Synthesis, characterisation, electrochemistry and Ion-Binding studies of ruthenium (II) and rhenium(I) bipyridine/Crown ether receptor molecules

Article abstract of DOI:10.1002/ejic.200801099

A number of molecular receptors containing a ruthenium(II)/ rhenium(I) bipyridine moiety as fluorophore and a crown ether, connected to the 4,4'-positions of the bipyridine/phenanthroline unit through >C=0 and -HC=N- spacers, as ionophore have been synthesised and characterised. The luminescence and electrochemical properties of these receptors have been studied. The cation-binding properties of these molecules have been investigated with the cations Na⁺, K⁺,Rb²⁺, Mg²⁺, Ca ²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb ²⁺and Cu²⁺ and the recognition event monitored by H NMR spectroscopy, luminescence, the oxidation potential of the metal ion and UV7 Vis absorption studies. The emission intensities of complexes 1 3 are strongly quenched by the addition of Pb²⁺, Cu²⁺,Hg²⁺ and Na²⁺, whereas a significant enhancement of the emission intensities is observed for 4 in the presence of Cu²⁺ and Hg²⁺ and for 5 in the presence of Cd²⁺and Hg²⁺ Luminescence titrations for 1-5 with the above-mentioned metal ions have been carried out. The binding constants (K_s) and stoichiometry of the complexes have been calculated from titration data, with values of K_s ranging from 9.97 × 10³ to 1.28 × 10² M^-1 in the decreasing order Pb²⁺ > Na⁺ > Cu²⁺ > Hg²⁺ > Cd^2-. The stoichiometries found for 1-3 and 5 are in the range 1.85-2.09 and for 4 0.99-1.04. A¹H NMR spectroscopic study with selected metal ions exhibits significant spectral changes for the protons attached to the crown moiety; a few significant changes are also noted in the aromatic region. Among the ions studied, the highest change is observed with Na⁺and Pb²⁺, whereas K⁺ does not show any significant change. The electrochemical study exhibits a significant cathodic shift: of the oxidation potentials of the Ru^II centre in the presence of Na⁺ and Pb²⁺, thereby indicating complexation of these ions with the crown moiety. The electronic spectra, however, do not show significant spectral changes with various metal ions except for that: of the Re¹ complex 6, which exhibits some change upon addition of Na+. The results obtained are presented and discussed in light of selectivity and intramolecular energy-transfer.

Full text of DOI:10.1002/ejic.200801099

FULL PAPER
DOI: 10.1002/ejic.200801099
Synthesis, Characterisation, Electrochemistry and Ion-Binding Studies of
Ruthenium(II) and Rhenium(I) Bipyridine/Crown Ether Receptor Molecules
[a]
[a]
[a]
[a]
Vinod P. Boricha, Subrata Patra, Yogendra S. Chouhan, Pankaj Sanavada,
[a]
[a]
E. Suresh, and Parimal Paul*
Keywords: Receptors / Ruthenium / Rhenium / Crown compounds / Electrochemistry
2
–1
in the decreasing order Pb2+ Ͼ Na Ͼ Cu
+
2+
A number of molecular receptors containing a ruthenium(II)/
rhenium(I) bipyridine moiety as fluorophore and a crown
ether, connected to the 4,4Ј-positions of the bipyridine/phen-
anthroline unit through ϾC=O and -HC=N- spacers, as iono-
phore have been synthesised and characterised. The lumi-
nescence and electrochemical properties of these receptors
have been studied. The cation-binding properties of these
1.28ϫ10
M
Ͼ
Hg Ͼ Cd2+. The stoichiometries found for 1–3 and 5 are in
the range 1.85–2.09 and for 4 0.99–1.04. A H NMR spectro-
2+
1
scopic study with selected metal ions exhibits significant
spectral changes for the protons attached to the crown moi-
ety; a few significant changes are also noted in the aromatic
region. Among the ions studied, the highest change is ob-
served with Na and Pb , whereas K does not show any
significant change. The electrochemical study exhibits a sig-
+
+
+
2+
+
molecules have been investigated with the cations Na , K ,
+
2+
2+
2+
2+
2+
2+
2+
Rb , Mg , Ca , Zn , Cd , Hg , Pb and Cu and the
1
II
recognition event monitored by H NMR spectroscopy, lumi-
nificant cathodic shift of the oxidation potentials of the Ru
+
2+
nescence, the oxidation potential of the metal ion and UV/
Vis absorption studies. The emission intensities of complexes
centre in the presence of Na and Pb , thereby indicating
complexation of these ions with the crown moiety. The elec-
tronic spectra, however, do not show significant spectral
changes with various metal ions except for that of the Re
complex 6, which exhibits some change upon addition of
2
+
2+
1
–3 are strongly quenched by the addition of Pb , Cu ,
2
+
+
I
Hg and Na , whereas a significant enhancement of the
2+
emission intensities is observed for 4 in the presence of Cu
and Hg and for 5 in the presence of Cd2+ and Hg . Lumi-
2
+
2+
Na . The results obtained are presented and discussed in
+
nescence titrations for 1–5 with the above-mentioned metal
light of selectivity and intramolecular energy-transfer.
ions have been carried out. The binding constants (K
s
) and
stoichiometry of the complexes have been calculated from
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
titration data, with values of K
s
ranging from 9.97ϫ103 to
Introduction
and ruthenium(II)/rhenium(I) polypyridine-based photo-
active metal complexes have been used as fluorophores, al-
though the latter are of special interest because of various
advantages they have over organic molecules. Thus, besides
exhibiting luminescence changes like organic molecules,
they also exhibit measurable changes in electrogenerated
The design and synthesis of functional molecules that
could serve as molecular devices for selective sensing,
switching and signalling is currently an area of intense re-
[
1]
search activity. Among various such functional molecules,
fluorescent sensors for the detection of ions are of great
interest because of their important role in many biological
and environmental processes.[ Such molecular sensors can
be constructed by the combination of an ionophore, de-
signed to bind a specific incoming ion, and a luminescent
fragment whose photophysical properties are perturbed
during the recognition process to produce a measurable
chemiluminesence and redox properties during the ion-re-
[4–6]
cognition process.
The spacers, which connect the flu-
2]
orophore and ionophore, also play an important role in en-
suring electronic communication between the two units. It
is desirable to have a short and/or conjugated bridging unit
to achieve a strong interaction between the two units.
Macrocyclic compounds, which are noted for their remark-
able selectivity towards specific cations, have been exten-
sively used as ionophores in cation recognition studies. In
this regard, crown ethers are excellent choices as complex-
[
3]
output signal. Photoactive units attached with a crown
ether or its derivatives, which serve as receptors, are gen-
erally used for the recognition of alkali, alkaline earth and
[
4,5]
heavy metal ions.
Both organic photoactive molecules
[5,6c–6d,6f]
ing agents for alkali and alkaline earth metal ions.
A significant amount of work has been done on fluoro-
[
a] Analytical Science Division, Central Salt and Marine Chemi-
cals Research Institute (under CSIR, New Delhi), G. B. Marg,
Bhavnagar 364002, India
II
I
ionophores containing Ru /Re polypyridine-based fluoro-
phore and crown ether-based ionophores. Beer et al., for
E-mail: ppaul@csmcri.org
II
I
example, have reported a number of Ru - and Re -based
photochemical receptors in which azacrown or benzocrown
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
1256
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Eur. J. Inorg. Chem. 2009, 1256–1267

Ruthenium(II) and Rhenium(I) Bipyridine/Crown Ether Receptor Molecules
1
ionophores are connected to a metal chromophore via an The low-field doublets at δ = 7.40 ppm for L and δ =
[
5a,5b,6c,6e]
2
amide moiety.
