Fluorescent chemosensors for heavy metal ions based on bis(terpyridyl) ruthenium(II) complexes containing aza-oxa and polyaza macrocycles

Article abstract of DOI:10.1002/1099-0682(200106)2001:6<1475::AID-EJIC1475>3.0.CO;2-N

Reactions of 4′-[4-(bromomethyl)phenyl]-2,2′:6′,2″-terpyridine with 4,10-diaza-15-crown-5 and 1-aza-12-crown-4 in dichloromethane yielded the ligands L¹ and L³, respectively. Reaction of an excess of 4′-[4-(bromomethyl)phenyl]-2,2′:6′,2″-terpyridine with 4,10-diaza-15-crown-5 yielded L², while treatment of the same terpyridine ligand with 1,4,7,10,13-pentaazacyclopentadecane afforded L⁴. Reactions of L¹, L³, and L⁴ with Ru(mtpy)Cl₃ (mtpy = 4′-methyl-2,2′:6′,2″-terpyridine) in methanol yielded the metallo receptors [Ru(L¹)(mtpy)][PF₆]₂, [Ru(L³)(mtpy)][PF₆]₂, and [Ru(L⁴)(mtpy)][PF₆]₂ after precipitation with ammonium hexafluorophosphate and column chromatography. On treating L³ with RuCl₃, the homoleptic ruthenium complex [Ru(L³)₂][PF₆]₂ was obtained. The synthesized metallo receptors contain oxa-aza crown or polyazacycloalkane moieties as recognition sites and [Ru(tpy)₂]²⁺ cores as the signal-generating centre. The electronic spectra of the complexes are as expected for an Ru(tpy)₂²⁺ chromophore, with the main Ru[d(π)] → tpy(π*) MLCT transition at ca. 484 nm and intense ligand-centred transitions in the UV region. One of the most interesting aspects of these ruthenium complexes is their multicomponent nature, as they contain both coordination sites and fluorescent Ru(tpy)₂²⁺ cores. The cations [Ru(L¹)(mtpy)]²⁺, [Ru(L³)(mtpy)]²⁺, and [Ru(L³)₂]²⁺ display an emission maximum at ca. 650 nm, the intensity of which is pH dependent, showing an enhancement upon protonation. The metallo receptor [Ru(L¹)(mtpy)]²⁺ selectively senses Hg²⁺ in preference to Cu²⁺, Cd²⁺, and Pb²⁺. The emission intensity vs. pH curve for [Ru(L²)(mtpy)]²⁺ in the presence of Cu²⁺ and Hg²⁺ ions is close to that of the free receptor, but the presence of Cd²⁺ or Pb²⁺ enhances the emission intensity in the range pH 4-6. For the [Ru(L³)₂]²⁺ complex, Cd²⁺, Pb²⁺, and Hg²⁺ induce an enhancement of the fluorescence of the Ru(tpy)₂²⁺ core in the range pH 3.5-7.5. These results are compared with those obtained for the metallo receptor [Ru(L⁴)(mtpy)]²⁺ containing a polyazacycloalkane moiety as the binding domain.

Full text of DOI:10.1002/1099-0682(200106)2001:6<1475::AID-EJIC1475>3.0.CO;2-N

FULL PAPER
Fluorescent Chemosensors for Heavy Metal Ions Based on Bis(terpyridyl)
Ruthenium(II) Complexes Containing Aza-Oxa and Polyaza Macrocycles
[a]
[a]
[a]
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Miguel E. Padilla-Tosta, Jose Manuel Lloris, Ramon Martınez-Manez,*
[a]
[a]
[a]
[a]
´
M. Dolores Marcos, Miguel A. Miranda, Teresa Pardo, Felix Sancenon, and
Juan Soto[a]
Keywords: Ruthenium / Terpyridine / Aza-oxa crowns / Fluorescence / Chemosensors
Reactions of 4Ј-[4-(bromomethyl)phenyl]-2,2Ј:6Ј,2ЈЈ-terpyri- ligand-centred transitions in the UV region. One of the most
dine with 4,10-diaza-15-crown-5 and 1-aza-12-crown-4 in interesting aspects of these ruthenium complexes is their
dichloromethane yielded the ligands L1 and L3, respectively. multicomponent nature, as they contain both coordination
2+
Reaction of an excess of 4Ј-[4-(bromomethyl)phenyl]- sites and fluorescent Ru(tpy)2
cores. The cations
2,2Ј:6Ј,2ЈЈ-terpyridine with 4,10-diaza-15-crown-5 yielded L2, [Ru(L1)(mtpy)]2+, [Ru(L3)(mtpy)]2+, and [Ru(L3)2]2+ display an
while treatment of the same terpyridine ligand with emission maximum at ca. 650 nm, the intensity of which is
1,4,7,10,13-pentaazacyclopentadecane afforded L4. Reac- pH dependent, showing an enhancement upon protonation.
tions of L1, L3, and L4 with Ru(mtpy)Cl3 (mtpy = 4Ј-methyl- The metallo receptor [Ru(L1)(mtpy)]2+ selectively senses Hg2+
2,2Ј:6Ј,2ЈЈ-terpyridine) in methanol yielded the metallo re- in preference to Cu2+, Cd2+, and Pb2+. The emission intensity
ceptors [Ru(L1)(mtpy)][PF6]2, [Ru(L3)(mtpy)][PF6]2, and vs. pH curve for [Ru(L2)(mtpy)]2+ in the presence of Cu2+ and
[Ru(L4)(mtpy)][PF6]2 after precipitation with ammonium Hg2+ ions is close to that of the free receptor, but the presence
hexafluorophosphate and column chromatography. On treat- of Cd2+ or Pb2+ enhances the emission intensity in the range
ing L3 with RuCl3, the homoleptic ruthenium complex pH 4−6. For the [Ru(L3)2]2+ complex, Cd2+, Pb2+, and Hg2+
[Ru(L3)2][PF6]2 was obtained. The synthesized metallo recep- induce an enhancement of the fluorescence of the Ru(tpy)2
2+
tors contain oxa-aza crown or polyazacycloalkane moieties core in the range pH 3.5−7.5. These results are compared
as recognition sites and [Ru(tpy)2]2+ cores as the signal-gen- with those obtained for the metallo receptor [Ru(L4)(mtpy)]2+
erating centre. The electronic spectra of the complexes are containing a polyazacycloalkane moiety as the binding do-
2+
as expected for an Ru(tpy)2 chromophore, with the main main.
