Lead(ii) tetrafluoroborate and hexafluorophosphate complexes with crown ethers, mixed O/S- and O/Se-donor macrocycles and unusual [BF4] - and [PF6]- coordination

Article abstract of DOI:10.1039/c3dt32999b

The reaction of Pb[BF₄]₂ in H₂O/MeCN solution with the macrocycle 18-crown-6 gave the dinuclear complex [{Pb(18-crown-6)(H₂O)(μ²-BF₄)} ₂][BF₄]₂, containing two nine-coordinate lead centres, each bound to all six oxygens of a crown ligand, one water molecule and bridged by two μ²-BF₄ groups. In contrast, the oxa-thia crown [18]aneO₄S₂ gave the mononuclear [Pb([18]aneO₄S₂)(H₂O)₂(BF ₄)][BF₄] in which the lead is coordinated O ₄S₂ within the puckered ring of the macrocycle, and with two water molecules on one side of the plane and a chelating (κ²) BF₄^- on the other. The [Pb([18]aneO₄Se₂)(BF₄)₂] has the two BF₄^- groups arranged mutually cis and with the macrocycle folded; within each BF₄^- group the Pb-F distances differ by ～0.5 A, producing a very unsymmetrical chelate. The 15-membered ring macrocycles 15-crown-5 and [15]aneO₃S₂ produce sandwich complexes [Pb(macrocycle)₂][BF₄]₂ which contain 10-coordinate lead centres. Pb[PF₆]₂ in H₂O/MeCN solution formed [Pb(18-crown-6)(H₂O) ₂(PF₆)][PF₆] and [Pb([18]aneO₄S ₂)(H₂O)₂(PF₆)][PF₆] which contain weak κ²-coordination of the PF₆^- group on the opposite side of the macrocyclic ring to two coordinated water molecules, giving 10-coordinate lead. In contrast, [Pb([18]aneO ₄Se₂)(PF₆)₂] has two κ²-coordinated PF₆^- groups disposed cis, with a very folded macrocycle conformation. In [Pb(18-crown-6)(NO ₃)(PF₆)] a chelating nitrate group occupies the coordination sites at Pb(ii) instead of the two water molecules, and the weakly coordinating PF₆^- group is tridentate. The crystal structures of the lead nitrate complexes, [Pb(15-crown-5)(NO₃) ₂] and [Pb([18]aneO₄Se₂)(NO₃) ₂], containing nine- and 10-coordinate lead respectively, are also reported. In solution the complexes are labile, and both conductivity and ¹⁹F NMR spectroscopic studies show the BF₄^- and PF₆^- groups are dissociated, whereas in the nitrate complexes the anion coordination is retained in solution. The identification of the coordination modes of the NO₃^- and BF₄ ^- groups in the solid complexes by IR spectroscopy is discussed. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3dt32999b

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PAPER
Lead(II) tetrafluoroborate and hexafluorophosphate
complexes with crown ethers, mixed O/S- and O/Se-
donor macrocycles and unusual [BF4]− and [PF6]−
coordination†
Cite this: Dalton Trans., 2013, 42, 4714
Paolo Farina, Thomas Latter, William Levason and Gillian Reid*
The reaction of Pb[BF4]2 in H2O/MeCN solution with the macrocycle 18-crown-6 gave the dinuclear
complex [{Pb(18-crown-6)(H2O)(μ2-BF4)}2][BF4]2, containing two nine-coordinate lead centres, each
bound to all six oxygens of a crown ligand, one water molecule and bridged by two μ2-BF4 groups. In
contrast, the oxa-thia crown [18]aneO4S2 gave the mononuclear [Pb([18]aneO4S2)(H2O)2(BF4)][BF4] in
which the lead is coordinated O4S2 within the puckered ring of the macrocycle, and with two water
molecules on one side of the plane and a chelating (κ2) BF4 on the other. The [Pb([18]aneO4Se2)(BF4)2]
−
−
−
has the two BF4 groups arranged mutually cis and with the macrocycle folded; within each BF4 group
the Pb–F distances differ by ∼0.5 Å, producing a very unsymmetrical chelate. The 15-membered ring
macrocycles 15-crown-5 and [15]aneO3S2 produce sandwich complexes [Pb(macrocycle)2][BF4]2 which
contain 10-coordinate lead centres. Pb[PF6]2 in H2O/MeCN solution formed [Pb(18-crown-6)(H2O)2(PF6)][PF6]
and [Pb([18]aneO4S2)(H2O)2(PF6)][PF6] which contain weak κ2-coordination of the PF6 group on the
−
opposite side of the macrocyclic ring to two coordinated water molecules, giving 10-coordinate lead. In
contrast, [Pb([18]aneO4Se2)(PF6)2] has two κ2-coordinated PF6 groups disposed cis, with a very folded
−
macrocycle conformation. In [Pb(18-crown-6)(NO3)(PF6)] a chelating nitrate group occupies the coordi-
−
nation sites at Pb(II) instead of the two water molecules, and the weakly coordinating PF6 group is
tridentate. The crystal structures of the lead nitrate complexes, [Pb(15-crown-5)(NO3)2] and [Pb([18]-
aneO4Se2)(NO3)2], containing nine- and 10-coordinate lead respectively, are also reported. In solution the
Received 13th December 2012,
Accepted 16th January 2013
complexes are labile, and both conductivity and 19F NMR spectroscopic studies show the BF4 and PF6
groups are dissociated, whereas in the nitrate complexes the anion coordination is retained in solution.
−
−
DOI: 10.1039/c3dt32999b
−
−
The identification of the coordination modes of the NO3 and BF4 groups in the solid complexes by
www.rsc.org/dalton
IR spectroscopy is discussed.
eleven in [Pb(15-crown-5)(NO3)3]−.6 The complexes often
display irregular geometries, reflecting both the steric
Introduction
Lead(II) has an extensive chemistry forming complexes with demands of the ligands and inter-ligand repulsions. The pres-
charged and neutral donor ligands from Groups 14–17.1–3 As a ence of a formal lone pair, which may or may not be stereo-
large metal centre (covalent radius 1.46 Å),4 it is able to form chemically active, also needs to be considered, although in the
compounds with coordination numbers ranging from two (in higher coordinated complexes with polydentate or macrocyclic
diaryllead compounds with bulky substituted aryl groups) to ligands the very irregular coordination geometries make it
nine (in Pb(OAc)2·3H2O),5 ten in [Pb(18-crown-6)(NO3)2],6 and difficult to assess the influence of the lone pair. Unusually for
a p-block metal, due to the insoluble and intractable nature of
the lead dihalides, the coordination chemistry with neutral
ligands is largely based upon oxo-salts such as acetate, nitrate
or perchlorate, which are commonly found in the first coordi-
nation sphere of the lead.2,3 Rare examples of lead halide com-
plexes are the 18-crown-6 derivatives, [PbCl2(18-crown-6)],
[Pb2I3(18-crown-6)2][SnI5], the polymer [Pb2Br4(18-crown-6)]
and [PbCl(18-crown-6)]SbCl6.7–10 Due to its large radius and
School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
E-mail: G.Reid@soton.ac.uk
†Electronic supplementary information (ESI) available: The ESI contains
improved preparations for several of the macrocycles, and crystallographic data
for [Pb(15-crown-5)2][H3O][BF4]3. CCDC 900327–900332, 912764, 912765 and
913970. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3dt32999b
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modest charge (and hence low charge/radius ratio), many lead
(II) complexes are extensively dissociated in solution, and this
has resulted in significant effort devoted to lead(II) complexes
with aza-, oxa- (crown ether) or thia-macrocycles.3,11,12 Lead is
a toxic element, widely distributed due to its many industrial
applications, and this has led to the use of macrocyclic ligands
in heavy metal sensors and extraction.13 Examples of the types
of complex found are [Pb(18-crown-6)(NO3)2] (10-coordinate
with bidentate nitrates), and the cation-anion complexes
[Pb(15-crown-5)2][Pb(15-crown-5)(NO3)3]2 and [Pb(12-crown-4)2-
(NO3)][Pb(12-crown-4)(NO3)3], which also contain 10-coordinate
cations and 10- or 11-coordinate anions.6,14 Ten-coordinate lead
is also present in [Pb(18-crown-6)(O2CMe)2]·3H2O,15 whilst the
thiocyanates [Pb(crown)(NCS)2] (crown = 18-crown-6 or dicyclo-
hexane-18-crown-6) are eight-coordinate.16 Thia-macrocycle
complexes of lead are fewer, but include [Pb([9]aneS3)2(ClO4)2]
Fig. 1 Crystal structure of the dimer cation in [{Pb(18-crown-6)(H2O)(μ2-BF4)}2]-
[BF4]2 showing the bridging BF4 groups. Ellipsoids are drawn at the 50% prob-
ability level and H atoms are omitted for clarity. Symmetry operation: a = −x, −y,
(eight-coordinate, S6O2),17 [Pb([10]aneS3)(H2O)-(ClO4)2] (nine- 2 − z. Selected bond lengths (Å) and angles (°): Pb1–O1 = 2.744(5), Pb1–O2 =
coordinate, S3O6),18 and [Pb2([28]aneS8)(ClO4)4] (dinuclear,
2.803(5), Pb1–O3 = 2.894(5), Pb1–O4 = 2.732(5), Pb1–O5 = 2.710(5), Pb1–O6 =
eight-coordinate, S4O4).19
2.701(5), Pb1–O7 = 2.406(6), Pb1⋯F3 = 2.677(5), Pb1⋯F4a = 2.813(4), O1–
Pb1–O2 = 58.93(14), O2–Pb1–O3 = 57.69(14), O3–Pb1–O4 = 57.75(14), O4–
Here we report the reactions of Pb(II) with crown ether, oxa-
Pb1–O5 = 61.11(14), O5–Pb1–O6 = 60.80(14), O1–Pb1–O6 = 60.13(14).
