Nickel(ii) and iron(ii) triple helicates assembled from expanded quaterpyridines incorporating flexible linkages

Article abstract of DOI:10.1039/c1dt10820d

In the present study the interaction of Fe(ii) and Ni(ii) with the related expanded quaterpyridines, 1,2-, 1,3- and 1,4-bis-(5′-methyl-[2,2′] bipyridinyl-5-ylmethoxy)benzene ligands (4-6 respectively), incorporating flexible, bis-aryl/methylene ether link

Full text of DOI:10.1039/c1dt10820d

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Metal ion directed self-assembly of sensors for ions, molecules and biomolecules
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Self-assembly between dicarboxylate ions and a binuclear europium complex: formation of stable
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Dalton Trans., 2011, DOI: 10.1039/C1DT11103E
Structural and metallo selectivity in the assembly of [2 × 2] grid-type metallosupramolecular
species: Mechanisms and kinetic control
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PAPER
Nickel(II) and iron(II) triple helicates assembled from expanded
quaterpyridines incorporating flexible linkages†
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 3rd May 2011, Accepted 30th June 2011
DOI: 10.1039/c1dt10820d
In the present study the interaction of Fe(II) and Ni(II) with the related expanded quaterpyridines, 1,2-,
1,3- and 1,4-bis-(5¢-methyl-[2,2¢]bipyridinyl-5-ylmethoxy)benzene ligands (4–6 respectively),
incorporating flexible, bis-aryl/methylene ether linkages in the bridges between the dipyridyl domains,
was shown to predominantly result in the assembly of [M2L3]4+ complexes; although with 4 and 6 there
was also evidence for the (minor) formation of the corresponding [M4L6]8+ species. Overall, this result
contrasts with the behaviour of the essentially rigid ‘parent’ quaterpyridine 1 for which only tetrahedral
[M4L6]8+ cage species were observed when reacted with various Fe(II) salts. It also contrasts with that
observed for 2 and 3 incorporating essentially rigid substituted phenylene and biphenylene bridges
between the dipyridyl domains where reaction with Fe(II) and Ni(II) yielded both [M2L3]4+ and [M4L6]8+
complex types, but in this case it was the latter species that was assigned as the thermodynamically
favoured product type. The X-ray structures of the triple helicate complexes [H2OÃNi2(4)3](PF6)4·THF·
-
2.2H2O, [Ni2(6)3](PF6)4·1.95MeCN·1.2THF·1.8H2O, and the very unusual triple helicate PF6 inclusion
complex, [(PF6)ÃNi2(5)3](PF6)3·1.75MeCN·5.25THF·0.25H2O are reported.
the organic component, careful design of both its structural and
Introduction
electronic properties are of course essential. Even factors such as
While considerable interest continues to be given to the metal-
its flexibility may influence a given supramolecular outcome. For
ion directed assembly of discrete metallosupramolecular systems
example, a considerable number of polypyridyl ligands displaying
that incorporate a central cavity,1 the assembly of new systems
different flexibilities have now been employed for the assembly
of this type displaying predetermined properties continues to be
of a wide variety of metallo-supramolecular structures whose
a challenge.2 This is due to the many influences that may affect
architectures, at least in part, reflect the inherent flexibility of the
particular ligand system used.3
the outcome of a given self-assembly experiment. In the first
instance the choice of the metal ion and the other components
(commonly an appropriately functionalised organic building block
or blocks) are obviously of key importance. Metal ion properties
such as its charge, radius, spin-state and the presence of any crystal
field properties that may influence the coordination behaviour
(including the degree of kinetic inertness of the resulting product)
may all influence a given supramolecular assembly outcome. For
Like many others, we have employed a metal-directed approach
of the type mentioned above for synthesising a range of structures
incorporating 2- and 3-dimensional voids, many of which include
guest molecules or ions.4–7 For example, it has now been well
demonstrated that when essentially linear bis-bidentate ligand
systems react with octahedral metal ions, M2L3 helicates (or
sometimes their corresponding meso isomers) or M4L6 tetrahedra
are commonly formed; sometimes these occur in combination.8–10
Although from entropic considerations alone the above reaction
type might be expected to favour formation of a smaller M2L3
assembly, if the generation of such an assembly is sterically
inhibited due to lack of flexibility in the organic component
(L) then frequently the larger homologue, M4L6, becomes the
preferred thermodynamic product.8,11,12 Hence, in such a situation
it is the balance between flexibility and rigidity of the ditopic
ligand that may largely control which of the above assembly types
predominates.
