Dyes that bear thiazolylazo groups as chromogenic chemosensors for metal cations

Article abstract of DOI:10.1002/ejic.201100834

A family of dyes (L¹-L⁶) that contain a thiazolylazo group as signalling subunit and several macrocyclic cavities with different ring sizes and type and number of heteroatoms as binding sites has been synthesized and characterized. Solutions of L¹-L⁶ in acetonitrile show broad and structureless absorption bands in the 554-577 nm range with typicalmolar absorption coefficients that range from 20000 to 32000 M ^-1 cm^-1. A detailed protonation study was carried out with solutions of L¹, L² and L⁵ in acetonitrile. Addition of one equivalent of protons to L¹ and L² resulted in the development of a new band at 425 and 370 nm, respectively, which was ascribed to protonation in the aniline nitrogen. In contrast, protonation of L⁵ resulted in a bathochromic shift of 25 nm of the absorption band that was conceivable with protonation of one of the nitrogen atoms of the azo moiety. These results were in agreement with ¹H NMR spectroscopic data. Theoretical studies on the model ligand L¹ and on different possible protonation species were also performed by using density functional theory (DFT) quantum mechanical calculations. Colour modulations in solutions of L¹-L⁶ in acetonitrile in the presence of the metal cations Fe³⁺, Ni²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and Hg²⁺ have been studied. A selective chromogenic response of L⁴ in the presence of Pb²⁺ and L⁵ in the presence of Hg²⁺ was observed. To get a better insight into the chromophoric nature in the presence of metal cations, the interaction of Hg²⁺ with the model compound L¹ in two different coordination modes was studied theoretically by using density functional theory (DFT) quantum mechanical calculations.

Full text of DOI:10.1002/ejic.201100834

FULL PAPER
DOI: 10.1002/ejic.201100834
Dyes That Bear Thiazolylazo Groups as Chromogenic Chemosensors for Metal
Cations
Tatiana Ábalos,[a,b,c] María Moragues,[a,b,c] Santiago Royo,[a,b,c] Diego Jiménez,[b]
Ramón Martínez-Máñez,*[a,b,c] Juan Soto,[a,b] Félix Sancenón,[a,b,c] Salvador Gil,[a,d] and
Joan Cano[e,f]
Keywords: Chemosensors / Cation sensors / Lead / Mercury / Density functional calculations / Dyes / Azodyes
1
A family of dyes (L1–L6) that contain a thiazolylazo group as
signalling subunit and several macrocyclic cavities with dif-
ferent ring sizes and type and number of heteroatoms as
binding sites has been synthesized and characterized. Solu-
tions of L1–L6 in acetonitrile show broad and structureless
absorption bands in the 554–577 nm range with typical
molar absorption coefficients that range from 20000 to
results were in agreement with H NMR spectroscopic data.
Theoretical studies on the model ligand L1 and on different
possible protonation species were also performed by using
density functional theory (DFT) quantum mechanical calcu-
lations. Colour modulations in solutions of L1–L6 in acetoni-
trile in the presence of the metal cations Fe3+, Ni2+, Zn2+
,
Cd2+, Pb2+ and Hg2+ have been studied. A selective chromo-
genic response of L4 in the presence of Pb2+ and L5 in the
presence of Hg2+ was observed. To get a better insight into
32000
M
–1 cm–1. A detailed protonation study was carried out
with solutions of L1, L2 and L5 in acetonitrile. Addition of one
equivalent of protons to L1 and L2 resulted in the develop- the chromophoric nature in the presence of metal cations,
ment of a new band at 425 and 370 nm, respectively, which
was ascribed to protonation in the aniline nitrogen. In con-
trast, protonation of L5 resulted in a bathochromic shift of
25 nm of the absorption band that was conceivable with pro-
tonation of one of the nitrogen atoms of the azo moiety. These
the interaction of Hg2+ with the model compound L1 in two
different coordination modes was studied theoretically by
using density functional theory (DFT) quantum mechanical
calculations.
ally those receptors are composed by two subunits, namely,
the binding site and the signalling unit that are coupled
through a covalent bond.[3] The binding sites are designed
to achieve a great complementarity with the target metal
cation and usually have a crown ether nature.[4] Macrocyclic
cavities with different sizes and shapes have been synthe-
sized and employed as binding sites.[5] Selectivity toward
certain metal cations can be achieved by varying the size
and the number and type of the heteroatoms on the macro-
cyclic cavity. In this respect, hard cations coordinate well
with hard donor atoms such as oxygen, whereas selectivity
toward soft cations can be achieved by the use of soft donor
atoms in the binding site. Additionally, and to obtain a vis-
ual response upon cation binding, one of the heteroatoms
of the macrocyclic cavity should be included in the elec-
tronic structure of the dye.