thia and oxa-selena macrocycles, focusing mainly on Pb[BF4]2
or Pb[PF6]2 as the lead(II) source. Oxa-selena macrocycle
coordination chemistry has been little studied due to the rela- coordination number of the lead based upon all the Pb–donor
tive unavailability of the ligands,20,21 and the only oxa-thia atom contacts within the Van der Waals sum, while emphasis-
macrocycle compounds of Pb(II) are [Pb([18]aneO4S2)(ClO4)2], ing particularly disparate bond lengths in the individual cases.
[Pb([18]aneO4S2)(NO3)2] and [Pb([18]aneO4S2)(NCS)2] ([18]- The relevant Van der Waals radii sums are Pb⋯O = 3.54, Pb⋯S =
aneO4S2 = 1,4,10,13-tetraoxa-7,16-dithiacyclooctadecane).22 Tetra- 3.82, Pb⋯Se = 3.92 and Pb⋯F = 3.49 Å.4
fluoroborate and hexafluorophosphate are markedly weaker
Reaction of a 50% aqueous solution of Pb[BF4]2 with one
−
− 23
coordinating anions than either ClO4 or NO3
.
In the mol. equiv. of 18-crown-6 in MeCN solution afforded the
present study we have explored the affinity of the lead(II) complex [{Pb(18-crown-6)(H2O)(μ2-BF4)}2][BF4]2 as a colourless
macrocycle fragments (both 15- and 18-membered rings) crystalline solid. A crystal structure determination showed
towards these fluoro-anions and the resulting structures.
(Fig. 1) the Pb(II) ion within the ring of the 18-crown-6 coordi-
nated to all six ether oxygens (2.744(5)–2.894(5) Å), a coordi-
−
nated H2O (2.406(6) Å), and with two μ2-BF4 groups linking
two Pb atoms to form a dinuclear species, and giving overall
nine-coordination at lead(II). Two other [BF4]− anions provide
charge balance. The most unusual feature of this complex is
the presence of the asymmetrically bridging [BF4]− groups,
with Pb–F distances Pb1–F3 = 2.677(5), Pb1–F4a = 2.813(4) Å,
and <F3–B1–F4 = 111.5(3)°. The only other example of Pb(II)
Results and discussion
As a result of the labile nature of Pb(II) in solution and the
unpredictable geometries present, spectroscopic techniques
provide limited characterisation. The key characterisation tech-
nique for complexes of this type is X-ray crystallography, and
thus the synthesis and structures of the new complexes are
described first, followed by discussion of the spectroscopic
data.
−
with bridging BF4 groups is in the organolead complex, [(η5-
C5Me5)Pb(μ2-BF4)2Pb(η5-C5Me5)], with d(Pb–F) = 2.901(9) and
2.831(9) Å.24 The coordinated water molecule, which has a sig-
nificantly shorter Pb–O bond (Pb1–O7 = 2.406(6) Å) than those
involving the crown ether, also forms two H-bonds to F atoms
Synthesis and X-ray crystal structures
The coordination geometries observed are generally highly of adjacent [BF4]− anions, O7⋯F8′ = 2.722(7), and O7⋯F5′ =
irregular, reflecting the constraints of the macrocyclic rings 2.689(7) Å. The known [Pb(18-crown-6)(NO3)2] is mononuclear
and, in some cases, the small chelate bites of the coordinated with κ2-NO3− groups on opposite sides of the PbO6 plane.6,14
anions, and therefore are not easily described in terms of
[Pb(15-crown-5)2][BF4]2 was obtained using either a 1 : 1 or
Euclidean shapes. The lead–donor bond lengths also show a 1 : 2 Pb[BF4]2 : 15-crown-5 molar ratio. Colourless crystals
range of values, described by some authors as a mixture of grown from the filtrate from the 1 : 1 reaction revealed a [Pb-
normal coordinate bonds and longer directional (weak) inter- (15-crown-5)2][H3O][BF4]3 constitution, with a disordered lead
actions.21,22 The distinction between the two descriptions is dication which precludes detailed structural comparison (see
not clear-cut and all Pb–donor atom bond distances in the ESI†). However, the partial structure does indicate a 10-coordi-
present systems are significantly within the sum of the appro- nate Pb(II) centre, with anionic tetrafluoroborate, and with a
priate Van der Waals radii. In this work we have described the hydroxonium cation also present in the asymmetric unit to
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Fig. 3 Crystal structure of the cation in [Pb([18]aneO4S2)(H2O)2(BF4)][BF4]
showing the atom numbering scheme and the coordination around Pb1. Ellip-
soids are drawn at the 50% probability level and H atoms bonded to C are
omitted for clarity. Selected bond lengths (Å) and angles (°): Pb1–O1 = 2.888(2),
Pb1–O2 = 2.842(2), Pb1–O3 = 2.726(2), Pb1–O4 = 2.731(2), Pb1–S1 = 3.0151(8),
Pb1–S2 = 3.0191(7), Pb1–O5 = 2.559(2), Pb1–O6 = 2.471(2), Pb1⋯F1 = 3.038(2),
Pb1⋯F2 = 2.877(2), O5–Pb1–O6 = 73.03(8), O3–Pb1–O4 = 62.68(6), O2–Pb1–O1
= 59.03(5), O4–Pb1–S1 = 66.64(5), O1–Pb1–S1 = 64.42(4), O3–Pb1–S2 = 65.07(4),
S1–Pb1–S2 = 147.40(2), F2⋯Pb1⋯F1 = 44.94(4).