Ru[d(π)] Ǟ tpy(π*) MLCT transition at ca. 484 nm and intense
Introduction
tion of multicomponent systems with fine control over the
geometry of the assembly.[9,10] Additionally, from a prac-
tical viewpoint, emission in the visible part of the spectrum
(as shown by Ru-tpy complexes) is much more convenient
than emission near the UV region, where many other or-
ganic fluorophores typically emit.
Ligands with a macrocyclic unit attached to a metal-
polypyridyl core are potentially useful in the preparation of
luminescent or electrochemical sensors, in which the macro-
scopic properties of the core are modified by molecular-
level interactions between the recognition centre and the
substrate.[1Ϫ4] The polypyridyl complexes of d6 metals, with
their strong metal-to-ligand charge transfer absorptions
and emitting excited states, are good candidates as signal-
We have recently reported the functionalization of the
2ϩ
Ru(tpy)2 unit with cyclam and the use of the resulting
compound as a potential sensing receptor for Cu2ϩ ions.[11]
Further, we are interested in the development of potential
ling subunits.[5,6] The metalϪpolypyridyl complex most
chemosensors for heavy transition metal ions such as Cd2ϩ
,
2ϩ [7,8]
widely used as a fluorophore is probably Ru(bipy)3
.
Hg2ϩ, and Pb2ϩ. Sensing receptors for toxic heavy metal
ions are of interest in areas such as environmental chem-
istry, where the development of highly selective analytical
tools is of importance. In order to direct the sensing ability
of Ru(tpy)22ϩ-based chemosensors towards the selective de-
termination of these metals, we have covalently func-
tionalized the fluorophore core with binding sites that are
known to show greater stability constants with large tran-
sition metal ions than with smaller ones.[12,13] In fact, it has
been established that a combination of O and N donor
atoms on such macrocyclic structures promotes the forma-
tion of complexes with large-sized transition metal cations
as opposed to those with smaller radii.[15] Based on the fact
that large stability constants could lead to a high selectiv-
In contrast, the rutheniumϪterpyridine Ru(tpy)22ϩ unit has
2ϩ
been less well studied. Although the Ru(tpy)2 core is less
fluorescent than Ru(bipy)32ϩ, terpyridine complexes may
have some advantages over their bipyridine counterparts.
Thus, for instance, it has been reported that the octahedral
tpy-type complex has the advantage of being non-chiral
(preventing the generation of stereoisomers that may arise
with bipy-Ru complexes) and, through functionalization of
the ligand at the appropriate position, allows the construc-
[a]
´
Departamento de Quımica,
Universidad Politecnica de Valencia,
´
Camino de Vera s/n, 46071 Valencia, Spain
Fax: (internat.) ϩ34Ϫ963877349
E-mail: rmaez@qim.upv.es
Eur. J. Inorg. Chem. 2001, 1475Ϫ1482
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/0606Ϫ1475 $ 17.50ϩ.50/0
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ity,[17] we report herein on the synthesis of three new oxa- tached to an O atom as well as those of the benzylic protons
2ϩ
1
aza functionalized Ru(tpy)2 receptors. The main goal of in the range δ ϭ 3.4Ϫ3.8. The H NMR spectrum of L4 is
this work has been the quest for new potential chemosen- also in agreement with the proposed formulation.
Reactions of equimolar amounts of L1, L3, or L4 with
sors for toxic heavy metal cations.
[Ru(mtpy)Cl3] in methanol in the presence of N-ethylmor-
pholine as
a mild reductant yielded the complexes
[Ru(L1)(mtpy)][PF6]2, [Ru(L3)(mtpy)][PF6]2, and [Ru(L4)-
(mtpy)][PF6]2, respectively, after precipitation with ammo-
nium hexafluorophosphate and column chromatography on
silica using acetonitrile/water/satd. aq. KNO3 (17:1:2, v/v)
as the eluent. The FAB mass spectra showed peaks at m/
z ϭ 1177, 1033, and 887 for [Ru(L1)(mtpy)][PF6]2, at m/z ϭ
1135, 990, and 845 for [Ru(L3)(mtpy)][PF6]2, and at m/z ϭ
1174, 1030, and 885 for [Ru(L4)(mtpy)][PF6]2, correspond-
ing to {[Ru(L)(mtpy)][PF6]2}, {[Ru(L)(mtpy)][PF6]ϩ}, and
Results and Discussion
Synthesis and Characterization
4Ј-[4-(Bromomethyl)phenyl]-2,2Ј:6Ј,2ЈЈ-terpyridine (Br-
mphtpy) was synthesized according to the procedure of
Spahni and Calzaferri.[18] From this derivative, terpyridine-
functionalized crowns could be readily prepared by reaction
with the appropriate macrocycle in dichloromethane in the
presence of Et3N at 30 °C for 24 h, followed by column
chromatography on alumina using a mixture of CH2Cl2/
MeOH as the eluent. This led to yields of ca. 30% for L1
and L2, of 35% for L3, and of 50% for L4.
{[Ru(L)(mtpy)]2ϩ}, respectively. The H NMR spectra of
1
the ruthenium complexes showed the expected signals due
to the aromatic protons in the region δ ϭ 7.1Ϫ9.1. They
were fully assigned with the assistance of 1H-1H correlation
spectroscopy (COSY). The spectra also featured signals due
to the protons of the terminal CH3 groups, at δ ϭ 2.93 in
each case. The signals due to the protons of the CH2 groups
Ligands L1 and L2 show very similar H NMR spectra,
1
the main difference being the appearance of the proton sig-
nal of the amine group at δ ϭ 2.5 in the spectrum of L1,
which is not observed in the case of L2. The pyridyl proton
signals are seen in the range δ ϭ 7.3Ϫ8.8. The spectra are
completed by two groups of signals, one in the range δ ϭ
2.7Ϫ3.0, corresponding to the protons of CH2 groups at-
tached to a nitrogen atom in the crown, and the other in
the range δ ϭ 3.6Ϫ3.9, attributable to benzylic protons and
to the protons of CH2 groups bonded to oxygen atoms. The
1H NMR spectrum of L3 shows signals due to the protons
of CH2 groups bonded to an N atom in the crown at δ ϭ
2.8, and signals due to the protons of the CH2 groups at-
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Fluorescent Chemosensors for Heavy Metal Ions
FULL PAPER
attached to a nitrogen atom appeared at ca. δ ϭ 3.3,
The fluorescence behaviour of the complexes
whereas those due to the protons of CH2 groups bonded to [Ru(L1)(mtpy)]2ϩ, [Ru(L3)(mtpy)]2ϩ, [Ru(L4)(mtpy)]2ϩ, and
oxygen atoms were seen at δ ϭ 3.6Ϫ4.0. The ruthenium [Ru(L3)2]2ϩ was investigated in acetonitrile/water mixtures
complex of L4 shows signals due to the protons of the poly- as a function of the pH, in the absence and presence of
azacycloalkane ring in the region δ ϭ 2.8Ϫ3.2.