A fluoroionophore containing a 7.62 ppm for L are due to 5-H and 5Ј-H of the bpy moiety
1
2
crown ether moiety directly fused with a bipyridine/1,10- of L and 3-H and 8-H of the phen moiety of L , respec-
1
2
phenanthroline unit, which coordinates to a metal ion, have tively. The singlets at δ = 8.48 (L ) and 7.87 ppm (L ) are
also been reported.[
7,8]
Diaza crown ethers, which act as a due to the 3-H and 3Ј-H protons of bpy and the 5-H and
bridging unit between photoactive metal chromophores, 6-H protons of phen, respectively. The protons attached to
2
+
[9]
II
have also been reported as receptors for Ba ions. Ru - the crown moieties appear as multiplets in the region δ =
polypyridine based complexes containing an azacrown as 3.5–4.0 ppm. The NMR spectroscopic data are consistent
1
ionophore have recently been reported as quadruple-chan- with the proposed structures shown in Scheme 1 (L ) and
2
3
nel sensors for the selective and quantitative analysis of Figure 1 (L ). In the case of L , four doublets and two sing-
Pb , Cu and Hg .
2
+
2+
2+ [10,11]
Upon ion recognition, changes lets, as expected for the unsymmetrically 4,4Ј-substituted
in the UV/Vis/NIR, luminescence and electrochemilumi- 2,2Ј-bipyridine unit (Figure 1), are observed in the range δ
[
11]
I
nescence (ECL) spectra occurred for selective metal ions.
= 8.78–7.17 ppm (a detailed peak assignment is given in the
Exp. Sect.). The protons of the benzocrown unit appear as
A complex containing an azacrown ether connected to Re
via an alkynyl pyridine has also been reported recently as a multiplets at δ = 6.92 (phenyl), 4.20, 3.96 and 3.77–
2
+ [12]
light-controlled ion switch for Ba .
3.70 ppm (crown ether), and the methyl group attached to
Herein we report the synthesis and characterisation of a the bpy moiety appears as a singlet at δ = 2.47 ppm. The
II
I
1
series of fluoroionophores containing a Ru /Re -polypyr- molecular structure of L was confirmed by a single-crystal
idine based unit as the fluorophore and an azacrown/benzo- X-ray study (see below).
crown moiety as the ionophore. The macrocyclic unit is
connected to the metal-bound bipyridine or 1,10-phenan-
throline unit through an amide (ϾC=O) or imino (-CH=
N-) moiety. The electrochemical properties and ion-recogni-
tion bhaviour of these fluoroionophores with a large
number of metal ions are reported. The ion-recognition
1
process is monitored by luminescence, H NMR and UV/
Vis spectral changes and also by electrochemical methods.
The binding constants and stoichiometry of the complexes
formed by the strongly interacting metal ions are reported,
along with a detailed discussion of the ion-recognition be-
haviour and intramolecular energy transfer.
Results and Discussion
1
3
Synthesis of Ligands L –L
1
The route followed for the synthesis of L is shown in
Scheme 1. A similar procedure was used for the synthesis
2
of L , with the exception that 4,7-dimethyl-1,10-phenan-
throline was used as starting material instead of 4,4Ј-di-
3
methylbipyridine. L was prepared by treating 4Ј-methyl-
Scheme 1.
2,2Ј-bipyridine-4-carbaldehyde with 4Ј-aminobenzo-18-
crown-6; the former was synthesised following a published
[
13]
procedure. Microanalytical (C, H and N), mass spectro-
1
metric, IR and H NMR spectroscopic data of all these
ligands are given in the Exp. Sect. The microanalytical and
mass spectrometric data are in agreement with the calcu-
lated values. It should be noted that the m/z values for all
+
+
these compounds correspond to the Na /K adducts (li-
+
+
gand + Na /K ), which is a well known phenomenon when
[
14]
1
using the LC-MS technique. In the H NMR spectra, the
1
2
aromatic regions of L and L exhibit two doublets and a
singlet, as expected for a symmetrically substituted bipyr-
idine/1,10-phenanthroline unit. The high-field doublets (δ =
.73 ppm for L and δ = 9.23 ppm for L ) are assigned to
-H and 6Ј-H of the bpy moiety of L and 2-H and 9-H of
1
2
8
6
1
2
the phen moiety of L (the usual numbering system for the
2
3
protons in 2,2Ј-bipyridine and 1,10-phenanthroline is used). Figure 1. Structural drawings of ligands L and L .
Eur. J. Inorg. Chem. 2009, 1256–1267
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1257

P. Paul et al.
FULL PAPER
Synthesis of Complexes 1–6
consistent with the proposed composition of the complexes.
The H NMR spectrum of 5 exhibits two doublets at δ =
1
The RuII complexes 1–4 (Figure 2) were synthesised by
9.03 and 7.64 ppm and a singlet at δ = 8.50 ppm for the
1
2
3
treating cis-[Ru(bpy) Cl ]/cis-[Ru(phen) Cl ] with L /L /L
2
2
2
2
aromatic protons. This spectral pattern is similar to that of
in refluxing ethanol/water. They were isolated as their PF6–
salts and purified by column chromatography, as described
in the Exp. Sect. All these complexes gave satisfactory C, H
and N analysis, and their mass spectrometry data are in
excellent agreement with the calculated values. It should be
noted that, like the ligands, the complexes also exhibit m/z
1
L , although a slight upfield shift of the doublets is noted
due to coordination of the bpy moiety to the metal ion. In
the aliphatic region, the NCH and OCH protons of the
2
2
azacrown moiety appear at δ = 3.75 and 3.52–3.62 ppm,
1
respectively. The H NMR spectral pattern for complex 6
3
is similar to that of L but with slight changes in the chemi-
+
–
1
values corresponding to the Na adduct with PF . The H
NMR spectra of complexes 1–4 were recorded in CD CN
6
cal shifts; a detailed peak assignment is given in the Exp.
3
Sect. The IR spectra of these complexes exhibit three strong
(see Exp. Sect. for the peak assignment). Peaks were as-
–1
bands at 2021, 1900 and 1894 cm for 5 and 2018, 1910
and 1889 cm–1 for 6. These CO stretching frequencies are
within the range normally found for a typical “fac-Re-
signed with the aid of COSY spectra recorded in the same
solvent. The COSY spectrum of 1 is provided as Supporting
Information (Figure S1), and the detailed peak assignment
for complex 1 is described below. The most deshielded sing-
let at δ = 8.58 ppm is due to 3-H and 3Ј-H of the bpy
(
CO) ” moiety with C symmetry (A and E for the one
3 3v 1
[
15]
high- and two low-energy bands, respectively).
The CO
frequencies therefore suggest a facial arrangement of the
carbonyl groups, as shown in the proposed structures (Fig-
ure 2).
1
moiety of L , the doublet at δ = 8.51 ppm (4 H, J = 8.0 Hz)
is due to 6-H and 6Ј-H of the two bpy ligands and the
overlapping triplets in the range δ = 8.06–8.10 ppm (4 H)
are due to 5-H and 5Ј-H of the bpy ligand. The doublets at
δ = 7.80 (2 H, J = 5.5 Hz) and 7.71 ppm (2 H, J = 5.5 Hz)
are due to 3-H and 3Ј-H of the bpy units. The other dou-
blets at δ = 7.76 (2 H, J = 5.5 Hz) and 7.44 ppm (2 H, J =
Crystal Structure of L1
1
The molecular structure of L was determined by single-
5
.5 Hz) are due to 6-H/6Ј-H and 5-H/5Ј-H of the bpy moi- crystal X-ray crystallography. It crystallises in the mono-
1
ety of L , respectively. The overlapping triplets in the range clinic space group P2 /n and possesses a centre of symmetry
1
δ = 7.40–7.45 ppm (4 H) are due to 4-H and 4Ј-H of the at the mid-point of the C1–C1a bond of the bipyridine moi-
bpy ligand. The signals due to the crown moiety appear as ety bridging the azacrowns on either side (Figure 3). The
multiplets in the region δ = 3.43–3.72 ppm. Detailed NMR two pyridine rings of the 2,2Ј-bipyridine moiety are planar
spectroscopic data for 2–4, along with the peak assign- but with the nitrogen atoms on opposite sides. The symmet-
ments, are given in the Exp. Sect. and will not be discussed rically disposed carbonyl oxygen O1 on either side of the
further here.