Fig. 2 Crystal structure of the [Pb(15-crown-5)(NO3)2] showing the atom num-
bering scheme. Ellipsoids are drawn at the 50% probability level and H atoms
are omitted for clarity. Pb to crown O atoms are shown as open bonds. Selected
bond lengths (Å) and angles (°): Pb1–O1 = 2.691(3), Pb1–O2 = 2.712(3), Pb1–
O3 = 2.711(3), Pb1–O4 2.709(3), Pb1–O5 = 2.716(3), Pb1–O6 = 2.574(4), Pb1–
O7 = 2.596(3), Pb1–O9 = 2.586(3), Pb1–O10 = 2.681(3), O6–Pb1–O7 = 49.93(11),
O9–Pb1–O10 = 48.84(9), O1–Pb1–O2 = 64.18(10), O2–Pb1–O3 = 62.78(10), O3–
Pb1–O4 = 61.36(9), O4–Pb1–O5 = 61.79(9), O5–Pb1–O6 = 85.33(12), O6–Pb1–
O1 = 144.50(11).
−
chelating BF4 completing the 10-coordinate environment at
balance the charge. In contrast, 15-crown-5 reacted with
Pb[NO3]2 in MeCN solution to give the 1 : 1 complex [Pb(15-
crown-5)(NO3)2]. The crystal structure shows (Fig. 2) pentaden-
tate coordination of the crown and two chelating NO3− ligands
giving nine-coordinate Pb(II). Unlike the structure of [Pb(18-
crown-6)(NO3)2],6,14 the 15-crown-5 lies on one side of the Pb
lead, Pb–Owater = 2.471(2), 2.559(2) Å. The OH2 molecules (O5
and O6) are involved in H-bonds to O and S atoms in the
crown and to F in the fluoroborates.
The structure can be compared with that found in [Pb([18]-
aneO4S2)(ClO4)2]22 in which the lead sits in the plane of the
macrocycle with κ1-perchlorate groups arranged trans across
the plane (eight-coordinate Pb). The Pb–O distances of 2.662
(2) and 2.744(2) Å, and Pb–OClO3 = 2.680(2) Å are slightly
shorter, but with a longer d(Pb–S) = 3.091(1) Å. In contrast,
[Pb([18]aneO4S2)(NO3)2]22 is different again, with a 10-coordi-
−
ion, with the κ2-NO3 groups cis. The Pb–O(crown) distances
lie in the range 2.691(3)–2.716(3) Å, while the nitrates are asym-
metrically coordinated with Pb–O(nitrate) distances 2.574(4)–
2.586(3) Å.
Previous work6 has reported that the reaction of Pb[NO3]2
with 15-crown-5 in a 1 : 2 molar ratio in hot MeOH/MeCN solu-
nate lead environment composed of two cis κ2-NO3 groups.
−
Here d(Pb–O) = 2.716(10)–2.879(11) Å, d(Pb–ONO2) = 2.553(17)–
tion, gives [Pb(15-crown-5)2][Pb(15-crown-5)(NO3)3]2 with
a
2.877(16) Å and d(Pb–S) = 3.114(6), 3.131(6) Å.
badly disordered cation (similar to the problem in [Pb(15-
crown-5)2][H3O][BF4]3 in this work). We observed only the
neutral [Pb(15-crown-5)(NO3)2] under our conditions.
Repeating this reaction with the smaller 15-membered
macrocycle, [15]aneO3S2 (1,4,7-trioxa-10,13-dithiacyclopenta-
decane), with a 2 : 1 crown : Pb ratio gave [Pb([15]aneO3S2)2]-
[BF4]2. The X-ray crystallographic analysis revealed a discrete
[Pb([15]aneO3S2)2]2+ sandwich dication (Fig. 4) with the [BF4]−
anions. Within the cation the Pb(II) centre can be considered
to be in a very distorted 10-coordinate environment. Although
all the Pb–O and Pb–S distances in both rings lie well within
the sum of the Van der Waals radii for the respective elements,
two of the Pb–O distances, Pb–O3 and Pb–O4 (2.898(5),
3.055(5) Å), are substantially longer compared to the others
and therefore an alternative description would be to consider
these as weaker, directional long contacts. The shorter Pb–O
distances are 2.688(5), 2.725(5), 2.761(4) and 2.750(4) Å, while
Aqueous lead tetrafluoroborate reacted with one mol. equiv.
of [18]aneO4S2 in MeCN to give colourless crystals formulated
as [Pb([18]aneO4S2)(H2O)2(BF4)][BF4], on the basis of micro-
analytical data. The crystal structure shows (Fig. 3) a complex
of 1 : 1 Pb : crown stoichiometry with a [Pb([18]aneO4S2)-
(H2O)2(κ2-BF4)]+ cation and a discrete BF4− anion. The lead ion
sits within the puckered oxa-thia ring, coordinated via all six
donor atoms (Pb–S = 3.0151(8), 3.0191(7) Å, Pb–O = 2.726(2)–
−
2.888(2) Å). One BF4 behaves as a bidentate chelate to Pb(II),
with Pb⋯F = 3.038(2), 2.877(2) Å, F2–B1–F1 = 108.1(2)°. Two
mutually cis coordinated water molecules lie trans to the
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Fig. 5 Structure of [Pb([18]aneO4Se2)(BF4)2] showing the atom numbering
scheme. Ellipsoids are drawn at the 50% probability level and hydrogen atoms
have been omitted for clarity. Symmetry operation: a = 1 − x, y, 1/2 − z. Selected
bond lengths (Å) and angles (°): Pb1–O2 = 2.584(5), Pb1–O1 = 2.717(4),
Pb1⋯F1 = 2.707(4), Pb1⋯F4 = 3.223(5), Pb1–Se1 = 3.1820(14), O2–Pb1–O1 =
63.95(14), O2a–Pb1–O1 = 74.62(14), O2a–Pb1–Se1 = 68.67(10), O1–Pb1–Se1 =
65.43(10), Se1–Pb1–Se1a = 155.61(3).
Fig. 4 Crystal structure of the cation in [Pb([15]aneO3S2)2][BF4]2·nCH2Cl2 (n =
1.22) showing the atom numbering scheme and the coordination around Pb1.
Ellipsoids are drawn at the 50% probability level and H atoms are omitted for
clarity. Selected bond lengths (Å) and angles (°): Pb1–O1 = 2.688(5), Pb1–O2 =
2.725(5), Pb1–O3 = 2.898(5), Pb1–O4 = 3.055(5), Pb1–O5 = 2.761(4), Pb1–O6 =
2.750(4), Pb1–S1 = 3.022(2), Pb1–S2 = 3.043(2), Pb1–S4 = 3.054(2), Pb1–S3 =
3.116(2), O1–Pb1–O2 = 63.83(14), S1–Pb1–S2 = 66.44(5), O6–Pb1–S4 = 67.66(10),
O6–Pb1–S3 = 71.07(10), S3–Pb1–S4 = 65.35(5).
suggesting a very similar affinity for the lead. A very noticeable
−
difference is in the coordination of the BF4 groups. In both
the Pb–S distances are in the range 3.022(2)–3.116(2) Å. On
this alternative basis, the lead is coordinated to two S atoms
and two O atoms in each ring, giving a “core” coordination
number of eight.
structures the coordination is asymmetric, in [Pb([18]aneO4S2)-
(H2O)2(BF4)][BF4] Pb1⋯F1 = 3.038(2), Pb1⋯F2 = 2.877(2) Å,
ΔPb–F = 0.16 Å, whilst in [Pb([18]aneO4Se2)(BF4)2] Pb1⋯F1 =
2.707(4), Pb1⋯F4 = 3.223(5) Å, ΔPb–F = 0.52 Å. In the latter, the
disparity is sufficiently great that κ1-coordination may be a
better description. Examination of the non-bonded contacts
involving the fluoroborate groups provides a possible expla-
nation; in [Pb([18]aneO4Se2)(BF4)2] the F4⋯F4a is 2.975 Å, very
close to the sum of the Van der Waals radius for two fluorines
(2 × 1.47 Å)4 and any attempt at closer approach of F4 to the
lead is prevented by this steric interaction. In all the fluoro-
borate complexes the effect of coordination on the B–F distances
or F–B–F angles is small, reflecting the very strong B–F bonding.
