New nickel(ii) and iron(ii) helicates and tetrahedra derived from expanded quaterpyridines

Article abstract of DOI:10.1039/c1dt10667h

As an extension of prior studies involving the linear quaterpyridine ligand, 5,5″′-dimethyl-2,2′:5′,5″:2″, 2″′-quaterpyridine 1, the synthesis of the related expanded quaterpyridine derivatives 2 and 3 incorporating dimethoxy-substituted 1,4-phenylene and tetramethoxy-substituted 4,4′-biphenylene bridges between pairs of 2,2′-bipyridyl groups has been carried out via double-Suzuki coupling reactions between 5-bromo-5′-methyl-2′- bipyridine and the appropriate di-pinacol-diboronic esters using microwave heating. Reaction of 2 and 3 with selected Fe(ii) or Ni(ii) salts yields a mixture of both [M₂L₃]⁴⁺ triple helicates and [M₄L₆]⁸⁺ tetrahedra, in particular cases the ratio of the products formed was shown to be dependent on the reaction conditions; the respective products are all sufficiently inert to allow their chromatographic separation and isolation. Longer reaction times and higher concentrations were found to favour tetrahedron formation. The X-ray structures of solvated [Ni₂(2)₃](PF₆)₄, [(PF₆) ? Fe₄(2)₆](PF₆) ₇, [Fe₄(3)₆](PF₆)₈ and [Ni₄(3)₆](PF₆)₈ have been determined, while the structure of the parent Fe(ii) cage in the series, [(PF₆) ? Fe₄(1)₆](PF₆) ₇, was reported previously. The internal volumes of the Fe(ii) tetrahedral cages have been calculated and increase from 102 A³ for [Fe₄(1)₆]⁸⁺ to 227 A³ for [Fe₄(2)₆]⁸⁺ to 417 A³ for [Fe₄(3)₆]⁸⁺ and to an impressive 839 A³ for [Ni₄(3)₆]⁸⁺. The corresponding void volume in the triple helicate [Ni₂(2) ₃]⁴⁺ is 29 A³.

Full text of DOI:10.1039/c1dt10667h

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PAPER
New nickel(II) and iron(II) helicates and tetrahedra derived from expanded
quaterpyridines†
Christopher R. K. Glasson,a George V. Meehan,*a Cherie A. Motti,b Jack K. Clegg,c,d Peter Turner,c
Paul Jensenc and Leonard F. Lindoy*c
Received 15th April 2011, Accepted 8th June 2011
DOI: 10.1039/c1dt10667h
As an extension of prior studies involving the linear quaterpyridine ligand, 5,5¢¢¢-dimethyl-2,2¢:5¢,5¢¢:2¢¢,
2¢¢¢-quaterpyridine 1, the synthesis of the related expanded quaterpyridine derivatives 2 and 3
incorporating dimethoxy-substituted 1,4-phenylene and tetramethoxy-substituted 4,4¢-biphenylene
bridges between pairs of 2,2¢-bipyridyl groups has been carried out via double-Suzuki coupling
reactions between 5-bromo-5¢-methyl-2¢-bipyridine and the appropriate di-pinacol-diboronic esters
using microwave heating. Reaction of 2 and 3 with selected Fe(II) or Ni(II) salts yields a mixture of both
[M2L3]4+ triple helicates and [M4L6]8+ tetrahedra, in particular cases the ratio of the products formed
was shown to be dependent on the reaction conditions; the respective products are all sufficiently inert
to allow their chromatographic separation and isolation. Longer reaction times and higher
concentrations were found to favour tetrahedron formation. The X-ray structures of solvated
[Ni2(2)3](PF6)4, [(PF6) Ã Fe4(2)6](PF6)7, [Fe4(3)6](PF6)8 and [Ni4(3)6](PF6)8 have been determined, while
the structure of the parent Fe(II) cage in the series, [(PF6) Ã Fe4(1)6](PF6)7, was reported previously. The
3
˚
internal volumes of the Fe(II) tetrahedral cages have been calculated and increase from 102 A for
3
8+
3
8+
3
8+
[Fe4(1)6]8+ to 227 A for [Fe4(2)6] to 417 A for [Fe4(3)6] and to an impressive 839 A for [Ni4(3)6] .
˚
˚
˚
3
The corresponding void volume in the triple helicate [Ni2(2)3]4+ is 29 A .
˚
More recently, we have focused our attention on the metal-directed
Introduction
assembly of such discrete systems exhibiting increased size and/or
structural complexity.8–12 Clearly an approach for achieving larger
systems is to increase the size of the organic component(s)
employed. Nevertheless, it is noted that as individual components
become larger they also tend to become more flexible and multiple
products, often in equilibrium, may result; sometimes these exhibit
similar component ratios. Thus, when essentially linear ligand
systems are involved, M3L3 triangles are frequently formed along
with M4L4 squares, or M2L3 helices with M4L6 tetrahedra.13–15
Hence, the balance between flexibility and rigidity of the (typically)
di- or polytopic ligands employed in self-assembly processes can
be an important factor in achieving a particular supramolecular
architecture.16,17 Clearly, in this context the choice of metal
ion is also important. For example, in previous studies, it was
shown that the near-rigid, linear ditopic ligand, 5,5¢¢¢-dimethyl-
2,2¢:5¢,5¢¢:2¢¢,2¢¢¢-quaterpyridine 1, yields [Fe4L6]8+ tetrahedra when
reacted with a range of Fe(II) salts (often spontaneously including
an anion in the central cavity of the tetrahedral cage).4,5 However,
with this ligand the slightly larger and more kinetically inert Ru(II)
forms a [Ru2L3]4+ triple helicate under the conditions employed.13
As an extension of the above studies, we now report the results of
a comparative investigation of the effect of extending the structure
of quaterpyridine 1 on the nature of the metallo-supramolecular
assemblies formed with selected Fe(II) and Ni(II) salts. In the
present study we have synthesised the extended quaterpyridine
Considerable interest continues to be given to the metal-ion
directed assembly of metallosupramolecular systems that enclose
a central cavity – especially when the latter displays host–guest
chemistry.1–3 However, the design and synthesis of such multi-
component assemblies showing predefined properties continues
to offer a considerable challenge. Typically the strategy employed
involves the selection of ligand(s) and metal(s) displaying appro-
priate electronic and steric properties that will act in concert to
promote formation of the required assembly. Like many others,
we have employed such an approach for the synthesis of a range of
discrete structures incorporating 2- and 3-dimensional voids, many
of which were demonstrated to include guest molecules or ions.4–7
aSchool of Pharmacy and Molecular Sciences, James Cook University,
Townsville, Qld. 4814, Australia. E-mail: George.Meehan@jcu.edu.au
bThe Australian Institute of Marine Science, Townsville, 4810, Qld.,
Australia
cSchool of Chemistry, F11, The University of Sydney, NSW, 2006, Australia.
E-mail: lindoy@chem.usyd.edu.au; Fax: +61 2 93513329
dDepartment of Chemistry, The University of Cambridge, Lensfield Rd,
Cambridge, UK, CB2 1EW
† Electronic supplementary information (ESI) available: further details of
the NMR, UV/vis, fluorescence studies and cage void representations
and organic precursor synthesis for selected systems. CCDC reference
numbers 822504–822507. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1dt10667h
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10481–10490 | 10481
©

ligands, 2 and 3, respectively incorporating methoxy-substituted
phenyl and biphenyl bridges between the bipyridyl metal-binding
domains of 1. It was of particular interest to probe what effect
the inherent additional flexibility of the extended ligand systems
2 and 3 might have on the corresponding metallosupramolecular
systems generated (Fig. 1).