transition metal ions M2ϩ (M2ϩ ϭ Cu2ϩ, Cd2ϩ, Hg2ϩ, and
The homoleptic complex of L3 was obtained by treating Pb2ϩ) {see Figure 1 (a) for [Ru(L1)(mtpy)]2ϩ, Figure 1 (b)
RuCl3 with two equivalents of L3 in methanol in the pres- for [Ru(L3)(mtpy)]2ϩ, Figure 1 (c) for [Ru(L3)2]2ϩ, and Fig-
ence of N-ethylmorpholine as a mild reductant, followed ure 1 (d) for [Ru(L4)(mtpy)]2ϩ}.
by precipitation with ammonium hexafluorophosphate and
The complexes [Ru(L1)(mtpy)]2ϩ, [Ru(L3)(mtpy)]2ϩ, and
column chromatography. The FAB mass spectrum of [Ru(L3)2]2ϩ display an emission maximum at ca. 650 nm,
[Ru(L3)2][PF6]2 showed peaks at m/z ϭ 1240, 1094, and 920, the intensity of which is seen to be pH-dependent. In the
corresponding to {[Ru(L3)2][PF6]2}, {[Ru(L3)2][PF6]ϩ}, and case of [Ru(L1)(mtpy)]2ϩ, an enhancement of the lumines-
1
{[Ru(L3)2]2ϩ}, respectively. The H NMR spectrum of the cence of ca. 60% is observed upon protonation, which is
[Ru(L3)2][PF6]2 complex was also in agreement with the close to the enhancement seen for the [Ru(L3)(mtpy)]2ϩ
proposed formulation.
complex. Remarkably, the enhancement in the emission in-
tensity of [Ru(L3)2]2ϩ upon protonation is ca. twice that
observed for the heteroleptic complexes. In contrast, the
emission intensity of the [Ru(L4)(mtpy)]2ϩ complex is seen
to be almost pH-independent, showing only a slight in-
crease at acidic pH. This suggests that the electron- or en-
ergy-transfer path from the amine to the Ru(tpy)22ϩ fluoro-
phore is more effective in aza-oxa derivatives than in the
polyazacycloalkane. In fact, negligible pH-dependence was
also found for the ruthenium(II) complex [Ru(cyphtpy)-
(mtpy)]2ϩ {cyphtpy ϭ 1-[4Ј-(p-tolyl)-2,2Ј:6Ј,2ЈЈ-terpyridyl]-
1,4,8,11-tetraazacyclotetradecane}, which contains a cyclic
tetraamine unit anchored to the ruthenium(II) bis(terpyrid-
ine) centre.[11]
Photophysical Characterization and pH-Dependence of the
Fluorescence
The electronic spectra of the complexes were found to be
as expected for an [Ru(tpy)2]2ϩ chromophore, with the main
Ru[d(π)] Ǟ tpy(π*) MLCT transition at ca. 484 nm and the
usual intense ligand-centred transitions in the UV re-
gion.[5,6] It is likely that the absorption band at ca. 484 nm
corresponds to a mixture of dπ(Ru) Ǟ π(mtpy) and dπ(Ru)
Ǟ π(Ln) transitions for the heteroleptic [Ru(L1)(mtpy)]-
[PF6]2, [Ru(L3)(mtpy)][PF6]2, and [Ru(L4)(mtpy)][PF6]2
complexes and to the transition dπ(Ru) Ǟ π(L3) in the case
of the homoleptic [Ru(L3)2][PF6]2 complex, which would
otherwise give a narrower absorption band.[19] The photo-
physical properties of the complexes [Ru(L1)(mtpy)][PF6]2,
Typical quantum yields for these complexes are around
5·10Ϫ5, comparable to those reported for similar ruthenium
bis(terpyridyl) complexes.[19] Unfortunately, these low
quantum yields prevent further studies on the lifetimes of
the excited states. As stated above, the intensities of the
emission maxima (or quantum yields) of the
[Ru(L1)(mtpy)]2ϩ, [Ru(L3)(mtpy)]2ϩ, and [Ru(L3)2]2ϩ com-
plexes are pH-dependent. In order to gain a better under-
standing of the pH-dependent fluorescent behaviour seen
for the aza-oxa-functionalized bis(terpyridyl) ruthenium(II)
complexes, further studies were carried out on the
[Ru(L1)(mtpy)]2ϩ complex. Two possible mechanisms may
be invoked to account for the fluorescence quenching of
[Ru(L3)(mtpy)][PF6]2,
[Ru(L4)(mtpy)][PF6]2,
and
[Ru(L3)2][PF6]2 in acetonitrile/water (70:30, v/v) at 298 K
are summarized in Table 1.
Table 1. Photophysical properties of the complexes [Ru(L1)-
(mtpy)][PF6]2, [Ru(L3)(mtpy)][PF6]2, [Ru(L4)(mtpy)][PF6]2, and
[Ru(L3)2][PF6]2 in acetonitrile/water (70:30, v/v) at 298 K
abs. (298 K)
λ [nm]
em. (298 K)
ε [Ϫ1 cmϪ1
]
λ [nm]
[Ru[L1](mtpy)][PF6]2
[Ru(L3)(mtpy)][PF6]2
[Ru(L4)(mtpy)][PF6]2
[Ru(L3)2][PF6]2
480
483
484
482
17500
17700
17000
16800
652
650
650
652
2ϩ
the Ru(tpy)2 signalling unit,[19] i.e. electron transfer and
energy transfer. The occurrence or otherwise of an electron-
transfer mechanism can be assessed on the basis of electro-
chemical and photophysical data. For instance, the free en-
One of the most attractive features of these complexes is ergy associated with the electron-transfer process
their multicomponent nature as they contain sites suitable [Ru(tpy)22ϩ*Ϫamine] Ǟ [Ru(tpy)2ϩϪamineϩ], where an
for coordinating metal ions in the vicinity of a fluorescent electron from the lone pair of the amine is transferred to
2ϩ
Ru(tpy)2 group. It is known that, compared to acyclic an orbital of the fluorophore leading to a quenching pro-
structures, macrocyclic receptors generally display more se- cess, can be calculated from the equation: ∆G ϭ Ϫ(hcNA/
lective complexation. Additionally, the introduction of cen- λ) ϩ F[E0
Ϫ E0fl/flϪ] (fl ϭ fluorophore), where
amineϩ/amine
tral oxygen donor atoms in macrocycles has been used to E0amineϩ/amine and E0fl/flϪ are the redox potentials associated
achieve selectivity for large metal ions as opposed to small with the redox processes ‘amineϩ ϩ 1 eϪ Ǟ amine’ and
ones.[15] The presence of aza-oxa macrocycles in the metallo ‘fl ϩ 1 eϪ Ǟ flϪ’, respectively, and λ relates to the so-called
receptors [Ru(L1)(mtpy)][PF6]2, [Ru(L3)(mtpy)][PF6]2, and spectroscopic energy that can be obtained from the emis-
[Ru(L3)2][PF6]2 thus makes them good candidates as fluor- sion fluorescence spectrum. Redox potentials were meas-
escent signalling systems for toxic heavy metal ions in solu- ured in dry acetonitrile (containing 0.1 mol dmϪ3 tetrabu-
tion.