Among organic dyes used as signalling subunits in the
development of chromogenic receptors,[6] azo dyes have
been widely used due to their simple synthesis and their
well-known spectroscopic properties.[7] Reaction between
N,N-disubstituted anilines and diazonium salts of a great
variety of aniline derivatives leads to azo dyes with charac-
teristic charge-transfer absorption bands in the 430–480 nm
interval and colours that range from light yellow to red-
orange. By changing aniline derivatives to 2-aminothiazole
Introduction
Since the discovery of crown ethers by Pedersen in the
early sixties, a huge amount of work that deals with the
synthesis of selective receptors for positively charged species
has been carried out.[1] In these first stages, the interaction
between abiotic receptors and the target cationic species
was studied by means of potentiometric and NMR spectro-
scopic measurements. An important improvement in the
field was introduced by Vögtle et al. in 1978 with the syn-
thesis of the first chromogenic receptors for cations.[2] Usu-
[a] Centro de Reconocimiento Molecular y Desarrollo Tecnológico
(IDM), Unidad Mixta Universidad Politécnica de Valencia,
Universidad de Valencia, Spain
E-mail: rmaez@qim.upv.es
[b] Departamento de Química, Universidad Politécnica de
Valencia,
Camino de Vera s/n, 46022, Valencia, Spain
[c] CIBER de Bioingeniería, Biomateriales
(CIBER-BBN)
y Nanomedicina
[d] Departamento de Química Orgánica, Facultad de Ciencias
Químicas, Universitat de Valencia,
46100 Burjassot, Valencia, Spain
[e] Instituto de Ciencia Molecular (ICMol),
c/ Catedrático José Beltrán no. 2,
46980 Paterna (Valencia), Spain
[f] Fundació General de la Universitat de València (FGUV)
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100834.
76
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Chromogenic Cation Sensors
and 2-aminobenzothiazole, a series of thiazolylazo dyes Receptor L1 has been used by several groups and its UV/
with absorption bands shifted to the 480–650 nm interval Vis behaviour extensively studied,[14] whereas L3 was syn-
can be obtained (with colours that range from orange to thesized by Dix and Vögtle who studied how the coordina-
deep blue). Some thiazolylazo dyes have been reported to tion of alkaline and alkaline-earth cations modified the
1
form coloured chelates with a great variety of transition- electronic levels of the dye.[12] The H NMR spectrum of
metal cations (Fe3+, Hg2+, Ni2+, Cu2+, Zn2+, Co2+, Mn2+
,
receptors L2–L6 shows protons of the macrocyclic unit in
Pd2+ and Cd2+) through interaction with nitrogen atoms the δ = 2.6 to 3.8 ppm range with two clearly defined zones
from the thiazole and azo moieties and with oxygen atoms for methylene protons adjacent to sulfur atoms (δ = 2.6–
usually presented in benzene rings.[8] Several thiazolylazo 2.9 ppm) and methylene protons adjacent to nitrogen or
dyes have been used for the remediation of the environmen- oxygen atoms (δ = 3.5–3.8 ppm). The thiazolylazo moieties
tally pollutant Hg2+ and Co2+ cations.[9] The use of these in L1–L6 show two doublets centred at δ ≈ 6.8 and 7.9 ppm
azo dyes has also been reported in capillary electrophoresis and a singlet at δ ≈ 8.6 nm that corresponds to the 1,4-
separations of Co2+, Ni2+, Zn2+ and Fe2+ and as masking disubstituted benzene and 2,5-disubstituted thiazole ring,
agents in several analytical determinations.[10] Nevertheless, respectively.
thiazolylazo dyes have barely been used as signalling sub-
units in the development of cation receptors based on sup-
ramolecular chemistry concepts.
Following our interest in the design of electrochemical
and chromo-fluorogenic probes for target guests,[11] herein
we report the synthesis, coordination and chromogenic
properties in the presence of metal cations of six receptors
that contain a thiazolylazo group as signalling subunit and
several macrocyclic cavities with different sizes and numbers
and types of heteroatoms as binding sites. Of the six recep-
tors presented here, four (L2, L4–L6) are described for the
first time; L1 was used as model because of the lack of
macrocyclic subunit and L3 was synthesized in 1978 by Dix
and Vögtle, who studied its coordination behaviour toward
alkaline and alkaline-earth cations.[12] To get a complete
understanding of the chromogenic behaviour of this family
of thiazolylazo dyes, different possible protonations on L1
and different coordination modes with Hg2+ have also been
studied theoretically using density functional theory (DFT)
quantum mechanical calculations.