2,2Ј-bipyridine moiety is involved in two intermolecular C–
I
The Re complexes (5 and 6) were synthesised by treating H···O interactions with the phenyl hydrogen H4 and the
1
3
[
Re(CO) Cl] with L /L in dry refluxing thf. The crude methylene hydrogen H112, which generates a layered net-
5
product was purified by column chromatography. The mi- work structure (Figure S2, Supporting Information). Sev-
croanalytical (C, H and N) and mass spectrometric data are eral strong intermolecular C–H···O interactions involving
Figure 2. Structural drawings of complexes 1–6.
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 1256–1267

Ruthenium(II) and Rhenium(I) Bipyridine/Crown Ether Receptor Molecules
the methylene hydrogen atoms on C17 and C18 and oxygen Electrochemistry
atoms O4, O2 and O3 of the crown moieties also exist. Fur-
ther details of these pertinent hydrogen-bonding interac-
tions, along with the symmetry codes, are given in Table S1
The cyclic voltammograms of all complexes were re-
corded in acetonitrile and the results are listed in Table 2.
The cyclic voltammogram of complex 3 is shown in Fig-
(Supporting Information).
II
ure 4 as an example. All the Ru complexes exhibit a quasi-
reversible redox couple in the potential range 1.43–1.55 V
II
III
[5a,8a,16]
due to Ru ǞRu oxidation.
ligand-based redox couples in the potential range –1.03 to
1.72 V, which are assigned to the sequential one-electron
They also show three
–
reduction of three bpy/phen moieties (bpy/phenǞbpy/
Table 2. Electrochemical data for complexes 1–6 in acetonitrile.
ox
red1
red2
red3
Complex
E
1/2 [V]
E
1/2
[V]
E
1/2
[V] [V]
E
1/2
(
∆E
p
[mV]) (∆E
p
[mV]) (∆E
p
[mV]) (∆E [mV])
p
1
2
3
4
5
6
1.55 (170) –1.06 (120) –1.34 (140)
1.55 (170) –1.03 (110) –1.29 (200)
–1.60 (155)
–1.60 (172)
–1.66 (135)
–1.72 (200)
–
1.43 (170)
–1.14 (78) –1.38 (146)
Figure 3. ORTEP diagram of ligand L1 with atom numbering
scheme (50% probability factor for the thermal ellipsoids).
1.52 (127) –1.21 (110) –1.44 (110)
1.53 (85)
1.57 (140) –1.28 (180)
–1.05 (90)
–
–
–
Absorption and Luminescence
The absorption and luminescence spectra of all com-
plexes were recorded in acetonitrile and the data are given
in the Exp. Sect. The low-energy bands in the region 435–
II
I
4
65 nm for Ru and at 385 and 342 nm for Re are due to
metal-to-ligand (bpy/phen) charge-transfer (MLCT) transi-
[
16]
tions (dπ Ǟ π*).
The high-energy bands, which appear
at around 290 and 245 nm, are ligand-centred charge trans-
fer (CT) bands due to π Ǟ π* transitions.[ The steady-
state emission spectra (λem) and quantum yield (φ) of all
complexes were recorded in acetonitrile at room tempera-
16]
II
ture and the data are given in Table 1. All the Ru com-
3
plexes exhibit a strong MLCT emission band in the region
I
6
17–633 nm, whereas the Re complexes show only weak
emission at 630 and 603 nm for 5 and 6, respectively.
Figure 4. Cyclic voltammogram of 3 recorded in acetonitrile.
s
Table 1. Luminescence data, binding constant (K ) and stoichiometry of complex formation for the ionophores.
λ
em
Quantum yield (φ)
Metal ion
Pb2
Binding constant K
s
ϫ10–2 –1
n[a]
+
1
2
3
633
627
617
0.0555
0.0628
0.0578
21.80
1.99
4.95
7.12
49.15
2.69
5.90
9.95
99.72
4.19
8.81
12.12
26.63
45.99
34.88
1.28
–
1.95
1.86
1.92
2.03
1.98
2.09
1.96
1.91
1.90
1.88
2.03
1.96
1.04
0.99
1.85
1.93
–
2
+
Hg
Cu
Na
2
+
+
2
+
Pb
2
+
Hg
2
+
Cu
Na
+
2
+
Pb
2
+
Hg
2
+
Cu
Na
+
2
+
4
5
6
624
630
603
0.0086
0.0030
0.0149
Hg
Cu
Hg
2
+
2
+
2
+
Cd
–
[a] Complex/guest metal ion ratio.
Eur. J. Inorg. Chem. 2009, 1256–1267
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1259

P. Paul et al.
FULL PAPER
·
–
[5a,8a,16]
For the ReI
phen ) coordinated to the metal ion.
complexes, a quasi-reversible metal-based oxidation wave
(
I
II
Re ǞRe ) appears at 1.53 and 1.57 V for 5 and 6, respec-
tively.
[
9a,17]
The ligand (bpy)-based single electron reduction
for these complexes occurs at –1.05 and –1.28 V for 5 and
, respectively.
6
Binding of Ionophores with Metal Ions
The binding of a number of metal ions (Na , K , Rb ,
+
+
+
2
+
2+
2+
2+
2+
2+
2+
Mg , Ca , Zn , Cd , Hg , Pb and Cu ) with the
ionophores 1–6 has been investigated. The host–guest inter-
actions were monitored by means of luminescence, 1
H
NMR and UV/Vis spectral changes and also by an electro-
chemical study of the oxidation potential of the metal ion.
The photoluminescence of all six ionophores (1–6) in the Figure 5. Emission spectral changes of 1 (2ϫ10–5 ) upon addition
of increasing concentrations of Pb(ClO
4 2
) . Excitation wavelength:
presence of various metal ions in acetonitrile has been in-
4
54 nm. Inset: linear regression fit (double-logarithmic plot) of the
titration data as a function of metal ion concentration.
vestigated. For complexes 1–3, the characteristic lumines-
3
cence from the MLCT state was found to decrease in inten-
sity in the presence of certain metal ions. Thus, the emission
intensities were quenched by 75–85% upon addition of
2
+
2+
Pb (100 equiv.) and 90–97% in the presence of Cu
500 equiv.) for all three complexes. The emission maxima
for all three complexes were red-shifted by 13 nm upon ad-
(
2
+
dition of Pb , although no shift of the emission maxima
was observed with Cu . The addition of Na and Hg
approx. 500 equiv.) resulted in a 25–40% reduction of the
2
+
+
2+
(
emission intensities for 1–3 and a small red shift (4–5 nm)
of the emission maxima. Among the other metal ions
2
+
studied, Cd produced some quenching but the others did
not show significant changes in emission intensities (Fig-
ure S3, Supporting Information). The changes in lumines-
cence intensities for 1, 2 and 3 upon addition of increasing
2
+
2+
+
concentrations of Pb , Cu and Na , respectively, are
shown in Figures 5, 6 and 7. Interestingly, the emission in-
tensity of complex 4 was enhanced by 140% and 124%
Figure 6. Emission spectral changes of 2 (2ϫ10–5 ) upon addition
2
+
2+
upon addition of Cu and Hg (100 equiv.), respectively,
of increasing concentrations of Cu(ClO
45 nm. Inset: linear regression fit (double-logarithmic plot) of the
titration data as a function of metal ion concentration.
4 2
) . Excitation wavelength:
and a substantial red-shift (47 nm) of the emission maxima
4
+
(
λem) was noted for both metal ions. Upon addition of Na ,
the emission intensity enhancement was about 20%,
whereas some initial intensity enhancement was observed
with Pb , although it soon started to decrease. No further lowing a literature procedure.[18] According to this pro-
2+
detailed studies were undertaken. The enhancement of lu- cedure, the fluorescence intensity (F) scales with the metal
minescence intensity for 4 upon addition of increasing con- ion concentration ([M]) according to the fomula (F – F)/
0
2
+
n
centrations of Hg is shown in Figure 8.