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: ESI-HRMS of
[Fe2(4)3](PF6)4 and an additional X-ray structure figure for the [Ni2(6)3]4+
cation. CCDC reference numbers [CCDC 824369–824371]. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c1dt10820d
In our previous studies, it was shown that the near-rigid, linear
ditopic ligand, 5,5¢¢¢-dimethyl-2,2¢:5¢,5¢¢:2¢¢,2¢¢¢-quaterpyridine 1,
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 12153–12159 | 12153
©

[M2L3]4+ complexes incorporating 4–6
We now report the results of metal-directed assembly reactions
involving the interaction of Fe(II) and Ni(II) with each of the new
flexibly-bridged quaterpyridines 4–6.
Fe(II) complexes. In an initial series of experiments,
FeCl2·5H2O or Fe(BF4)2·6H2O were reacted with each of 4–6 in
a 2 : 3 (M : L) ratio in a microwave reactor using methanol or
acetonitrile as solvent. For the catechol-bridged species 4, thin
layer chromatography (TLC) of the crude product indicated the
predominant formation of a single deep red product. This product
was subjected to chromatography on silica gel and isolated as its
PF6- salt. The deep red colouration is characteristic of the presence
of a low-spin [Fe(bipyridine)3]2+ chromophore.14
The 1H NMR spectrum of this material indicated that the
complexed ligand had retained its two-fold symmetry; there
were eight aromatic resonances (Fig. 1a). However, despite the
chromatographic purification step, there was evidence for the
presence of a small amount (~10%) of a second product of high
symmetry (see arrows in Fig. 1a).
yields solely [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).4,6 However the slightly larger (and
more kinetically inert) Ru(II) yielded a [Ru2L3]4+ triple helicate
under the conditions employed for the reaction.9 In a further
study in our laboratories, the related expanded quaterpyridine
derivatives 2 and 3 incorporating rigid dimethoxy-substituted 1,4-
phenylene and tetramethoxy-substituted 4,4¢-biphenylene bridges
respectively between pairs of 2,2¢-bipyridyl groups were prepared
and in a comparative investigation their interaction with Fe(II) and
Ni(II) was undertaken.13 In each case these fully conjugated ligand
systems yielded a mixture of [M2L3]4+ triple helicate and a [M4L6]8+
tetrahedral species – behaviour that, at least in part, was at-
tributed to the greater flexibility of these extended quaterpyridines
allowing generation of both the above species type (although
evidence suggested that the tetrahedral structures are of some-
what higher stability than the corresponding triple helicates in
each case).
As an extension of the above studies, we now report the results
of a further comparative investigation of the effect of extending
the structure of quaterpyridine 1 to yield the flexibly-linked, bis-
ether containing quaterpyridine ligands 4–6 on the nature of
the metallosupramolecular assemblies formed with Ni(II) and
Fe(II). In particular, it was of interest to observe what influence
the increased flexibility of 4–6 would have on the nature of the
corresponding metallosupramolecular systems generated relative
to those formed by 1–3.
The ESI-HRMS of the above product revealed +2 to +4 ions
-
corresponding to successive losses of PF6 from the formula
[Fe2(4)3](PF6)4 (see ESI†). There was also evidence of a second
series of ions (much weaker peaks) corresponding to the successive
-
losses of PF6 anions from the formula [Fe4(4)6](PF6)8. The
presence of this latter series is exemplified by the theoretical and
5+
observed isotopic distributions for the +5 ion, {[Fe4(4)6](PF6)3}
(see ESI†). Thus, the presence of a [Fe4L6]8+ complex likely
accounts for the symmetrical by-product observed in the 1H NMR
spectrum of this material. Based on the H NMR spectrum and
1
mass spectrum of the complex, [Fe2(4)3](PF6)4, it is assumed that
the structure is either a true helicate (namely, metal centres: DD or
KK) or a meso-helicate (metal centres: DK).
TLC of the product from an analogous metal-directed assembly
experiment employing Fe(BF4)2·6H2O and the resorcinol-bridged
5 indicated the formation of a complex mixture of products. In this
case, separation of these by chromatography on silica gel or by size
exclusion chromatography was in each case unsuccessful leading
1
to only a partially purified product whose H NMR spectrum
showed an underlying broadness and indicated the presence of
impurities. However, the spectrum confirmed that in the major
product the ligand maintains its two-fold symmetry. The ESI-
HRMS of the above product showed the presence of +2 and
-
+3 ions corresponding to the successive losses of BF4 from the
formula [Fe2(5)3](BF4)4. No ions that could be assigned to arise
from a [Fe4L6] (BF4)8 species were observed.
Results and discussion
The interaction of the hydroquinone-bridged quaterpyridine
6 with FeCl2·5H2O gave a deep red crude product that was
isolated by addition of NH4PF6. This was redissolved then passed
Expanded quaterpyridine ligand synthesis
The reaction of 5-chloromethyl-5¢-methyl-2,2¢-bipyridine with
catechol, resorcinol and hydroquinone in the presence of K2CO3 in
dimethylformamide afforded the flexibly bridged quaterpyridines
4–6 in 90, 93 and 58 percent yield, respectively. The H and 13C
-
down a silica gel column and was again isolated as its PF6 salt.