Results and Discussion
Scheme 1. Synthesis and chemical structure of receptors L1–L6.
Receptors L1–L6 were synthesized (see Scheme 1) by di-
azotization reaction between the diazonium salt of 2-
amino-5-nitrothiazole and N,N-dimethylaniline (to obtain
L1) or the corresponding 4-(N-crown)phenyl derivatives (to
1
UV/Vis and H NMR Spectroscopic Behaviour upon
obtain L2–L6). The ligands L2–L6 carry different macro-
Coordination with Protons
cycles that vary in both the ring size and the type and
number of heteroatoms. The 4-(N-crown)phenyl macro-
As stated above, receptors L1–L6 contain an aniline-type
cycles, which contain oxygen and nitrogen atoms, were syn- donor moiety attached through an azo linker with an ac-
thesized by the Richman–Atkins procedure in which N,N- ceptor 5-nitrothiazole heterocycle, exhibiting π-electron de-
phenyldiethanolamine was deprotonated with sodium hy- localization over the entire chromophoric system. As a con-
dride followed by treatment under high dilution conditions sequence, L1–L6 receptors showed an intramolecular
with methanesulfonyl ester derivatives of the corresponding charge-transfer band (vide infra) typical of such donor–ac-
polyethylene glycol.[13] The macrocycles that contained sul- ceptor-substituted dyes. These lowest-energy absorption
fur atoms, which were used to obtain receptors L5 and L6, bands are broad and structureless and centred at around
were synthesised by a modified procedure in which 3,6-di- 575 nm in acetonitrile. Typical molar absorption coeffi-
oxaoctane-1,8-dithiol and 3,6-dithiaoctane-1,8-diol were cients range from 20000 to 32000 m–1 cm–1 (see Table 1).
deprotonated with potassium carbonate and sodium hy- The subtle differences in the optical properties of the dif-
dride, respectively, followed by treatment with the meth- ferent dyes are imposed by the variations in the substituents
anesulfonyl ester of N,N-phenyldiethanolamine. The syn- on the aniline group. In fact, it has been reported that the
thesis of the receptors L1 and L3 was previously published. presence of other heteroatoms in the crown unit attached
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R. Martínez-Máñez et al.
FULL PAPER
to the aniline moiety can have an effect in the electronic and the singlet of the proton located in the nitrothiazole
properties of the chromophore through an influence in the ring was shifted from δ = 8.83 to 8.67 ppm. These upfield
electron-donor capacity of the aniline moiety.[15]
shifts could be ascribed to a second protonation process in
one of the nitrogen atoms of the azo moiety. The fact that
larger amounts of protons were required to protonante the
azo group is indicative of its lower basicity than the aniline
nitrogen.
Table 1. Absorption maxima and molar absorption coefficients of
L1–L6.
L1
L2
L3
L4
L5
L6
Receptor L2 contains a macrocyclic subunit with three
oxygen and one nitrogen atoms. Upon addition of increas-
ing amounts of protons to solutions of L2 in acetonitrile,
λmax [nm]
577
574
575
574
575
554
ε [m–1 cm–1] 21400 29000 24400 23000 31600 20000
Ligands L1–L6 can act as polibases due to the presence the charge-transfer band at 574 nm suffered a hypochromic
in their structure of several nitrogen atoms that could, in shift in a progressive fashion and at the same time a new
principle, be protonated. However, a closer look into the absorption band at 370 nm appeared. This significant hyp-
reported basicity of these nitrogen atoms indicates that sochromic shift of 204 nm was ascribed to protonation of
most likely the protonation of the thiazole nitrogen is hin- the aniline nitrogen atom that is embedded in the crown
dered because this is a poorly basic group that shows pro- subunit. Additionally, the presence of a clear isosbestic
tonation constants in the range –1.50 to 0.60.[16] In con- point at 430 nm strongly suggested that protonation only
trast, the reported protonation constants of azo dyes that takes place at the aniline nitrogen in L2. This preferential
bear the thiazole rings are in the range 1.80–2.80 in water protonation at the aniline moiety is due to favourable hy-
and in organic solvents,[17] whereas the protonation con- drogen-bonding interactions between the protonated nitro-
stant for aniline is 4.65 (in water).[18] These results suggest gen atom and the oxygen atoms of the crown cavity and it
that protonation will take most likely in the aniline and/or has been already reported in other dyes that also contain
azo groups. The effect that the secondary heteroatoms on this macrocycle.[15] This stabilization of the protonated spe-
the macrocycle can have in relation to the protonation be- cies by hydrogen bonding is reflected in the distinctly higher
haviour is an additional issue related with the protonation logarithm of the constant found for the protonation process
of these compounds. In a recent report we observed that that amounts to 6.88Ϯ0.05 for receptor L2 (obtained from
1
different sizes and types of atoms in aniline crowns can least-square treatment of the titration profiles). H NMR
modulate the basicity of the aniline nitrogen.[19] Addition- spectroscopic experiments with L2 in the presence of in-
ally, protonation studies might clarify the coordination creasing quantities of protons were also carried out and
preferences of this family of receptors toward transition- confirmed the UV/Vis results.
metal cations (vide infra).