tylammonium perchlorate) at 25 °C. Cyclic voltammograms
Eur. J. Inorg. Chem. 2001, 1475Ϫ1482
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Figure 1. Relative emission intensity versus pH for the L and LϪM2ϩ systems: (a) L ϭ [Ru(L1)(mtpy)][PF6]2, M2ϩ ϭ Cu2ϩ, Cd2ϩ, Pb2ϩ
,
Hg2ϩ; (b) L ϭ [Ru(L3)(mtpy)][PF6]2, M2ϩ ϭ Cu2ϩ, Cd2ϩ, Pb2ϩ, Hg2ϩ; (c) L ϭ [Ru(L3)2][PF6]2, M2ϩ ϭ Cu2ϩ, Cd2ϩ, Pb2ϩ, Hg2ϩ; (d) L ϭ
[Ru(L4)(mtpy)][PF6]2, M2ϩ ϭ Ni2ϩ, Cu2ϩ, Cd2ϩ, Pb2ϩ, Hg2ϩ
of the ruthenium complex [Ru(L1)(mtpy)]2ϩ show two ox- increase in the emission intensity would be expected at
idation processes, at 1.05 V and 1.23 V. The first of these is acidic pH, as is indeed observed (Figure 1).
irreversible and can be ascribed to the oxidation of the 4,10-
Sensing Response towards Transition Metal Ions
diaza-15-crown-5, whereas the second corresponds to the
oxidation of the RuII centre. The complex [Ru(L1)(mtpy)]2ϩ
The I/I0 vs. pH curve for the free receptor [Ru(L1)-
also displays two quasi-reversible reduction processes at (mtpy)]2ϩ remains essentially unchanged in the presence of
Ϫ1.25 and Ϫ1.52 V, attributable to the formal reduction of the transition metal ions Cu2ϩ, Cd2ϩ, and Pb2ϩ (see Fig-
2ϩ
the Ru(tpy)2 core. Taking these data into account, the ure 1). In contrast, in the presence of Hg2ϩ, a different I/I0
∆G value obtained is ca. Ϫ6.5 kcal/mol. This negative value vs. pH profile is seen over a wide pH range. The presence
suggests that a photoinduced electron-transfer process from of Hg2ϩ led to an enhancement of the emission intensity by
2ϩ
the amine to the Ru(tpy)2 fluorophore is possible. This is as much as 60% at pH 6.5, with some enhancement even
probably the mechanism that is operative under conditions being observed at lower pH. This intensity increase may
of basic pH (where the amine is not protonated). When the be attributed to the formation of [Ru(L1)(mtpy)]2ϩϪHg2ϩ
pH is decreased, the amine groups are protonated, and the species, in which the lone pair of the nitrogen atom would
oxidation of the amine becomes more difficult, thus making no longer be available for the photoinduced electron-trans-
∆G positive. A positive value of the free energy reduces the fer process owing to its involvement in the coordinative in-
probability of electron-transfer processes and therefore an teraction. At this point it is interesting to note that the 4,10-
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Fluorescent Chemosensors for Heavy Metal Ions
FULL PAPER
diaza-15-crown-5 cycle has also been N-functionalized with seen in the presence of this cation. An exhaustive and de-
the organic anthrylmethyl fluorophore.[20] Whereas the tailed coordination study was beyond the scope of this ar-
metal ions Ni2ϩ, Cu2ϩ, Zn2ϩ, Cd2ϩ, and Pb2ϩ had no ticle, mainly due to the relatively low yields achieved in the
modifying effect on the fluorescence intensity vs. pH profile synthesis of the complex [Ru(L1)(mtpy)][PF6]2 and of the
of the anthryl derivative, the presence of Hg2ϩ enhanced related complexes mentioned in this paper.
the emission intensity in the range pH 5Ϫ9. This result is
From the refinement of the potentiometric data in the
similar to that found for the [Ru(L1)(mtpy)]2ϩ complex in range pH 2Ϫ10.5 in the presence of Hg2ϩ, the species
the presence of metal ions, suggesting that both fluoro- {Hg[Ru(HL1)(mtpy)]}5ϩ
,
{Hg[Ru(L1)(mtpy)]}4ϩ
,
{Hg-
phores, i.e. the Ru(tpy)22ϩ and the anthryl signalling subun- (OH)[Ru(L1)(mtpy)]}3ϩ, and {Hg(OH)2[Ru(L1)(mtpy)]}3ϩ
its, are able to selectively detect the presence of Hg2ϩ were found. The stability constant for the equilibrium Hg2ϩ
through a combination of coordination to an appropriate ϩ [Ru(L1)(mtpy)]2ϩ o {Hg[Ru(L1)(mtpy)]}4ϩ was evalu-
binding site (the 4,10-diaza-15-crown-5 cycle) and enhance- ated as log K ϭ 6.23. We have recently studied the interac-
ment of the fluorescence.