Interestingly, in contrast to the 1H NMR spectra of the respective
1
1
products derived from 4 and 5, the H NMR spectrum of this
NMR of the respective products confirmed their expected C2-
material indicated that two different ligand environments were
present. The most clearly seen proton resonances reflecting this are
those corresponding to the hydroquinone-bridge protons, which in
the free ligand are equivalent, but are now present as two singlets
of relative intensities close to 1 : 1(see peaks marked with asterisks
in Fig. 1b). As well, there are two overlapping AB systems for the
symmetries and in each case the spectra were in overall accord with
1
the expected structures. In particular, for the H NMR spectra
NOEs were observed between methyl protons at ~2.4 ppm and
protons in the 4¢- and 6¢-positions for each compound, allowing
full assignment of the respective spectra.
12154 | Dalton Trans., 2011, 40, 12153–12159
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©

Fig. 1 1H NMR spectra in CD3CN of (a) [Fe2(4)3](PF6)4 and (b) [Fe2(6)3](PF6)4. The two singlets arising from the hydroquinone-bridge proton in the
latter spectrum are marked with asterisks (see discussion in main text).
phenoxymethylene protons (see expanded peaks marked with red
circle in Fig. 1b). The ESI-HRMS of this material revealed +2 and
+3 ion species corresponding to successive losses of PF6- from the
formula [Fe2(6)3](PF6)4 (while much less intense peaks were also
present corresponding to the successive loss of PF6- ions from the
formula [Fe4(6)6](PF6)8).
Based on the above evidence, the ~1 : 1 relative intensities
for the ligand singlet peaks rule out possible simple [Fe2L3]4+
helicate or meso structures (as well as a dinuclear structure of
this stoichiometry incorporating two terminally coordinated 6
ligands and one bridging 6 ligand)15 in which two ligands are in one
environment and one is in another. The most probable rationale
for the observed NMR data appears to be that the product is a
~1 : 1 mixture of the corresponding (isomeric) triple helicate and
meso-helicate. Although a single helicate or meso-helicate structure
in which opposite ends are non-equivalent would also fit the data,
we consider this unlikely since it is difficult to see what the driving
force for the formation of such species would be.
(see, for example Fig. 2b). It is noted that the spectrum of
[Ni2(5)3](PF6)4 only showed ions corresponding to the loss of
-
PF6 anions from this formula; no evidence for formation of
[Ni4(5)6](PF6)8 was observed in this case.
X-ray structures
Crystals of [Ni2(4)3](PF6)4, [Ni2(5)3](PF6)4 and [Ni2(6)3](PF6)4
suitable for X-ray diffraction were grown from a tetrahydrofu-
ran/acetonitrile solvent mixture in each case. The structure of
[H2OÃNi2(4)3](PF6)4·THF·2.2H2O (Fig. 3) confirmed the [M2L3]4+
formulation of the complex cation. The product crystallised in the
centrosymmetric monoclinic space group C 2/c with Z = 4; thus
the molecule has a two-fold axis. The two octahedral Ni(II) centres
˚
are separated by 10.8 A and bridged by three quaterpyridine
ligands such that the stereochemistry of the metal centres of each
discrete unit are either DD (P) or KK (M). Thus, the solid state
structure of [Ni2(4)3](PF6)4 is a true helicate. There is a guest water
molecule encapsulated in the centre of the helix.
Ni(II) complexes. In a subsequent set of experiments, a similar
series of metal-directed assembly experiments to those just dis-
cussed for Fe(II) and 4–6 were undertaken in which NiCl2·6H2O
was substituted for the iron salt. The ESI-HRMS of the resulting
products indicated that the major species were the [M2L3]4+
complexes, [Ni2(4)3](PF6)4, [Ni2(5)3](PF6)4, and [Ni2(6)3](PF6)4 re-
spectively; the spectrum of [Ni2(4)3](PF6)4, which is representative
of those for of the other two products, is shown in Fig. 2a. In
parallel to the corresponding Fe(II) systems of 4 and 6, there
was again mass spectral evidence for the additional formation
of [Ni4L6]8+ species for these two ligands. In each case, +3 ion
[(PF6)ÃNi2(5)3](PF6)3·1.75MeCN·5.25THF·0.25H2O crystalli-
sed in the centrosymmetric monoclinic space group P 21/c. The
˚
two octahedral Ni(II) centres are separated by 12.8 A and bridged
by three quaterpyridine ligands such that the stereochemistry of
the metal centres of each discrete unit is again either DD (P) or
-
KK (M). The structure reveals that a PF6 anion is encapsulated
in the central cavity of the helicate such that in the solid state the
structure corresponds to [(PF6)ÃNi2(5)3](PF6)3 (Fig. 4).