15 13C resonances were present). The ESI-HRMS of the higher Rf
product showed +2, +3, and +4 ions corresponding to successive
-
losses of PF6 from the formula Fe2(2)3(PF6)4, while that for the
lower Rf material gave +3, +4, and +5 ions corresponding to
successive losses of PF6- from the formula Fe4(2)6(PF6)8. Thus the
MS and NMR data (see ESI) are in accord with the formulation of
these products as [Fe2(2)3](PF6)4 and [Fe4(2)6](PF6)8, respectively
– with the possibility that the latter complex might encapsulate an
anion, as occurs in [(PF6) Ã Fe4(1)6](PF6)7,5 not able to be ruled
out.
In subsequent experiments in which the microwave reaction
time was lengthened and/or the concentration of the reactants
increased it was observed that the reaction was driven towards
the sole formation of [Fe4(2)6](PF6)8, in agreement with the
[Fe4(2)6]8+cation being the thermodynamic product. The 19F NMR
spectrum of [Fe4(2)6](PF6)8 in CD3CN gave a single resonance
-
for the PF6 counterions – indicating the presence of a single
Fig. 1 The quaterpyridine ligands, 2 and 3 synthesised as part of the
present study.
environment with respect to the NMR time scale. Thus the
spectrum is not diagnostic for anion inclusion in the cationic
tetrahedral cage (if inclusion were to occur, exchange in and out
of the cage was anticipated to be fast given the expected larger size
of both the cavity and the faces of the [Fe4(2)6]8+ cation relative to
Results and discussion
those of [Fe4(1)6]8+ for which slow PF6 exchange was observed).5
-
Quaterpyridine ligand synthesis
No crystals of [Fe2(2)3](PF6)4 suitable for X-ray crystallography
were obtained. However, reaction of 2 with Ni(II) resulted in yellow
crystals that were suitable. The resulting crystal structure revealed
the formation of a dinuclear triple helicate of type [Ni2(2)3](PF6)4
The syntheses of expanded quaterpyridine 2 in 83% and its
further expanded analogue 3 in 95% yield were conducted using
microwave driven18 bis-Suzuki couplings of bipyridine with the
boronic esters, 1,4¢-Bis-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan)-
2,5-dimethoxybenzene and 4,4¢-bis-(4,4,5,5-tetramethyl[1,3,2]-
dioxaborolan)-1,1¢-(2,2¢,5,5¢-tetramethoxy)biphenyl, respective-
ly.19 The 1H and 13C NMR spectra of both 2 and 3 were consistent
with the expected two fold symmetry for these products. Signals for
the 2,2¢-bipyridyl moieties of each compound were assigned using
NOESY and COSY measurements. As expected, the assignment
of shifts corresponding to the dimethoxyphenylene bridge of 2
was straightforward, with one aromatic singlet (d = 7.07 ppm)
and one methoxy singlet (d = 3.86 ppm) being evident. However,
the presence of closely spaced peaks for the different aromatic
and methoxy protons on the tetramethoxybiphenylene-bridge of
˚
with its two octahedral Ni(II) centres separated by 11.8 A and
bridged by three quaterpyridine ligands (Fig. 2). The helicate
crystallises in the hexagonal chiral space group P6322 with one
third of the complex in the asymmetric unit; the stereochemistry
of the metal centres in each discrete helix is either DD (P) or
KK (M) and each crystal is itself optically active. The chiral
twist of the helicate extends the entire length of the molecule
and equates to 66◦. Despite full conjugation the ligands are not
flat but are bent 35◦ from an idealised planar form. The central
dimethoxyphenylene rings are twisted such that they are orientated
about the centre of the helix to form an enclosed void-space, the
3
volume of which was calculated by Voidoo22 to be 29 A (Fig. 2).
˚
1
3 made full assignment of its H NMR spectrum difficult. The
HRMS data for both 2 and 3 were both in accord with the
proposed structures.
[M2L3]4+ helicates and [M4L6]8+ tetrahedra
In an initial experiment, microwave heating of Fe(BF4)2·6H2O and
2 in acetonitrile in a pressurised microwave vessel resulted in a red
solution; thin layer chromatography (TLC) of this solution showed
that a mixture of two deep red products was present. The 1H NMR
spectrum of the mixture was in accord with the two fold symmetry
of quaterpyridine 2 being retained in each case and indicated that
a 1 : 2 ratio of the two species was formed under the reaction
conditions employed. Subsequent column chromatography on
silica gel using previously reported conditions20 resulted in their
efficient separation. The deep red colour of each compound was
in keeping with the presence of a low-spin d6 [Fe(bipyridine)3]2+
Fig. 2 a) Crystal structure of [Ni2(2)3](PF6)4 viewed perpendicular to its
C3-axis; b) view down the C3-axis showing the helical twist and c) with
Voidoo22 calculated void volume shown as a green mesh.
Crystals of [Fe4(2)6](PF6)8 suitable for X-ray diffraction were
grown from tetrahydrofuran/acetonitrile and the resulting struc-
ture confirmed the formation of a tetrahedral assembly (Fig. 3a
1
chromophore in each case.21 The respective H NMR and 13C
-
NMR spectra of the separated products in CD3CN once again
confirmed that 2 exhibited C2 symmetry in each species (8 1H and
and 3b). Interestingly, a PF6 anion (disordered over two posi-
tions) and a quarter occupancy acetonitrile solvent molecule are
10482 | Dalton Trans., 2011, 40, 10481–10490
This journal is
The Royal Society of Chemistry 2011
©

455 nm and a weaker emission at 761 nm were observed when
[Fe4(2)6](PF6)8 was irradiated at 386 nm. The higher energy
emissions of both complexes are strongly concentration dependent
in agreement with the presence of intermolecular quenching
and thus there is the possibility that aggregation behaviour may
occur in solution. Clearly the photophysical characteristics suggest
potential applications;23,24 for example, for fluorescent signalling
of a host–guest interaction for use in a guest-specific sensor.25
In this context we have already demonstrated that [Fe4(1)6]8+
discriminates between particular anions.5
In a parallel synthesis to that of [Fe2(2)3](PF6)4, reaction of the
tetramethoxybiphenylene quaterpyridine 3 with Fe(II) resulted in
the generation of both [Fe2(3)3](PF6)4 and [Fe4(3)6](PF6)8 as prod-
ucts in an approximate 1 : 9 ratio respectively (based on the NMR
spectrum of the initial crude product). In subsequent syntheses
the individual assemblies were isolated following chromatography
on silica gel. The mass spectrum of [Fe2(3)3](PF6)4 gave +3 and
-
+4 ions consistent with the successive losses of PF6 from the
above formula. At 300 K the 1H NMR spectrum of this product
showed five relatively sharp aromatic signals corresponding to
pyridyl protons in the 3- and 4-positions together with the
phenylene protons in the 6,6¢-positions. Three broad aromatic
peaks corresponding to pyridyl protons in the 6¢¢-positions and
biphenylene protons in the 3,3¢-positions were also present (see
ESI)†. This suggested the presence of a dynamic process on the
Fig. 3 Representations of the crystal structure of [Fe4(2)6 … PF6](PF6)7; a)
illustrates the encapsulated PF6- guest, b) is a space filling diagram viewed
down a C3-axis and c) shows the void volume of the cage (green mesh) as
calculated by Voidoo;22 counterions, solvent and disorder are removed for
clarity.
1
NMR timescale. Variable temperature H NMR measurements
over a limited temperature range resulted in a clear change in
the spectrum: at 290 K the broad peaks observed at ambient
temperature are further broadened, whilst at 310 K the peaks
begin to sharpen; some minor signal shifts were also observed.