tion of Hg2ϩ with the ferrocene-functionalized ligand 7,13-
To gain insight into the interaction of Hg2ϩ with ferrocenylmethyl-7,13-diaza-15-crown-5. In this case, the
[Ru(L1)(mtpy)]2ϩ, protonation and coordination studies logarithm of the formation stability constant of the ligand
were carried out by means of potentiometric titrations of with Hg2ϩ was measured as log K ϭ 8.79 in dioxane/water
previously acidified solutions of the ruthenium(II) complex (70:30, v/v).[21] Although a different solvent system has been
in acetonitrile/water (70:30, v/v, 0.1 mol dmϪ3 tetrabutylam- used for the study of the interaction between Hg2ϩ and the
monium perchlorate) with KOH. Protonation constants are aforementioned Ru(tpy)22ϩ- and ferrocene-functionalized
given in Table 2, while stability constants for the formation receptors, it seems that the presence of the positively
2ϩ
of Hg2ϩ complexes with [Ru(L1)(mtpy)]2ϩ are given in charged, bulky Ru(tpy)2 signalling subunit might impose
Table 3. The [Ru(L1)(mtpy)]2ϩ complex displays two pro- some constraints on the coordination of Hg2ϩ by the aza-
tonation process with basicity constants of log K ϭ 9.47 oxa macrocycle and makes the stability constant with
and log K ϭ 7.67. These values are close to those found for [Ru(L1)(mtpy)]2ϩ lower than that with the analogous ferro-
the analogous ferrocenylmethyl-functionalized derivative cene-functionalized derivative. Figure 2 shows the distribu-
7,13-ferrocenylmethyl-7,13-diaza-15-crown-5 (log K ϭ 8.49 tion diagram for the [Ru(L1)(mtpy)]2ϩϪHg2ϩϪHϩ system.
and log K ϭ 6.69 in dioxane/water, 70:30, v/v).[21]
Table 2. Stepwise protonation constants in acetonitrile/water
(70:30, v/v, 0.1 mol dmϪ3 tetrabutylammonium perchlorate) for
[Ru(L1)(mtpy)]2ϩ
Reaction
log K[a]
[Ru(L1)(mtpy)]2ϩ ϩ Hϩ o [Ru(HL1)(mtpy)]3ϩ
[Ru(L1)(mtpy)]2ϩ ϩ 2 Hϩ o [Ru(H2L1)(mtpy)]4ϩ
9.47(1)
17.14(2)
[a]
Values in parentheses are standard deviations in the last signific-
ant digit.
Table 3. Stability constants (log K) for the formation of the Hg2ϩ
complexes of [Ru(L1)(mtpy)]2ϩ in acetonitrile/water (70:30, v/v, 0.1
mol dmϪ3 tetrabutylammonium perchlorate) at 25 °C
Reaction
log K[a]
Figure 2. Distribution diagram of the species for the system
[Ru(L1)(mtpy)]ϪHg2ϩϪHϩ
Hg2ϩ ϩ [Ru(HL1)(mtpy)]3ϩ o {Hg[Ru(HL1)(mtpy)]}5ϩ 14.24(3)
Hg2ϩ ϩ [Ru(L1)(mtpy)]2ϩ o {Hg[Ru(L1)(mtpy)]}4ϩ
Hg2ϩ ϩ [Ru(L1)(mtpy)]2ϩ ϩ H2O
6.23(3)
Ϫ3.57(4)
o {Hg(OH)[Ru(L1)(mtpy)]}3ϩ ϩ Hϩ
Hg2ϩ ϩ [Ru(L1)(mtpy)]2ϩ ϩ 2 H2O
Figure 1b shows the I/I0 vs. pH curves for the
[Ru(L3)(mtpy)]2ϩ complex in the presence of metal ions.
The I/I0 vs. pH profiles for this complex are similar with
Cu2ϩ and Hg2ϩ, but in the presence of Cd2ϩ and Pb2ϩ an
enhancement of the emission intensity of the order of 30%
is observed in the range pH 4Ϫ6. The 1,4,7-trioxa-10-azacy-
Ϫ13.27(3)
o {Hg(OH)2[Ru(L1)(mtpy)]}2ϩ ϩ 2 Hϩ
[a]
Values in parentheses are standard deviations in the last signific-
ant digit.
The coordination behaviour of the receptor clododecane unit has also been N-functionalized with
[Ru(L1)(mtpy)]2ϩ towards Hg2ϩ has been studied. Our aim anthryl groups as fluorescent signalling subunits.[20] In con-
was to explore the coordination ability of the aza-oxa cycle trast to the fluorescent behaviour of the [Ru(L3)(mtpy)]2ϩ
and the effect of the presence of a bulky, charged complex, the anthracene-containing derivative does not
2ϩ
Ru(tpy)2 group on the coordination of metal ions. Hg2ϩ show any response in the presence of the metal ions Ni2ϩ
,
was chosen because of the selective fluorescence response Cu2ϩ, Zn2ϩ, Cd2ϩ, Pb2ϩ, or Hg2ϩ. The signalling fluores-
Eur. J. Inorg. Chem. 2001, 1475Ϫ1482
1479

´
´
R. Martınez-Man˜ez et al.
FULL PAPER
cence behaviour of the ruthenium and anthrylazamacrocy- Hg2ϩ enhance the fluorescence of the receptor. The fluores-
cle compounds in the presence of metal ions is quite differ- cent response as a function of the pH in the presence of
ent, highlighting the active role that the signalling subunit Cu2ϩ resembles that found with the receptor
might play in the selectivity of the sensing event.
[Ru(cyphtpy)(mtpy)]2ϩ, which contains a cyclic tetraamine
The fluorescence response of the [Ru(L3)2]2ϩ complex has moiety anchored to the ruthenium(II) bis(terpyridine)
also been studied in acetonitrile/water (70:30, v/v) as a func- centre.[11] It is interesting to note that there seems to be a
tion of pH in the presence of two equivalents of Cu2ϩ
,
close relationship between the emission intensity and the
Cd2ϩ, Hg2ϩ, and Pb2ϩ. This receptor contains two peri- radii of the metal cations; large metal ions enhance the
2ϩ
pheral aza-oxa units, rather than just one as in the analog- fluorescence of the Ru(tpy)2 core, whereas smaller ones
ous [Ru(L3)(mtpy)]2ϩ complex. The I vs. pH curve for have a quenching effect. This represents rather unusual be-
[Ru(L3)2]2ϩ does not change in the presence of Cu2ϩ, but haviour, which, to the best of our knowledge, has not been
the presence of Cd2ϩ, Pb2ϩ, or Hg2ϩ induces an enhance- reported previously. In Figure 3, the relative fluorescence at
2ϩ
ment in the luminescence of the Ru(tpy)2
core in the pH 7.5 found in the presence of Ni2ϩ, Cu2ϩ, Cd2ϩ, Hg2ϩ
,
range pH 3.5Ϫ7.5 (see Figure 1c). The behaviour observed and Pb2ϩ ions is plotted as a function of the cationic radius.
for the [Ru(L3)2]2ϩ complex is quite similar to that seen for A linear response between emission intensity and cation
[Ru(L3)(mtpy)]2ϩ, the only difference being the sensing of size can be seen.