The corresponding nitrate complex, [Pb([18]aneO4Se2)-
(NO3)2], was obtained in high yield, and the crystals are iso-
Few structurally authenticated complexes containing endo
coordination of [15]aneO3S2 are known, examples include
[Ag([15]aneO3S2)]+,25 [Ca([15]aneO3S2)I2],26 and [GeCl([15]-
aneO3S2)]+,27 and it is notable that all contain quite a wide range
of M–O and M–S bond lengths within each complex, suggesting
that these are a characteristic of this particular macrocycle.
The reaction of lead fluoroborate in H2O/MeCN with
[18]aneO4Se2 (1,4,10,13-tetraoxa-7,16-diselenacyclooctadecane),
reproducibly (by checking unit cell measurements) gave col-
ourless crystals which were found to be [Pb([18]aneO4Se2)-
(BF4)2] (Fig. 5). This contrasts with the structure of the
hydrated thia-crown complex, [Pb([18]aneO4S2)(H2O)2(BF4)]-
[BF4], described above. However, even upon repeated recrystal-
lisations from MeCN, we were unable to obtain pure bulk
samples of the anhydrous [18]aneO4Se2 complex; the IR and
1H NMR spectra both reveal some H2O present. There is a
marked changed in geometry between the two complexes, the
−
morphous with the BF4 analogue above. The structure was
solved in the space group C2/c and is shown in Fig. 6. The
molecule has two-fold symmetry in which the lead is 10-coor-
dinate with two κ2-nitrate groups, which are disordered over
two sites (see Experimental). The structure was also solved in
the non-centrosymmetric Cc space group which removed the
−
water molecules in [Pb([18]aneO4S2)(H2O)2(BF4)][BF4] are on
NO3 disorder, but the data failed to converge satisfactorily.
−
This is a well known crystallographic problem,28–30 and we
note that similar problems were apparent in the CIF file depos-
ited for the structure of [Pb([18]aneO4S2)(NO3)2],22 although
not discussed. In that case the structure was reported in space
group Cc with a large number of restraints.
the opposite side of the Pb-macrocycle plane to the BF4
,
whereas in [Pb([18]aneO4Se2)(BF4)2], which has two-fold sym-
−
metry, the BF4 groups lie on the same side (mutually cis) of
the lead. The Pb–O distances are rather shorter in the selena-
crown complex (2.584(5), 2.717(4) Å), although the differences
between the Pb–S and Pb–Se distances (∼0.16 Å) corresponds
to the difference in covalent radii of the two donor atoms,4
From a chemical viewpoint the structure of [Pb([18]-
aneO4Se2)(NO3)2] is not in doubt, but the crystallographic
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Fig. 6 Structure of [Pb([18]aneO4Se2)(NO3)2] refined in the space group C2/c
showing the atom numbering scheme. The molecule has two-fold symmetry.
Atomic displacement ellipsoids are drawn at the 25% probability level and
hydrogen atoms have been omitted for clarity. The disordered nitrate was mod-
elled as O4A/B and O5A/B and both components are shown. The bonds to Pb1
involving O4B and O5B are shown dashed. Symmetry operation: i = −x, y, 1/2 − z.
Selected bond lengths (Å) and angles (°): Pb1–O2 = 2.77(8), Pb1–O2 = 2.929(8),
Pb1–O4A = 2.61(2), Pb1–O5A = 2.61(2), Pb1–Se1 = 3.174(2), O1–Pb1–O2 60.3(2),
O2–Pb1–Se1 62.72(15), O1–Pb1–Se1 68.01(15), Se1–Pb–Se1i = 165.01(4).
Fig. 7 The structure of [Pb(18-crown-6)(NO3)(PF6)] showing the atom labelling
scheme. The displacement ellipsoids are drawn at the 50% probability level and
H atoms are omitted for clarity. The molecule has mirror symmetry with Pb1–O
shown as open bonds and the Pb1⋯F contacts shown as dashed lines. Sym-
metry operation: a = 1 − x, y, z. Selected bond lengths (Å) and angles (°): Pb1–
O1 = 2.715(9), Pb1–O2 = 2.736(6), Pb1–O4 = 2.801(10), Pb1–O3 = 2.811(6),
Pb1–O5 = 2.525(7), Pb1⋯F2 = 2.975(9), Pb1⋯F4 = 3.174(8), O5–Pb1–O5A =
50.6(3), O1–Pb1–O2 = 61.82(13), O2–Pb1–O3 = 60.7(2), O4–Pb1–O3 = 58.85(14).
problem precludes detailed comparison of bond lengths and
angles between the structures.
Attempts to isolate a complex of the corresponding oxa-
tellura macrocycle [18]aneO4Te2 with Pb[BF4]2 in MeCN solu-
tion were unsuccessful.
In order to further explore the structural consequences of
−
changing the anions, we also prepared some PF6 salts.
[Pb([18]aneO4Se2)(PF6)2] were obtained. In all three cases col-
ourless crystals grew from the concentrated reaction mixture,
and these were carefully separated and dried in vacuo. It
proved impossible to recrystallise the compounds without
decomposition, and examination of the mother liquors from
the preparations showed large amounts of decomposition pro-
Attempts to convert [Pb(18-crown-6)(NO3)2] to the bis(hexa-
fluorophosphate) complex by metathesis with excess [NH4]-
[PF6] in aqueous solution, gave some colourless crystals which
were identified spectroscopically and by their X-ray crystal
structure, as [Pb(18-crown-6)(NO3)(PF6)]. The structure (Fig. 7)
shows the lead in the plane of the crown, κ2-coordinated to the
ducts, identified by a combination of 19F and 31P NMR spec-
−
nitrate group, and with the PF6 group on the opposite side of
n− 31
troscopy as [PO3F]2−, [PO2F2]−, F− and [PO4H3−n
]
.
The
the crown, interacting via three fluorines (κ3), Pb1⋯F2 = 2.975(9),
Pb1⋯F4 = 3.174(8) Å (Fig. 7). The Pb⋯F distances are well
within the Van der Waals radii sum (3.49 Å),4 and the three
lead-coordinated P−F bonds are slightly lengthened (P1–F2 =
1.605(9), P1–F4 = 1.610(7) Å) compared to the others (P1–F3 =
1.564(9), P1–F1 = 1.586(9) Å).
isolated solids also degrade (and blacken) considerably over a
few days. For these reasons it has not been possible to obtain
satisfactory microanalytical data for the hexafluorophosphate
salts. Although [PF6]− is usually viewed as a stable anion,
degradation/hydrolysis in the presence of some metal salts has
been reported previously.23,31,32
An alternative approach to the lead hexafluorophosphate
complexes was via direct reaction of an aqueous solution of
Pb[PF6]2‡ (made by dissolving PbCO3 in aqueous HPF6) with
the macrocycles in MeCN. In this way, [Pb(18-crown-6)-
In the structure of [Pb(18-crown-6)(H2O)2(PF6)][PF6] (Fig. 8)
the two water molecules are on the opposite side of the Pb-
−
crown unit to the PF6 group which is coordinated as a biden-
tate, with shorter Pb⋯F (Pb1⋯F2 = 2.881(9) Å) bonds than in
the tridentate example in [Pb(18-crown-6)(NO3)(PF6)]. The water
molecules are hydrogen bonded to a (partially occupied) lattice
water, and charge is balanced by an ionic PF6− group. The simi-
larity to the structure of [Pb([18]aneO4S2)(H2O)2(BF4)][BF4] is
(H2O)2(PF6)][PF6],
[Pb([18]aneO4S2)(H2O)2(PF6)][PF6]
and
‡It is important to note that 207Pb, 19F and 31P NMR spectroscopy showed only
[Pb(H2O)x]2+ and PF6− ions present in the initial aqueous solution.
