Competitive binding of Ba2+and Sr2+ to 18-crown-6 in a receptor with a 1-methoxyanthraquinone analogue as the other binding site

Article abstract of DOI:10.1002/ejic.201100472

Owing to their immense biological significance, development of sensors for the selective detection of alkaline earth metal ions has attracted vast research interest. In this article we have reported the synthesis, characterisation and ion binding studies of a new Ru^II-polypyridyl-crown-anthraquinone complex (5). Studies confirm selective binding of Ba^II, Sr ^II and Ca^II ions, with Ka_Baa2+ > Ka_Sra2+ >> Ka_Caa2+, over all other metal ions, to the crown ether moiety and not to the methoxy anthraquinone component, the latter being the second binding site available and known for its affinity towards alkaline earth metal ions from one of our previous reports. A new Ru^II-polypyridyl complex with two probable binding sites for metal ions has been synthesised to which Ca²⁺, Sr²⁺ and Ba²⁺ were found to bind selectively over all other alkali, alkaline earth, transition and lanthanide metal ions. Studies also confirmed binding of these metal ions solely to the 18-crown-6 and not to the methoxyanthraquinone moiety known to bind alkaline earth metal ions. Copyright

Full text of DOI:10.1002/ejic.201100472

FULL PAPER
DOI: 10.1002/ejic.201100472
Competitive binding of Ba2+and Sr2+ to 18-Crown-6 in a Receptor with a
1-Methoxyanthraquinone Analogue as the Other Binding Site
Tanmay Banerjee,[a] Moorthy Suresh,[a] Hirendra N. Ghosh,*[b] and Amitava Das*[a]
Keywords: Sensors / Receptors / Crown compounds / Alkaline earth metals / Ruthenium
Owing to their immense biological significance, develop- BaII, SrII and CaII ions, with KBa2+ Ͼ KSr2+ ϾϾ KCa2+, over all
ment of sensors for the selective detection of alkaline earth
metal ions has attracted vast research interest. In this article
we have reported the synthesis, characterisation and ion
binding studies of a new RuII-polypyridyl-crown-anthra-
quinone complex (5). Studies confirm selective binding of
other metal ions, to the crown ether moiety and not to the
methoxy anthraquinone component, the latter being the sec-
ond binding site available and known for its affinity towards
alkaline earth metal ions from one of our previous reports.
sors for Ca2+ [8]
More recently, a new PET based fluores-
.
Introduction
cent sensor for Ca2+ using an aryl anthryl diaza 18-crown-
6 derivative has been reported.[9] A number of reports also
The role that different alkaline earth metal ions play in
various critical biological processes is well acknowledged.
Among different alkaline earth metal ions, calcium is per-
haps the most important because of the imperative role that
it plays in neurotransmitter release, in muscle contraction,
in blood clotting and in the electrical conduction system
of the heart.[1] Calcium also plays the central role in the
development and strengthening of the skeletal system in al-
most all animal life forms and its deficiency leads to dis-
eases such as rickets and osteoporosis.[1a,1b,2] Strontium be-
ing similar to calcium, is incorporated in the bones and is
known to aid bone growth and prevent fractures.[3] The
87Sr/86Sr ratio in the bones also helps in dating archaeologi-
cal specimens.[4] Barium, in lower concentrations, acts as a
muscle relaxant.[5] However, the presence of Sr2+ and Ba2+
beyond a threshold concentration is known to have adverse
effects causing cardiac and nervous system disorders and
even paralysis.[6] Thus, development of suitable sensors for
the selective and efficient detection of these ions is of im-
mense interest in current research.
exist on selective sensing of Ba2+ [10]
A recent article reports
.
the utilisation of self assembling processes of fluorophore-
crown ether systems for the detection of Ba2+ present in
micromolar concentrations.[11] Reports on recognition of
Sr2+ in solution, however, are extremely scarce and all the
existing reports show a poor selectivity towards Sr2+ [12]
Se-
.
lective sensing of this alkaline earth metal ion has predomi-
nantly been achieved using carrier based PVC membrane
ion sensitive electrodes.[13] Existing literature reports, there-
fore, suggest that there is ample opportunity and challenge
for designing receptors that show selectivity to these alka-
line earth metal ions.
In one of our earlier reports, we have shown that 1,2-
dihydroxy- or 1,2-dimethoxy anthraquinone show moderate
binding affinity (ca. 103 to 104 m–1 in DMF) towards the
different alkaline earth metal ions and the affinities follow
[14]
the order KMg2+ ϾϾ KCa2+ Ͼ KSr2+ ϾϾ KBa2+
.
Studies
revealed that the OOMe or OOH atoms of one of the two
methoxy/hydroxy functionalities and one of the two OCO
atoms are actually involved in the coordination to these
metal ions (Scheme 1). The affinity of 18-crown-6 deriva-
tives towards the alkaline earth metal ions is also well docu-
mented throughout the literature.[15] Such crown ether de-
rivatives bind to the alkaline earth metal ions with moder-
A considerable number of reports exist for selective cal-
cium sensing with different kinds of reporter groups and
receptors.[7] Crown ether derivatives have clearly been one
of the most popular choices for the design of selective sen-
[a] Analytical Science Discipline, Central Salt and Marine
Chemicals Research Institute,
Bhavnagar, Gujarat, India
Fax: +91-278-2567562
E-mail: amitava@csmcri.org
[b] Radiation and Photo Chemistry Division, Bhabha Atomic
Research Center,
Mumbai, India
Fax: +91-22-25505151
E-mail: hnghosh@barc.gov.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100472.
Scheme 1. Binding mode of alkaline earth metal ions to anthra-
quinone moiety as in ref.[14]
.
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Competitive Binding of Ba and Sr Cations
ate binding affinities as well (ca. 103 to 104 m–1 in ety, has also been synthesised as the model compound for
MeOH).[15j]
unambiguous assignment of the binding site. The choice of
M. D. Ward and his coworkers found that Ba2+ binds the RuII-polypyridyl moiety as the signalling unit is gov-
to ReI-phenanthroline-18-crown-6 complex.[16] On the other erned by its rich spectroscopic properties.[17b,19]
hand, Finney et al. showed that a more flexible oxa-crown-
6 moiety, coupled with a RuII-polypyridyl core, binds to cium, strontium and barium ions to the crown ether moiety
Ca2+, Mg2+ and Pb2+ with preference for Pb2+ [17]
Erk et al. in 5 and not to the methoxyanthraquinone end (see binding
Experimental studies reveal a preferential binding of cal-
.
have prepared anthraquinone 18-crown-6 ethers and have mode B in Scheme 3) which marks a self-sorting type of
shown that Na+ and K+ have appreciable binding affinity binding behaviour of the ions mentioned.
with these.[18] Thus, literature reports tend to suggest that
with a little change in the flexibility and the electronic envi-
ronment of the crown ether moiety, preference of binding
to metal ions changes.
Results and Discussion
Synthesis
In order to verify whether, in this process, one can
achieve any preference towards any particular metal ion
and to study two competitive binding modes for the binding
of the alkaline earth metal ion(s), we have synthesised a
new receptor molecule 5 in which the 18-crown-6 moiety is
coupled to anthraquinone and to the RuII-polypyridyl unit.