However, in the absence of further data it is inappropriate to
speculate further about the origins of this behaviour. As for
[Fe2(2)3]4+ and [Fe4(2)L6]8+, [Fe2(3)3]4+ and [Fe4(3)L6]8+ can be
separated chromatographically; however, in this case the dinuclear
species, [Fe2(3)3]4+, in acetonitrile was observed to undergo partial
conversion to [Fe4(3)6]8+ over a three day period. Once again,
the evidence suggests that the tetrahedral cage [Fe4(3)6]8+ is the
thermodynamically favoured product.
encapsulated within the cage such that the solid state formula
is [{(PF6)(MeCN)0.25} Ã Fe4(2)6]·7PF6· 2.75 MeCN·9.35H2O. The
¯
product crystallises P1 and individual Fe(II) centres in each tetra-
hedron contain homochiral metal centres; that is, each tetrahedron
is either KKKK or DDDD rendering the cage T-symmetric. Each
of the ligands (which bridge metals of the same handedness) are
arranged such that the chelating groups are orientated mutually
anti to each other. The chiral twist associated with each [Fe4(2)6]8+
tetrahedron is evident when viewed down one of the C3-axes
(Fig. 3b); the ligands are twisted some 20◦ from an idealised
planar anti-configuration. The average distance between each of
In contrast to the 1H NMR spectrum of [Fe2(3)3](PF6)4,
[Fe4(3)6](PF6)8 gave a sharp spectrum with the expected 11 1H and
19 13C resonances, indicating again that 3 exhibits C2-symmetry
within the complex. As before, protons in the 6¢¢- and 6¢¢¢-positions
give resonances that were shifted upfield relative to those of the free
ligand (see ESI†). This product is stable in solution for months,
consistent with it being favoured thermodynamically. The mass
spectrum showed +3 to +7 ions corresponding to successive losses
˚
the Fe(II) centres is 13.43 A, which is significantly longer than the
8+
˚
9.45 A observed in the crystal structures of [Fe4(1)6] reported
previously.5 As calculated by Voidoo22 the void volume of the
small tetrahedral cation, [Fe4(1)6]8+ (see ESI), is 102 A , similar
3
˚
to that reported for other similarly sized tetrahedra while that for
the larger tetrahedron incorporating 2 now reported is increased
3
-
˚
to 227 A . Interestingly, this calculated volume is lower than that
of PF6 from the formula [Fe4(3)6](PF6)8.
calculated if the encapsulated volume is considered a tetrahedron
The red colour of both [Fe2(3)3](PF6)4 and [Fe4(3)6](PF6)8
once again suggested the presence of a [Fe(bipyridine)3]2+
chromophore.21 The UV-vis and fluorescence properties of
[Fe2(3)3](PF6)4 and [Fe4(3)6](PF6)8 parallel those described for
[Fe2(2)3](PF6)4 and [Fe4(2)6](PF6)8. Each shows a MLCT band at
~530 nm. The most noticeable differences in the UV-vis spectra
are the CT (p–p*) bands associated with the presence of the
tetramethoxybiphenylene bridge; there is a small blue shift for
[Fe2(3)3](PF6)4 (365 nm) relative to the corresponding absorption
for [Fe4(3)6](PF6)8 (376 nm) (see ESI†). Fluorescence spectroscopy
revealed a strong emission (blue) at 451 nm and a weaker emission
at 719 nm resulting from excitation of [Fe2(3)3](PF6)4 at 365 nm.
3
˚
with edge length equal to the metal–metal distance (285 A ). This
in part reflects the twisted orientations of the dimethoxyphenylene
rings, with the methoxy groups intruding into the cavity reducing
the encapsulated volume somewhat.
The most noticeable difference in the UV-vis spectra of
[Fe4(2)6](PF6)8 and [Fe2(2)3](PF6)4 (see ESI†) is that the MLCT
band for the former (386 nm) shows a small shift relative to
the latter (374 nm). The fluorescence spectrum of [Fe2(2)3](PF6)4
in acetonitrile (see ESI†) revealed a strong emission at 450 nm
(blue) and a weaker emission at 736 nm resulting from excitation
of this complex at 374 nm. Similarly, a strong emission at
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10481–10490 | 10483
©

Similarly a strong emission at 453 nm and a weaker emission
at 743 nm were observed when [Fe4(3)6](PF6)8 was irradiated
at 376 nm (see ESI†). As for the corresponding complexes of
2, the higher energy emissions for both complexes are strongly
concentration dependent26 in keeping with the occurrence of
intermolecular quenching and possible concomitant aggregation
behaviour.
The chelating moieties of each ligand are approximately planar.
˚
The average Fe–Fe distance is 16.9 A, which corresponds to a
substantial Voidoo22 calculated cavity volume of approximately
3
3
˚
˚
417 A , which again is smaller than 570 A encapsulated by the
metal–metal tetrahedron.
The possibility that [Fe4(3)6]8+ may encapsulate a BPh4 anion
-
-
3 31
˚
was also probed. BPh4 has a volume of 368 A , which corre-
sponds to a fill ratio of 44% for the T-symmetric [M4(3)6]8+ species
(see below). Based on related species, such a ratio suggested that
BPh4- would be a suitable guest.1,9,32 From inspection of the crystal
structure of [Fe4(3)6]8+, paying particular attention to the size of the
Crystals of [Fe4(3)6](PF6)8 suitable for X-ray diffraction were
grown from THF/CH3CN and the resulting structure once again
confirmed the presence of a tetrahedral assembly (Fig. 4). The
product crystallises in the centric tetragonal space group I 41/a and
-
¯
is situated around a 4 special position. In contrast to the tetrahedra
faces, it seems likely that a BPh4 anion would be able to undergo
so far discussed, in the X-ray structure there are no encapsulated
guest molecules. Each tetrahedron possesses two K and two D
metal centres resulting in idealised S4 symmetry. Interestingly,
the 1H NMR of this material (see earlier) indicated that this
is not the case in the solution where the spectrum is in accord
with a T-symmetric isomer exclusively. Perhaps this indicates
the presence of a level of fast equilibration in solution with
respect to the NMR timescale. However, reported rates27–29 for the
racemisation reaction of [Fe2(2,2¢-bipyridine)3)]2+ (using a range
of experimental conditions) are slow in comparison to the NMR
timescale. Hence fast racemisation at the metal centres seems
unlikely, particularly since M4L6 systems related to the current
system are reported to result in much slower rates of racemi-
sation than their mononuclear counterparts.30 Alternatively, the
preferential crystallisation of the KKDD stereoisomer following
a slow isomerisation from either KKKK or DDDD-steroisomers
may occur. Related solution/crystallisation behaviour has been
observed in similar sized cage molecules.7,9 Reflecting the S4
symmetry of [Fe4(3)6]8+, and in contrast to the T-symmetric com-
plexes [Fe4(1)6]8+ and [Fe4(2)6]8+, there are two ligand arrangements
present. The bipyridine domains in two individual ligands adopt
approximate anti arrangements (linking metal centres of the same
chirality), with the remaining four ligands exhibiting near syn
arrangements (linking metal centres of opposite chirality)7,9,30
a ‘through side’ exchange process (assuming some flexibility in the
bound ligand structures).33 1H NMR experiments to investigate
this possibility were undertaken. One equivalent of BPh4 was
-
added to a solution of [Fe4(3)6](BF4)8 in CD3CN and the changes
in the spectrum compared (see ESI†). Significant broadening of
the 6,6¢-proton and the 2,2¢-methoxy-proton signals were observed
and the possibility that dynamic behaviour was present was probed
using variable temperature NMR. As the temperature was lowered
further broadening occurred until at 280 K the above-mentioned
peaks were almost obscured; increasing the temperature to 340 K
led to a sharpening of these peaks. This behaviour is consistent
with an anion exchange process occurring on the NMR timescale.
-
Further evidence for possible BPh4 encapsulation came from a
-
fluorescence study. One equivalent of BPh4 was added to an
acetonitrile solution of [Fe4(3)6](BF4)8 and comparison of the
fluorescence emission spectra of this and the starting solution on
irradiation at 376 nm revealed a large increase in emission intensity
at 453 nm for the former coupled with a decrease at 742 nm (ESI†).