Finally the crystal structure of [Ni2(6)3](PF6)4·1.95MeCN·
1.2THF·1.8H2O confirmed its formulation as [Ni2(6)3](PF6)4
(Fig. 5). This product crystallised in the centrosymmetric triclinic
-
¯
species corresponding to the loss of three PF6 anions from
space group P1. The two octahedral Ni(II) centres are separated by
˚
the formulae [Ni4(4)6](PF6)8 and [Ni4(6)6](PF6)8 were observed.
Good agreement between the theoretical and observed isotopic
distributions leaves little doubt as to the identity of these species
14.1 A and bridged by three quaterpyridine ligands such that the
stereochemistry of the metal centres of each discrete unit are once
again either DD (P) or KK (M). Interestingly, in this product the
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 12153–12159 | 12155
©

Fig. 2 (a) The mass spectrum of [Ni2(4)3](PF6)4 and the theoretical (top) and observed (bottom) isotopic distributions for (b) {[Ni4(4)6](PF6)5}3+ and (c)
2+
{[Ni2(4)3](PF6)2}
.
the plane of the hydroquinone bridge which is coplanar to the other
bipyridyl group. The other ligand is in a near planar conformation
throughout, with each coordination domain orientated ~180◦ to
the other. The latter is related to the S-shaped conformation that
Albrecht described as being beneficial for helicate formation.12
Conclusions
In this report we have demonstrated that the interaction of
Fe(II) and Ni(II) with the expanded flexible quaterpyridines 4–
6 predominantly results in the formation of [M2L3]4+ complexes
although with 4 and 6 there was also evidence for the (minor) for-
mation of the corresponding [M4L6]8+ species under the conditions
employed. This result contrasts with the behaviour of the quite
rigid ‘parent’ quaterpyridine 1 for which only [M4L6]8+ species
were observed. To a lesser degree the present results for 4–6 also
contrast with those obtained for the expanded quaterpyridines
of intermediate flexibility, 3 and 4, for which both [M2L3]4+ and
[M4L6]8+ species were seen to occur but in these cases the [M4L6]8+
appears to be the favoured (thermodynamic) product. Finally, it
is noted that the structure of the complex cation [(PF6)ÃNi2(5)3]3+
is quite unusual in that it provides a rare example of the inclusion
of a large polyatomic anion in a dinuclear triple helicate complex.
Fig.
3
(a) Stick representation of the crystal structure of
[Ni2(4)3](PF6)4·THF·2.2H2O and (b) space filling representation (hydro-
gens, counterions and solvents removed for clarity).
Fig.
4
(a) Stick representation of the crystal structure of
[(PF6)ÃNi2(5)3](PF6)3·1.75MeCN·5.25THF·0.25H2O and (b) space filling
-
representation both views showing the encapsulated PF6 anion (hydro-
gens, counterions and solvents are removed for clarity).
Experimental
All reagents were of analytical grade unless otherwise in-
dicated. 5-Trimethylsilylmethyl-5¢-methyl-2,2¢-bipyridine and 5-
chloromethyl-5¢-methyl-2,2¢-bipyridine were prepare using a com-
bination of literature methods.16,17 Chromatography grade solvents
were distilled through a fractionation column packed with glass
helices. 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) measure-
ments were obtained on a Bruker BioAPEX 47e mass spectrometer
Fig.
5
(a) Stick representation of the crystal structure of
[Ni2(6)3](PF6)4·1.95MeCN·1.2THF·1.8H2O illustrating the two bound
ligand conformations present in this helicate and (b) a space filling
representation (hydrogens, counterions and solvents removed for clarity).
three ligands exist in two different conformations. For two ligands
one of the bipyridyl groups is orientated at approximately 80◦ to
12156 | Dalton Trans., 2011, 40, 12153–12159
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The Royal Society of Chemistry 2011
©

◦
equipped with an Analytica of Branford electrospray ionisation
(ESI) source.
2 min using 100% of 400 W; Step 2 – held at 130 C for 20 min
using 25% of 400 W). The reaction mixture was filtered and the
crude product precipitated by the addition of an excess of aqueous
NH4PF6. This deep red material was purified by chromatography
on silica gel with a mixture of acetonitrile, H2O and saturated
KNO3 (7 : 1 : 0.5) as eluent. The resulting product was isolated by
precipitation with excess aqueous NH4PF6 in H2O (20 mL) and
removed by filtration to afford crude [Fe2(4)3](PF6)4 (132 mg, 90%)
as a red solid. 1H-NMR (see Fig. 1a) d (300 MHz, CD3CN) 2.16
(s, 18 H, CH3), 4.93 (s, 12 H, OCH2Ar), 6.56 (dd, 3J = 6.0 Hz, 4J =
3.6 Hz, 6 H, Ar–H), 6.94 (dd, 3J = 6.0 Hz, 4J = 3.6 Hz, 6 H, Ar–H),
1,2-Bis-(5¢-methyl-[2,2¢]bipyridinyl-5-ylmethoxy)benzene
(4).