This is expected to allow coordination of metal ions to both
the probable binding sites, namely the crown ether and the
methoxyanthraquinone moiety (Schemes 2 and 3). Further-
more, a new compound 6, without the anthraquinone moi-
The synthetic methodologies adopted for the synthesis of
the bipyridine based ligands 4 and 4a and the correspond-
ing RuII-polypyridyl complexes 5 and 6 are outlined in
Schemes 4 and 5, respectively.
Compound 1 was prepared according to a previously re-
ported procedure and the analytical data matched well with
the reported results. Compound 2 was prepared by simple
O-alkylation of alizarin with 2-(2-chloroethoxy)ethanol in
dry and distilled DMF with potassium carbonate as a base
in the presence of KI. The crude product was purified by
column chromatography to isolate 2 in pure form. This was
tosylated with 4-methylbenzenesulfonyl chloride in a THF/
acetonitrile mixture in the presence of NaOH. Column
chromatography yielded pure 3 which was subsequently
treated with 1 in the presence of K2CO3 in dried and dis-
tilled DMF. The solvent was evaporated and pure 4 was
isolated by subsequent precipitation from chloroform using
methanol. This was then made to react with Ru(2,2Ј-bpy)2-
Cl2·2H2O in ethanol and the crude compound 5 was iso-
lated as the hexafluorophosphate salt and purified sub-
sequently by column chromatography and recrystallisation.
The synthesis of compound 6 was done following a sim-
ilar methodology. The analogous tosylation step was, how-
ever, carried out in a slightly different manner using Et3N
as the base in dichloromethane in the presence of a catalytic
amount of DMAP. The reaction time for this method was
only 12 h compared with a 5 d reaction time for the synthe-
sis of 3 from 2.
Scheme 2. Molecular structures of compounds 5 and 6.
Ion Binding Studies
Figure 1 shows the absorption and the fluorescence spec-
tra of 5 in acetonitrile. The low energy broad absorption
peak with maxima at 463 nm arises predominantly due to
dπRuII Ǟπ*2,2Ј-bpy and dπRuII Ǟπ*4 based MLCT transi-
2+
tions.[20] Literature reports reveal that the Ru(2,2Ј-bpy)3
moiety shows MLCT absorption maxima at 452 nm.[21]
Shift of the absorption maxima of the MLCT transition
to a longer wavelength compared with Ru(2,2Ј-bpy)3 is
2+
perhaps due to the extended conjugation in the coordinated
ligand 4. This hypothesis is supported by the previous re-
ports from our group.[22] Strong ligand centred π-π* transi-
tions at 288 nm and higher energy MLCT d-π* transitions
Scheme 3. Possible binding modes of the alkaline earth metal ions
to 5.
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FULL PAPER
Scheme 4. Synthetic methodology of 5 and its precursors.
ceptor,[14,23] along with contributions from πbpy Ǟπ*4 and
π
bpy Ǟπ*bpy based interligand charge transfer transi-
tions.[20,22] The analogous band for the reference compound
6 has a maximum at 357 nm (Figure 1). This difference of
12 nm arises due to the absence of the relatively lower en-
ergy anthraquinone based nǞπ* charge transfer transition
3
as discussed before. A broad MLCT emission band (φ =
0.0023) with a maxima at 653 nm can be observed upon
excitation of 5 at 463 nm.
Scheme 5. Synthetic methodology of 6 and its precursors.
Figure 1. Absorption and fluorescence spectrum (λexc = 463 nm) of
5 (2.0ϫ10–5 m) and 6 (1.33ϫ10–5 m) in acetonitrile.
at 245 nm could also be observed.[20] The absorption band
at 369 nm could be ascribed to an overlap of several transi-
tions, namely, nǞπ* charge transfer transitions with the
A significant change in the electronic spectral pattern
crown ether as the donor and the low lying π* orbital in- was observed upon addition of Ca2+, Sr2+ and Ba2+ ions to
volving the phenyl conjugated bipyridine part of 4 as the an acetonitrile solution of 5 (Figure 2). The extent of the
acceptor, nǞπ* charge transfer transition with the crown observed changes was a little less for Ca2+ when compared
ether moiety as the donor and anthraquinone as the ac- with Ba2+ and Sr2+
.
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Competitive Binding of Ba and Sr Cations
band at 357 nm for complex 6 further supports the contri-
bution of an nǞπ* charge transfer transition, with the
crown ether as the donor and the low lying π* orbital in-
volving the phenyl conjugated bipyridine part of 4 as the
acceptor, to the absorption band at 369 nm for complex 5.
On addition of Ba2+ ions to an acetonitrile solution of
5, the absorption band at 369 nm was found to decrease
with a concomitant increase in the absorption at 344 nm.
Occurrence of an isosbestic point at 365 nm during titration
with Ba2+ ions indicates the presence of two species in equi-
librium (Figure 4a). Similar trends were observed for ti-
trations with Sr2+ and Ca2+ ions with respective isosbestic
points at 365 nm and at 361 nm (Figure 4). This change in
the absorption spectrum for 5 can be explained if one con-
siders that the aforesaid metal cations bind to the donor,
the crown ether moiety – the excited state will therefore be
more strongly destabilised by the cation than the ground
state, resulting in an hypsochromic shift of the absorption
band at 369 nm.[24] The relative affinity of these three ions
(Ca2+, Ba2+ and Sr2+) towards 5 was evaluated by the com-
parative change in the absorbance data at λ342 nm while
varying the concentration of the three metal ions. Binding
constants for the formation of the complexes 5·Ca2+, 5·Sr2+
and 5·Ba2+ were evaluated from the Benesi–Hildebrand plot
using Equation (2) (see Exp. Sect.) and were found to be
1.59ϫ103 m–1, 5ϫ103 m–1 and 6.1ϫ103 m–1, respectively
(Figure 5). The linearity of the plots in Figure 5 indicates
the formation of a 1:1 complex for all the three metal ions
discussed. Binding constant for the formation of the com-
plex 6·Ba2+ at λ344 nm has also been determined for com-
parison with 5 and was found to be 4.3ϫ104 m–1.
Figure 2. UV/Vis spectrophotometric scan of 5 (2.0ϫ10–5 m) in the
presence of 100 equiv. of different metal ions in acetonitrile.
No such spectroscopic change was observed upon the
addition of any other alkali, alkaline earth, lanthanide or
transition metal ions (Figures 2 and 3). On addition of the
aforesaid metal ions to an acetonitrile solution of the refer-
ence compound 6, a total loss in the selectivity is observed
(Figure S30, Supporting Information). Almost all the metal
ions elicit some change in the spectral pattern. However,
relatively prominent changes could be obtained for Ba2+
,
Sr2+, Ca2+, Pb2+ and K+ for which a hypsochromic shift in
the absorption band at 357 nm could be observed similar
to that for complex 5. The appearance of the absorption
Formation of a 1:1 complex for these three metal ions
was also ascertained by mass spectrometric analysis of an
acetonitrile solution of 5 in the presence of an excess of
these metal ions. For 1:1 binding of CaII with 5, a promi-
nent peak can be observed at m/z = 1394.04 ascribed to 5 –
2PF6 + Ca + 2ClO4 + H2O + K (Figure S32, Supporting
Information). For Sr2+, a 1:1 complexation peak can be ob-
served with the desired isotopic distribution at m/z =
1323.59, 5 – 2PF6 + Sr + ClO4 + K (Figure S33, Supporting
Information), while for Ba2+ this peak can be observed at
m/z = 1258.59, 5 – 2PF6 + Ba + Na (Figure S34, Support-
ing Information).
