (s, [3H]), (s, [3H]), 2.51 (s, [3H]), 1.38 (t, J = 7.34 Hz, [3H]). Anal. required
1.39 (t, J = 7.34 Hz, [3H]), (CD2Cl2, 300 K): d = 7.64 (d, J = 2.20 Hz, for C21H39I6LaN6: C, 19.77; H, 3.08; N, 6.59%. Found: C, 19.60;
[H]), 7.46 (d, J = 2.20 Hz, [H]), 4.23 (q, J = 7.5 Hz, [2H]), 3.97 H, 3.15; N, 6.39%.
(s, [3H]) 2.75 (s, [3H]), 1.50 (t, J = 7.34 Hz, [3H]). 139La NMR
[EMIM]3[CeCl6]. Synthesised in an analogous way, using
(CH3CN/CD3CN): d = 864 (s, W1/2 = 600 Hz). Anal. required for CeCl3 (100 mg, 0.406 mmol) and [EMIM]Cl (208 mg, 1.42 mmol),
C21H39Cl6LaN6: C, 34.68; H, 5.41; N, 11.56%. Found: C, 34.55; H, forming a white crystalline product. Yield: 175 mg, 63%. Raman
1
5.34; N, 11.45%.
(solid): 244 cmÀ1 (A1g [CeCl6]3À). H NMR (CD3CN, 300 K): d =
[BMPYRR]3[LaCl6]. LaCl3 (100 mg, 0.407 mmol) was suspended 9.77 (s, [H]), 7.45 (s, [H]), 7.40 (s, [H]), 4.44 (q, J = 7.2 Hz, [2H]),
in MeCN (10 mL) and a solution of [BMPYRR]Cl, (255 mg, 4.01 (s, [3H]), 1.51 (t, J = 6.6 Hz, [3H]). Anal. required for
1.43 mmol) in MeCN (10 mL) was added. The mixture was heated C18H33CeCl6N6: C, 31.50; H, 4.85; N, 12.24%. Found: C, 31.21;
briefly and then stirred for one hour. The resulting suspension was H, 4.58; N, 12.54%.
filtered and diethyl ether (10 mL) was added to the filtrate, leading
[EMIM]3[YCl6]. Synthesised in an analogous way, using YCl3
to the precipitation of a fine white crystalline product. The solvent (100 mg, 0.512 mmol) and [EMIM]Cl (225 mg, 1.54 mmol).
was removed via cannula and the solid was dried under vacuum. White crystalline product. Yield: 277 mg, 85%. Infrared (Nujol):
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Table 6 X-ray crystallographic dataa
Compound
[EMIM]3[ScCl6]
[EMIM]3[YCl6]
[EMIM]3[CeCl6]
[EMIM]3[LaBr6]
Formula
C18H33Cl6N6Sc
591.16
150(2)
Orthorhombic
Pna21 (33)
19.411(2)
13.059(1)
11.046(1)
90
C18H33Cl6N6Y
635.11
100(2)
Orthorhombic
Pna21 (33)
19.580(2)
13.036(2)
11.166(1)
90
C18H33CeCl6N6
686.32
100(2)
Monoclinic
P21/c (14)
15.492(3)
12.549(2)
14.708(3)
90
C18H33Br6LaN6
951.87
100(2)
Monoclinic
P21/c (14)
15.925(5)
12.787(4)
15.252(5)
90
M/g molÀ1
Temp./K
Crystal system
Space group (no.)
a/Å
b/Å
c/Å
a/1
b/1
90
90
2800.0(4)
4
0.853
90
90
2849.9(5)
4
2.626
90.482(3)
90
2859.2(9)
4
2.170
1372
90.588(5)
90
3106(2)
4
9.111
1800
g/1
U/Å3
Z
m(Mo-Ka) mmÀ1
F(000)
1224
1296
Total reflections
Unique reflections
Rint
15 098
5189
0.027
1.023
0.026
14 268
6374
0.037
0.796
0.028
12 086
5811
0.122
0.962
0.063
14 407
6318
0.092
1.145
0.082
Goodness-of-fit on F2
b
R1 [Io 4 2s(Io)]
R1 (all data)
wR2 [Io 4 2s(Io)]
0.029
0.063
0.043
0.045
0.090
0.167
0.116
0.134
b
wR2 (all data)
0.064
0.048
0.187
0.148
Compound
[EMIM]3[LaI6]
[EDMIM]3[YCl6]
[EDMIM]3[LaCl6]
[EDMIM]3[LaI6]
Formula
C
18H33I6LaN6
C21H39Cl6N6Y
677.19
100(2)
Monoclinic
P21/n (14)
9.9170(8)
16.274(1)
19.028(2)
90
99.973(1)
90
3024.6(4)
4
C21H39Cl6LaN6
727.19
100(2)
Monoclinic
P21/n (14)
10.027(2)
16.306(2)
19.133(3)
90
99.265(3)
90
3087.4(9)
4
C21H39I6LaN6
1275.89
100(2)
M/g molÀ1
1233.81
120(2)
Monoclinic
P21/c (14)
18.803(7)
11.133(2)
17.017(2)
90
102.162(7)
90
3482(1)
4
Temp./K
Crystal system
Space group (no.)
a/Å
b/Å
c/Å
a/1
b/1
Triclinic
%
P1 (2)
10.347(2)
11.075(3)
16.577(3)
92.594(3)
90.255(3)
106.930(4)
1815.1(7)
2
g/1
U/Å3
Z
m(Mo-Ka) mmÀ1
F(000)
6.562
2232
2.480
1392
1.924
1464
6.299
1164
Total reflections
Unique reflections
Rint
34 033
7929
0.059
1.073
0.031
16 980
6878
0.027
1.028
0.028
26 415
7055
0.020
1.078
0.023
16 557
8311
0.028
0.984
0.019
Goodness-of-fit on F2
b
R1 [Io 4 2s(Io)]
R1 (all data)
wR2 [Io 4 2s(Io)]
0.036
0.075
0.039
0.064
0.026
0.055
0.021
0.041
b
wR2 (all data)
0.078
0.067
0.057
0.042
P
P
P
P
a
b
2
4 1/2
Common items: wavelength (Mo-Ka) = 0.71073 Å; y(max) = 27.51. R1
=
||Fo| À |Fc||/ |Fo|; wR2 = [ w(Fo À Fc2)2/ wFo
]
.