Hg2ϩ by the homoleptic complex, which is not observed for
the heteroleptic one. This behaviour is not easy to rational-
ize, but it nevertheless seems to highlight the importance of
Conclusions
slight structural modifications of the receptor in determin-
ing the final fluorescent behaviour. It is noteworthy that the
[Ru(L3)(mtpy)]2ϩ receptor is able to sense the presence of
all three toxic heavy metal ions Cd2ϩ, Pb2ϩ, and Hg2ϩ in an
aqueous environment (acetonitrile/water) at the commonly
encountered neutral pH in preference to smaller metal ions
New terpyridine derivatives attached to aza-oxa macro-
cycles have been synthesized and their homoleptic or heter-
oleptic ruthenium(II) complexes have been prepared. One
of the most interesting features of these metallo receptors
is their multicomponent nature, in that they consist of an
Ru(tpy)22؉ core capable of acting as a fluorescent signalling
subunit and an aza-oxa macrocycle unit that acts as a cat-
ion binding site. Studies have been mainly carried out with
a view to achieving discrimination between toxic heavy
metal ions by means of fluorescence techniques. The recep-
tors [Ru(L1)(mtpy)]2ϩ, [Ru(L3)(mtpy)]2ϩ, and [Ru(L3)2]2ϩ
are capable of transforming a coordination event occurring
at the molecular level into a measurable macroscopic signal,
such as Cu2ϩ
.
Finally, the emission properties of the [Ru(L4)(mtpy)]2ϩ
complex in the presence of Ni2ϩ, Cu2ϩ, Cd2ϩ, Hg2ϩ, and
Pb2ϩ were monitored as a function of pH. This receptor
contains a polyazacycloalkane unit covalently attached to
2ϩ
the Ru(tpy)2 fluorophore rather than an aza-oxa macro-
cycle as in [Ru(L1)(mtpy)]2ϩ
, , and
[Ru(L3)(mtpy)]2ϩ
[Ru(L3)2]2ϩ. This is reflected in the observation of a quite
different response towards metal ions. All five metals induce
thus allowing the sensing of heavy metal ions such as Cd2ϩ
,
Pb2ϩ, and especially of Hg2ϩ in water/acetonitrile (70:30,
v/v) mixtures. The [Ru(L4)(mtpy)]2ϩ receptor, containing a
polyazacycloalkane moiety as a binding site, shows a quite
a
change in the fluorescence response of the
[Ru(L4)(mtpy)]2ϩ receptor, as shown in Figure 1d. Ni2ϩ
,
Cu2ϩ, and Cd2ϩ quench the fluorescence intensity of the
free receptor over a wide pH range. In contrast, Pb2ϩ and
2؉
different response with the fluorescence of the Ru(tpy)2
core being enhanced by large metal ions and quenched by
smaller ones. A linear response between emission intensity
and cation size was found for this metallo receptor.
Experimental Section
General Remarks: [Ru(mtpy)Cl3][22] and 4Ј-[4-(bromomethyl)-
phenyl]-2,2Ј:6Ј,2ЈЈ-terpyridine (Br-mphtpy)[18] were prepared ac-
cording to the published methods; all other reagents were obtained
from commercial sources and were used as received.
Preparations
Synthesis of L1 and L3: A solution of 4Ј-[4-(bromomethyl)phenyl]-
2,2Ј:6Ј,2ЈЈ-terpyridine (Br-mphtpy) (200 mg, 0.5 mmol) in CH2Cl2
(20 mL) was added dropwise to a solution of 4,10-diaza-15-crown-
5 (545 mg, 2.5 mmol) in order to obtain L1, or to a solution of 1-
aza-12-crown-4 (438 mg, 2.5 mmol) in CH2Cl2 (20 mL) in order to
afford L3. The respective solutions were treated with 5 drops of
Et3N and then heated at 30 °C for 24 h. Each reaction mixture was
washed with water (3 ϫ 3 mL). The organic phases were dried with
MgSO4 and concentrated under reduced pressure. The residues
Figure 3. Relative fluorescence at pH 7.5 found for the interaction
of Ni2ϩ, Cu2ϩ
, ,
Cd2ϩ Hg2ϩ, and Pb2ϩ ions with [Ru(L4)-
(mtpy)][PF6]2 as a function of the cationic radius
1480
Eur. J. Inorg. Chem. 2001, 1475Ϫ1482

Fluorescent Chemosensors for Heavy Metal Ions
were purified by column chromatography on alumina using 7.70Ϫ7.80 (2 H, tpy 4-,4ЈЈ-H and 2 H, Ph), 8.55Ϫ8.60 (2 H, tpy
FULL PAPER
CH2Cl2/CH3OH (99:1, v/v) as the eluent. A yellow oil was ob-
tained, which solidified on keeping the flask under reduced pres-
sure. Yields: 81 mg, 30% for L1; 87 mg, 35% for L3.
6-,6ЈЈ-H), 8.65Ϫ8.70 (2 H, tpy 3-,3ЈЈ-H and 2 H, tpy 3Ј-,5Ј-H). Ϫ 13C
NMR (CDCl3): δ ϭ 48.8 (CH2), 56.3 (CH2), 60.1 (CH2), 68.5Ϫ71.0
(CH2), 118.7 (CH, tpy), 121.2 (CH, tpy), 123.8 (CH, tpy), 127.2
(CH, tolyl), 129.4 (CH, tolyl), 148.9 (CH, tpy), 155.8 (C, tpy), 156.3
(C, tpy). Ϫ C32H40N8 (536.7): found C 71.2, H 7.8, N 20.8; L4
requires C 71.6, H 7.5, N 20.9. Ϫ FAB MS: m/z (%) ϭ 537 (100),
323 (100), 281 (35), 237 (35).