Figure 3. 3D depiction of the binding of Ca2+, Sr2+ and Ba2+ in
the UV/Vis scan of 5 with the metal ions. Changes shown are those
at 385 nm. Each of the points in the xy plane represents a metal
ion, the names of which have been omitted for clarity.
Figure 4. Spectrophotometric titration of (a) 5 (2.11ϫ10–5 m) in the presence of (0–12.3)ϫ10–4 m Ba(ClO4)2 in acetonitrile, (b) 5
(1.916ϫ10–5 m) in the presence of (0–7.44)ϫ10–4 m Sr(ClO4)2 in acetonitrile and (c) 5 (1.916ϫ10–5 m) in the presence of (0–28.39)ϫ10–4
Ca(ClO4)2 in acetonitrile.
m
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Figure 5. BenesiϪHildebrand plots for binding constant calculation with (a) Ba2+, (b) Sr2+ and (c) Ca2+ from the specrophotometric
titrations for 5.
Emission spectroscopic studies of 5 in acetonitrile show The Stern–Volmer plot i.e., the plot of τ0/τ, where τ0 is the
lifetime in the absence of Cu2+ vs. the concentration of CuII,
shows an increase in the τ0/τ values with increasing concen-
trations of Cu2+, i.e., the lifetime decreases steadily as the
concentration of Cu2+ is increased (Figure S38, Supporting
Information). This confirms that no ground state complex
is formed between Cu2+ and 5 and that the quenching is
purely dynamic in nature.[25] No change in the emission
profile on the addition of CaII, SrII or BaII ions is probably
because of the fact that the rate of excited state decay of
the anthraquinone moiety is much less than the rate of re-
pulsion between the cations and the receptor in the excited
state. The lifetime of 5 in the presence of Ca2+, Sr2+ and
Ba2+ at 653 nm could not be measured because of the ex-
ceedingly low quantum yield of the RuII-polypyridyl fluoro-
phore at that wavelength.
an enhancement in the emission intensity at 653 nm in the
presence of added Ca2+, Ba2+ and Sr2+ with changes being
more prominent for Sr2+ and Ba2+ than for Ca2+ (φ = 0.003,
0.0032 and 0.0032 for 5·Ca2+, 5·Sr2+ and 5·Ba2+, respec-
tively) (Figure 6). As was observed in the electronic spectro-
scopic studies, no change was observed for any other metal
ion in the emission spectrum. A similar experiment with
compound 6 did not yield any selectivity towards any metal
ion. (Figure S35, Supporting Information).
The enhancement in the emission intensity of the
3MLCT emission band at 653 nm on binding to the afore-
said metal ions is suggestive of a photoinduced electron
transfer process being operational. Binding to these metal
ions to the oxygen atoms of the crown ether moiety inter-
rupts the photoinduced electron transfer process and an en-
hancement in the RuII-polypyridyl based emission re-
sults.[24b,26] Binding constants were evaluated from system-
atic fluorescence titrations using Equation (3) (see Exp.
Sect.) and were found to be 2.63ϫ103 m–1,
Figure 6. Emission scan of 5 (2ϫ10–5 m) in the presence of
100 equiv. of different metal ions in acetonitrile (λexc = 463 nm).
6.08ϫ103 m–1 and 7.76ϫ103 m–1, respectively, for Ca2+
,
In the present study, a broad charge transfer emission
band appears at 425 nm on excitation of the charge transfer
absorption band of 5 at 369 nm.[14] This assignment is fur-
ther corroborated by the observation that no such emission
band could be obtained when an acetonitrile solution of 6
was excited at 357 nm (Figure S36, Supporting Infor-
mation). No change in the emission profile at 425 nm was
observed when an acetonitrile solution of 5 was scanned
with the various metal ions, except for Cu2+ ion which
quenches the fluorescence appreciably (Figure S37, Sup-
porting Information). This response can be attributed to
dynamic quenching by Cu2+ on the basis of a lifetime ti-
tration experiment. The free complex 5 shows monoexpon-
ential decay with a lifetime of 1.076Ϯ0.009 ns (χ2 = 1.08)
when monitored at 425 nm in acetonitrile using a 340 nm
Sr2+ and Ba2+ (Figure 7). This was found to corroborate
nicely with the binding constants calculated from the spec-
trophotometric titrations. The binding constants therefore
obey the order KBa2+ Ͼ KSr2+ ϾϾ KCa2+. The binding con-
stant for the formation of the complex 6·Ba2+ has also been
determined from a similar spectrophotometric titration as
carried out for 5 and was found to be 1.8ϫ104 m–1 (Figure
S39, Supporting Information). The relatively lower binding
constant for 5·Ba2+ compared with that for 6·Ba2+ might
be due to the presence of the electron withdrawing anthra-
quinone fragment in 5 which reduces the basicity of the
O
Crown atoms – especially that of the two OCrown atoms that
are in conjugation with the anthraquinone fragment.
Literature reports on the binding of the alkaline earth
LED as an excitation source. This lifetime of 5 was mea- metals to 18-crown-6 moiety are plentiful.[15] On the other
sured in the presence of varying concentrations of Cu2+
.
hand, we, in one of our previous reports, have explored 1,2-
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Competitive Binding of Ba and Sr Cations
Figure 7. Emission titration of 5 (1.988ϫ10–5 m) in presence of (a) (0–5.9)ϫ10–4 m Ba2+, (b) (0–6.2)ϫ10–4 m Sr2+ and (c) (0–14.2)ϫ10–4
m
Ca2+in acetonitrile. Respective logarithmic plots (log[F0 – F]/[F – Fϱ] as the ordinate and log[M2+] as the abscissa) for the calculation of
binding constants are shown as insets.
dimethoxy anthraquinone as a sensor for the alkaline earth
metal ions.[14] In that study, spectrophotometric, fluores-
cence and theoretical calculations confirmed binding of the
metal ions to the ether and the carbonyl oxygen atom
(Scheme 1).
Both of the aforesaid binding sites have been combined
in 5 in order to establish the relative binding affinity of the
alkaline earth metal ions towards these two binding sites.