4718 | Dalton Trans., 2013, 42, 4714–4724
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Fig. 9 The structure of [Pb([18]aneO4Se2)(PF6)2] showing the atom labelling
scheme. The displacement ellipsoids are drawn at the 50% probability level and
H atoms are omitted for clarity. The molecule has two-fold symmetry and the
long F⋯Pb1 interactions are shown with dashed bonds. Symmetry operation:
a = −x, y, 1/2 − z. Selected bond lengths (Å) and angles (°): Pb1–O2 = 2.543(4),
Pb1–O1 = 2.664(3), Pb1–Se1 = 3.173(1), F3⋯Pb1 = 2.908(4), F1⋯Pb1 = 2.920(3).
O2–Pb1–O1 = 63.68(10), O2–Pb1–Se1 = 69.60(7), O1–Pb1–Se1 = 65.13(7), Se1–
Pb1–Se1 = 156.02(2). (There is a F5⋯Se1’ contact of 3.167(4) Å).
Fig. 8 The structure of the cation in [Pb(18-crown-6)(H2O)2(PF6)][PF6]·H2O
showing the atom labelling scheme. The displacement ellipsoids are drawn at
the 40% probability level and H atoms are omitted for clarity. The molecule has
crown Pb1–O shown as open bonds and the Pb1⋯F and O⋯O contacts shown
as dashed lines. Selected bond lengths (Å) and angles (°): Pb1–O1 = 2.704(10),
Pb1–O3 = 2.731(7), Pb1–O4 = 2.733(11), Pb1–O2 = 2.77(2), Pb1–O5 = 2.545(19),
Pb1–O6 = 2.57(3), Pb1⋯F2 = 2.881(9), O1–Pb1–O2 = 60.0(1), O3–Pb1–O2 =
60.1(2), O1–Pb1–O2a = 60.0(1), O3–Pb1–O4 = 61.1(2).
carried out in 10−3 mol dm−3 MeCN showed that the nitrate
complexes exhibited molar conductivities33 much less than
those of 1 : 1 electrolytes (see Experimental), showing the
nitrates remain coordinated in solution. However, the fluoro-
borates had much higher values, indicating the anions dis-
sociate in solution. The MeCN does not however compete as a
ligand for the lead in the solid state, since the complexes are
recovered unchanged from MeCN solution. They could also be
recrystallised from acetone, but were decomposed by MeNO2.
The solution (CDCl3 or CD3CN) 1H NMR data of all the
complexes at 295 K show resonances for the geometrically dis-
tinct CH2 units in the macrocycles, slightly shifted to higher
frequency as a result of coordination to the lead, but either
with ill-defined splittings or as broad singlets showing the
dynamic nature of the complexes, which are probably under-
going reversible ligand dissociation. In the case of [Pb(15-
crown-5)2][BF4]2 cooling the CD3CN solution, showed some ill-
defined second order patterns, and then at 230 K an AB
quartet pattern as the ligand exchange slowed. Several of the
other complexes showed similar but less well-defined spectra
at low temperatures. We were unable to observe 207Pb or (for
the [18]aneO4Se2 complexes) 77Se{1H} NMR resonances over
the temperature range 295–220 K, again attributed to dynamic
processes. Similarly, although several of the tetrafluoroborate
complexes contain coordinated anions in the solid state, in
CD3CN or CDCl3 solution the 19F{1H} NMR spectra each show
also notable. Although the X-ray structure was not determined,
the similarity of the spectroscopic data strongly suggests that
the [18]aneO4S2 has the same constitution as the 18-crown-6
complex–[Pb([18]aneO4S2)(H2O)2(PF6)][PF6].
Unexpectedly the structure of the colourless crystals
obtained from Pb[PF6]2 and [18]aneO4Se2 showed these had
the constitution [Pb([18]aneO4Se2)(PF6)2] (Fig. 9) with two cis
−
disposed κ2-PF6 groups and a very puckered macrocyclic ring.
There is an overall similarity to the structure of [Pb([18]-
−
aneO4Se2)(BF4)2] but, whereas the BF4 groups are very asym-
metrically coordinated to the lead (∼κ1 as discussed above),
the PF6− groups are symmetrically bound. The macrocycle con-
formation is similar in both compounds.
These lead systems are unusual examples of coordination
(albeit weak), of the hexafluorophosphate ion,23 and it is
notable that in the published structure of [PbCl(18-crown-6)]-
−
SbCl6,10 although the SbCl6 anion is on the “open” side of
the Pb-crown plane opposite to the axial Cl, the nearest
Pb⋯ClSb contact is ∼3.80 Å which is greater than the Van der
Waals radii sum (3.77 Å),4 indicating no significant bonding
−
interaction. The very ready hydrolysis of the PF6 anions
observed for the Pb(II) complexes is very unusual.
−
a singlet due to one BF4 environment. Coordinated tetra-
fluoroborate has been identified by 19F{1H} NMR spectroscopy
in some kinetically inert organometallic species.22
Spectroscopic studies
In labile systems the speciation may differ significantly
between the solid and solution phases, and this is evident
in the present complexes. Molar conductivity measurements
In the solid state, the most useful technique was IR spec-
troscopy, which showed features due to the anions present, as
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well as water (where present) and the macrocycle. The strong environment, 8–11, by ligating to counter anions or water.
and quite complex absorptions arising from the macrocycles A combination of the high coordination numbers, different
make identification of the anion vibrations difficult, but by donor groups and the steric constraints of both the macro-
comparison of the corresponding nitrate and tetrafluoroborate cycles and the anions, produce irregular geometries, but there
salts, peaks due to the macrocycle can be identified with is no evidence for a stereochemically active lone pair on the
reasonable certainty. κ2-Coordinated nitrate groups identified lead centre. The overall picture that emerges from comparing
crystallographically in [Pb(18-crown-6)(NO3)2], [Pb(15-crown-5)- the structures is of a large metal centre with no strong stereo-
(NO3)2] and [Pb([18]aneO4Se2)(NO3)2] have approximate C2v chemical preferences, and with the lead geometry/coordi-
symmetry§ for which three stretching modes are expected, 2A1 nation accommodating to the steric demands of the
+ B2 – all IR active.34 A good comparison for these are lantha- macrocycles and the different anions to maximise the Pb–
−
nide nitrate complexes with κ2-NO3 groups which also have donor interactions and minimise repulsions between the
high coordination number, large metal centres with no strong ligands. Overall the potential well about the lead is probably
−
stereochemical preferences. Typically C2v coordinated NO3
quite shallow and one should not overinterpret the observed
groups on these metals show IR stretching bands ∼1470, 1310 differences in bond lengths, especially set against the different
and 1030 cm−1 and a bending mode ∼820 cm−1 35–37
The coordination numbers and donor atom geometries.
∼1470 cm−1 band is obscured in the present cases, but the
The 15-membered ring macrocycles adopt sandwich or half-
.
other three features were identified in the spectra (Experimen- sandwich structures as the ring is too small for the Pb2+ to fit
tal section), which also show the absence of ionic nitrate ions. in the plane, but the 18-ring macrocycles have a sufficiently
Although not assigned, the published IR spectrum of [Pb([18]- large cavity to accommodate the metal centre if desired. The
aneO4S2)(NO3)2] shows21 bands at 1357, 1012, and 801 cm−1
also consistent with the nitrate coordination present.