5-Chloromethyl-5¢-methyl-2,2¢-bipyridine (241 mg, 1.1 mmol),
catechol (55 mg, 0.5 mmol) and K2CO3 (415 mg, 3.0 mmol) in
dimethylformamide (10 mL) was stirred at room temperature
over 12 h. H2O (20 mL) was then added to the reaction mixture,
and the resulting precipitate filtered off and washed with water
followed by a minimum volume of chilled methanol. The crude
product was purified by chromatography on silica gel with
dichloromethane (98.75%), methanol (1%) and saturated NH3
(0.25%) as eluent to afford 4 (215 mg, 90%) as a white powder.
1H-NMR d (CDCl3, 300 MHz) 2.40 (s, 6 H, CH3), 5.22 (s, 4 H,
OCH2Ar), 6.96 (m, 4 H, Ar–H), 7.63 (dd, 3J = 8.1, 4J = 1.8 Hz, 2
H, H-4¢), 7.90 (dd, 3J = 8.1, 4J = 2.1 Hz, 2 H, H-4), 8.29 (d, 3J =
3
7.00 (br s, 6 H), 7.22 (br s, 6 H), 7.91 (br m, 12 H), 8.07 (d, J =
8.4 Hz, 6 H), 8.24 (d, 3J = 8.3 Hz, 6 H; positive ion ESI-HRMS:
m/z (M = C90H78P4F24Fe2N12O6 in acetonitrile/methanol): calc
for [M - 2PF6]2+: 912.2073, found 912.2130; calc for [M - 3PF6]3+:
559.8166, found 559.8168; calc for [M - 4PF6]4+: 383.6213, found
383.6210.
3
4
8.1 Hz, 2 H, H-3¢), 8.38 (d, J = 8.1 Hz, 2 H, H-3), 8.50 (d, J =
4
1.8 Hz, 2 H, H-6¢), 8.72 (d, J = 2.1 Hz, 2 H, H-6); 13C-NMR d
(75 MHz, CDCl3) 18.61, 69.17, 115.70, 120.97, 121.07, 122.43,
132.73, 133.86, 136.57, 137.97, 148.45, 148.87, 149.61, 153.26,
155.88; positive ion ESI-HRMS: m/z (M = C30H26N4O2 in
dichloromethane/methanol): calc for [M + Na]+: 497.1948, found
497.1948.
[Fe2(5)3](BF4)4.
A
mixture of Fe(BF4)2·6H2O (47 mg,
0.14 mmol) and quaterpyridine 5 (110 mg, 0.232 mmol) in
acetonitrile (10 mL) was heated with microwave energy in a
sealed pressurised microwave vessel with temperature and pressure
sensors (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).
The solvent was evaporated and the crude deep red material was
purified by chromatography on Sephadex LH-20 with acetonitrile
as eluent. This allowed the isolation of [Fe2(5)3](BF4)4 (109 mg,
1,3-Bis-(5¢-methyl-[2,2¢]bipyridinyl-5-ylmethoxy)-benzene (5).
The procedure was similar to that employed for the synthesis of
4. 5-Chloromethyl-5¢-methyl-2,2¢-bipyridine (241 mg, 1.1 mmol),
resorcinol (55 mg, 0.5 mmol) and K2CO3 (415 mg, 3.0 mmol) were
reacted in DMF (10 cm3) for 12 h. Standard workup yielded 5
(220 mg, 93%) as a white powder. 1H NMR d (CDCl3, 300 MHz)
2.41 (s, 6 H, CH3), 5.12 (s, 4 H, OCH2Ar), 6.64 (dd, 3J = 8.1, 4J =
1
83%) as a deep red solid. H-NMR d (300 MHz, CD3CN) 2.21
(s, 18 H, CH3), 4.94 (d, 2J = 14.8 Hz, 6 H, OCH2Ar), 5.04
2
(d, J = 14.8 Hz, 6 H, OCH2Ar), 6.35, 6.38, 7.15, 7.93, 8.04,
8.39; positive ion ESI-HRMS: m/z (M = C90H78B4F16Fe2N12O6 in
acetonitrile/methanol): calc for [M - 2BF4]2+: 854.2472, found
854.2486; calc for [M - 3BF4]3+: 540.4966, found 540.4973.