245 cmÀ1 (T1u [YCl6]3À). Raman (solid): 264 cmÀ1 (A1g [YCl6]3À).
[EMIM]3[ScCl6]. Synthesised in an analogous way, using ScCl3.
1H NMR (CD3CN, 300 K): d = 9.26 (s, [H]), 7.39 (s, [H]), 7.34 White crystalline product, 85%. Infrared (Nujol): 290 cmÀ1
(s, [H]), 4.31 (q, J = 7.34 Hz, [2H]), 3.93 (s, [3H]), 1.46 (t, J = (T1u [ScCl6]3À). 1H NMR (CD3CN, 300 K): d = 9.41 (s, [H]), 7.41
7.34 Hz, [3H]). Anal. required for C18H33Cl6N6Y: C, 34.04; H, (s, [H]), 7.38, (s, [H]), 4.26 (q, J = 7.34 Hz, [2H]), 3.90 (s, [3H]), 1.46
5.24; N, 13.23%. Found: C, 33.90; H, 5.15; N, 13.18%.
(t, J = 7.21 Hz, [3H]). 45Sc NMR (CH3CN/CD3CN): d = 254.5. Anal.
[EDMIM]3[YCl6]. Synthesised in an analogous way, 72%. required for C18H33Cl6N6Sc: C, 36.57; H, 5.63; N, 14.22%. Found: C,
White crystalline solid. Infrared (Nujol): 238 cmÀ1 (T1u [YCl6]3À). 36.39; H, 5.71; N, 14.09%.
1H NMR (CD3CN, 300 K): d = 7.40 (s, [2H]), 4.12 (q, J = 7.16 Hz,
X-ray experimental. Crystals suitable for single crystal X-ray
[2H]), 3.75 (s, [3H]), 2.54 (s, [3H]), 1.39 (t, J = 7.34 Hz, [3H]). analysis were obtained as described above. Details of the crystallo-
(CD2Cl2, 300 K): d = 7.64 (d, J = 2.20 Hz, [H]), 7.46 (d, J = 2.20 Hz, graphic data collection and refinement parameters are given in
[H]), 4.23 (q, J = 7.5 Hz, [2H]), 3.97 (s, [3H]), 2.75 (s, [3H]), 1.50 Table 6. Data collections were carried out on a Rigaku AFC12
(t, J = 7.34 Hz, [3H]). 139La NMR (CH3CN/CD3CN): d = 864 goniometer equipped with an enhanced sensitivity (HG) Saturn724+
(s, W1/2 = 600 Hz). Anal. required for C21H39Cl6N6Y: C, 37.25; detector mounted at the window of an FRE+ SuperBright
H, 5.80; N, 12.41%. Found: C, 37.12; H, 5.93; N, 12.20%.
molybdenum rotating anode generator (l1 = 0.71073 Å) with
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VHF Varimax optics (70 or 100 mm focus), apart from [EMIM]3[LaI6]
which was collected on a Rigaku R-axis Spider including curved
Fuji-film image plate and a graphite monochromated sealed tube
Mo generator (l1 = 0.71073 Å). For all datasets: cell determination,
data collection, data reduction, cell refinement and absorption
correction were carried out using CrystalClear-SM Expert 2.0 r7.15
Structure solution and refinement were straightforward
using WinGX and software packages within,16 except as detailed
below. Although Q-peaks corresponding to the location of protons
were observed in the Fourier difference map, hydrogen atoms were
placed in geometrically assigned positions with C–H distances
of 0.95 Å (CH), 0.98 Å (CH3) or 0.99 Å (CH2) and refined using a
riding model, with Uiso(H) = 1.2Ueq(C) (CH, CH2) or 1.5Ueq(C)
(CH3). Mercury17and enCIFer18 were used to prepare material
for publication.
All the crystals of [EMIM]3[CeCl6] looked at in this study
were multiply twinned and all attempts at multi-component
twin integration failed. A satisfactory dataset was obtained by
integrating on just the major component and ignoring the
minor overlaps from the other domains. This caused a couple
of large Q-peaks to appear close to the cerium atoms (3.2 e ÅÀ3 at
B1.04 Å distance from Ce) as well as two large holes (À5.9 e ÅÀ3
at B0.84 Å from Ce). This explains the level A and B CheckCIF
errors PLAT971_ALERT_2_A (holes) and PLAT971_ALERT_2_B
(Q-peaks). The crystals of [EMIM]3[LaBr6] were all also multi-
component twins and treated in a similar fashion.
Acknowledgements
This work was funded by EPSRC through a Programme Grant
(EP/I033394/1) and also through EP/K039466/1. The SCFED
Project (www.scfed.net) is a multidisciplinary collaboration of
British universities investigating the fundamental and applied
aspects of supercritical fluids.
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