(F – F ) = ([M]/K ) . The binding constant (K ) is ob-
The Re complex of L (5), which shows weak emission tained by plotting log[(F – F)/(F – F )] vs. log[M], where
ϱ
diss s
I
1
0
ϱ
in acetonitrile (φ = 0.003), underwent a 17- and 20-fold en- F0 and Fϱ are the relative fluorescence intensities of the
hancement of its emission intensity, with a hypsochromic complex without addition of guest metal ion and with
shift of the emission wavelength (λem) of 57 and 55 nm, maximum concentration of metal ion (when no further
2
+
2+
upon addition of Cd and Hg , respectively. The change change in emission intensity takes place), respectively. The
in luminescence intensity for 5 upon addition of increasing slope of the plot obtained from the experimental data gives
2
+
2+
concentrations of Cd and Hg is illustrated in Figures 9 the value of n, the number of metal ions bound to each
and 10, respectively. The other metal ions did not induce complex, whereas the value of log[M] at log[(F – F)/(F –
0
significant changes in the emission intensity. Complex 6 did Fϱ)] = 0 gives the value of log(Kdiss), the reciprocal of which
not show a significant change in its emission spectra upon is the binding constant (K ). The log[(F – F)/(F – F )] vs.
s
0
ϱ
addition of any metal ion.
log[M] plots are shown as insets in Figures 5, 6, 7, 8, 9, and
2
The binding constants of strongly interacting metal ions 10. The titration data showed a nice linear fit (R = 0.99)
for 1–5 were calculated from the emission titration data fol- with the above equation. The binding constants and values
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Ruthenium(II) and Rhenium(I) Bipyridine/Crown Ether Receptor Molecules
Figure 7. Emission spectral changes of 3 (2ϫ10–5 ) upon addition
of increasing concentrations of NaClO
4
. Excitation wavelength:
Figure 9. Emission spectral changes of 5 (2ϫ10–5 ) upon addition
of increasing concentrations of Hg(ClO . Inset: Excitation wave-
length: 385 nm. Inset: linear regression fit (double-logarithmic plot)
of the titration data as a function of metal ion concentration.
4
35 nm. Inset: linear regression fit (double-logarithmic plot) of the
titration data as a function of metal ion concentration.
4 2
)
Figure 8. Emission spectral changes of 4 (2ϫ10–5 ) upon addition
of increasing concentrations of Hg(ClO ) . Inset: Excitation wave-
4 2
length: 465 nm. Inset: linear regression fit (double-logarithmic plot)
of the titration data as a function of metal ion concentration.
Figure 10. Emission spectral changes of 5 (2ϫ10–5 ) upon ad-
dition of increasing concentrations of Cd(ClO ) . Excitation wave-
4 2
length: 385 nm. Inset: linear regression fit (double-logarithmic plot)
of the titration data as a function of metal ion concentration.
of n for all complexes are summarised in Table 1. The values
of n for 1–3 and 5 with all metal ions studied are in the
range 1.85–2.09, which suggests 1:2 complex formation and 3.2 Å, which matches very well with the ionic diameter of
+
therefore that both crown cavities are occupied by the guest K (2.66 Å), therefore this ion expected to form stable com-
[
19]
metal ions. The n values of 0.99 and 1.04 for complex 4 plexes with these ionophores.
indicate 1:1 complex formation. cence and NMR studies (see below) suggest a poor com-
Analysis of the data (Table 1) showed that the binding plexing ability of these ionophores with K . The ionic dia-
However, both fluores-
+
2+
constants (K ) for complexes 1–3 follow the order Pb
Ͼ
meter of those metal ions which form stable complexes
s
+
2+
2+
2+
+
2+
2+
Na Ͼ Cu Ͼ Hg ; complex 4 also follows a similar order (Pb = 2.34, Na = 1.96, Hg = 1.86, Cu = 1.84 and
2+
2+
+
2+
+
[19b]
1
(
Cu Ͼ Hg ; K for Na was not calculated because of Cd = 1.84 Å) are less than that of K (2.66 Å).
only small changes in the emission intensity). For 5, the NMR study of ligand L in the presence of K indicates
binding constant with Hg is significantly higher than that that it forms a complex with this ion (see below). The above
with Cd . The complexing ability of macrocyclic iono- results therefore suggest that the crown rings in these com-
phores such as crown ethers with various metal ions de- plexes are twisted rather than planar and that the effective
pends on the size of the macrocyclic cavity and the diameter cavity size of the crown moiety available for incoming metal
of the metal ion (size matching), the conformation of the ions is less than that observed for a planar conformation.
macrocycles and the type of donor atoms. The diameter of This means that metal ions with an ionic diameter greater
A H
s
1
+
2
+
2
+
+
the 18-crown-6 moiety used in this study is in the range 2.6– or equal to that of K will not form stable complexes with
Eur. J. Inorg. Chem. 2009, 1256–1267
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1261

P. Paul et al.
2+
FULL PAPER
+
these ionophores. This non-planarity of the crown moiety ionic size and charge of the metal ions (Na = 1.96 Å; Pb
might be due to steric hindrance and/or intra-/intermo- = 2.34 Å) Ϫ coordination of these metal ions in the same
lecular interactions.
crown cavity results in a different chemical environment for
1
The emission quantum yield (φ, approx. 0.06) and com- the CH protons of the crown moiety. Similar H NMR
plexation properties of complexes 1–3 with guest metal ions spectral changes are observed in the aliphatic region for Re
are similar, which suggests that the significant emission complexes in the presence of Na and Pb ions. Like Ru ,
quenching of these ionophores in the presence of the above- the Re complexes also exhibit minor spectral changes in
2
I
+
2+
II
I
+
+
mentioned metal ions is probably related to the orientation the presence of K even though the ionic diameter of K
of the complexed crown moiety with respect to the attached matches the cavity size of the crown very well. To under-
1
1
bpy/phen unit. The crown moieties attached to bpy/phen standing this finding better, the H NMR spectrum of L
+
are flexible and these units, together with the amide in the presence of K (20 quiv) was recorded. The spectrum
(ϾC=O), are involved in intra- and intermolecular hydro- shows a significant change in the region of the crown moi-
gen-bonding interactions. After complexation of the crown ety (Figure S4, Supporting Information), thereby indicating
units, these interactions are expected to change or break to stable complex formation. Taken together, these observa-
II
minimize steric hindrance. This effect changes the orienta- tions therefore suggest that the crown moiety in the Ru /
I
tion and conformation of the complexed crown moieties, as Re complexes is not planar and that the effective cavity size
indicated by NMR spectroscopic and electrochemical stud- is smaller than that of a free crown moiety, consistent with
ies (see below), and the change of orientation with respect the observations noted in the fluorescence study.
II
II
to the coordination sphere of Ru probably promotes non-
The redox behaviour of the Ru centre in 1–3 in the pres-
radiative decay processes.[
6a,6e,20]
The enhancement of emis- ence of Na , K and Pb ions was also investigated. Upon
sion intensity observed in 4 and 5 is probably due to block- addition of these ions (50 equiv.), the Ru ǞRu oxidation
ing of the intramolecular electron-transfer quenching pro- potential of 1 is shifted cathodically by 88 and 128 mV for
+
+
2+
II
III
+
2+
+
cess as coordination of a metal ion in the crown cavity re- Na and Pb , respectively (Figure 13), whereas with K
duces the ability of the donor atoms of the crown moiety to only a very small shift (Ͻ50 mV) is observed. Similar
3
quench the emissive MLCT state by photoinduced electron changes were also noted for 2 and 3. However, 4 and the
[
6c,7a,21]
I
transfer.
It should be noted that 4 contains only one Re complexes 5 and 6 do not show significant changes in
3
I
crown moiety (L ) and 5 is the Re complex containing CO the presence of these metal ions. Generally, an anodic shift
and Cl, instead of bpy, as ligand, therefore the steric crowd- of the Ru ǞRu oxidation wave is noted upon complex-
ing and intra-/intermolecular interactions of these two com- ation of a crown moiety with a metal ion.