4
3
2.3 Hz, 2 H, H-b), 6.65 (d, J = 2.3 Hz, 1 H, H-a), 7.23 (t, J =
3
4
8.1 Hz, 1 H, H-c), 7.65 (dd, J = 8.1, J = 2.1 Hz, 2 H, H-4¢),
7.89 (dd, J = 8.1, J = 2.1 Hz, 2 H, H-4), 8.30 (d, J = 8.1 Hz,
3
4
3
3
4
2 H, H-3¢), 8.41 (d, J = 8.1 Hz, 2 H, H-3), 8.52 (d, J = 2.1 Hz,
[Fe2(6)3](PF6)4. The procedure was similar to that em-
ployed for the synthesis of [Fe2(4)3](PF6)4. FeCl2·5H2O (30 mg,
0.14 mmol) and quaterpyridine 6 (110 mg, 0.232 mmol) afforded
[Fe2(6)3](PF6)4 (125 mg, 85%) as a red solid. 1H-NMR (see Fig. 1b)
2 H, H-6¢), 8.72 (d, J = 2.1 Hz, 2 H, H-6); 13C NMR (75 MHz,
4
CDCl3): d = 18.61, 67.75, 102.60, 107.89, 120.99, 121.07, 130.41,
132.43, 133.96, 136.61, 138.05, 148.50, 149.60, 153.21, 155.93,
159.88; positive ion ESI-HRMS: m/z (M = C30H26N4O2 in
dichloromethane/methanol): calc. for [M + H]+: 475.2129, found
475.2200; calc. for [M + Na]+: 497.1948, found 497.1945.
2
d (300 MHz, CD3CN) 2.21 (s, CH3), 2.22 (s, CH3), 4.79 (d, J =
14.5 Hz, OCH2Ar), 4.81 (d, 2J = 14.9 Hz, OCH2Ar), 4.88 (d, 2J =
2
14.5 Hz, OCH2Ar), 4.96 (d, J = 14.9 Hz, OCH2Ar), 6.59 (s, 6
H, Ar–H), 6.73 (s, 6 H, Ar–H), 7.06 (s, 3 H), 7.07 (s, 3 H), 7.17
(s, 3 H), 7.21 (s, 3 H), 7.94 (m, 6 H), 8.06 (m, 6 H), 8.42 (m,
12 H); positive ion ESI-HRMS: m/z (M = C90H78P4F24Fe2N12O6
in acetonitrile/methanol): calc for [M - 2PF6]2+: 912.2073, found
912.2130; calc for [M - 3PF6]3+: 559.8166, found 559.8179.
1,4-Bis-(5¢-methyl-[2,2¢]bipyridinyl-5-ylmethoxy)-benzene (6).
The procedure was similar to that employed for the synthesis of
4. 5-Chloromethyl-5¢-methyl-2,2¢-bipyridine (241 mg, 1.1 mmol),
hydroquinone (55 mg, 0.5 mmol) and K2CO3 (415 mg, 3.0 mmol)
were reacted in DMF (10 cm3) for 12 h. Standard workup
yielded 6 (138 mg, 58%) as a sparingly soluble white powder.
[Ni2(4)3](PF6)4. A stirred solution of NiCl2·6H2O (17 mg,
0.07 mmol) and 4 (50 mg, 0.105 mmol) in methanol (10 mL) was
heated with microwave energy in a sealed pressurised microwave
vessel with temperature and pressure sensors (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). The product was isolated by pre-
cipitation with excess aqueous NH4PF6 in H2O (20 mL) followed
by filtration affording [Ni2(4)3](PF6)4 quantitatively as a yellow
solid. Positive ion ESI-HRMS: m/z (M = C90H78P4F24Ni2N12O6
in acetonitrile/methanol): calc for [M - 2PF6]2+: 915.2073, found
915.1991; calc for [M - 3PF6]3+: 561.8166, found 561.8224; calc
for [M - 4PF6]4+: 385.1213, found 385.1229. Found: C, 49.15; H,
3.75; N, 7.55%. Calc. for C90H78P4F24Ni2N12O6·4H2O: C 49.31, H
1
This material was used without further purification. H NMR d
(CDCl3, 300 MHz) 2.41 (s, 6 H, CH3), 5.09 (s, 4 H, OCH2Ar),
3
4
3
7.65 (dd, J = 8.1, J = 1.8 Hz, 2 H, H-4¢), 7.89 (dd, J = 8.4,
4J = 2.1 Hz, 2 H, H-4), 8.31 (d, J = 8.1 Hz, 2 H, H-3¢), 8.41 (d,
3
3J = 8.4 Hz, 2 H, H-3), 8.52 (d, J = 1.8 Hz, 2 H, H-6¢), 8.71
4
4
(d, J = 2.1 Hz, 2 H, H-6); positive ion ESI-HRMS: m/z (M =
C30H26N4O2 in dichloromethane/methanol): calc. for [M + Na]+:
497.1948, found 497.1956.