This enhancement of the higher energy emission may possibly
be related to partial desolvation of the [Fe4(3)6]8+ cavity through
-
inclusion of BPh4 , leading to a subsequent reduction in solvent
mediated quenching.24 However such a proposal is, of course, not
unequivocal.
Interestingly, an analogous metal-directed assembly of
3
a
using NiCl2·6H2O in place of Fe(BF4)2·6H2O, yielded
solid product whose ESI-HRMS revealed the presence
of both [Ni2L3]4+ and [Ni4L6]8+ assemblies. Recrystallisation
from an acetonitrile/methanol/tetrahydrofuran mixture, how-
ever, yielded single crystals of [{(H2O)0.5(THF)0.75(MeCN)0.5}
à Ni4(3)6](PF6)8·5.5MeCN·5THF·MeOH·4.075H2O suitable for
X-ray diffraction. The structure revealed, in contrast to
[Fe4(3)6](PF6)8, that a T-symmetric homochiral tetrahedron re-
sulted. Once again, like [Fe4(1)6](PF6)8 and [Fe4(2)6](PF6)8, each
tetrahedron corresponds to either a KKKK-[Ni4(3)6](PF6)8 or
a DDDD-[Ni4(3)6](PF6)8 entity (Fig. 5) with the average Ni–Ni
˚
distance being 17.4 A. As with other homochiral tetrahedra,
each of the ligands is arranged with its chelating moieties in
an approximate anti orientation and the bipyridine groups are
not co-planar, with a twist from planarity of 22◦ being observed.
1
3
˚
The Voidoo calculated volume of this species is 839 A placing
it amongst the largest encapsulated volumes reported for such
a complex.1,9,15 This volume is almost twice that calculated for
[Fe4(3)6](PF6)8 which reflects both the higher symmetry of the cage
(resulting in longer M–M distances), the presence of guest solvent
molecules, and a more open structure with the methoxy groups
aligned closer to the faces of the tetrahedron. This substantial
difference in volume also indicates the flexibility of the cage
Fig. 4 X-ray structure of [Fe4(3)6](PF6)8·12.5THF.
10484 | Dalton Trans., 2011, 40, 10481–10490
This journal is
The Royal Society of Chemistry 2011
©

Individual products have been isolated and in four cases their
crystal structures determined. The calculated cavity volumes of
the present series of Fe(II) and Ni(II) tetrahedral cages increase
3
8+
3
8+
3
˚
˚
˚
from 102 A for [Fe4(1)6] to 227 A for [Fe4(2)6] to 417 A for
[Fe4(3)6]8+ and to an impressive 839 A for [Ni4(3)6] . Preliminary
evidence suggests that the larger tetrahedral cages may display
interesting host–guest chemistry and further studies to probe this
aspect are planned for the future.
3
8+
˚
Experimental
NMR spectra were recorded on a Bruker AM-300 or a Varian
Mercury 300 MHz spectrometer (300.133 MHz) at 298 K.
Electrospray (ES) high resolution Fourier transform ion cyclotron
resonance mass spectrometry (FTICR-MS) measurements on
a Bruker BioAPEX 47e mass spectrometer equipped with an
Analytica of Branford electrospray ionisation (ESI) source.
The fluorescence spectrum was obtained on a Perkin Elmer
LS55 spectrofluorimeter, 2-bromo-1,4-dimethoxybenzene,34
2-trimethylstannyl-5-methyl pyridine, 5-bromo-5¢-methyl-2,2¢-
bipyridine35 and 1,4-diiodo-2,5-dimethoxybenzene36 were
prepared by reported procedures. The boronic esters 1,4¢-bis-(4,4,
5,5-tetramethyl[1,3,2]dioxaborolan)-2,5-dimethoxybenzene and
4,4¢-bis-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan)-1,1¢-(2,2¢,5,5¢-
tetramethoxy)biphenyl were prepared by a modification of a
reported procedure37 (see below) in which the more reactive
t-butyllithium was employed in two-fold excess and reaction times
were extended up to 3 h at -78 ◦C to ensure that bis-lithiation
had occurred prior to treatment with 2-isopropoxy-4,4,5,5-
tetramethyl-[1,3,2]dioxaborolane. An additional comment on
the synthesis of 4,4¢-dibromo-2,5,2¢,5¢-tetramethoxy-biphenyl is
presented in the ESI.†
Fig. 5 a) The crystal structure of [Ni4(3)6](PF6)8, b) a space filling
representation and c) the void volume in the cage (green mesh) as calculated
by Voidoo;22 counterions, solvent and disorder are removed for clarity.
system15,33 and hence reinforces the observations concerning anion
binding discussed above.
Finally, a comparison of the structures of the cations in
[Fe4(3)6](PF6)8 and [Ni4(3)6](PF6)8 viewed perpendicular to a C3-
axis illustrating the difference in the chiral arrangements at the
metal centres is presented in Fig. 6.
1,4¢-Bis-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan)-2,5-
dimethoxybenzene
t-Butyllithium (9.4 cm3, 1.7 M in pentane, 16 mmol) was added
dropwise to a stirred solution of 1,4-diiodo-2,5-dimethoxybenzene
(1.56 g, 4 mmol) in dry tetrahydrofuran (30 cm3) at -78 ◦C.
The reaction was stirred for a further 1 h at -78 ◦C and this
was followed by the dropwise addition of 2-isopropoxy-4,4,5,5-
tetramethyl-[1,3,2]dioxaborolane (2.98 g, 16 mmol). The reaction
mixture was allowed to warm to room temperature and stirred
overnight. After removal of the tetrahydrofuran under vacuum,
H2O (30 cm3) was added and the pH adjusted to 8 using 1 M
HCl. The product was extracted with Et2O (2 ¥ 30 cm3) and
the combined organic phases washed with brine and dried over
Na2SO4. The solvent was removed under vacuum and the crude
material purified by recrystallisation from petrol affording the
product (1.17 g, 80%) as white microcrystals.1H NMR (300 MHz,
CDCl3): d = 1.36 (s, 24 H, CH3), 3.75 (s, 6 H, OCH3), 7.05 (s, 2
H, H-3,6); 13C NMR (75 MHz, CDCl3): d = 25.05, 57.17, 83.81,
119.03, 158.27.
Fig.
6 Comparative views of the X-ray crystal structures of a)
[Fe4(3)6](PF6)8 and b) [Ni4(3)6](PF6)8 viewed perpendicular to a C3-axis;
[Fe4(3)6](PF6)8 has S4 symmetry; anti-ligands bridge metals of the same
chirality, syn-ligands bridge metals of opposite handedness; [Ni4(3)6](PF6)8
has T symmetry; anti-ligands bridge all metals as it is homochiral;
hydrogens, counterions and solvent are removed for clarity.
Concluding remarks
In this report we have demonstrated that the interaction of the
extended quaterpyridines 2 and 3 with octahedral Fe(II) or Ni(II)
metal ions resulted in mixtures of [M2L3]4+ helicates and [M4L6]8+
tetrahedra. A level of control over the relative ratio of these
products was demonstrated using a variation of the reaction
time and/or the degree of dilution employed for the synthesis.