In contrast, receptor L5 shows a completely different be-
A detailed protonation study was carried out with com- haviour. In this case, the charge-transfer band centred at
pounds L1, L2 and L5 in acetonitrile solutions. The addition 575 nm suffered a hyper- and bathochromic shift of 25 nm
of protons (up to 1 equiv.) to solutions of L1 led to a re- upon addition of protons. This shift is conceivable with pro-
duction in intensity of the band at 577 nm and the develop- tonation of the azo unit. Additionally, the presence of two
ment of a new band at 425 nm. When higher acid concen- isosbestic points at 565 and 510 nm indicated that only one
trations were employed, an additional bathochromic shift protonation occurs. In L5 the two bulky S atoms in the
(around 10 nm) of the band centred at 577 nm occurred. neighbourhood of the aniline nitrogen effectively shield the
These observed shifts and the fact that no clear isosbestic N atom from protonation and therefore only the nitrogen
points were observed in the course of the titration pointed atom of the azo moiety was able to interact with protons.
toward the presence of two protonation equilibria for recep- From the titration curves, and by least-squares treatment of
tor L1. The initial hypsochromic shift was assigned to a the profiles, a value of the logarithm of the protonation
preferential protonation in the aniline nitrogen that de- constant of 3.03Ϯ0.01 was obtained for the protonation of
creases its donor strength, whereas the second batho- L5. The protonation site in receptor L5 was also confirmed
1
chromic shift is conceivable with protonation of one of the by H NMR spectroscopic titration experiments in deuter-
nitrogen atoms of the azo moiety. From the titration curves ated acetonitrile. Upon addition of an excess amount of
values of logarithms of 4.77Ϯ0.04 and 3.01Ϯ0.03 were ob- protons, the signals of the macrocyclic subunit located in
tained for these protonation processes.[20]
the 2.50–3.70 interval remained unaltered, whereas the aro-
To confirm the protonation sites, 1H NMR spectroscopic matic signals suffered remarkable shifts. For instance, an
titration experiments with L1 in deuterated acetonitrile were upfield shift from δ = 8.81 to 8.70 ppm was observed for
carried out. The most significant and remarkable change the proton of the nitrothiazole ring.
detected upon addition of one equivalent of protons was
To get a better insight into the chromophoric nature of
observed for the methyl signal that was shifted from δ = the title dyes, the model compound L1 was studied theore-
3.20 to 4.56 ppm. This downfield shift strongly suggests a tically by using density functional theory (DFT) calcula-
quaternization of the aniline nitrogen atom due to proton- tions with the Gaussian 09 package (see the Experimental
ation. In the presence of an excess amount of protons, the Section for details). Energies and oscillator strengths of the
aromatic doublets at δ = 7.89 and 7.02 ppm from the 1,4- electronic transitions were obtained from calculations based
disubstituted benzene ring shifted to δ = 7.71 and 6.97 ppm on the time-dependent (TD) formalism. In the most stable
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Chromogenic Cation Sensors
trans conformation of the azo group, TD calculations pre- UV/Vis Behaviour Upon Coordination with Metal Cations
dicted for L1 the existence of an electronic absorption at
The behaviour observed in the presence of different
562 nm that corresponded to the more intense electronic
excitation observed. This result is in a good agreement with
the experimental data (577 nm). This electronic transition
metal cations (vide infra) for solutions of L1–L6 in acetoni-
trile can be rationalized in a similar fashion to that de-
scribed above for protonation processes. The ILCT transi-
involves an electron transfer from the HOMO to the
tion at approximately 575 nm will be shifted to around
LUMO orbitals (see Figure 1), which entails a π-intraligand
600 nm when the cation is coordinated to the azo group,
charge transfer (ILCT) that moves electronic density from
thereby strengthening its acceptor character. On the con-
the phenylamino group to the thiazole fragment (see Fig-
trary, coordination at the aniline nitrogen would result in a
ure 1).
hypsochromic shift. Studies of metal coordination were car-
ried out with ligands L1–L6 in acetonitrile, and three dif-
ferent behaviours were observed (i.e., selective coordination
at the aniline, selective coordination at the azo moiety and
no coordination). The possible coordination modes and the
expected colorimetric behaviour are summarized in
Figure 1. Frontier MOs for L1 compound as obtained from the
DFT quantum chemical calculations.