Studies corroborate preferential binding of Ca2+, Sr2+ and
Ba2+ ions to the crown ether and not to the methoxyanthra-
quinone moiety. This is confirmed from an analysis of the
infrared spectrum of 5 in absence and in the presence of
these ions. Free complex 5 shows carbonyl stretching fre-
quencies at 1653 cm–1 (C1) and 1635 cm–1 (C2) (Figure S23,
Supporting Information). On addition of an excess of Ca2+
,
Figure 8. Changes in the IR spectroscopic pattern upon addition
of the metal ions.
the peak at 1635 cm–1 does not shift much but the
1653 cm–1 peak shifts to 1665 cm–1. Addition of an excess
Sr2+ and Ba2+ shifts these peaks to 1707 cm–1, 1669 cm–1
and to 1709 cm–1, 1669 cm–1, respectively (Figure 8). In our are most prominent. Addition of Ba2+ ions to an acetoni-
earlier report, for binding of Mg2+ to one of the ether and trile solution of 5 causes the spectrum to become very
the carbonyl oxygen atoms (Scheme 1), a shift of the car- broad which may be due to a very fast relaxation of the
bonyl stretching frequency in the FTIR spectrum to lower complex formed. Similar broadening has been observed by
energy was observed.[14] In the present study, however, the other groups as well.[26,27] For Ba2+, a set of new complex-
carbonyl stretching frequencies are found to shift to higher ation peaks could be observed at δ = 4.96 and 4.84 ppm
energies. The shifting of the ν(C=O) values to higher ener- (Figure 9).
gies is because of the metal ions binding to the crown ether
The appearance of a new complexation peak is reminis-
moiety which draws electron density from the carbonyl oxy- cent of slow exchange in the NMR time scale which is ex-
gen atoms towards the anthraquinone ring system making pected in the case of strong binding of Ba2+ ions.[27,28] For
the carbonyl bond stronger. For Sr2+ and Ba2+, the shifts Ca2+ and Sr2+ respectively, the set of eight protons i.e., H9,
are more pronounced indicating stronger binding of these H10, H11 and H12, at δ = 4.29–4.2 ppm, were found to shift
metal ions than calcium. This inference corroborates our to δ = 4.38–4.29 ppm and δ = 4.58–4.41 ppm (see Fig-
results obtained from the spectrophotometric and fluores- ures 10 and S40, the latter in the Supporting Information).
cence measurements.
A final confirmation comes from the 13C NMR studies
1H NMR titrations were carried out in the presence of in acetone. 13C NMR spectra of 5 were recorded for each
the aforesaid ions and the results support our ideas of the metal ion when present in equivalent amounts and in excess.
ions binding to the crown ether part. The signals arising Acetone was used in order to prevent interference from the
from almost all of the hydrogens of the crown ether moiety signals arising from acetonitrile itself in the aromatic region
were found to shift downfield on addition of either of these of the spectrum. Though 5 was less soluble in acetone, the
metal ions indicating binding to the ethereal oxygen atoms. solubility increased on the addition of the metal ions indi-
However, for H9, H10, H11 and H12 protons, i.e. the protons cating complex formation of 5 with the metal ions.[15c,29]
corresponding to the centre of the crown ether, the effects For 5, the carbonyl carbons appear at δ = 182.5 and
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Figure 9. Changes in the 1H NMR spectrum on addition of in-
creasing equivalents of Ba2+ in acetonitrile. The appearance of
complexation peaks at δ = 4.96 and 4.84 ppm is marked with ar-
rows.
Figure 11. 13C NMR spectrum of 5 in the presence of 1 equiv. and
excess of Sr2+ in [D6]acetone. The peaks due to the carbonyl carbon
atoms (δ = 182.5 and 182.1 ppm) are not seen to shift. The C sig-
nals of the crown ether moiety can, however, be seen to become
deshielded.
(Scheme 1), the binding constant value is reported to be
equal to 0.6ϫ103 m–1 in DMF.[14] Although the solvent
plays a dominant role in the binding phenomena, the rela-
tively higher binding affinity of the aforesaid alkaline earth
metal ions to the crown ether moiety compared with the
methoxyanthraquinone part is apparently, therefore, the
possible reason for the selective binding to the crown ether
in 5.
Conclusions
We have synthesised and characterised a new RuII-polyp-
ypyridyl/anthraquinone-based molecule 5 with two prob-
able binding sites for the binding of metal ions, an 18-
crown-6 ether and a methoxyanthraquinone moiety. Com-
pound 5 was found to bind selectively with Ca2+, Sr2+ and
Ba2+ ions in acetonitrile over all other alkali, alkaline earth,
transition and lanthanide metal ions and the binding phe-
nomena have been probed by spectrophotometric, fluori-
Figure 10. Changes in the 1H NMR spectrum on addition of in-
creasing equivalents of Ca2+ in acetonitrile. The initial and the final
positions of the H9, H10, H11 and H12 protons are marked with the
black dot.
1
metric and mass spectrometric measurements. H, 13C and
IR spectroscopic studies prove binding of the aforesaid
metal ions selectively to the crown ether part and not to the
methoxyanthraquinone moiety.
182.1 ppm. In case of a possibility of the metal ions inter-
acting with the carbonyl oxygen, one of the aforesaid sig-
nals would be expected to shift downfield. No such shift
was observed for any of the metal ions when present in
either equivalent amounts or in excess (Figure 11).
The signals arising from the carbons of the crown ether
moiety in the region δ = 73.59–69.2 are instead seen to be-
come affected in every case which confirms our proposition
of the metal ions binding to the crown ether moiety (Fig-
ures S41 and S42, Supporting Information).
Experimental Section
Materials and Methods: RuCl3·xH2O, 4,4Ј-dimethyl-2,2Ј-bipyr-
idine, n-butyllithium, 3,4-dimethoxybenzaldehyde, 2,2Ј-bipyridine,
4-methoxybenzaldehyde, alizarin, 2-(2-chloroethoxy)ethanol, 4-
methylbenzenesulfonyl chloride, ammonium hexafluorophosphate,
4-(dimethyamino)pyridine, LiClO4, NaClO4, KClO4, CsClO4,
Mg(ClO4)2, Ca(ClO4)2·4H2O, Sr(ClO4)2·xH2O, Ba(ClO4)2,
Cr(ClO4)3·6H2O, Mn(ClO4)2, Fe(ClO4)2·xH2O, Co(ClO4)2·6H2O,
Ni(ClO4)2·6H2O, Cu(ClO4)2·6H2O, Zn(ClO4)2·6H2O, Cd(ClO4)2·
UV/Vis and emission titrations reveal a binding constant
an order of magnitude higher for Ba2+ binding to 6 (ca.
104 m–1) than to 5 (ca. 103 m–1) in acetonitrile. For Ba2+
binding separately to the methoxyanthraquinone moiety H2O, Hg(ClO4)2·xH2O, Pb(ClO4)2·3H2O, La(NO3)3·6H2O,
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Competitive Binding of Ba and Sr Cations
Ce(NO3)3·6H2O, Pr(NO3)3·6H2O, Nd(NO3)3·6H2O, Sm(NO3)3· Kd is the dissociation constant, n is the number of metal ions bound
6H2O, Eu(NO3)3·5H2O, Gd(NO3)3·6H2O, Tb(NO3)3·5H2O, to each complex, F0 is the fluorescence intensity of the complex in
Dy(NO3)3·xH2O, Ho(NO3)3·5H2O, Er(NO3)3·5H2O, Tm(NO3)3· the absence of any metal ion, Fϱ is the fluorescence intensity at the
5H2O, Yb(NO3)3·5H2O and Lu(NO3)3·xH2O were purchased from
the Sigma–Aldrich Chemical Co. and were used as received. Diiso-
propylamine, triethylamine, POCl3, pyridine, HCl, K2CO3, KI,
NaOH, MgSO4 and all other chemicals (AR grade) were purchased
from S. D. Fine Chemicals (India) and were used without any fur-
ther purification. Dimethyl formamide (DMF), dichloromethane
(DCM), tetrahydrofuran (THF) and pyridine, used for synthesis,
were dried and distilled before use according to standard pro-
cedures.[30] All other solvents used (AR grade) were purchased from
S. D. Fine Chemicals (India). Spectroscopic grade solvents were
used for all spectroscopic and photophysical studies. Ru(2,2Ј-bpy)2-
Cl2·2H2O was prepared following a previously reported pro-
cedure.[31]
1H and 13C NMR spectra were recorded with either a Bruker
200 MHz FT NMR (model: Avance-DPX 200) or a Bruker
500 MHz FT NMR (model: Avance-DPX 500) spectrometer at
room temperature (r.t., 25 °C). Tetramethylsilane (TMS) was used
as an internal standard for all 1H NMR spectroscopic studies. ESI-
MS measurements were carried out with a Waters QTof-Micro in-
strument. Microanalyses (C, H, N) were performed by using a Per-
kin–Elmer 4100 elemental analyser. Infrared spectra were recorded
as KBr pellets by using a Perkin–Elmer Spectra GX 2000 spectrom-
eter. HRMS measurements were done using a micromass Q-Tof
microTM instrument. UV/Vis spectra were obtained by using either
a Shimadzu UV-3101 PC or a Cary 500 Scan UV/Vis/NIR spectro-
photometer. Room-temperature steady state emission spectra were
obtained by using either a Fluorolog (Horiba Jobinyvon) or an
Edinburgh Instruments Xe 900 luminescence spectrofluorimeter.