II
III
[
10,11]
However, in
plexes are expected to be different from those of 1–3. En- most of these cases the crown moiety is directly attached to
hancement and quenching of the emission intensity of the a bipyridine unit, and in those cases where a ϾC=O or
same/similar complexes in the presence of different ions is -HN–C=O type spacer connects the crown and bipyridine
[
6a,6e,7a,11,20]
II
well documented.
units the Ru -based oxidation potential does not show a
1
[5a]
The H NMR spectra of selected complexes were re- significant change. It should be noted that the redox po-
corded in the presence of various metal ions. A typical spec- tentials of the metal centres of complexes 1–3 are rather
+
+
2+
trum of 1 and those in the presence of Na , K and Pb
high (1.55–1.65 V) compared to those found in other sim-
ions are shown in Figure 11. It should be noted that the ilar systems (1.01–1.07 V) containing an azacrown con-
+
2+
spectra recorded in the presence of Na and Pb ions exhi- nected to the 5,5Ј-position of a bipyridine unit through a
[
5a]
bit significant changes in both the aliphatic and aromatic ϾC=O or an amide moiety.
This difference is probably
regions compared to 1 whereas the spectrum recorded in related to strong H-bonding between ϾC=O and the hydro-
+
the presence of K does not show a significant change ex- gen atoms attached to the 3,3Ј-positions of the bipyridine
cept for a slight upfield shift of the signals due to the pro- unit and the 5,6-positions of the 1,10-phenanthroline moi-
tons attached to the crown moiety and the 4,4Ј-H signals ety. The ϾC=O moieties of complexes 1–3 are attached at
+
2+
of two bpy moieties. Upon addition of Na and Pb ions, the 4,4Ј-positions of the bpy/phen unit, which means that
the signals of the crown moiety are deshielded, with a sig- the oxygen atom of the ϾC=O unit is in a favourable posi-
nificant change in their splitting pattern indicating complex tion to form a ϾC=O···H interaction with the hydrogen
formation between the crown moiety and the guest metal atoms at the 3,3Ј-position of the bipyridine unit and gener-
ion. This complexation results in changes in the chemical ate a five-membered ring, as shown in Figure 14. The strong
environment of the coordination sphere, which, in turn, af- electron withdrawing effect of the ϾC=O units through the
fects the chemical shift of some of the protons of the bipyr- hydrogen atoms makes the bipyridine moiety more electron
1
idine ligand (Figure 11). Similar changes in the H NMR deficient, which results in an anodic shift of the oxidation
+
spectra of complexes 2 and 3 in the presence of Na and potential of the metal centre. The orientation of the com-
2
+
Pb ions were observed in both the aliphatic and aromatic plexed crown moiety changes upon complexation, which re-
regions (see Figure 12 for 2). It should be noted that the sults in a loss of this ϾC=O···H interaction and, in turn,
splitting pattern and the change in chemical shifts of the reduces the electron-withdrawing ability of the amide
signals due to the crown moiety are significantly different moiety and causes a cathodic shift of the oxidation poten-
+
2+
for Na and Pb (cf. Figures 11 and 12) for any particular tial of the metal ion. Evidence to support this argument is
receptor molecule. This difference is due to the different provided by the NMR spectra. Upon complexation of L1
1262
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Eur. J. Inorg. Chem. 2009, 1256–1267

Ruthenium(II) and Rhenium(I) Bipyridine/Crown Ether Receptor Molecules
1
Figure 11. Selected portion of the H NMR spectra of 1, 1 + NaClO
4
, 1 + KClO
4
and 1 + Pb(ClO
4
)
2
, recorded in CD
3
CN at room
temperature.
1
Figure 12. Selected portion of the H NMR spectra of 2, 2 + NaClO
4
and 2 + Pb(ClO
4
)
2
, recorded in CD
3
CN at room temperature.
with the Ru(bpy) unit, the chemical shift of the protons tons attached to the 3,3Ј-positions are deshielded (∆δ =
2
attached to the 6,6Ј-positions of the bipyridine unit of L1 0.12 ppm). Shielding of the adjacent protons (6,6Ј) is ex-
are substantially shielded (∆δ =0.98 ppm), whereas the pro- pected upon coordination through nitrogen, although there
Eur. J. Inorg. Chem. 2009, 1256–1267
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1263

P. Paul et al.
FULL PAPER
is no obvious explanation for the deshielding of the protons Conclusions
attached to the 3,3Ј-positions other than their involvement
A series of luminophores containing a ruthenium(II)/
rhenium(I) bipyridine moiety as fluorophore and a crown
ether as ionophore have been synthesised and characterised.
The cation-binding properties of these receptor molecules
have been investigated for a large number of cations by
means of fluorescence, H NMR, electrochemistry and UV/
Vis spectral studies. The receptors 1–3 experience strong
in some kind of H-bonding interaction. Again, after com-
+
2+
plexation of the crown moiety with a metal ion (Na /Pb ),
the deshielding effect on these protons is lost and the pro-
tons at the 3,3Ј-positions shift to their original positions
found in the ligand (δ = 8.48 ppm), whereas the chemical
shift of the protons at the 6,6Ј-positions remains unchanged
1
(Figures 11 and 12). This observation is consistent with that
quenching of their emission intensity in the presence of
noted in the electrochemical study.
2+
2+
2+
+
Pb , Cu , Hg and Na , whereas 4 and 5 show a sub-
stantial increase of emission intensity in the presence of
2+
+
2+
Hg and Cu /Cd . Coordination of the metal ion with
the crown moiety blocks the intramolecular photoinduced
reductive electron-transfer process, which results in an en-
hancement of the emission intensity. The stoichiometry and
binding constants for strongly interacting metal ions with
1
–5 have been calculated from fluorescence titration data.
1
2
The complexes containing ligands L and L form 1:2 com-
plexes encapsulating metal ions in both the crown cavities,
3
whereas complexes containing L form 1:1 complexes. The
2+
+
binding constants for 1–5 decrease in the order Pb Ͼ Na
Ͼ Cu2 Ͼ Hg Ͼ Cd , with the size of the cation playing
an important role in the formation of stable complexes. The
effective size of the crown cavity in the complexes is less
+
2+
2+
+
than that of the free crown ring, which means that K does
not form stable complexes. Steric crowding and intramolec-
ular interactions are probably responsible for twisting the
crown moiety. Strong complex formation with Pb and
II
Figure 13. Oxidation potential (DPV) of the Ru centre of 1 and
2+
+
+
2+
in the presence of K , Na and Pb (50 equiv.) in acetonitrile.
+
1
Na has also been demonstrated by H NMR spectroscopy,
with significant spectral changes being observed in the pres-
ence of these metal ions. The electrochemical oxidation of
II
Ru in the absence and presence of metal ions also suggests
2+
a strong interaction between the ionophores and Pb and
+
Na . The ϾC=O spacer apparently plays a significant role
in the intramolecular interactions by promoting electronic
communication between the fluorophore and ionophore, as
evident from electrochemical studies and the 1H NMR
spectral changes.
Experimental Section
Methods: Elemental analyses (C, H and N) were performed with a
model 2400 Perkin–Elmer elemental analyzer. NMR spectra were
recorded with DPX 200 and Avance II 500 MHz Bruker FT-NMR
instruments. Infrared spectra were recorded with a Perkin–Elmer
Figure 14. Partial drawing of complexes 1 and 2 showing the H-
bonding interactions between the oxygen atom of C=O and the
hydrogen atoms at the 3,3Ј-positions of bpy and the 5,6-positions
of the phen moieties.