,
structures observed in individual cases may also reflect crystal
packing and (in some cases) H-bonding interactions. Although
The ionic tetrafluoroborate anion, exhibits a broad, often a range of structures is observed, these are obtained reproduci-
asymmetric, band at ∼1070 cm−1 and a sharp band at bly under the conditions used, and the same species crystallise
∼520 cm−1 due to the stretching and bending modes respect- from MeCN or acetone (sometimes also CH2Cl2); we have no
ively,34 although hydrogen bonding to neighbouring groups or evidence that isomeric forms are obtainable, suggesting the
site symmetry can cause some ill-defined splitting in the solvent/conditions used are not responsible for the variations
higher frequency band, as seen in the spectrum of [Pb([15]- observed with different macrocycles. Whether the co-ligands
−
aneO3S2)2][BF4]2 (see ESI†). The BF4 stretching region of are disposed trans across the Pb-macrocycle plane or cis with a
[{Pb(18-crown-6)(H2O)(BF4)}2][BF4]2
and
[Pb([18]aneO4S2)- more folded conformation of the macrocycle, will depend
(H2O)2(BF4)][BF4] are clearly different (ESI†), but the broad upon the subtle packing forces and inter-ligand interactions
bands and the occurrence of the ligand modes in the same (note also the presence of H⋯O and H⋯F hydrogen bonds in
region make detailed assignment uncertain, and the IR several structures), and the structures observed will reflect this
spectra alone would not permit certain identification of the interplay of individually rather small energy terms. The low
anion coordination mode. The hexafluorophosphate anion charge/radius ratio largely accounts for the relatively weak
shows stretching and bending modes at ∼850 and ∼560 cm−1 binding of the ligands and the solution lability observed. A
−
−
respectively.34 The free, κ2- and κ3-coordinated PF6 groups in number of different coordination modes of the BF4 group
[Pb(18-crown-6)(H2O)2(PF6)][PF6], [Pb([18]aneO4S2)(H2O)2(PF6)]- have been identified – μ2, κ2 and possibly κ1, as well as
[PF6] and [Pb([18]aneO4Se2)(PF6)2] show only broadened examples of κ2 and κ3 coordinated PF6 groups, and
−
vibrations with no resolved splittings, even when two forms, the results show that these groups are less strongly coordi-
e.g. free and κ2-PF6 are present in the same compound, and nated to lead than nitrate or perchlorate, readily dissociating
−
as with the tetrafluoroborates described above, 19F (and 31P) in solution.
NMR studies in MeCN or CDCl3 show the anions are disso-
ciated from the metal centre in solution.
Experimental
Infrared spectra were recorded as Nujol mulls between CsI
Conclusions
plates using a Perkin-Elmer Spectrum100 spectrometer over
the range 4000–200 cm−1 1H NMR spectra were recorded
.
The structures of the macrocyclic complexes reported in this
work and related literature6,10,13,14,21 show that lead(II) typically
coordinates to all donors of the macrocycle, albeit with a range
of bond lengths, and completes a high coordination number
using a Bruker AV300 spectrometer. 19F{1H} and 31P{1H} NMR
spectra were obtained on a Bruker DPX400 and are referenced
to CFCl3 and H3PO4 respectively. Microanalyses were under-
taken by Medac Ltd. Conductivities were measured for solu-
tions in MeCN using
a Cambridge conductivity bridge.
§The coordinated nitrates are bound asymmetrically to the metal, but even
allowing for lower actual symmetry three stretching modes are predicted; the fre-
quencies distinguish coordinated from ionic nitrate, but identification of the
coordination mode (κ1 vs. κ2) has been controversial in many systems.34
Solvents were dried by distillation prior to use, CH2Cl2 and
MeCN from CaH2, hexane from sodium benzophenone ketyl.
Lead nitrate, lead tetrafluoroborate (50% solution in water),
4720 | Dalton Trans., 2013, 42, 4714–4724
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Paper
18-crown-6 and 15-crown-5 were obtained from Aldrich and The filtrate was left to slowly evaporate for 12 h and afforded
used as received. The oxa-thia crowns [18]aneO4S2, [18]- colourless crystals which were washed with CH3CN (2 mL) and
aneO2S4, [15]aneO3S2, and [18]aneO4Se2 and [18]aneO4Te2 CH2Cl2 (2 mL), then dried in vacuo. Yield: 0.080 g, 25%.
were prepared by the original methods38–40 or modifications as Required for C10H20N2O11Pb (551.3): C, 21.8; H, 3.7; N 5.1.
described in the ESI.† Lead hexafluorophosphate (as an Found: C, 22.1; H, 3.8; N 5.1%. 1H NMR (CDCl3, 293 K): δ =
aqueous solution) was made by adding a small excess of basic 3.79 (s, CH2). IR (Nujol): 1352m, 1025, 805 (NO3) cm−1
lead carbonate (Aldrich) to a known volume of aqueous HPF6 ΛM (10−3 mol dm−3, CH3CN) = 40 ohm−1 cm2 mol−1
(65%), and after reaction had ceased, filtering off any residual [Pb([18]aneO4S2)(H2O)2(BF4)][BF4]: [18]aneO4S2 (0.060 g,
solid, and concentrating the solution in vacuo. Aliquots of this 0.20 mmol) dissolved in CH3CN (2 mL) was added dropwise to
.
.
solution were used for the syntheses.
Pb(BF4)2 as a 50% aqueous solution (0.155 g, 0.20 mmol). This
[{Pb(18-crown-6)(H2O)(BF4)}2][BF4]2: Pb(BF4)2 as
a
50% was stirred at room temperature for 2 h. before being concen-
aqueous solution (0.402 g, 0.53 mmol) was added dropwise to trated in vacuo to colourless oil. Dichloromethane (1 mL) was
18-crown-6 (0.139 g, 0.53 mmol) dissolved in CH3CN (5 mL). added and afforded a cloudy white suspension which upon
The resulting colourless mixture was allowed to evaporate at slow evaporation afforded colourless crystals. These were
room temperature for 12 h, which afforded colourless crystals washed with CH3CN (2 mL) followed by CH2Cl2 (2 mL) and
that were collected by filtration, washed with CH3CN (2 mL) dried in vacuo. Yield: 0.155 g, 97%. Required for
and CH2Cl2 (2 mL), then dried in vacuo. Yield: 0.250 g, 72%. C12H28B2F8O6PbS2·CH2Cl2 (798.2): C 19.6, H 3.8; found: C 19.2,
1
Required for C12H26B2F8O7Pb (633.4): C, 21.7; H, 3.9. Found: H 3.4%. H NMR (CDCl3, 293 K): δ = 3.13 (t, [8H], SCH2), 3.70
1
C, 21.8; H, 3.4%. H NMR (CD3CN, 293 K): δ = 3.82 (s, CH2). (s, [8H], OCH2), 4.01 (m, [8H], OCH2), 5.3 (CH2Cl2). 19F{1H}
19F{1H} NMR (CD3CN, 293 K): −151.8 (s).¶ IR (Nujol): 3470br NMR (CD3CN, 293 K): −148.5 (s). IR (Nujol): 3470 br (νOH),
(νOH), 1620s (δH2O), 1143sh, 1090br,m, 969br,m (νBF4), 517s 1612s (δH2O), 1081m, 1020m, 990m (νBF4), 518s (δBF4) cm−1
.
(δBF4) cm−1
[Pb(15-crown-5)2][BF4]2: Pb(BF4)2 as a 50% aqueous solution
.
ΛM (10−3 mol dm−3, CH3CN) = 314 ohm−1 cm2 mol−1
[Pb([15]aneO3S2)2][BF4]2: Pb(BF4)2 as a 50% aqueous solu-
.