2,5,2¢,5¢-Tetramethoxybiphenyl
A suspension of [NiCl2(PPh3)2] (4.38 g, 7 mmol), zinc metal (1.96 g,
30 mmol) and tetraethylammonium iodide (5.66 g, 22 mmol) in
dry tetrahydrofuran (50 cm3) was degassed with N2 for 0.5 h. This
solution was then stirred until a deep maroon colour developed
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10481–10490 | 10485
©

(~0.5 h). To this was added a nitrogen purged tetrahydrofuran
(10 cm3) solution of 2-bromo-1,4-dimethoxybenzene (4.34 g,
20 mmol) and the reaction mixture was heated at 50 ◦C for
20 h. On cooling to room temperature, 5 M NH3 (50 cm3) was
added and the resulting reaction mixture stirred overnight. Ethyl
acetate (40 cm3) was added and the mixture was filtered through
celite. The organic phase was isolated and the aqueous layer
was extracted with ethyl acetate (40 cm3). The organic fractions
were combined and extracted with 4 M HCl (3 ¥ 40 cm3). The
aqueous layer was neutralised with NaOH pellets, extracted with
dichloromethane (3 ¥ 40 cm3) and the dichloromethane extracts
dried over Na2SO4. The solvent was removed under vacuum and
the solid that remained was purified by chromatography on silica
gel with a 2 : 1 mixture of petrol: dichloromethane as eluent to
sealed pressurised microwave vessel with temperature and pressure
sensors and a magnetic stirrer bar (Step 1 – the temperature was
ramped to 120 ◦C over 2 ◦min using 100% of 400 W; Step 2 – the
solution was held at 120 C for 8–20 min using 30% of 400 W).
H2O (20 cm3) was added and the res ulting precipitate was isolated
by filtration. Recrystallisation of the crude product from methanol
1
afforded 2 (1.06 g, 83%) as pale yellow microcrystals. H NMR
(300 MHz, CDCl3): d = 2.42 (s, 6 H, CH3), 3.86 (s, 6 H, OCH3),
7.07 (s, 2 H, H-3,6), 7.67 (dd, 3J = 8.1 Hz, 4J = 1.8 Hz, 2 H, H-4¢¢),
3
4
3
8.07 (dd, J = 8.1 Hz, J = 2.1 Hz, 2 H, H-4¢), 8.36 (d, J = 8.1
Hz, 2 H, H-3¢¢), 8.46 (d, 3J = 8.1 Hz, 2 H, H-3¢); 8.55 (d, 4J = 1.8
Hz, 2 H, H-6¢¢), 8.91 (d, J = 2.1 Hz, 2 H, H-6¢) (Scheme 1);13C
4
NMR (75 MHz, CDCl3): d = 18.64, 56.67, 114.47, 120.29, 120.45,
120.93, 127.51, 127.74, 133.77, 137.91, 149.64, 149.77, 151.32,
153.46, 154.74; positive ion ESI-HRMS: m/z (M = C30H27N4O2; in
dichloromethane/methanol): calcd for [M + H]+: 475.2134, found
475.2124; calcd for [M + Na]+: 497.1954, found 497.1940.
1
afford the product (1.92 g, 70%) as a white crystalline solid. H
NMR (300 MHz, CDCl3): d = 3.74 (s, 6 H, OCH3), 3.79 (s, 6 H,
OCH3), 6.84–6.95 (m, 6 H, H-3,3¢,4,4¢,6,6¢).
4,4¢-Dibromo-2,5,2¢,5¢-tetramethoxy-biphenyl
A stirred solution of 2,5,2¢,5¢-tetramethoxybiphenyl (1.70 g,
6.2 mmol) and N-bromosuccinimide (3.31 g, 18.6 mmol) in
dichloromethane (30 cm3) was refluxed for 10 h. The resulting
reaction mixture was washed with H2O and the organic layer dried
over Na2SO4. The crude material was purified by chromatography
on silica gel with a 1 : 1 mixture of dichloromethane/petrol as
eluent to afford the product (2.57 g, 96%) as a white crystalline
solid. 1H NMR (300 MHz, CDCl3): d = 3.74 (s, 6 H, OCH3), 3.86
(s, 6 H, OCH3), 6.83 (s, 2 H, H-6,6¢), 7.18 (s, 2 H, H-3,3¢); 13C
NMR (75 MHz, CDCl3): d = 56.79, 57.10, 111.17, 115.42, 117.06,
126.85, 150.06, 151.42.
Scheme 1 The numbering scheme used for the assignment of the 1H NMR
resonances in 2.
4,4¢-Bis[5¢¢-(5¢¢¢-methyl-2¢¢,2¢¢¢-bipyridyl)]-(2,2¢,5,5¢-
tetramethoxy)biphenyl (3)
4,4¢-Bis-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan)-1,1¢-(2,2¢,5,5¢-
The procedure was as for the synthesis of 2 but using 5-bromo-
5¢-methyl-2,2¢-bipyridine (277 mg, 1.11 mmol), 4,4¢-bis-(4,4,5,5-
tetramethyl[1,3,2]dioxaborolan)-1,1¢-(2,2¢,5,5¢-tetramethoxy)bi-
phenyl (263 mg, 0.5 mmol), K2CO3 (460 mg, 3.33 mmol) and
Pd(PPh3)4 (38 mg, 0.03 mmol) in DMF (7 cm3). After standard
workup the crude product was purified by chromatography on
silica gel with dichloromethane (97.5%), methanol (2%) and
saturated aqueous NH3 (0.5%) as eluent to afford the product
(260 mg, 95%) as an off-white solid. 1H NMR (300 MHz, CDCl3):
d = 2.41 (s, 6H, CH3), 3.82 (s, 6H, 2,2¢ or 5,5¢-OCH3), 3.85 (s, 6H,
2,2¢ or 5,5¢-OCH3), 7.03 (s, 2H, H-3,3¢ or 6,6¢), 7.06 (s, 2H, H-3,3¢ or
6,6¢), 7.69 (dd, 3J = 8.1 Hz, 4J = 1.5 Hz, 2H, H-4¢¢¢), 8.09 (dd, 3J = 8.3
Hz, 4J = 2.1 Hz, 2H, H-4¢¢), 8.38 (d, 3J = 8.1 Hz, 2H, H-3¢¢¢), 8.48
(d, 3J = 8.3 Hz, 2H, H-3¢¢), 8.54 (d, 4J = 1.5 Hz, 2H, H-6¢¢¢), 8.94 (d,
4J = 2.1 Hz, 2H, H-6¢¢) (Scheme 2);13C NMR (75 MHz, CDCl3):
d = 18.60, 56.53, 56.85, 114.19, 115.50, 120.62, 121.09, 126.83,
128.16, 133.87, 134.30, 138.20, 149.45, 149.54, 150.71, 151.52,
153.06, 153.96; positive ion ESI-HRMS: m/z (M = C38H34N4O4; in
dichloromethane/methanol): calcd for [M + H]+: 611.2653, found
611.2623; calcd for [M + Na]+: 633.2472, found 633.2467.
tetramethoxy)biphenyl
The procedure was as for the synthesis of 1,4¢-bis-(4,4,5,5-
tetramethyl[1,3,2]dioxaborolan)-2,5-dimethoxybenzene but using
4,4¢-dibromo-2,5,2¢,5¢-tetramethoxy-biphenyl (1.3 g, 3 mmol), t-
butyllithium (7 cm3, 1.7 M in pentane, 12 mmol) and 2-isopropoxy-
4,4,5,5-tetramethyl-[1,3,2]dioxaborolane (2.23 g, 12 mmol) in
tetrahydrofuran (30 cm3). The tetrahydrofuran was removed under
vacuum followed by the addition of H2O. This mixture was neu-
tralised with 2 M HCl and then extracted with dichloromethane
(2 ¥ 50 cm3). The combined organic fractions were dried over
Na2SO4. The dichloromethane was removed and the solid that
remained recrystallised from petrol to afford the product (1.1 g,
70%) as white microcrystals. 1H NMR (300 MHz, CDCl3): d = 1.36
(s, 24 H, CH3), 3.75 (s, 6 H, OCH3), 3.79 (s, 6 H, OCH3) 6.80 (s,
2 H, H-6,6¢), 7.30 (s, 2 H, H-3,3¢); 13C NMR (75 MHz, CDCl3):
d = 25.05, 56.87, 57.12, 83.69, 114.88, 119.83, 132.03, 150.95,
158.60.