Time-resolved fluorescence measurements were carried out using
Horiba Jobinyvon FluoroHub spectrofluorimeter. The instrument
works on the principle of the time-correlated single-photon count-
ing technique (TCSPC). The fluorescence quantum yields (φf) were
estimated using Equation (1) in acetonitrile by using the integrated
emission intensity of Ru(bpy)3(PF6)2 (φf = 0.062 in acetonitrile at
r.t.) as a reference.[21]
maximum concentration of the metal ion i.e., when the emission
intensity does not change any more. We plotted log[(F0 – F)/(F –
Fϱ)] against log[Mx+]. The value of log[Mx+] at log[(F0 – F)/(F –
Fϱ)] = 0 gives Kd, the reciprocal of which is the binding constant.
Synthesis
4-[2-(4Ј-Methyl-2,2Ј-bipyridinyl-4-yl)vinyl]benzene-1,2-diol (1): This
compound was prepared following a literature procedure.[34] ESI-
MS (m/z): calcd. for C19H16N2O2 304.34; found 305.22 [M + 1]+.
1H NMR (500 MHz, CD3OD): δ = 8.54 [d, J = 5.5 Hz, 1 H, H6Ј
(bpy)], 8.52 [d, J = 5 Hz, 1 H, H6 (bpy)], 8.34 [s, 1 H, H3Ј (bpy)],
8.13 [s, 1 H, H3 (bpy)], 7.53 [dd, J = 4, 1 Hz, 1 H, H5Ј (bpy)], 7.43
[d, J = 16 Hz, 1 H, H (ethenyl)], 7.32 [dd, J = 4, 1 Hz, 1 H, H5
(bpy)], 7.11 [d, J = 1.5 Hz, 1 H, H2 (phenyl)], 7.02–6.98 [m, 2 H,
H (ethenyl) and H6 (phenyl)], 6.79 [d, J = 8 Hz, 1 H, H5 (phenyl)],
2.49 (s, 3 H, bpy-CH ) ppm. IR (KBr pellet): ν = 3238 [ν (OH)],
˜
3
1590 [ν(C=C)] cm–1. C19H16N2O2 (304.35): calcd. C 74.98, H 5.30,
N 9.20; found C 74.6, H 5.28, N 9.16.
1,2-Bis[2-(2-hydroxyethoxy)ethoxy]anthraquinone (2): Alizarin
(2.5 g, 0.01 mol) was dissolved in pre-dried and distilled DMF
(80 mL). Anhydrous K2CO3 (4.83 g, 0.035 mol) was ground and
added in a powdered form to this solution with constant stirring
under an inert atmosphere (oxygen- and moisture-free argon gas
blanket). The reaction mixture was heated to 90 °C. 2-(2-Chloro-
ethoxy)ethanol (3.2 mL, 0.03 mol) was dissolved in dry DMF
(10 mL) and was added in a dropwise manner to the resultant solu-
tion. When the addition was complete, anhydrous KI (5.81 g,
0.035 mol) was added and the reaction mixture was stirred at
100 °C for 6 d in the inert atmosphere. The solvent was evaporated
thereafter and solvent extraction was carried out with the crude
mixture. Undesired inorganic salts were removed in the aqueous
phase and the organic (chloroform) layer was collected. This was
dried with anhydrous magnesium sulfate before chloroform was fi-
nally removed under reduced pressure to obtain the crude product.
This crude solid was subjected to column chromatography using
silica as the stationary phase and CHCl3/MeOH solvent mixture
as the eluent. The major fraction was eluted as the second band to
yield the desired compound 2 in pure form; yield 1.3 g, 30%. ESI-
MS (m/z): calcd. for C22H24O8 416.42; found 417.52 [M + 1]+,
φf = φfЈ (Isample/Istd)(Astd/Asample)(η2sample/η2
)
(1)
std
φfЈ is the absolute quantum yield for the Ru(bpy)3(PF6)2 used as
reference, Isample and Istd are the integrated emission intensities,
Asample and Astd are the absorbances at the excitation wavelength,
and ηsample and ηstd are the respective refractive indices.
1
439.52 [M + Na]+. H NMR (500 MHz, CD3OD): δ = 8.29 (d, J
= 8 Hz, 1 H, H1), 8.22–8.18 (m, 1 H, H2), 8.08 (d, J = 8.5 Hz, 1
H, H3), 7.75–7.71 (d, J = 8.5 Hz, 1 H, H4), 7.73 (m, 1 H, H5), 7.25–
7.22 (m, 1 H, H6), 4.37–4.35 [m, 4 H, H7 (two protons), H8 (two
protons)], 4.30 (t, J = 4.5 Hz, 2 H), 4.12 (t, J = 4.5 Hz, 2 H), 4.09
(t, J = 4.5 Hz, 2 H), 3.96 (t, J = 4.5 Hz, 2 H), 3.76 (t, J = 4.5 Hz,
Binding constants were calculated from the UV titrations by using
the Benesi–Hildebrand Equation (2).[32]
2 H), 3.69 (t, J = 4.5 Hz, 2 H) ppm. IR (KBr pellet): ν = 3406, 3259
˜
[ν(OH)], 1672 [ν(C=O)] cm–1. C22H24O8 (416.43): calcd. C 63.45, H
5.81; found C 63.38, H 5.76.
(2)
A0 is the absorbance of 5/6 in the absence of any metal ion Mx+
,
2,2Ј-{2,2Ј-[1,2-Phenylenebis(oxy)]bis(ethane-2,1-diyl)}bis(oxy)di-
ethanol (2a): Catechol (1.65 g, 0.015 mol) was dissolved in pre-dried
and distilled DMF (80 mL). Anhydrous K2CO3 (5 g, 0.036 mol)
was ground and added in a powdered form to this solution with
constant stirring under an inert atmosphere. The reaction mixture
was heated to 90 °C. 2-(2-Chloroethoxy)ethanol (4.7 mL,
0.045 mol) was dissolved in dry DMF (10 mL) and was added in a
dropwise manner to the resultant solution. When the addition was
complete, anhydrous KI (6 g, 0.036 mol) was added and the reac-
tion mixture was stirred at 100 °C for 6 d in the inert atmosphere.