L1: 1H NMR (300 MHz, CDCl3): δ ϭ 2.4 (1 H, NH), 2.70Ϫ2.85
(8 H, CH2N), 3.5Ϫ3.7 (12 H, CH2O and 2 H, CH2Ph), 7.28Ϫ7.32
(2 H, tpy 5-,5ЈЈ-H), 7.42Ϫ7.48 (2 H, Ph), 7.75Ϫ7.85 (2 H, tpy
4-,4ЈЈ-H and 2 H, Ph), 8.55Ϫ8.60 (2 H, tpy 6-,6ЈЈ-H), 8.65Ϫ8.70 (2
H, tpy 3-,3ЈЈ-H and 2 H, tpy 3Ј-,5Ј-H). Ϫ 13C NMR (CDCl3): δ ϭ
Synthesis of [Ru(L1)(mtpy)][PF6]2, [Ru(L3)(mtpy)][PF6]2, and
48.8 (CH2), 54.3 (CH2), 60.1 (CH2), 69.0Ϫ71.0 (CH2), 118.8 (CH, [Ru(L4)(mtpy)][PF6]2: These ruthenium complexes were all pre-
tpy), 121.3 (CH, tpy), 123.8 (CH, tpy), 127.2 (CH, tolyl), 129.4 pared in the same way. A mixture of the appropriate ligand (L1
(CH, tolyl), 149.1 (CH, tpy), 155.9 (C, tpy), 156.1 (C, tpy). Ϫ 108 mg, L3 99.4 mg, L4 107 mg; 0.2 mmol), [Ru(mtpy)Cl3] (90 mg,
C32H37N5O3·CH2Cl2 (624.6): found C 64.0, H 6.0, N 10.8; L1 re-
quires C 63.5, H 6.2, N 11.2. Ϫ FAB MS: m/z (%) ϭ 540 (60), 461
(35), 401 (30), 327 (65), 281 (50), 221 (55).
0.2 mmol), and 3 drops of N-ethylmorpholine, as a mild reductant,
in MeOH (20 mL) was heated to reflux under stirring for 1 h. The
resulting deep-red solution was then filtered through Celite to re-
move any unchanged [Ru(mtpy)Cl3]. Further purification was ac-
complished by chromatography on silica using acetonitrile/water/
satd. aq. KNO3 solution (17:2:1) as the eluent. The complexes were
isolated as their hexafluorophosphate salts.
L3: 1H NMR (300 MHz, CDCl3): δ ϭ 2.8 (4 H, CH2N), 3.65Ϫ3.75
(12 H, CH2O and 2 H, CH2Ph), 7.33Ϫ7.36 (2 H, tpy 5-,5ЈЈ-H),
7.52Ϫ7.54 (2 H, Ph), 7.85Ϫ7.87 (2 H, tpy 4-,4ЈЈ-H and 2 H, Ph),
8.69Ϫ8.72 (2 H, tpy 6-,6ЈЈ-H), 8.72Ϫ8.73 (2 H, tpy 3-,3ЈЈ-H), 8.74
(s, 2 H, tpy 3Ј-,5Ј-H). Ϫ 13C NMR (CDCl3): δ ϭ 54.9 (CH2), 60.6 [Ru(L1)(mtpy)][PF6]2: Yield 48 mg, 20%. Ϫ 1H NMR (300 MHz,
(CH2), 70.2 (CH2), 70.5 (CH2), 71.3 (CH2), 119.7 (CH, tpy), 121.3 CD3CN): δ ϭ 2.98 (s, 3 H, CH3), 3.3Ϫ3.4 (4 H, CH2N), 3.60Ϫ3.65
(CH, tpy), 123.7 (CH, tpy), 127.1 (CH, tolyl), 129.5 (CH, tolyl),
(4 H, CH2N), 3.7Ϫ3.9 (12 H, CH2O and 2 H, CH2Ph), 7.15Ϫ7.20
136.8 (CH, tpy), 149.1 (CH, tpy), 150.7 (C, tolyl), 155.8 (C, tpy), (4 H, tpy 5-,5ЈЈ-H1,2), 7.40Ϫ7.45 (4 H, tpy 6-,6ЈЈ-H1,2), 7.90Ϫ8.00
156.1 (C, tpy). Ϫ C30H32N4O3·CH2Cl2 (581.5): found C 65.0, H
6.0, N 9.8; L3 requires C 64.0, H 5.8, N 9.6. Ϫ FAB MS: m/z (%) ϭ
497 (100), 322 (45), 193 (15).
(2 H, Ph and 2 H, tpy 4-,4ЈЈ-H1,2), 8.30Ϫ8.32 (2 H, Ph), 8.48Ϫ8.50
(2 H, tpy 3-,3ЈЈ-H1), 8.68Ϫ8.70 (2 H, tpy 3-,3ЈЈ-H2), 8.70 (s, 2 H,
tpy 3Ј-,5Ј-H1), 9.08 (s, 2 H, tpy 3Ј-,5Ј-H2); 1 ϭ mtpy; 2 ϭ Phtpy.
Ϫ C48H50F12N8O3P2Ru·CH2Cl2 (1262.5): found C 45.9, H 3.8, N
9.3; [Ru(L1)(mtpy)][PF6]2 requires C 46.4, H 4.1, N 8.8. Ϫ FAB
MS: m/z (%) ϭ 1177 (25), 1033 (65), 887 (100), 671 (10).
Synthesis of L2:
A solution of 4Ј-[4-(bromomethyl)phenyl]-
2,2Ј:6Ј.2ЈЈ-terpyridine (Br-mphtpy) (200 mg, 0.5 mmol) in CH2Cl2
(20 mL) was added dropwise to a solution of 4,10-diaza-15-crown-
5 (54.5 mg, 0.25 mmol) in CH2Cl2 (20 mL). The resulting mixture
was treated with 5 drops of Et3N and then heated at 30 °C for 24 h.
[Ru(L3)(mtpy)][PF6]2: Yield 45 mg, 20%. Ϫ 1H NMR (300 MHz,
CD3CN): δ ϭ 2.97 (s, 3 H, CH3), 3.5 (4 H, CH2N), 3.7Ϫ3.8 (8 H,
It was subsequently washed with water (3 ϫ 3 mL). The organic CH2O), 3.95Ϫ4.0 (4 H, CH2O), 4.52 (2 H, CH2Ph), 7.15Ϫ7.25 (4
phase was dried with MgSO4 and concentrated under reduced pres-
sure. The residue was purified by column chromatography on alu-
mina using CH2Cl2/CH3OH (99:1, v/v) as the eluent. A yellow oil
was obtained, which solidified on keeping the flask under reduced
pressure. Yield: 63 mg, 30%.