[Fe2(4)3](PF6)4. A mixture of FeCl2·5H2O (30 mg, 0.14 mmol)
and 4 (110 mg, 0.232 mmol) in methanol (10 mL) was heated with
microwave energy in a sealed pressurised microwave vessel with
temperature and pressure sensors (Step 1 – ramped to 130 ◦C over
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 12153–12159 | 12157
©

3.96, N 7.67%. X-ray quality crystals were obtained by diffusion
of tetrahydrofuran into an acetonitrile solution of the product.
The crude product before recrystallisation also showed ev-
idence for the presence of the corresponding M4L6 com-
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.
plex, [Ni4(4)6](PF6)8. Positive ion ESI-HRMS: m/z (M
=
C180H156P8F48Ni4N24O12 in acetonitrile/methanol): calc for [M -
3PF6]3+: 1268.5984, found 1268.6407.
[H2OÃNi2(4)3](PF6)4·THF·2.2H2O
Formula C94H86.4F24N12Ni2O10.20P4, M 2244.61, Monoclinic, space
[Ni2(5)3](PF6)4. The procedure was similar to that em-
ployed for the synthesis of [Ni2(4)3](PF6)4. NiCl2·6H2O (17 mg,
˚
group C2/c(#15), a 23.0800(16), b 15.0530(11), c 32.656(3) A,
3
-3
˚
b 105.778(4), V 10918.0(15) A , Dc 1.362 g cm , Z 4, crystal
size 0.300 ¥ 0.250 ¥ 0.100 mm, colour yellow, habit needle,
0.07 mmol) and quaterpyridine
5 (50 mg, 0.105 mmol)
yielded [Ni2(5)3](PF6)4 quantitatively as a yellow solid. Positive
ion ESI-HRMS: m/z (M = C90H78P4F24Ni2N12O6 in acetoni-
trile/methanol): calc for [M - 2PF6]2+: 915.2073, found 915.1989;
calc for [M - 3PF6]3+: 561.8130, found 561.8224; calc for [M -
4PF6]4+: 385.1213, found 385.1192. Found: C 49.31, H 3.72, N
7.66%. Calc. for C90H78P4F24Ni2N12O6·4H2O: C 49.31, H 3.96,
N 7.67%. X-ray quality crystals were obtained by diffusion of
tetrahydrofuran into an acetonitrile solution of the product.
-1
˚
temperature 150(2) K, l(MoKa) 0.71073 A, m(MoKa) 0.502 mm ,
T(SADABS)min,max 0.813, 0.951, 2qmax 50.00, hkl range -21 27, -17
17, -38 38, N 111989, Nind 9594(Rmerge 0.0267), Nobs 8211(I >
2s(I)), Nvar 798, residuals R1(F) 0.0735, wR2(F2) 0.2345, GoF(all)
-
-3
˚
1.094, Drmin,max -0.568, 1.084 e A .
Specific details. The O(3)-containing ligand is disordered over
two equal occupancy positions and the P(2)-containing PF6 is
disordered over two positions with occupancies of 0.7 and 0.3.
The THF molecule is also disordered over two unequal positions
(0.35 and 0.15) and the remaining disordered water molecules were
modelled over 10 positions with a total occupancy of 1.2. Some
bond length and angle restraints were required to facilitate realistic
models.
[Ni2(6)3](PF6)4. The procedure was similar to that em-
ployed for the synthesis of [Ni2(4)3](PF6)4. NiCl2·6H2O (17 mg,
0.07 mmol) and quaterpyridine
6 (50 mg, 0.105 mmol)
yield [Ni2(6)3](PF6)4 quantitatively as a yellow solid. Positive
ion ESI-HRMS: m/z (M = C90H78P4F24Ni2N12O6 in acetoni-
trile/methanol): calc for [M - 2PF6]2+: 915.2073, found 915.1974;
calc for [M - 3PF6]3+: 561.8130, found 561.8131; calc for [M -
4PF6]4+: 385.1213, found 385.1235. Found: C, 49.43; H, 3.80; N,
7.75%. Calc. for C90H78P4F24Ni2N12O6·4H2O: C, 49.31; H, 3.96;
N, 7.67%. X-ray quality crystals were obtained by diffusion of
tetrahydrofuran into an acetonitrile solution of the product.