The solvent was evaporated thereafter and solvent extraction was
(3) carried out with the crude mixture. Undesired inorganic salts were
A is the absorbance in the presence of the metal ion, Amax is the
absorbance in presence of added [Mx+
]max and K is the association
constant. This association constant (K) could be determined from
the slope of the linear plot of 1/(AϪA0) vs. 1/[Mx+].
Binding constants from the fluorescence titrations were calculated
using Equation (3).[33]
Eur. J. Inorg. Chem. 2011, 4680–4690
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4687

T. Banerjee, M. Suresh, H. N. Ghosh, A. Das
FULL PAPER
1
removed in the aqueous phase and the organic (chloroform) layer
was collected. This was dried with anhydrous magnesium sulfate
before chloroform was finally removed under reduced pressure to
obtain the crude product. This crude solid was subjected to column
chromatography using silica as the stationary phase and CHCl3/
594.69; found 617.45 [M + Na]+. H NMR (200 MHz, CDCl3): δ
= 7.75 [d, J = 8.2 Hz, 4 H, HaЈ (four protons)], 7.26 [d, J = 8 Hz,
4 H, HbЈ (four protons)], 6.87–6.86 (m, 4 H, H1Ј, H2Ј, H3Ј and H4Ј),
4.15 [t, J = 4 Hz, 4 H, H5Ј (two protons) and H6Ј (two protons)],
4.03 [t, J = 4.4 Hz, 4 H, H7Ј (two protons) and H8Ј (two protons)],
MeOH solvent mixture as the eluent. The major fraction was eluted 3.76–3.70 [m, 8 H, H9Ј (two protons), H10Ј (two protons), H11Ј (two
as the second band to yield the desired compound 2a in pure form;
yield 3.67 g (85.5%). ESI-MS (m/z): calcd. for C14H22O6 286.32;
protons), H12Ј (two protons)], 2.37 [s, 6 H, HcЈ (six protons)] ppm.
IR (KBr pellet): ν = 1179 [ν(S=O)] cm–1. C H O S (594.69):
˜
28 34 10
2
found 287.84 [M + 1]+, 309.82 [M + Na]+, 325.8 [M + K]+. 1H calcd. C 56.55, H 5.76; found C 56.58, H 5.75.
NMR (500 MHz, CD3OD): δ = 6.98–6.96 (m, 2 H, H2Ј and H3Ј),
3-{2-[4Ј-Methyl-(2,2Ј-bipyridin)-4-yl]vinyl}-6,7,9,10,21,22,24,25-
octahydroanthra[1,2-b]benzo[k][1,4,7,10,13,16]hexaoxacycloocta-
decine-14,19-dione (4): 1 (331 mg, 1.09 mmol) was dissolved in dry
DMF (50 mL). To this was added K2CO3 (527 mg, 3.815 mmol)
and the mixture stirred at 90 °C for 30 min. Compound 3 (790 mg,
1.09 mmol) was dissolved in dry DMF (30 mL) and was added
dropwise to the resultant solution over a period of 30 min. The
reaction was then stirred under argon atmosphere at 100 °C for
5 d. After this time the DMF was evaporated from the reaction
mixture. The desired organic compounds were removed by repeated
solvent extractions with chloroform which was then dried with an-
hydrous magnesium sulfate and the solvents evaporated to dryness.
The residue so obtained was dissolved in a minimum volume of
chloroform and methanol was added dropwise to it which precipi-
tated 4 as a deep yellow solid. This was kept in a refrigerator for
half an hour to ensure complete precipitation and was later filtered
through a grade-4 sintered glass crucible, washed with cold meth-
anol and dried in a vacuum desiccator to yield pure compound 4;
yield 400 mg (54%). ESI-MS (m/z): calcd. for C41H36N2O8 684.73;
6.91–6.89 (m, 2 H, H1Ј and H4Ј), 4.13 [t, J = 4 Hz, 4 H, H5Ј (two
protons) and H6Ј (two protons)], 3.82 [t, J = 4.5 Hz, 4 H, H7Ј (two
protons) and H8Ј (two protons)], 3.69 [t, J = 4.5 Hz, 4 H, H9Ј (two
protons) and H10Ј (two protons)], 3.63 [t, J = 4.5 Hz, 4 H, H11Ј
(two protons) and H12Ј (two protons)] ppm. IR (KBr pellet): ν =
˜
3397 [ν(OH)] cm–1. C14H22O6 (286.32): calcd. C 58.73, H 7.74;
found C 58.78, H 7.70.
{[(9,10-Dioxo-9,10-dihydroanthracene-1,2-diyl)bis(oxy)bis(ethane-
2,1-diyl)]bis(oxy)}bis(ethane-2,1-diyl)bis(4-methylbenzenesulfonate)
(3): 2 (1.15 g, 2.76 mmol) was dissolved in THF/CH3CN mixture
(95:5, v/v) and the temperature was lowered to 0 °C. Aqueous
NaOH (1.104 m, 11.04 mmol, 10 mL) was added to it with constant
stirring. 4-Methylbenzenesulfonyl chloride (2.1 g, 11.04 mmol) was
dissolved in THF (20 mL) and was added in a dropwise manner to
the resultant solution under ice cold conditions. The reaction mix-
ture was then allowed to attain room temperature and was stirred
for 6 d. The solvent was then evaporated and the crude product
was redissolved in chloroform and the undesired water soluble ionic
impurities were discarded in the aqueous phase following a solvent
extraction process. The organic layer was collected, dried with an-
hydrous magnesium sulfate and was evaporated to dryness to ob-
tain the crude desired compound (3). This was further purified and
isolated by column chromatography using silica as the stationary
1
found 685.89 [M + 1]+. H NMR (500 MHz, CDCl3): δ = 8.63 (d,
J = 5 Hz, 1 H, H25), 8.58 (d, J = 4.5 Hz, 1 H, H21), 8.50 (s, 1 H,
H23), 8.27–8.25 (m, 3 H, H1, H2, H22), 8.15 (d, J = 8.5 Hz, 1 H,
H17), 7.78–7.73 (m, 2 H, H3, H4), 7.41 (d, J = 16 Hz, 1 H, H19),
7.36 (d, J = 4.5 Hz, 1 H, H24), 7.17 (d, J = 4.5 Hz, 1 H, H20), 7.15–
phase and CHCl3/hexane solvent mixture as the eluent; yield 7.11 (m, 3 H, H5, H6, H16), 6.99 (d, J = 16 Hz, 1 H, H18), 6.91 (d,
790 mg (39.5 %). ESI-MS (m/z): calcd. for C36H36O12S2 724.79; J = 8 Hz, 1 H, H15), 4.38 [t, J = 4 Hz, 2 H, H7 (two protons)], 4.29
found 747.10 [M + Na]+. 1H NMR (500 MHz, CD3OD): δ = 8.26–
[t, J = 4.5 Hz, 6 H, H9 (two protons), H10 (two protons), H12 (two
8.25 (m, 1 H, H1), 8.24–8.22 (m, 1 H, H2), 8.13 (d, J = 8.5 Hz, 1 protons)], 4.21–4.16 [m, 4 H, H8 (two protons), H11 (two protons)],
H, H3), 7.79 [m, 3 H, Ha (two protons), H4], 7.77 [m, 2 H, Hb (two 4.14–4.12 [m, 2 H, H14 (two protons)], 4.07–4.04 [m, 2 H, H13 (two
protons)], 7.75 (m, 1 H, H5), 7.32 [d, J = 8 Hz, 4 H, Hc (four
protons)], 7.25 (d, J = 8.5 Hz, 1 H, H6), 4.235 [m, 4 H, H7 (two
protons), H8 (two protons)], 4.20–4.16 [m, 4 H, H9 (two protons),
H10 (two protons)], 3.936 [t, J = 4.5 Hz, 2 H, H11 (two protons) or
H12 (two protons)], 3.9 [t, J = 4.5 Hz, 2 H, H11 (two protons) or
H12 (two protons)], 3.81 [t, J = 4.5 Hz, 4 H, H13 (two protons), H14
(two protons)], 3.09 [s, 3 H, Hd (two protons)], 3.02 [s, 3 H, He
protons)], 2.47 [s, 3 H, H26 (three protons)] ppm. IR (KBr pellet):
ν = 1670 [ν(C=O)], 1586 [ν(C=C)] cm–1. C41H36N2O8 (684.74):
˜
calcd. C 71.92, H 5.30, N 4.09; found C 71.96, H 5.24, N 4.12.