1,4-Bis[5¢-(5¢¢-methyl-2¢,2¢¢-bipyridyl)]-2,5-dimethoxybenzene (2)
A
6
solution of 5-bromo-5¢-methyl-2,2¢-bipyridine (1.49 g,
mmol) 1,4¢-bis-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan)-2,5-
[Fe2(2)3](PF6)4
dimethoxybenzene (1.00 g, 2.7 mmol) and K2CO3 (2.50 g,
18 mmol, in 5 cm3 of H2O) in DMF (15 cm3) was degassed with
N2. Pd(PPh3)4 (208 mg, 0.18 mmol) was added to this solution
and the reaction mixture was heated with microwave energy in a
A mixture of Fe(BF4)2·6H2O (24 mg, 0.07 mmol) and 2 (50 mg,
0.105 mmol) in acetonitrile (50 cm3) was heated in a sealed pres-
surised microwave vessel with temperature and pressure sensors
and a magnetic stirrer bar (Step 1 – ramped to 130 ◦C over 2 min
10486 | Dalton Trans., 2011, 40, 10481–10490
This journal is
The Royal Society of Chemistry 2011
©

H, 3.90; N, 7.75%. X-ray quality crystals were obtained by slow
diffusion of methanol into an acetonitrile solution of the above
product.
[Ni2(2)3](PF6)4·2H2O
A mixture of NiCl2·6H2O (13.3 mg, 0.056 mmol) and 2 (40 mg,
0.084 mmol) in methanol (10 cm3) was heated in a sealed pres-
surised microwave vessel with temperature and pressure sensors
and a magnetic stirrer bar (Step 1 – ramped to◦ 130 ◦C over
2 min using 100% of 400 W; Step 2 – held at 130 C for 20 min
using 25% of 400 W). Excess NH4PF6 in water (20 cm3) was
then added and the resulting solid isolated by filtration in near
quantitative yield. This crude product gave MS evidence for the
presence of the corresponding dinuclear complex, [Ni4(2)6](PF6)8.
Positive ion ESI-HRMS: m/z (M = C180H156P8F48Ni4N12O6; in
acetonitrile/methanol): calcd for [M – 3PF6]3+: 1268.5984, found
1268.5931. This material was recrystallised by diffusion of tetrahy-
drofuran into an acetonitrile solution to afford the product
(48 mg, 39%) as yellow crystals. Found: C, 50.14; H, 3.95; N,
7.89%. Calc. for C90H78P4F24Ni2N12O6·2H2O: C, 50.13; H, 3.84;
N, 7.80. Positive ion ESI-HRMS: m/z (M = C90H78P4F24Ni2N24;
in acetonitrile/methanol): calc. for [M - 2PF6]2+: 915.2073, found
915.2093.
Scheme 2 The numbering scheme used for the assignment of the 1H NMR
resonances in 3.
using 100% of 400 W; Step 2 – held at 130 ◦C for 10 min using 25%
of 400 W). The crude product was purified by chromatography on
silica gel with acetonitrile, water and saturated KNO3 (7 : 1 : 0.5)
as eluent. The first of the two observed red bands to be eluted
was collected. The purified product (49 mg, 70%) was isolated
as a red solid by precipitation with excess aqueous NH4PF6 in
water (20 cm3) followed by filtration. UV/Vis (acetonitrile, nm) :
l
max(e dm-3 mol-1 cm-1) = 263 (50 360), 318 (138 000), 374 (75 370),
1
537 (13 190); H NMR (300 MHz, CD3CN): d = 2.28 (s, 18 H,
CH3), 3.49 (s, 18 H, OCH3), 6.78 (s, 6 H, H-3,6), 7.23 (d, 4J = 1.2
Hz, 6 H, H-6¢), 7.30 (d, 4J = 1.2 Hz, 6 H, H-6¢¢), 8.01(dd, 3J = 8.1
4
3
4
Hz, J = 1.2 Hz, 6 H, H-4¢), 8.39 (dd, J = 8.4 Hz, J = 1.2 Hz,
3
3
6 H, H-4¢¢); 8.50 (d, J = 8.1 Hz, 6 H, H-3¢), 8.91 (d, J = 8.4
Hz, 6 H, H-3¢¢); 13C NMR (75 MHz, CD3CN): d = 19.09, 58.22,
116.80, 124.60, 124.89, 126.13, 137.22, 137.37, 139.88, 140.52,
151.21, 154.53, 156.02, 157.02, 159.58; positive ion ESI-HRMS:
m/z (M = C90H78P4F24Fe2N12O6; in acetonitrile/methanol): calcd
for [M - 2PF6]2+: 912.7086, found 912.7042; calcd for [M - 3PF6]3+:
560.1508, found 560.1490; calcd for [M - 4PF6]4+: 383.8719, found
383.8708.
It is noted that the spectrum also gave evidence for the presence
of the corresponding [Ni4L6]8+ species – apparently generated
under the conditions employed for the HRMS determination.
X-Ray quality crystals were obtained by slow diffusion of
tetrahydrofuran into an acetonitrile solution of the above product.
[Fe2(3)3](PF6)4
A mixture of Fe(BF4)2·6H2O (7.4 mg, 0.022 mmol) and 3
(20 mg, 0.033 mmol) in acetonitrile (50 cm3) was heated in a
sealed pressurised microwave vessel with temperature and pressure
sensors and a magnetic stirrer bar (Step 1 – ramped to 130 ◦C
over 2 min using 100% of 400 W; Step 2 – held at 130 ◦C for
10 min using 25% of 400 W). The crude product was purified by
chromatography on silica gel with acetonitrile, water and saturated
KNO3 (7 : 1 : 0.5) as eluent. The second of the two observed red
bands to be eluted was collected. The purified product was isolated
by precipitation with excess aqueous NH4PF6 in water (20 cm3)
followed by filtration, to afford the product (17 mg, 62%) as a red
solid. UV/Vis (acetonitrile, nm): lmax(e dm-3 mol-1 cm-1) = 267
[Fe4(2)6](PF6)8
A mixture of Fe(BF4)2·6H2O (24 mg, 0.07 mmol) and 2 (50 mg,
0.105 mmol) in acetonitrile (10 cm3) was heated in a sealed pres-
surised microwave vessel with temperature and pressure sensors
and a magnetic stirrer bar (Step 1 – ramped to 130 ◦C over 2 min
using 100% of 400 W; Step 2 – held at 130 ◦C for 30 min using 25%
of 400 W). The crude product was purified by chromatography on
silica gel with acetonitrile, water and saturated KNO3 (7 : 1 : 0.5) as
eluent. The second of the two observed red bands to be eluted was
collected. The purified product was isolated by precipitation with
excess aqueous NH3PF6 in water (20 cm3) followed by filtration to
yield the product (68 mg, 96%) as a red solid. UV/Vis (acetonitrile,
nm) : lmax(e dm-3 mol-1 cm-1) = 256 (94, 410), 318 (266 840), 386
1
(40 156), 307 (100 390), 365 (60 387), 532 (9555); H NMR (300
MHz, CD3CN): d = 2.29 (s, 18 H, CH3), 2.82 (br s, 18 H, OCH3),
1
(157 450), 535 (27 420); H NMR (300 MHz, CD3CN): d = 2.19
3.56 (s, 18 H, OCH3), 6.59 (br s, 6 H), 7.00 (br s, 6 H), 7.15
(s, 36 H, CH3), 3.35 (s, 36 H, OCH3), 6.86 (s, 12 H, H-3,6), 7.12
(d, 4J = 1.2 Hz, 12 H, H-6¢), 7.94 (dd, 3J = 8.4 Hz, 4J = 1.2 Hz, 12
H, H-4¢), 8.02 (d, 4J = 1.8 Hz, 12 H, H-6¢¢), 8.31 (dd, 3J = 8.7 Hz,
3
4
(s, 6 H), 7.84 (br s, 6 H), 8.02 (dd, J = 8.1 Hz, J = 1.2 Hz, 6
3
4
3
H), 8.36 (dd, J = 8.4 Hz, J = 1.8 Hz, 6 H), 8.51 (d, J = 8.1
3
Hz), 8.61 (d, J = 8.4 Hz, 6 H). Positive ion ESI-HRMS: m/z
4J = 1.8 Hz, 12 H, H-4¢¢); 8.50 (d, J = 8.4 Hz, 12 H, H-3¢),
3
(M = C114H102P4F24Fe2N12O12; in acetonitrile/methanol): calcd for
[M - 3PF6]3+: 696.2033, found 696.2033; calcd for [M - 4PF6]4+:
485.9113, found 485.9084.