Spectrum GX FT-IR system. Mass spectra were recorded with a
TM
Q-Tof micro
LC-MS instrument. The UV/Vis spectra were re-
corded with a CARY 500 scan Varian spectrophotometer. Lumi-
nescence spectra were recorded with a Perkin–Elmer LS-50B spec-
trofluorimeter. Quantum yields were measured for optically dilute
The UV/Vis spectra of ionophores 1–6 were recorded in
acetonitrile in the presence of a 100-fold excess of the vari-
ous metal ions. No significant change was noted except for
complex 6, where a spectral change observed upon addition
2
+
solution following the literature procedure, with [Ru(bpy)
0
3
]
(φ =
.062) as reference emitter.[
22a]
Electrochemical measurements were
made using a CHI 660A electrochemical workstation equipment.
Cyclic and DPV studies were carried in a three-electrode cell con-
sisting of a glassy-carbon working electrode, a platinum-wire auxil-
iary electrode and an SCE reference electrode. Solutions of the
+
of increasing concentrations of Na ion resulted in a shift
3
of the MLCT band from 342 to 360 nm and a slight in-
crease in absorption intensity, with an isosbestic point at complexes in purified acetonitrile containing 0.1  tetrabutylam-
46 nm (Figure S5, Supporting Information). monium tetrafluoroborate as supporting electrolyte were deaerated
2
1264
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Eur. J. Inorg. Chem. 2009, 1256–1267

Ruthenium(II) and Rhenium(I) Bipyridine/Crown Ether Receptor Molecules
by bubbling nitrogen for 15 min prior to each experiment. The cy-
H, 6Ј-H or 6-H of bpy), 8.28 (s, 1 H, 3Ј-H or 3-H of bpy), 7.85 (d,
J = 4.8 Hz, 1 H, 5-H or 5Ј-H of bpy), 7.17 (d, J = 4.8 Hz, 1 H, 5Ј-
H or 5-H of bpy), 6.92 (m, 3 H, phenyl), 4.20 (m, 4 H, -CH
crown ether), 3.96 (m, 4 H, -CH O crown ether), 3.77–3.70 (m, 12
H, -CH O crown ether), 2.47 (s, 3 H, CH
2
+
clic voltammogram of [Ru(bpy)
3
]
was recorded first for cali-
bration of the instrument. Single crystal structures were determined
using a Bruker SMART 1000 (CCD) diffractometer.
2
O
2
2
3
) ppm. LC-MS: m/z (%)
Reagents: The complexes cis-[Ru(bpy)
2
Cl
O were prepared following the literature pro-
Hydrated ruthenium trichloride was purchased from
2
]·2H
2
O
and cis-
3
+
3
+
5
5
30.70 (16) [L + Na ] (calcd. 530.57), 508.74 (11) [L + H ] (calcd.
[
2 2 2
Ru(phen) Cl ]·2H
–
1
08.59). IR (KBr pellets): ν˜ = 1594 cm (C=N). C28
H
33
N
3
O
6
[
22b]
cedure.
(
507.58): calcd. for C 66.26, H 6.55, N 8.28; found C 66.10, H 6.84,
Arora Matthey. All other starting materials and reagents used in
this study were purchased from Aldrich and S. D. Fine Chemicals.
All solvents were analytical grade and were purified by standard
N 8.24.
1
General Procedure for the Synthesis of [Ru(bpy)
2
(L )][PF
6
]
2
·2H
·2H O (3)
O (4): A mixture of cis-[Ru(bpy)
]·2H O (0.2 mmol) and the appropri-
2
O
2
2
procedures before use.[
23]
(1), [Ru(bpy)
and [Ru(bpy)
Cl ]·2H
2
(L )][PF
6
]
2
·2H
·2H
Cl
2
O (2), [Ru(phen)
2
(L )] [PF
6
]
2
2
3
2
(L )] [PF
6
]
2
2
2
-
1
Synthesis of L : A mixture of 2,2Ј-bipyridine-4,4Ј-dicarboxylic acid
0.244 g, 1 mmol), which was prepared following a published pro-
2
2
O/cis-[Ru(phen)
2
2
2
(
1
2
3
ate ligand (L /L /L , 0.2 mmol) in ethanol/water (1:1, 50 mL) was
refluxed for 12 h. The volume of the reaction mixture was then
reduced to around 20 mL by rotary evaporation, filtered and an
[
24]
cedure,
and thionyl chloride (10 mL) was refluxed under nitro-
gen at 80 °C for 20 h. Excess thionyl chloride was then removed by
rotary evaporation and the yellowish solid mass thus obtained was
used directly in the next step. In the second step, 1-aza-18-crown-6
4 6
aqueous solution of NH PF (0.20 g, 1.3 mmol) added to the fil-
trate. The precipitate was filtered off and washed with water and
diethyl ether. The compound was purified by column chromatog-
raphy on neutral alumina, with acetonitrile/toluene (3:2) as eluent.
The solvent was removed from the desired fraction on a rotary
evaporator and the compound washed with diethyl ether and vac-
uum dried. Yield 0.2 g (72%) for 1, 0.19 g (66%) for 2, 0.14 g (53%)
for 3 and 0.12 g (54%) for 4.
(
0.50 g, 1.90 mmol) was dissolved in dry thf (50 mL) and triethyl-
amine (2 mL) was added to this solution. The thf solution (10 mL)
of the acid chloride obtained in the previous step was added drop-
wise to the reaction mixture over a period of 0.5 h and the solution
was stirred at room temperature for 24 h. The product, which sepa-
rated during stirring, was isolated by filtration and the solid mass
was dissolved in dichloromethane (50 mL) and extracted with water
1
Complex 1: H NMR (500 MHz, CD
3
CN): δ = 8.58 (s, 2 H, 3-H
(
50 mL, 3 times) to remove triethylamine hydrochloride. The or-
1
and 3Ј-H of bpy of L ), 8.51 (d, J = 8.0 Hz, 4 H, 6-H and 6Ј-H of
bpy), 8.06–8.10 (overlapped triplets, 4 H, 5-H and 5Ј-H of bpy),
ganic layer was dried with anhydrous sodium sulfate and the sol-
vent was evaporated to dryness. The crude product was purified by
column chromatography on silica gel (100–200 mesh) with dichlo-
romethane containing 5% methanol as eluent. Yield 0.40 g (54%).
3
H NMR (200 MHz, CDCl ): δ = 8.73 (d, J = 4.4 Hz, 2 H, 6-H
and 6Ј-H of bpy), 8.48 (s, 2 H, 3-H and 3Ј-H of bpy ), 7.40 (d, J =
.4 Hz, 2 H, 5-H and 5Ј-H of bpy), 3.83 (s br, 8 H, -CH N of crown
ether), 3.67–3.58 (m, 40 H, -CH O of crown ether) ppm. LC-MS:
7
2
.80 (d, J = 5.5 Hz, 2 H, 3-H and 3Ј-H of bpy), 7.76 (d, J = 5.5 Hz,
H, 6-H and 6Ј-H of bpy of L ), 7.71 (d, J = 5.5 Hz, 2 H, 3-H
1
1
and 3Ј-H of bpy), 7.44 (d, J = 5.5 Hz, 2 H, 5-H and 5Ј-H of bpy
1
Ј
of L ), 7.40–7.45 (overlapped triplets, 4 H, 4-H and 4Ј-H of bpy),
3
1
2
.43–3.72 (m, 48 H, -CH O of crown ether) ppm. LC-MS: m/z (%)
4
2
+
– +
6
461.69 (31) [1 + Na ] (calcd. 1461.33), 1293.62 (94) [1 – PF ]
2
+
– +
1
+
1
6
(calcd. 1293.24), 1147.62 (18) [1 – H – 2PF ] (calcd. 1147.27).
IR (KBr pellets): ν˜ = 1634 (C=O), 840 cm (PF ). UV/Vis
6
(CH
m/z (%) 773.63 (31) [L + K ] (calcd. 773.47), 757.57 (94) [L +
–
1
–
+
1
+
Na ] (calcd. 757.36), 735.68 (18) [L + H ] (calcd. 735.38). IR (KBr
4
4
–1
–1
pellets): ν˜ = 1619 cm–1 (C=O). C36
3
CN): λ (ε) = 454 (1.28ϫ10 ), 288 nm (6.31ϫ10  cm ).