(0.400 g, 0.53 mmol) was added dropwise to 15-crown-5 tion (0.300 g, 0.39 mmol) was added dropwise to [15]aneO3S2
(0.231 g, 1.05 mmol) dissolved in CH3CN (5 mL). The colour- (0.200 g, 0.79 mmol) dissolved in CH3CN (3 mL). The colourless
less reaction mixture was left to stir for 24 h, and upon reaction solution was left to stir for 24 h and upon slow evapo-
slow evaporation afforded colourless crystals. These were ration of the solvent colourless crystals formed, which were
washed with CH3CN (2 mL) followed by CH2Cl2 (2 mL) washed with CH2Cl2 (2 mL) and dried in vacuo. Yield: 0.203 g,
and dried in vacuo. Yield: 0.21 g, 49%. Required for 59%. Required for C20H40B2F8O6PbS4·2CH2Cl2 (1055.5): C, 25.0,
C20H40B2F8O10Pb·CH2Cl2 (906.3): C, 27.8; H, 4.7. Found: H 4.2. Found: C, 24.6; H, 3.8%. 1H NMR (CDCl3, 293 K): δ = 3.31
1
C, 28.2, H, 4.5%. H NMR (CD3CN, 293 K): δ = 3.92 (m), 3.86 (t, [4H], SCH2), 3.36 (s, [4H], SCH2), 3.86 (br,s, [8H], OCH2), 3.95
2
(m), 5.3 (s) (CH2Cl2); (230 K): 3.89 (d), 3.77 (d) JHH = 4 Hz. (t, [4H], OCH2), 5.24 (s, CH2Cl2). 19F{1H} NMR (CD3CN, 293 K):
19F{1H} NMR (CD3CN, 293 K): −152.2(s). IR (Nujol): 1087sh, −151.3 (s). IR (Nujol): 1051br,m, 1030sh,m (νBF4), 520s (δBF4)
1052br,s (νBF4), 520s (δBF4) cm−1. ΛM (10−3 mol dm−3, CH3CN) = cm−1. ΛM (10−3 mol dm−3, CH3CN) = 350 ohm−1 cm2 mol−1
.
335 ohm−1 cm2 mol−1
.
[Pb([18]aneO4Se2)(BF4)2]: [18]aneO4Se2 (0.084 g, 0.215 mmol)
[Pb(18-crown-6)(NO3)2]: 18-crown-6 (0.239 g, 0.91 mmol) and 50% aqueous Pb(BF4)2 (0.082 g, 0.215 mmol) were dis-
dissolved in deionised water (3 mL) was added dropwise to a solved in MeCN (20 mL) and allowed to stir overnight. A small
saturated aqueous solution (5 mL) of Pb(NO3)2 (0.301 g, amount of very fine white powder precipitated. The solution
0.91 mmol). A white microcrystalline solid precipitated from was filtered and the filtrate was slowly allowed to evaporate,
the reaction mixture after ∼1 h stirring at room temperature. giving colourless crystals identified crystallographically as [Pb-
The precipitate was collected by vacuum filtration and washed ([18]aneO4Se2)(BF4)2], but analytically pure samples were not
with 5 mL of deionised water and then dried in vacuo. Yield: obtained even after recrystallization from MeCN. 1H NMR
0.190 g, 72%. Required for C12H24N2O12Pb (595.3): C, 24.2; (CD3CN): δ = 2.4 (br, H2O), 3.10 (t, [8H], SeCH2), 3.84 (s, [8H],
H, 4.1; N, 4.7. Found: C, 24.2; H, 4.0; N, 4.7%. 1H NMR (CDCl3, OCH2), 4.02 (t, [8H], OCH2). 19F{1H} NMR (CD3CN, 293 K):
293 K): δ = 3.79 (s, CH2). IR (Nujol): 1350, 1030, 823 (NO3) −150.5. IR (Nujol): 3600vbr (νOH), 1630s (δH2O), 1068s,
cm−1. ΛM (10−3 mol dm−3, CH3CN) = 50 ohm−1 cm2 mol−1
[Pb(15-crown-5)(NO3)2]: 15-crown-5 (0.133 g, 0.60 mmol)
.
1051sh, 1038s (νBF4), 519s (δBF4) cm−1
[Pb([18]aneO4Se2)(NO3)2]: [18]aneO4Se2
.
(0.070
g,
dissolved in a minimum amount of dry CH3CN (5 mL) was 0.018 mmol) was dissolved in MeCN (20 mL) after which 50%
slowly added to a suspension of Pb(NO3)2 (0.200 g, 0.60 mmol) aqueous Pb(NO3)2 (0.059 g, 0.018 mmol) was added and the
in dry acetonitrile (5 mL). The mixture was left to stir for granular suspension allowed to stir overnight. Slowly a fine
2 days and the remaining solids were removed by filtration. white powder began to form. The solid was filtered and crys-
tals were grown from the filtrate. Yield: 0.10 g, 77%. Required
for C12H24N2O10PbSe2 (721.4): C, 20.0; H, 3.4; N, 3.9. Found:
¶Under high resolution two very closely spaced singlets in approximate ratio
1 : 4 due to 10B and 11B isotopomers are seen in all the BF4 complexes. R. K.
C, 19.9; H, 3.2; N, 4.1. 1H NMR (CD3CN): δ = 3.01 (t, [8H],
SeCH2), 3.74 (s, [8H], OCH2), 3.91 (t, [8H], OCH2). IR (Nujol):
Harris and B. E. Mann, NMR and the Periodic Table, Academic Press, NY. 1977.
1JBF couplings are very small and not resolved.
1348, 1027, 816 (NO3) cm−1
.
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[Pb(18-crown-6)(NO3)(PF6)]: Pb(NO3)2 (0.100 g, 0.301 mmol) began to clear and was left to react overnight. A small amount
and 18-crown-6 (0.080 g, 0.301 mmol) were left to stir in de- of fine white solid remained which was removed by filtration,
ionised water (40 mL) for 30 min. To the resulting clear solu- and the filtrate concentrated in vacuo. X-ray quality crystals
tion [NH4][PF6] (0.245 g, 1.506 mmol) was added and left to grew upon concentration. These were removed. Yield: 0.045 g.
stir for 12 h. A small amount of fine white solid formed was 1H NMR (CDCl3, 293 K): δ = 3.80 (s, CH2). 19F{1H} NMR
1
filtered off, and the remaining clear solution concentrated (CDCl3): −72.1 (d, JPF = 710 Hz). 31P{1H} NMR (CDCl3, 295 K):
1
in vacuo. Large colourless crystals formed which were washed −143.3 (sept. JPF = 710 Hz). IR (Nujol): 3500br, 1680br (H2O),
1
with ethanol and dried in vacuo. H NMR (CDCl3, 293 K): δ = 837s (νPF6), 558m (δPF6) cm−1
.
3.77 (s, CH2). 31P{1H} NMR (CDCl3, 295 K): −143.3 (sept). IR
[Pb([18]aneO4S2)(H2O)2(PF6)]PF6: was made similarly to the
(Nujol): 1356, 1025, 813 (NO3), 836s (νPF6), 560m (δPF6) cm−1
.
18-crown-6 complex. H NMR (CDCl3, 293 K): δ = 3.10 (t, [8H],
1
[Pb(18-crown-6)(H2O)2(PF6)]PF6: A aqueous solution of Pb- SCH2), 3.78 (s, [8H], OCH2), 3.89 (m, [8H], OCH2). 19F{1H}
(PF6)2 (0.14 mmol) was added to MeCN (10 mL) resulting in an NMR (CDCl3): −72.2 (d, JPF = 710 Hz). 31P{1H} NMR (CDCl3,
1
immediate white solid forming. To the stirring mixture was 295 K): −143.3 (sept). IR (Nujol): 3500br, 1680br (H2O), 840s
added 18-crown-6 (0.037 g, 0.141 mmol) and the solution (νPF6), 558m (δPF6) cm−1
.