H, tpy 5-,5ЈЈ-H1,2), 7.40Ϫ7.45 (4 H, tpy 6-,6ЈЈ-H1,2), 7.84 (2 H, Ph),
7.95 (4 H, tpy 4-,4ЈЈ-H1,2), 8.3 (2 H, Ph), 8.46Ϫ8.48 (2 H, tpy
3-,3ЈЈ-H2), 8.66Ϫ8.68 (2 H, tpy 3-,3ЈЈ-H1), 8.71 (s, 2 H, tpy 3Ј-,5Ј-
H2), 9.01 (s, 2 H, tpy 3Ј-,5Ј-H1); 1 ϭ mtpy; 2 ϭ Phtpy. Ϫ
C46H45F12N7O3P2Ru·2H2O (1170.9): found C 47.3, H 3.9, N 8.3;
[Ru(L3)(mtpy)][PF6]2 requires C 47.2, H 4.2, N 8.4. Ϫ FAB MS:
m/z (%) ϭ 1135 (20), 990 (55), 845 (100), 671 (10).
L2: 1H NMR (300 MHz, CDCl3): δ ϭ 2.7Ϫ2.85 (8 H, CH2N),
3.40Ϫ3.70 (12 H, CH2O), 4.5 (4 H, CH2Ph), 7.2Ϫ7.3 (4 H, tpy
5-,5ЈЈ-H), 7.38Ϫ7.44 (4 H, Ph), 7.80Ϫ7.90 (4 H, tpy 4-,4ЈЈ-H and 4 [Ru(L4)(mtpy)][PF6]2: Yield 52 mg, 20%. Ϫ 1H NMR (300 MHz,
H, Ph), 8.60Ϫ8.62 (2 H, tpy 6-,6ЈЈ-H), 8.66Ϫ8.72 (4 H, tpy 3-,3ЈЈ-
CD3CN): δ ϭ 2.8Ϫ3.2 (20 H, CH2), 2.98 (s, 3 H, CH3), 3.95 (2 H,
H and 4 H, tpy 3Ј-,5Ј-H). Ϫ 13C NMR (CDCl3): δ ϭ 54.4 (CH2), CH2Ph), 7.15Ϫ7.20 (4 H, tpy 5-,5ЈЈ-H1,2), 7.40Ϫ7.45 (4 H, tpy
60.1 (CH2), 69.5 (CH2), 70.7 (CH2), 118.1 (CH, tpy), 121.3 (CH,
tpy), 123.8 (CH, tpy), 127.1 (CH, tolyl), 129.4 (CH, tolyl), 136.8
(CH, tpy), 149.1 (CH, tpy), 155.9 (C, tpy), 156.1 (C, tpy). Ϫ
C54H52N8O3·CH2Cl2 (946.0): found C 69.0, H 6.0, N 10.8; L2 re-
quires C 69.8, H 5.7, N 11.8. Ϫ FAB MS: m/z (%) ϭ 861 (40), 322
(90), 281 (45), 207 (60).
6-,6ЈЈ-H1,2), 7.70Ϫ7.72 (2 H, Ph2), 7.9Ϫ7.94 (4 H, tpy 4-,4ЈЈ-H1,2),
8.25Ϫ8.28 (2 H, Ph), 8.50Ϫ8.52 (2 H, tpy 3-,3ЈЈ-H1), 8.68Ϫ8.70 (2
H, tpy 3-,3ЈЈ-H2), 8.70 (s, 2 H, tpy 3Ј-,5Ј-H1), 9.08 (s, 2 H, tpy
3Ј-,5Ј-H2); 1 ϭ mtpy; 2 ϭ Phtpy. Ϫ C48H50F12N8O3P2Ru·2H2O
(1214.0): found C 54.5, H 5.5, N 14.8; [Ru(L4)(mtpy)][PF6]2 re-
quires C 54.0, H 5.3, N 14.5. Ϫ FAB MS: m/z (%) ϭ 1174 (20),
1030 (30), 885 (40), 670 (65).
Synthesis of L4:
A solution of 4Ј-[4-(bromomethyl)phenyl]-
2,2Ј:6Ј,2ЈЈ-terpyridine (Br-mphtpy) (200 mg, 0.5 mmol) in CH2Cl2 Synthesis of [Ru(L3)2][PF6]2: The homoleptic ruthenium complex
(20 mL) was added dropwise to a solution of 1,4,7,10,13-pentaaza-
cyclopentadecane (500 mg, 2.5 mmol). The resulting mixture was
treated with 5 drops of Et3N and then heated at 30 °C for 24 h. It
was subsequently washed with water (3 ϫ 3 mL). The organic
phase was dried with MgSO4 and concentrated under reduced pres-
sure. The residue was purified by column chromatography on alu-
mina using CH2Cl2/CH3OH (99:1, v/v) as the eluent. A yellow oil
was obtained, which solidified on keeping the flask under reduced
pressure. Yield: 120 mg, 50%.
of L3 was prepared by reacting L3 (200 mg, 0.4 mmol) with
RuCl33H2O (52.3 mg, 0.2 mmol), in the presence of 3 drops of N-
ethylmorpholine as a mild reductant, in MeOH (20 mL). The mix-
ture was heated to reflux under stirring for 2 h. The resulting deep-
red solution was filtered through Celite to remove any unchanged
RuCl3. Further purification was accomplished by chromatography
on silica using acetonitrile/water/satd. aq. KNO3 solution (17:2:1)
as the eluent. The complex was isolated as its hexafluorophos-
phate salt.
L4: 1H NMR (300 MHz, CDCl3): δ ϭ 2.5Ϫ2.9 (20 H, CH2), 3.6 (2 [Ru(L3)2][PF6]2: Yield 28 mg, 19%.
Ϫ
1H NMR (300 MHz,
H, CH2Ph), 7.25Ϫ7.28 (2 H, tpy 5-,5ЈЈ-H), 7.40Ϫ7.42 (2 H, Ph), CD3CN): δ ϭ 3.5Ϫ3.6 (8 H, CH2N), 3.6Ϫ4.1 (12 H, CH2O), 4.55
Eur. J. Inorg. Chem. 2001, 1475Ϫ1482
1481

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R. Martınez-Man˜ez et al.
FULL PAPER
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[11]
[12]
´
´
M. E. Padilla-Tosta, J. M. Lloris, R. Martınez-Man˜ez, A. Be-
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experimental points, corresponding to at least three titration
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centrations ca. 1.0·10Ϫ3 mol dmϪ3) could be treated either as a
single set or as separate entities without significant variation in the
values of the stability constants. Finally, the sets of data were
merged together and treated simultaneously to give the quoted
stability constants.
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Acknowledgments
We would like to thank the DGICYT (proyecto PB98-1430-C02-
02, 1FD97-0508-C03-01, and AMB99-0504-C02-01) for support.
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