H
54
N
4
O12 (734.37): calcd. C
C H F N O P Ru (1474.2): calcd. for C 45.62, H 5.02, N 7.60;
56 74 12 8 14 2
found C 45.49, H 4.84, N 7.43.
5
8.85, H 7.35, N 7.63; found C 58.42, H 7.39, N 7.51.
2
Synthesis of L : This compound was synthesised following a similar
method to that described for L . The required intermediates 1,10-
phenanthroline-4,7-dicarboxaldehyde and 1,10-phenanthroline-4,7-
dicarboxylic acid were synthesised following published pro-
The corresponding acid chloride and ligand L were
synthesised following the method mentioned above for L . Yield
1
Complex 2: H NMR (500 MHz, CD
3
CN): δ = 8.68 (d, J = 8.0 Hz,
1
2
H, 6-H and 6Ј-H of bpy), 8.61 (s, 2 H, 5-H and 6-H of phen of
2
L ), 8.56 (d, J = 8.0 Hz, 2 H, 6-H and 6Ј-H of bpy), 8.28 (d, J =
5
4
.5 Hz, 2 H, 3-H and 3Ј-H of bpy), 8.23–8.28 (overlapped triplets,
H, 5-H and 5Ј-H of bpy), 7.88 (d, J = 5.5 Hz, 2 H, 3-H and 3Ј-
[
24]
2
cedures.
1
H of bpy), 7.83 (dd, J
bpy), 7.70 (d, J = 6.0 Hz, 2 H, 2-H and 9-H of phen of L ), 7.57
1 2
= 8.0, J = 5.5 Hz, 2 H, 4-H and 4Ј-H of
1
0
.15 g (53%, with respect to the dicarboxylic acid derivative). H
NMR (200 MHz, CDCl ): δ = 9.23 (d, J = 4.4 Hz, 2 H, 2-H and
-H of phen), 7.87 (s, 2 H, 5-H and 6-H of phen), 7.62 (d, J =
.4 Hz, 2 H, 3-H and 8-H of phen), 4.00–3.93 (m, 8 H, -CH N of
O of crown ether) ppm.
2
3
(
=
4
dd, J
6.0, J
2
8 H, -CH
1
= 8.0, J
= 1.5 Hz, 2 H, 3-H and 8-H of phen of L ), 3.35–3.70 (m,
O of crown ether) ppm. LC-MS: m/z (%) 1341.92 (38)
2 1
= 5.5 Hz, 2 H, 4-H and 4Ј-H of bpy), 7.33 (dd, J
9
4
2
2
2
crown ether), 3.76–3.42 (m, 40 H, -CH
2
+
+
–
+ +
6
[2 – H – PF + Na ] (calcd. 1341.25). IR (KBr pellets): ν˜ = 1632
2
LC-MS: m/z (%) 781.45 (100) [L + Na ] (calcd. 781.84), 759.49
–1
–
4
(
2
C=O), 840 cm (PF
62 (7.66ϫ10  cm ). C58
6
). UV/Vis (CH
3
CN): λ (ε) = 445 (1.62ϫ10 ),
8 14 2
O P Ru (1498.3): calcd. for
44) [L2 + H ] (calcd. 759.86). IR (KBr pellets): ν˜ = 1617 cm
+
–1
(
(
4
–1
–1
H
74
F
12
N
C=O). C38 12 (758.85): calcd. C 60.14, H 7.17, N 7.38;
54 4
H N O
C 46.50, H 5.00, N, 7.48; found C 46.28, H 5.14, N 7.3.
found C 59.82, H 7.30, N 7.31.
1
Complex 3: H NMR (200 MHz, CD
3
CN): δ = 8.63 (d, J = 5.0 Hz,
3
Synthesis of L : A mixture of 4Ј-methyl-2,2Ј-bipyridine-4-carbal-
2 H, 2-H and 9-H of phen), 8.59 (d, J = 5.0 Hz, 2 H, 2-H and 9-
dehyde (0.20 g, 1.01 mmol), which was prepared following a pub-
H of phen), 8.25 (s, 4 H, 5-H and 6-H of phen), 8.13 (s, 2 H, 5-H
[
13]
2
lished procedure,
and 4Ј-aminobenzo-18-crown-6 (0.33 g,
and 6-H of phen of L ), 7.99–8.08 (m, 6 H, 4-H and 7-H of phen;
2
1.0 mmol) was refluxed in ethanol (20 mL) for 8 h. After refluxing,
and 2-H and 9-H of phen of L ), 7.60–7.71 (m, 6 H, 3-H and 8-H
2
the dark red solution was kept at room temperature overnight, dur-
ing which time a brown microcrystalline compound precipitated.
of phen including L ), 3.47–3.84 (m, 48 H, -CH
2
+
O of crown ether)
+
ppm. LC-MS: m/z (%) 1532.09 (5) [3 + Na ] (calcd. 1533.25),
1364.74 (30) [3 – PF ] (calcd. 1365.30). IR (KBr pellets): ν˜ = 1633
6
+
This compound was isolated by filtration, washed with diethyl
1
–1
–
4
ether and dried. Yield 0.425 g (83%). H NMR (200 MHz, CDCl
3
):
(C=O), 841 cm (PF
6
). UV/Vis (CH
3
CN): λ (ε) = 435 (1.54ϫ10 ),
Ru (1546.3):
calcd. for C 48.15, H 4.82, N 7.24; found C 47.86, H 4.96, N 7.10.
4
–1
–1
δ = 8.78 (d, J = 5.2 Hz, 1 H, 6-H or 6Ј-H of bpy), 8.75 (s, 1 H,
CH=N), 8.58 (s, 1 H, 3-H or 3Ј-H of bpy), 8.57 (d, J = 5.2 Hz, 1
263 nm (8.22ϫ10  cm ).
62 74 12 8 14 2
C H F N O P
Eur. J. Inorg. Chem. 2009, 1256–1267
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1265

P. Paul et al.
FULL PAPER
Complex 4: 1H NMR (200 MHz, CD
CN): δ = 8.91 (s, 1 H, SHELXL-97 program package.[27,28] Graphics for the packing dia-
3
gram were generated using PLATON.[ All non-hydrogen atoms
were refined anisotropically until convergence. Hydrogen atoms at-
tached to the ligand moieties were either located from the differ-
ence Fourier map or stereochemically fixed.
29]
-CH=N), 8.74 (s, 1 H, benzocrown-ArH), 8.50 (d, J = 8.0 Hz, 4 H,
6-H and 6Ј-H of bpy), 8.06 (t, J = 8.0 Hz, 4 H, 5-H and 5Ј-H of
3
bpy), 7.81 (m, 2 H, 6-H and 6Ј-H of bpy of L ) 7.73 (d, J = 5.6 Hz,
4
H, 3-H and 3Ј-H of bpy), 7.56 (d, J = 6.0 Hz, 1 H, 5-H or 5Ј-H
3
of bpy of L ), 7.37–7.44 (m, 4 H, 4-H and 4Ј-H of bpy), 7.27 (d, J
3
=
6.0 Hz, 1 H, 5Ј-H or 5-H of bpy of L ), 7.02–7.06 (m, 3 H, Ar-
H of benzocrown), 4.20 (m, 4 H, -CH O of crown ether), 3.78 (m,
H, -CH O of crown ether), 3.56–3.60 (m, 12 H, -CH O of crown
ether), 2.57 (s, 3 H, CH ) ppm. LC-MS: m/z (%) 1234.29 (4) [4 +
Table 3. Crystal, data collection and refinement details for L1.
2
Formula
36 54 4 12
C H N O
734.83
yellow
0.23ϫ0.16ϫ0.06
293
4
2
2
Molecular weight
Crystal colour
Crystal size [mm]
T [K]
3
+
+
Na ] (calcd. 1233.93), 1066.29 (100) [4 – PF
6
]
(calcd. 1065.98),
20.31 (10) [4 – H+ – 2PF
] (calcd. 920.02). IR (KBr pellets): ν˜
6
– +
9
=
(
(
4
–1
–
1621 (C=N), 842 cm (PF
6
). UV/Vis (CH
3
CN): λ (ε) = 465
Ru
1246.97): calcd. for C 46.23, H 4.28, N 7.86; found C 45.92, H
.32, N 7.78.