4-Methyl-4Ј-(2-(6,7,9,10,17,18,20,21-octahydrodibenzo[b,k][1,4,7,
10,13,16]hexaoxacyclooctadecin-2-yl)vinyl)-2,2Ј-bipyridine (4a): 1
(100 mg, 0.329 mmol) was dissolved in dry DMF (40 mL). To this
was added K2CO3 (159 mg, 1.1515 mmol) and the mixture was
stirred at 90 °C for 30 min. 3a (196 mg, 0.329 mmol) was dissolved
in dry DMF (20 mL) and was added dropwise to the resultant solu-
tion over a period of 30 min. The reaction was then stirred under
(two protons)] ppm. IR (KBr pellet): ν = 1674 [ν(C=O)], 1283
˜
[ν(S=O)] cm–1. C36H36O12S2 (724.79): calcd. C 59.66, H 5.01; found
C 59.70, H 4.97.
2,2Ј-{2,2Ј-[1,2-Phenylenebis(oxy)]bis(ethane-2,1-diyl)}bis(oxy)bis- argon atmosphere at 100 °C for 6 d. After this time the DMF was
(ethane-2,1-diyl)bis(4-methylbenzenesulfonate) (3a): 2a (3 g,
0.01 mol) was dissolved in dry DCM (50 mL) and dry triethylamine
(7 mL, 0.05 mol) was added to it. 4-(Dimethylamino)pyridine
(20 mg, 0.1637 mmol) was then added to the reaction mixture. The
evaporated from the reaction mixture. The desired organic com-
pounds were removed by repeated solvent extractions with chloro-
form which was then dried with anhydrous magnesium sulfate and
the solvents evaporated to dryness. The residue so obtained was
temperature was lowered to 0 °C and the reaction mixture was dissolved in a minimum volume of chloroform and was added
stirred as such for 0.5 h under an inert argon atmosphere. 4-Meth-
ylbenzenesulfonyl chloride (3.813 g, 0.02 mol) was dissolved in dry
DCM (20 mL) and was added in a dropwise manner to the afore-
said solution under ice cold conditions. The reaction mixture was
then allowed to attain room temperature and was stirred for 12 h.
After 12 h, the reaction mixture was evaporated to dryness and
loaded for column chromatography on silica gel and eluted with
MeOH/CHCl3 to yield the pure desired compound 2a as the second
band; yield 2.81 g (45%). ESI-MS (m/z): calcd. for C28H34O10S2
dropwise to diethyl ether (30 mL) which precipitated 4a as a deep
yellow solid. This was kept in a refrigerator for half an hour to
ensure complete precipitation and was later filtered through a grade
4 sintered glass crucible, washed with cold ether and dried in a
vacuum desiccator to yield pure compound 4a; yield 101 mg
(55.4 %). ESI-MS (m/z): calcd. for C33H34N2O6 554.63; found
577.25 [M + Na]+, 593.23 [M + K]+. 1H NMR (500 MHz, CD2Cl2):
δ = 8.58 (d, J = 5 Hz, 1 H, H23Ј), 8.53 (m, 2 H, H19Ј and H21Ј),
8.29 (s, 1 H, H20Ј), 7.42–7.38 (m, 2 H, H15Ј and H17Ј), 7.17 (d, J =
4688
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Eur. J. Inorg. Chem. 2011, 4680–4690

Competitive Binding of Ba and Sr Cations
4.5 Hz, 1 H, H22Ј), 7.13–7.11 (m, 2 H, H13Ј and H18Ј), 7.03 (d, J =
16 Hz, 1 H, H16Ј), 6.91–6.85 (m, 5 H, H1Ј, H2Ј, H3Ј, H4Ј and H14Ј),
4.25–4.20 [m, 2 H, H12Ј (two protons)], 4.19–4.16 [m, 2 H, H11Ј
(two protons)], 4.16–4.11 [m, 4 H, H9Ј (two protons), H10Ј (two
tation after which it was filtered, washed with cold water and dried
in a desiccator. The crude compound so obtained was purified by
column chromatography over neutral Al2O3 (Grade I) using aceto-
nitrile/toluene as the eluent. The first fraction was collected and
protons)], 4.03–3.93 [m, 8 H, H5Ј (two protons), H6Ј (two protons), the solvent was removed to isolate 6; yield 20 mg (36.7%). ESI-MS
H7Ј (two protons) and H8Ј (two protons)], 2.45 [s, 3 H, H24Ј (three
(m/z): calcd. for C53H50F6N6O6PRu 1113.03 [M – PF6 ] ; found
– +
protons)] ppm. IR (KBr pellet): ν = 1589 [ν(C=C)] cm–1
.
1113.98 [M – PF6 ] . H NMR (200 MHz, CD3CN): δ = 8.56 [s, 1
H, H3 (bpy) or H3Ј (bpy)]; 8.49 [d, J = 8 Hz, 4 H, H3 (bpy) and
H3Ј (bpy) (three protons), H6 (bpy) or H6Ј (bpy)], 8.12–8.01 [m, 4
H, H6 (bpy) and H6Ј (bpy) (two protons), H21Ј and H23Ј], 7.85 (d,
J = 5.6 Hz, 1 H, H19Ј), 7.75–7.66 [m, 4 H, H4 (bpy, two protons)
and H4Ј (bpy, two protons)], 7.57 (d, J = 6 Hz, 1 H, H22Ј), 7.50 [d,
J = 8.4 Hz, 1 H, H5 (bpy) or H5Ј (bpy)], 7.44–7.35 [m, 4 H, H5
(bpy) and H5Ј (bpy) (three protons), H6 (bpy) or H6Ј (bpy)], 7.30–
7.20 (m, 3 H, H17Ј, H18Ј and H20Ј), 7.16 (d, J = 5.4 Hz, 1 H, H15Ј),
7.05 (m, 2 H, H14Ј and H16Ј), 6.98–6.85 (m, 4 H, H1Ј, H2Ј, H3Ј and
H4Ј), 6.84 (d, J = 6 Hz, 1 H, H13Ј), 4.25–4.18 [m, 2 H, H12Ј (two
protons)], 4.16–4.03 [m, 6 H, H9Ј (two protons), H10Ј (two protons)
and H11Ј (two protons)], 3.97–3.77 [m, 8 H, H5Ј (two protons), H6Ј
(two protons), H7Ј (two protons) and H8Ј (two protons)], 2.56 [s, 3
H, H24Ј (three protons)] ppm. 13C NMR [200 MHz, (CD3)2CO]: δ
= 157.6, 157.2, 156.8, 151.8, 150.9, 148.3, 147.3, 147, 138.1, 136.1,
135.5, 129.5, 128.1, 127, 124.4, 121.7, 120.9, 120.3, 119.8, 111.7,
111.1, 110.6, 101.4, 100.9, 100.2, 68.9, 68.8, 68.5, 68.1, 67.8,
– +
1
˜
C
33H34N2O6 (554.64): calcd. C 71.46, H 6.18, N 5.05; found C
71.48, H 6.18, N 5.02.