Table 1 Crystal data and structure refinement detailsa
[Pb([15]aneO3S2)2][BF4]2·
nCH2Cl2 (n = 1.22)
[Pb([18]aneO4S2)-
(OH2)2(BF4)]BF4
[{Pb(18-crown-6)(H2O)-
(BF4)}2][BF4]2
[Pb(15-crown-5)-
(NO3)2]
Compound
Formula
M
Crystal system
Space group (no.)
a/Å
b/Å
c/Å
α/°
C
21.22H42.44B2Cl2.44F8O6PbS4
C12H28B2F8O6PbS2
713.27
C24H52B4F16O14Pb2
1326.28
Monoclinic
P21/c (14)
12.818(4)
10.661(3)
15.298(5)
90
C10H20N2O11Pb
551.47
989.18
Orthorhombic
Pccn (56)
18.747(3)
28.254(10)
13.263(2)
90
Orthorhombic
Pbca (61)
16.5374(15)
15.5893(15)
17.703(6)
90
Monoclinic
P21/c (14)
15.307(4)
8.303(2)
13.152(4)
90
β/°
90
90
7025(3)
8
5.304
90
90
94.66(2)
90
2083.6(10)
2
8.199
1272
92.815(4)
90
1669.5(8)
4
10.165
1056
γ/°
U/Å3
4564.1(17)
8
7.667
Z
μ(Mo-Kα)/mm−1
F(000)
3898
2752
Total number reflns
Rint
Unique reflns
No. of params, restraints
R1, wR2 [I > 2σ(I)]b
R1, wR2 (all data)
17 991
0.040
7968
394, 16
0.046, 0.096
0.071, 0.107
11 444
0.020
5184
293, 4
0.021, 0.047
0.030, 0.050
11 962
0.083
4753
277, 11
0.049, 0.077
0.082, 0.085
9241
0.076
3811
217, 0
0.031, 0.071
0.034, 0.073
[Pb([18]aneO4Se2)-
(BF4)2]
[Pb([18]aneO4Se2)-
(NO3)2]
[Pb(18-crown-6)(NO3)-
(PF6)]PF6
[Pb(18-crown-6)-
(H2O)1.6(PF6)][PF6]·0.6H2O
[Pb([18]-
aneO4Se2)2(PF6)2]
Compound
Formula
M
Crystal system
Space group (no.)
a/Å
b/Å
c/Å
α/°
C12H24B2F8O4PbSe2
771.04
C12H24N2O10PbSe2
721.44
C12H24F6NO9PPb
678.48
Orthorhombic
Pmn21 (31)
12.958(5)
8.475(3)
9.296(3)
90
C12H28.4F12O8.20P2Pb
801.08
Monoclinic
P21/m (11)
8.754(3)
15.230(4)
9.254(3)
90
C12H24F12O4P2PbSe2
887.36
Monoclinic
C2/c (15)
10.953(5)
12.060(5)
15.530(7)
90
Monoclinic
C2/c (15)
10.969(4)
11.735(5)
15.385(6)
90
Monoclinic
C2/c (15)
11.012(4)
12.949(5)
16.105(6)
90
β/°
90.693(6)
90
2051.2(14)
4
11.862
1440
90.382(6)
90
1980.4(14)
4
12.248
1360
90
90
1020.8(5)
2
8.441
91.453(6)
90
1233.4(7)
2
7.096
772
95.402(7)
90
2286.3(14)
4
10.819
1664
γ/°
U/Å3
Z
μ(Mo-Kα)/mm−1
F(000)
652
Total number reflns
Rint
6169
0.057
9116
0.109
6653
0.079
5846
0.030
9667
0.054
Unique reflns
No. of parameters,
restraints
2340
132, 7
2271
141, 4
2334
148, 1
2908
178, 2
2599
150, 0
R1, wR2 [I > 2σ(I)]b
R1, wR2 (all data)
0.039, 0.070
0.056, 0.075
0.060, 0.119
0.085, 0.134
0.049, 0.097
0.058, 0.097
0.063, 0.141
0.076, 0.150
0.031, 0.076
0.033, 0.077
4 1/2
a Common items: temperature = 100 K; wavelength (Mo-Kα) = 0.71073 Å; θ(max) = 27.5°. b R1 = Σ||Fo| − |Fc||/Σ|Fo|; wR2 = [Σw(Fo2 − Fc2)2/ΣwFo
]
.
4722 | Dalton Trans., 2013, 42, 4714–4724
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[Pb([18]aneO4Se2)(PF6)2]: was made similarly to the 18- instruction did not lead to satisfactory convergence (R1
=
crown-6 complex. 1H NMR (CDCl3, 293 K): δ = 3.06 (t, [8H], 0.067). Hence we report the C2/c refinement in Table 1, recog-
SCH2), 3.79 (s, [8H], OCH2), 3.96 (t, [8H], OCH2). 19F{1H} NMR nising that there remains a space group uncertainty. For [Pb-
1
(CDCl3): −72.2 (d, JPF = 710 Hz). 31P{1H} NMR (CDCl3, 295 K): (18-crown-6)(NO3)(PF6)] the data clearly supported the ortho-
1
−143.3 (sept. JPF = 710 Hz). IR (Nujol): 844s (νPF6), 560m rhombic space group Pmn21 (or less likely Pnmm), but the use
(δPF6) cm−1
X-ray crystallography
.
of the usual structure solution software failed to produce a
trial model that developed. A trial structure did arise in the
monoclinic space group P21 with the same cell (β = 90°) which
Details of the crystallographic data collection and refinement refined to R1 = 0.052, but inspection of the cell packing
parameters are given in Table 1. Crystals suitable for single diagram showed a convincing mirror plane and comments in
crystal X-ray analysis were obtained as described above. Data ‘checkcif’ supported the additional symmetry. Transformation
collections used a Rigaku AFC12 goniometer equipped with an of the coordinate system to suit the orthorhombic cell and
enhanced sensitivity (HG) Saturn724+ detector mounted at the positioning the monoclinic (pseudo) mirror on the genuine
window of an FR-E+ SuperBright molybdenum (λ = 0.71073 Å) mirror by shifting the atomic coordinates finally yielded the
rotating anode generator with VHF Varimax optics (100 μm reported structure.
focus) with the crystal held at 100 K (N2 cryostream). Structure
solution and refinement were straightforward,41,42 except as
detailed below, with H atoms bonded to C being placed in cal-
culated positions using the default C–H distance. For [Pb([15]-
Acknowledgements
aneO3S2)2][BF4]2·nCH2Cl2 (n = 1.22) the [BF4]− (B2 centred)
We thank the EPSRC and the University of Southampton for
support, and Dr M. Webster for assistance with the X-ray
crystallography.
anion was modelled as two conformations, with F6–F8 were
split into A and B sites, and DFIX constraints were applied to
the B–F and F⋯F distances of the A and B positions and
retaining isotropic adp’s. The proportions of A and B were
allowed to vary through FVAR2. The discrete CH2Cl2 solvent
identified in the difference map also showed disorder, which
was modelled satisfactorily. For the partially occupied (0.22)
CH2Cl2 molecule Cl3 (A and B) were included in the model
based on the Cl3A⋯Cl3A′ and Cl3B⋯Cl3B′ distances, but the
C atom was not identified (sof for Cl3A = 0.26 and for Cl3B =
0.17). For [Pb(15-crown-5)2][H3O][BF4]3 the positions of the Pb,
the [BF4]− anions and O atoms of the [H3O]+ were readily
located, and the 15-crown-5 ligands are clearly coordinated to
form [Pb(15-crown-5)2]2+. However, the C and O atoms of the
crowns were badly disordered, and resisted a satisfactory dis-
order model. Similar disorder has been noted in other crown
ether complexes.6,43 Hence, the data reported simply serve to
confirm the gross structure and the absence of any significant
[BF4]− interactions with the Pb ion.
The crystals for [Pb([18]aneO4Se2)(NO3)2] are isostructural
with [Pb([18]aneO4Se2)(BF4)2], and the data were solved in
space group C2/c, leading to a molecule with two-fold sym-
metry and disordered nitrate groups (but all other atoms
refined well). These were modelled using split O atom occu-
pancies for O4 and O5 with sofs of 0.5 (see Fig. 6). The alterna-
tive, non-centrosymmetric Cc refinement was also attempted,
(in which the molecule has no crystallographic symmetry). In
this model the two independent nitrate anions (N1, N2, O5–
O10) are not related by an approximate 2-fold axis – the two
plane normals are approximately perpendicular to each other
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