Crystal system
Space group
a [Å]
monoclinic
P2 /n
1
10.5750(7)
10.4136(7)
4
4
–1
–1
1.92ϫ10 ), 288 nm (5.92ϫ10  cm ). C48
H
53
F
12
N
7
O
8
P
2
b [Å]
c [Å]
α [°]
16.8608(11)
90
1
3
Synthesis of [Re(L )(CO)
3 3
Cl]·THF (5) and [Re(L )(CO) Cl]·THF (6):
A mixture of [Re(CO)
5
Cl] (0.10 g, 0.275 mmol) and the appropriate β [°]
107.1990(10)
90
1
3
ligand (L /L , 0.275 mmol) was refluxed in dry thf (30 mL) under
nitrogen for 15 h. The solution was then cooled to room temperature
and the solvent removed on a rotary evaporator. The residue thus
obtained was dissolved in dichloromethane (10 mL) and added drop-
wise to n-hexane (50 mL) with stirring. The precipitate thus obtained
was isolated by filtration and purified by column chromatography
packed with neutral alumina using acetonitrile/toluene (1:1) as eluent.
The solvent was removed from the desired fraction by evaporation.
Yield 0.13 g (47%) for 5 and 0.1 g (40%) for 6.
γ [°]
Z
V [Å ]
2
3
1773.7(2)
1.376
0.103
788
–
3
ρ [gcm ]
Absorption coefficient [mm ]
F(000)
–
1
Reflections collected
Independent reflections
Number of parameters
10193
4079 [R(int) = 0.0171]
343
2
GOF on F
1.240
R1, wR2 [I Ͼ 2σ(I)]
wR1, wR2 (all data)
0.0552/0.1230
0.0566/0.1238
1
Complex 5: H NMR (200 MHz, CDCl
2
(
3
): δ = 9.03 (d, J = 5.6 Hz,
H, 6-H and 6Ј of bpy), 8.50 (s, 2 H, 3-H and 3Ј-H of bpy), 7.64
d, J = 5.6 Hz, 2 H, 5-H and 5Ј-H of bpy), 3.75 (s, 8 H, -CH N of
crown ether), 3.52–3.62 (m, 40 H, -CH O of crown ether and
of thf) ppm. LC-MS: m/z (%)
2
2
–5
Ion-Binding Study: Stock solutions of the complexes (4ϫ10 )
and the perchlorate salts (4ϫ10 ) of various cations were pre-
-
1
2
(
(
CH
2
O of thf), 1.92 (m, 4 H, -CH
2
–3
+
063.52 (100) [5 + Na ] (calcd. 1063.51). IR (KBr pellets): νCO
), 1900 and 1894 (E) cm . UV/Vis (CH
4.13ϫ10 ), 297 nm (1.77ϫ10  cm ).
=
pared in freshly purified acetonitrile. Then, 5 mL of complex stock
solution and 5 mL of metal salt stock solution were placed in a 10-
mL volumetric flask such that the effective concentration of the
–
1
021 (A
1
3
CN): λ (ε) = 385
3
3
–1
–1
C
43 4
H62ClN O16Re
1112.6): calcd. for C 46.42, H 5.62, N 5.04; found C 46.19, H 5.98,
–5
–3
complex is 2ϫ10  and that of the metal ions 2ϫ10  (100-
fold excess). The luminescence spectra of the resulting solutions
were recorded with excitation at the absorption maxima (λmax) of
N 4.97.
1
Complex 6: H NMR (200 MHz, CDCl
3
): δ = 9.07 (d, J = 5.6 Hz,
1
H, 6-H or 6Ј-H of bpy), 8.87 (d, J = 5.6 Hz, 1 H, 6Ј-H or 6-H the MLCT band Ϫ 454, 445, 435, 465 nm for 1–4, respectively, and
of bpy), 8.66 (s, 1 H, 3-H or 3Ј-H of bpy), 8.34 (s, 1 H, 3Ј-H or 3-
H of bpy), 8.16 (s, 1 H, -CH=N), 7.84 (dd, J = 5.8, J = 1.4 Hz,
385 nm for 5. For the emission titration study, the same complex
stock solutions were used and the metal perchlorate solutions of
1
2
1
H, 5-H or 5Ј-H of bpy), 7.47 (d, J = 5.8 Hz, 1 H, 5Ј-H or 5- desired concentration were prepared by diluting the concentrated
–
2
H of bpy), 7.38 (s, 1 H, benzocrown-Ph-H), 7.21–7.25 (m, 2 H,
standard solution (4ϫ10 ). Then, 5 mL of each solution was
mixed in a 10-mL volumetric flask and the luminescence spectra
of the resulting solutions were recorded. The binding constant and
stoichiometry of complex formation were calculated following the
benzocrown-Ph-H), 4.33 (m, 4 H, -CH
H, -CH O of crown ether), 3.55–3.70 (m, 16 H, -CH
ether and-CH O of thf), 2.54 (s, 3 H, CH ), 1.94 (m, 4 H, -CH
2
2
O of crown ether), 3.84 (m,
O of crown
of
4
2
2
2
3
+
thf) ppm. LC-MS: m/z (%) 907.7 (50) [6 + Na ] (calcd. 908.36). IR literature procedure described in the Results and Discussion sec-
–
1
(
(
C
KBr pellets): νCO = 2018 (A
1
), 1910 and 1889 (E) cm . UV/Vis
tion. The same solutions were also used to study UV/Vis spectral
changes. For the NMR study, 5 mg of the complex was dissolved
4
4
–1
–1
CH
3
CN): λ (ε) = 342 (1.37ϫ10 ), 292 nm (2.04ϫ10  cm ).
41ClN
1
35
H
3
O
10Re (885.37): calcd. for C 47.48, H 4.68, N 4.75; in 0.5 mL of [D
3
]acetonitrile and the H NMR spectrum of the
found C 47.13, H 4.84, N 4.35.
resulting solution was recorded. The solid perchlorate salt of the
metal ion (50 equiv.) was added to the solution and the spectra of
the resultant solutions were re-recorded after 30 min. The electro-
chemical studies were also carried out in dry acetonitrile Ϫ the
DPV of the complexes in the region 1.2 to 1.8 V for metal oxidation
1
X-ray Crystallography for L : The crystallographic data and details
of data collection are given in Table 3. A crystal of suitable size
was selected from the mother liquor, mounted on the tip of a glass
fibre and cemented using epoxy resin. Intensity data for the crystal
+
+
2+
was recorded first and then solid metal salt (Na , K and Pb
,
α
were collected at 100 K using Mo-K (λ = 0.71073 Å) radiation on
50 equiv.) was added to the solution and the DPV of the same
a Bruker SMART APEX diffractometer equipped with a CCD area
detector. The data integration and reduction were processed with
region recorded.
[
25]
SAINT software.
An empirical absorption correction was ap-
Supporting Information (see also the footnote on the first page of
this article): COSY NMR spectra of 1 (Figure S1); packing dia-
[25,26]
plied to the collected reflections with SADABS using XPREP.
1
The structure was solved by direct methods using SHELXTL and
gram of L (Figure S2); luminescence spectra of 1 in the presence
2
1
1
refined on F by the full-matrix least-squares technique using the
of various metal ions (Figure S3); H NMR spectra of L with
1266
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 1256–1267

Ruthenium(II) and Rhenium(I) Bipyridine/Crown Ether Receptor Molecules
and without KClO
addition of increasing concentrations of NaClO
details of the hydrogen-bonding interaction in L with symmetry
code (Table S1).
4
(Figure S4); UV/Vis spectral change of 6 upon
(Figure S5); and
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Received: November 12, 2008
Published Online: February 11, 2009
Eur. J. Inorg. Chem. 2009, 1256–1267
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1267