The crude product before recrystallisation also showed ev-
idence for the presence of the corresponding M4L6 com-
[(PF6)ÃNi2(5)3](PF6)3·1.75MeCN·5.25THF·0.25H2O
Formula C114.50H125.75F24N13.75Ni2O11.50P4, M 2575.83, monoclinic,
space group P21/c(#14), a 26.028(2), b 22.7450(17), c 21.4660(16)
3
-3
˚
˚
A, b 113.663(2), V 11639.6(16) A , Dc 1.470 g cm , Z 4, crystal size
0.100 ¥ 0.050 ¥ 0.050 mm, colour yellow, habit needle, temperature
-1
˚
100(2) K, l(synchrotron) 0.49594 A, m (synchrotron) 0.259 mm ,
plex, [Ni4(6)6](PF6)8. Positive ion ESI-HRMS: m/z (M
=
T(SADABS)min,max 0.5994, 0.7444, 2qmax 38.62, hkl range -33 33,
-30 26, -27 28, N 99393, Nind 27767(Rmerge 0.0847), Nobs 16878(I >
2s(I)), Nvar 1577, residuals R1(F) 0.0624, wR2(F2) 0.1880, GoF(all)
C180H156P8F48Ni4N24O12 in acetonitrile/methanol): calc for [M -
3PF6]3+: 1268.5984, found 1268.6423.
-
-3
˚
1.010, Drmin,max -0.858, 1.628 e A .
X-ray studies
Specific details. The O(3T)-containing THF is modelled as
disordered over 3 positions with a total occupancy of 1 and the
O(5T)-containing THF is modelled over two equal occupancy
positions. The O(6T)-containing THF is 0.75 occupancy and is
superimposed with a 0.25 occupancy MeCN. A number of bond
length and angle constraints were required to facilitate realistic
modelling.
Data for [H2OÃNi2(4)3](PF6)4·THF·2.2H2O and [Ni2(6)3](PF6)4·
1.95MeCN·1.2THF·1.8H2O were collected on
a
Bruker-
Nonius APEX2-X8-FR591 diffractometer employing graphite-
monochromated Mo-Ka radiation generated from a rotat-
˚
ing anode (0.71073 A) with w and y scans to approxi-
mately 56◦ 2q at 150(2) K.18 Data for [(PF6)ÃNi2(5)3](PF6)3·
1.75MeCN·5.25THF·0.25H2O were collected at approximately
100 K using double diamond monochromated synchrotron ra-
[Ni2(6)3](PF6)4·1.95MeCN·1.2THF·1.8H2O
˚
diation (0.48595 A) and w and y scans at the ChemMatCARS
Formula C98.70H97.05F24N13.95Ni2O9P4, M 2317.49, triclinic, space
beamline at the Advanced Photon Source. Data integration
and reduction were undertaken with SAINT and XPREP.19
Subsequent computations were carried out using the WinGX-32
graphical user interface.20 Structures were solved by direct methods
using SIR97.21 Multi-scan empirical absorption corrections, when
applied, were applied to the data set using the program SADABS.22
Data were refined and extended with SHELXL-97 and SHELXH-
97.23 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. As oxygen bound hydrogen atoms could not be
located in the difference Fourier map they were not modelled. In
¯
˚
group P 1(#2), a 14.9978(6), b 15.066◦6(6), c 25.7786(11) A,
3
˚
a 91.398(2), b 104.152(2), g 99.563(2) , V 5556.9(4) A , Dc
1.385 g cm-3, Z 2, crystal size 0.300 ¥ 0.100 ¥ 0.100 mm, colour
˚
yellow, habit needle, temperature 150(2) K, l(MoKa) 0.71073 A,
m(MoKa) 0.496 mm-1, T(SADABS)min,max 0.799, 0.952, 2qmax 50.00,
hkl range -17 17, -17 17, -30 30, N 107006, Nind 19484(Rmerge
0.0534), Nobs 13655(I > 2s(I)), Nvar 1534, residuals R1(F2) 0.0734,
wR2 (F2) 0.2194, GoF(all) 1.072, Drmin,max -0.552, 0.993 e A .
-
-3
˚
Specific details. Each of the anions is disordered over two
positions as is the O(1T) and O(2T)-containing THFs. The N(4S)-
containing MeCN and O(3T)-containing THF have occupancies
12158 | Dalton Trans., 2011, 40, 12153–12159
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The Royal Society of Chemistry 2011
©

of less that 1 and have disordered water molecules superimposed
on their positions. A number of bond length constraints were
required to produce realistic models.
5 F. Li, J. K. Clegg, L. F. Lindoy, R. B. Macquart and G. V. Meehan, Nat.
Commun., 2011, 2, 205; J. K. Clegg, F. Li, K. A. Jolliffe, G. V. Meehan
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Iremonger, M. J. Hayter, P. D. Southon, R. B. Macquart, M. B. Duriska,
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Acknowledgements
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.
6 C. R. K. Glasson, G. V. Meehan, J. K. Clegg, L. F. Lindoy, P. Turner,
M. B. Duriska and R. Willis, Chem. Commun., 2008, 1190.
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©