8.57 (d, 3J = 8.7 Hz, 12 H, H-3¢¢); 13C NMR (75 MHz, CD3CN):
d = 18.91, 57.45, 114.87, 124.28, 124.50, 125.91, 136.27, 139.09,
139.62, 140.45, 151.99, 155.25, 155.38, 157.16, 158.89; 19F NMR
(282.4 MHz, CD3CN): d = -73.28 (d, 1J = 706.8 Hz, 48 F, 8PF6);
positive ion ESI-HRMS: m/z (M = C180H156P8F48Fe4N24O12 in
acetonitrile/methanol): calcd for [M - 3PF6]3+: 1264.9324, found
1264.9310; calcd for [M - 4PF6]4+: 912.4581, found 912.4574; calcd
for [M - 5PF6]5+: 700.9736, found 700.9731. Found: C, 49.85; H,
3.94; N, 7.35%. Calc. for C180H156P8F48Fe4N24O12·6H2O: C, 49.80;
[Fe4(3)6](PF6)8
A mixture of FeCl2·5H2O (12 mg, 0.055 mmol) and 3 (50 mg,
0.082 mmol) in methanol (10 cm3) was heated with microwave
energy in a sealed pressurised microwave vessel with temperature
and pressure sensors and a magnetic stirrer bar (Step 1 – ramped
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10481–10490 | 10487
©

to 130 ◦C over 2 min using 100% of 400 W; Step 2 – held at 130 ◦C
for 20 min using 25% of 400 W). The crude product was purified by
chromatography on silica gel with acetonitrile, water and saturated
KNO3 (7 : 1 : 0.5) as eluent. The second of the two observed red
bands to be eluted was collected. The purified product was isolated
by precipitation with excess aqueous NH4PF6 in water (20 cm3)
followed by filtration, to afford the product (62 mg, 90%) as a red
solid. UV/Vis (acetonitrile, nm): lmax(e dm-3 mol-1 cm-1) = 271
monochromated synchrotron radiation (0.48595 A) and w and y
˚
scans at the ChemMatCARS beamline at the Advanced Photon
Source. Data integration and reduction were undertaken with
SAINT and XPREP.39 Subsequent computations were carried
out using the WinGX-32 graphical user interface.40 Structures
were solved by direct methods using SIR97.41 Multi-scan empir-
ical absorption corrections, when applied, were applied to the
data set using the program SADABS.42 Data were refined and
extended with SHELXL-97 and SHELXH-97.43 In general, non-
hydrogen atoms with occupancies greater than 0.5 were refined
anisotropically. Carbon-bound hydrogen atoms were included in
idealised positions and refined using a riding model. Oxygen and
nitrogen bound hydrogen atoms were first located in the difference
Fourier map before refinement. Where these hydrogen atoms could
not be located, they were not modelled. In all cases the crystals
employed were extremely solvent sensitive and required rapid
handling (~30 s) at low temperatures in order to facilitate data
collection. Crystallographic data and specific details pertaining to
structural refinements is summarised below.
1
(114 304), 306 (310 254), 376 (187 839), 529 (29 000); H NMR
(300 MHz, CD3CN): d = 2.24 (s, 36 H, CH3), 3.43 (s, 36 H, 2,2¢-
OCH3), 3.57 (s, 36 H, 5,5¢-OCH3), 6.86 (s, 12 H, H-6,6¢), 6.88 (s,
4
12 H, H-3,3¢), 7.28 (s, 12 H, H-6¢¢¢), 7.76 (d, J = 1.8 Hz, 12 H,
3
3
H-6¢¢), 8.01 (d, J = 8.1 Hz, 12 H, H-4¢¢¢), 8.33 (dd, J = 8.4 Hz,
4J = 1.8 Hz, 12 H, H-4¢¢); 8.55 (d, J = 8.1 Hz, 12 H, H-3¢¢¢),
3
8.60 (d, 3J = 8.4 Hz, 12 H, H-3¢¢); 13C NMR (75 MHz, CD3CN):
d = 18.94, 56.97, 57.09, 114.47, 116.72, 123.81, 124.51, 124.72, 3.52,
137.42, 139.45, 139.83, 140.35, 150.79, 152.35, 155.13, 155.44,
157.40, 158.50; 19F NMR (282.4 MHz, CD3CN): d = -73.49
1
(d, J = 706.1 Hz, 48 F, 8PF6). Positive ion ESI-HRMS: m/z
(M = C228H204P8F48Fe4N24O24; in acetonitrile/methanol): calcd for
[M - 3PF6]3+: 1537.3716, found 1537.3467; calcd for [M - 4PF6]4+:
1116.7875, found 1116.7867; calcd for [M - 5PF6]5+: 864.4370,
found 864.4375; calcd for [M - 6PF6]6+: 696.2034, found 696.1976;
calcd for [M - 7PF6]7+: 576.0365, found 576.0365. Found: C, 52.99,
H, 3.96, N, 6.46%. Calc. for C228H204P8F48Fe4N24O24·7H2O: C,
52.91; H, 4.25; N, 6.50%. X-ray quality crystals were obtained
by diffusion of tetrahydrofuran into an acetonitrile solution of the
product.
[Ni2(2)3](PF6)4·2.5MeCN
Formula C95H85.50F24N14.50Ni2O6P4, M 2223.58, hexagonal, space
˚
group ◦P63(#173), a 13.460(2), b 13.460(2), c 30.805(5) A, g
3
-3
˚
120.00 , V 4833.3(12) A , Dc 1.528 g cm , Z 2, crystal size 0.150 ¥
0.10 ¥ 0.05 mm, colour yellow, habit plate, temperature 150(2) K,
-1
˚
l(MoKa) 0.71073 A, m(MoKa) 0.564 mm , T(SADABS)min,max
0.831645, 1.00000, 2qmax 50.00, hkl range -16 16, -15 16, -36 36,
N 62378, Nind 5653(Rmerge 0.0458), Nobs 5090(I > 2s(I)), Nvar 438,
residuals‡ R1(F) 0.0878, wR2(F2) 0.2395, GoF(all) 1.003, Drmin,max
[Ni4(3)6](PF6)8
-3
˚
-1.526, 0.671 e- A .
NiCl2·6H2O (5.2 mg, 0.022 mmol) and 3 (20 mg, 0.033 mmol)
in methanol (10 cm3) were heated in a sealed pressurised mi-
crowave vessel with temperature and pressure sensors and a
magnetic stirrer bar (Step 1: ramped to 130 ◦C over 2 min
using 100% of 400 W; Step 2: held at 130 ◦C for 20 min using
25% of 400 W). Excess NH4PF6 in water (20 cm3) was then
added and the resulting yellow solid isolated by filtration in
near quantitative yield. This product before recrystallisation also
gave MS evidence for the additional presence of [Ni2(3)3](PF6)4.