{Bis(2,2Ј-bpy)-(3-(2-(4Ј-methyl-[2,2Ј-bipyridin]-4-yl)vinyl)-6,7,9,10,
21,22,24,25-octahydroanthra[1,2-b]benzo[k][1,4,7,10,13,16]hexa-
oxacyclooctadecine-14,19-dione)}ruthenium(II) Hexafluorophos-
phate (5): Ru(bpy)2Cl2·2H2O (100 mg, 0.192 mmol) and 4
(131.5 mg, 0.192 mmol) were heated to reflux in ethanol for 12 h
with continuous stirring. The solvent was then evaporated and the
product was dissolved in a minimum volume of water. Saturated
aqueous NH4PF6 (10 mol equiv.) was added to the resultant solu-
tion to precipitate the desired RuII-polypyridyl complex as the
hexafluorophosphate salt. This was kept as such for 4–5 h in a re-
frigerator to ensure complete precipitation after which it was fil-
tered, washed with cold water and dried in a desiccator. The crude
compound so obtained was purified by column chromatography
over neutral Al2O3 (Grade I) using acetonitrile/toluene as the elu-
ent. The first fraction was collected and the solvent was removed
to isolate 5 which was further purified by recrystallisation carried
out by diffusion of diethyl ether vapour into an acetonitrile solu-
tion of 5. The recrystallised compound was found to be pure
enough to carry out further studies; yield 120 mg (50%). HRMS
20.4 ppm. IR (KBr pellet): ν = 1582 [ν(C=C)], 842 [ν(PF )] cm–1.
˜
6
C53H50F12N6O6P2Ru (1258.01): calcd. C 50.60, H 4.01, N 6.68;
found C 50.9, H 3.96, N 6.66.
Supporting Information (see footnote on the first page of this arti-
cle): ESI-MS, FTIR and FTNMR spectra of 5 and 6 and their
precursors, HRMS spectrum of 5, ESI-MS spectrum of 5 in pres-
ence of Ca2+, Sr2+ and Ba2+, spectrophotometric and fluorescence
scan of 6 with different metal ions, fluorescence scan of 5 with
different metal ions (λex = 369 nm), spectrophotometric and fluo-
rescence titration of 6 with Ba2+, Stern–Volmer plot for lifetime
titration of 5 with Cu2+, changes in the 1H NMR spectrum of 5
on addition of Sr2+, changes in the 13C NMR spectrum of 5 on
addition of Ca2+, changes in the 13C NMR spectrum of 5 on ad-
– +
(m/z): calcd. for C61H52N6O8PF6Ru 1243.2532 [M – PF6 ] ; found
– +
1243.2532 [M – PF6 ] . 1H NMR (500 MHz, CD3CN): δ = 8.56 [s,
1 H, H3 (bpy) or H3Ј (bpy)], 8.49 [d, J = 8 Hz, 3 H, H3 (bpy) and
H3Ј (bpy) (three protons)], 8.47 (s, 1 H, H23), 8.19 [d, J = 7.5 Hz,
1 H, H6 (bpy) or H6Ј (bpy)], 8.16 [d, J = 7.5 Hz, 1 H, H6 (bpy) or
H6Ј (bpy)], 8.08–8.03 [m, 6 H, H4 (bpy), H4Ј (bpy), H6 (bpy), H6Ј
(bpy), H1, H2], 7.82–7.8 (m, 2 H, H4, H22), 7.78 [d, J = 7 Hz, 1 H,
H4 (bpy) or H4Ј (bpy)], 7.75 (d, J = 6 Hz, 1 H, H25), 7.73 (d, J =
5 Hz, 2 H, H3, H21), 7.61 (d, J = 16.5 Hz, 1 H, H19), 7.57 (d, J =
6 Hz, 1 H, H24), 7.54 (d, J = 5.5 Hz, 1 H, H20), 7.42–7.37 [m, 6 H,
H4 (bpy) or H4Ј (bpy), H5 (bpy, two protons), H5Ј (bpy, two pro-
tons), H16], 7.26–7.24 (m, 2 H, H5, H6), 7.18 (d, J = 7.5 Hz, 1 H,
dition of Ba2+
.
H17), 7.13 (d, J = 16 Hz, 1 H, H18), 6.98 (d, J = 8 Hz, 1 H, H15), Acknowledgments
4.29–4.28 [m, 2 H, H9 (two protons)], 4.27–4.23 [m, 4 H, H10 (two
protons), H12 (two protons)], 4.21–4.2 [m, 2 H, H11 (two protons)],
Department of Science and Technology (DST), India, Board of
4.11 [t, J = 5 Hz, 2 H, H7 (two protons)], 4.01 [t, J = 4 Hz, 2 H,
H8 (two protons)], 3.98–3.96 [m, 2 H, H14 (two protons)], 3.93–3.92
[m, 2 H, H13 (two protons)], 2.56 [s, 3 H, H26 (three protons)] ppm.
13C NMR [200 MHz, (CD3)2CO]: δ = 182.5, 182.1, 158.9, 157.8,
152.3, 151.3, 150.7, 149.8, 149, 147.8, 138.4, 137.5, 136.9, 135.6,
134.4, 134.1, 133.5, 129.9, 129.2, 128.4, 127.3, 126.8, 125.7, 124.9,
122.7, 121.2, 117.8, 114.2, 113.6, 111.9, 73.59, 71.6, 71.1, 70.2, 69.8,
Research in Nuclear Sciences (BRNS, DAE), India and Council of
Scientific and Industrial Research (CSIR), India have supported
this work. T. B. and M. S. acknowledge BRNS and CSIR, respec-
tively, for research fellowships. We thank Dr. P. K. Ghosh
(CSMCRI), Dr. S. K. Sarkar (BARC) and Dr. T. Mukherjee
(BARC) for their interest in this work.
69.2, 20.8 ppm. IR (KBr pellet): ν = 1653 [ν(C1=O)], 1635
˜
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Eur. J. Inorg. Chem. 2011, 4680–4690
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4689

T. Banerjee, M. Suresh, H. N. Ghosh, A. Das
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Received: May 5, 2011
Published Online: September 6, 2011
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