Positive ion ESI-HRMS: m/z (M = C114H102P4F24Ni2N12O12; in
acetonitrile/methanol): calcd for [M - 2PF6]2+: 1119.2866, found
1119.2896. The crude material was recrystallised by slow diffusion
of tetrahydrofuran into an acetonitrile solution to afford (15 mg,
58%) as yellow cubic crystals. Positive ion ESI-HRMS: m/z
(M = C228H204P8F48Ni4N24O24; in acetonitrile/methanol): calcd
for [M - 3PF6]3+: 1541.0371, found 1541.0573. X-ray quality
crystals were obtained by slow diffusion of tetrahydrofuran into
an acetonitrile solution of the above product.
Specific details. The methoxy groups in the structure are
disordered over two positions. The O(1) containing group was
modelled over two unequal positions (occupancy 0.75 and 0.25),
while the O(2) containing group was modelled in two equal
occupancy positions. Each of the anions is disordered over special
positions with several fluorine positions required for each and were
included with identical thermal parameters. In addition, there is a
large region of smeared electron density present in the lattice and
despite several attempts at modelling this as solvent including the
use of bond restraints and rigid-bodies no satisfactory model could
be found. The SQUEEZE function of PLATON44 was employed to
remove this contribution from the model and it was included in the
formula weight calculations as five acetonitrile solvent molecules
per unit cell. The refined Flack parameter of 0.34(4) suggests that
although each helix is chiral there was some racemic twinning
present in the crystal employed.
[{(PF6)(MeCN)0.25} Ã Fe4(2)6](PF6)7·2.75MeCN·9.35H2O
X-Ray studies
Formula C186H183.70F48Fe4N27O21.35P8, M 4522.06, triclinic, space
¯
˚
group P1(#2), a 20.2470(12), b 20.7900(12), c 30.5460(17) A, a
Data for [{(PF6)(MeCN)0.25} Ã Fe4(2)6](PF6)7·2.75MeCN·9.35-
H2O, [Ni2(2)3](PF6)4·2.5MeCN and [{(H2O)0.5(THF)0.75(Me-
CN)0.5} Ã Ni4(3)6](PF6)8·5.5MeCN·5THF·MeOH·4.075H2O were
collected on a Bruker-Nonius APEX2-X8-FR591 diffractometer
employing graphite-monochromated Mo-Ka radiation generated
◦
3
˚
82.126(3), b 76.935(3), g 73.436(3) , V 11969.0(12) A , Dc 1.255
g cm-3, Z 2, crystal size 0.250 ¥ 0.150 ¥ 0.100 mm, colour red, habit
˚
prism, temperature 150(2) K, l(MoKa) 0.71073 A, m(MoKa)
˚
from a rotating anode (0.71073 A) with w and y scans to approx-
2
‡ R1 = RꢀFo| - |Fcꢀ/R|Fo| for Fo > 2s(Fo); wR2 = (Rw(Fo
-
imately 56◦ 2q at 150(2) K.38 Data for [Fe4(3)6](PF6)8·12.5THF
Fc2)2/R(wFc2)2)1/2 all reflections w = 1/[s (Fo2)+(0.1276P)2 +16.3939P]
2
2
were collected at approximately 100 K using double diamond
where P = (Fo + 2Fc2)/3
10488 | Dalton Trans., 2011, 40, 10481–10490
This journal is
The Royal Society of Chemistry 2011
©

0.387 mm-1, T(SADABS)min,max 0.744008, 1.00000, 2qmax 50.70, hkl
range -24 24, -25 25, -36 36, N 280847, Nind 43649(Rmerge 0.0424),
Specific details. The crystals employed in this study were very
small, diffracted poorly and rapidly suffered solvent loss. Despite
the use of synchrotron radiation, rapid handling times and a low
temperature collection no reflection data were observed at better
N
obs 33936(I > 2s(I)), Nvar 2760, residuals§ R1(F) 0.1192, wR2(F2)
-3
˚
0.3245, GoF(all) 1.384, Drmin,max -1.173, 1.761 e- A .
˚
than 1.0 A resolution. In addition, the crystals appeared to decay
Specific details. There is a significant amount of disorder
present in the structure. One of the central dimethoxyphenylene
rings is disordered over two 50% occupancy positions, the anions
are disordered over 11 positions with a total occupancy of 8, the
acetonitriles over 7 positions and the water molecules over 38
positions. A number of restraints and constraints were required
to facilitate realistic modelling in the phenylene ring and the
disordered anions and where multiple fluorine positions were
present they were modelled with identical thermal parameters.
The water hydrogen atoms could not be located in the difference
Fourier map and were not included in the final model.
further during data collection resulting in lower than ideal data
completeness. Despite these limitations the data is of more than
sufficient quality to unambiguously determine the connectivity
of the structure. The P(2) and P(3) containing anions were each
disordered and modelled over two equal occupancy positions and
the methyl hydrogens were also all modelled as disordered over
two equal positions. The C(13) containing dimethoxyphenylene
ring was also modelled as disordered over two equal positions.
While one 0.5 occupancy THF could be modelled in the lattice, the
remaining solvent is significantly disordered and despite numerous
attempts at modelling, including with multiple rigid bodies no
satisfactory model for the electron-density associated with them
could be found. Therefore the SQUEEZE function of PLATON44
was employed to remove the contribution of the electron density
associated with the anions from the model, which resulted in far
more satisfactory residuals and was included in the formula weight
calculations as 42 tetrahydrofuran solvent molecules per unit
cell. Because of the use of synchrotron radiation no adsorption
correction was applied.
[{(H2O)0.5(THF)0.75(MeCN)0.5} Ã Ni4(3)6](PF6)8·5.5MeCN·
5THF·MeOH·4.075H2O
Formula C264H279.75F48N30Ni4O35.315P8, M 5832.63, triclinic, space
¯
˚
group P1(#2), a 21.1588(12), b 24.20◦22(14), c 37.7344(22) A,
3
˚
a 78.498(4), b 79.573(4), g 76.780(3) , V 18247.0(18) A , Dc
1.062 g cm-3, Z 2, crystal size 0.250 ¥ 0.180 ¥ 0.100 mm, colour
˚
yellow, habit block, temperature 150(2) K, l(MoKa) 0.71073 A,
m(MoKa) 0.318 mm-1, T(SADABS)min,max 0.6737, 0.7457, 2qmax
50.00, hkl range -25 24, -28 28, -44 44, N 443400, Nind 63078(Rmerge
Acknowledgements
0.0693), Nobs 39105(I > 2s(I)), Nobs 3755, residuals¶ R1(F) 0.1123,
-3
wR2(F2) 0.3001, GoF(all) 1.173, Drmin,max -1.723, 4.107 e- A .
˚
GVM and LFL thank the Australian Research Council for sup-
port. JKC acknowledges a Marie Curie International Incoming
Fellowship within the 7th European Community Framework Pro-
gramme. Use of the ChemMatCARS Sector 15 at the Advanced
Photon Source was supported by the Australian Synchrotron
Research Program, which is funded by the Commonwealth of
Australia under the Major National Research Facilities Program.
ChemMatCARS Sector 15 is also supported by the National
Science Foundation/Department of Energy under grant numbers
HE9522232 and CHE0087817, and by the Illinois board of higher
education. The Advanced Photon Source is supported by the US
Department of Energy, Basic Energy Sciences, Office of Science,
under contract no. W-31-109-Eng-38.
Specific details. There is a significant amount of disorder
present in the structure. The P(5)-containing anion is modelled
as disordered over two equal occupancy positions and each of the
methyl groups was modelled with disordered hydrogen atoms over
two equal positions leading to some artificial close H–H contacts.
The remaining solvent was successfully modelled as a number of
both full and partial occupancy solvent molecules including THF,
MeCN, MeOH and water. A number of bond length restraints
were required to facilitate the realistic modelling of this solvent.
The water hydrogen atoms could not be located in the difference
Fourier map and were not included in the final model.
[Fe4(3)6](PF6)8·12.5THF
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10490 | Dalton Trans., 2011, 40, 10481–10490
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The Royal Society of Chemistry 2011
©