Scheme 2.
As we have seen before in the spectroscopic studies that
involve protons, from the point of view of chemical ad-
dressability, ligand L1 possesses four potential protonation
sites (i.e., the aniline nitrogen, the two nitrogen atoms from
the azo moiety and the thiazole ring). Additionally, to get
a better understanding of the protonation behaviour, dif-
ferent possible protonations on L1 were studied theoretic-
ally by using DFT calculations, and the energies of the elec-
tronic transitions obtained from the TD formalism were
compared with the position of the absorption bands found
experimentally. Table 2 shows the theoretical energies (λ, in
nm) for the ILCT transition associated with the L1 ligand
and the corresponding protonated molecules. In the table,
species L1, L1 , L1 , L1 and L1 correspond to species pro-
Scheme 2. Coordination modes and colorimetric behaviour of re-
ceptors L1–L6 in the presence of metal cations.
Upon addition of equimolar quantities of Cd2+, Ni2+
,
Pb2+ and Zn2+ cations to a solution of L1 in acetonitrile,
negligible changes in the UV/Vis spectrum profile were ob-
served (see Figure 2), thereby indicating that very weak or
no interaction of those cations with receptor L1 occurs. In
contrast, the addition of equimolar quantities of Hg2+ in-
duced the charge-transfer band at 560 nm to be shifted to
612 nm and the appearance of a broad shoulder at 580 nm,
which suggests a coordination of this metal cation with the
azo-thiazole moiety. On the other hand, the presence of
Fe3+ induced a blueshift of the absorption band of L1 from
1
2
3
4
tonated in nitrogen atoms 1, 2, 3 and 4, respectively (see
Scheme 1).
Table 2. Theoretical energies (λ, in nm) for the ILCT electronic
transition for L1 ligand, the corresponding protonated molecules
and two mercury(II) complexes (see text).
1
1
1
1
L1
L1
409
L2
572
L3
477
L4
510
Hg(L1)-1 Hg(L1)-2
613 407
λmax [nm] 567
When comparing the computational results with the ex- 575 to 563 nm and the apparition of a new band at 485 nm.
perimental spectrum, the absorption bands at 425 and 370 This behaviour suggested an interaction of this cation with
for the protonated derivatives of receptors L1 and L2, the nitrogen of the aniline group. Those observed shifts
respectively, are in agreement with protonation at the ani- were reflected in the colour of the L1 solutions that modu-
line for which a theoretical value of 409 nm for the elec- lated from dark violet to blue and red-magenta for Hg2+
tronic transition of lower energy was predicted for L1. and Fe3+, respectively. Upon the addition of increasing
Other predicted protonations at N3 and N4 suggested lower quantities of Hg2+ cation to solutions of L1 in acetonitrile,
hypsochromic shifts that were not in agreement with the clear isosbestic points were found that suggested the forma-
observed behaviour. Additionally, from the theoretical stud- tion of 1:1 complexes. Monitoring the changes at 610 nm
ies, protonation at N2 is the only protonated species that is upon Hg2+ addition, and through nonlinear least-square
predicted to induce a bathochromic shift of the absorption treatment of the titration profile, a logarithm of the stability
band with respect to the unprotonated species (from 567 to constant of 5.51Ϯ0.01 for the formation of the [Hg-
572 nm). This behaviour is in agreement with that observed (L1)]2+ complex was obtained (see Table 3). Analogous ti-
experimentally for L5, which suffered a bathochromic shift tration studies with Fe3+ (monitoring the changes in the
of 25 nm, thus strongly suggesting that the protonation in band at 575 nm) were carried out. In this case the complex
the azo group occurs in the nitrogen that is bonded to the stability constant logK for the formation of the complex
aniline moiety.
[Fe(L1)]3+ was determined to be 4.68Ϯ0.02.
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Table 3. Logarithms of the stability constants of receptors L1–L6 with Hg2+ and Pb2+ cations.
L1
L2
L3
L4
L5
L6
Hg2+
Pb2+
5.51Ϯ0.02
4.79Ϯ0.02
5.20Ϯ0.2
5.33Ϯ0.02
6.17Ϯ0.05
7.63Ϯ0.09
4.93Ϯ0.02
–
–
–
–
–
above cases, the redshift observed upon Hg2+ addition is
ascribed to preferential coordination with the thiazolylazo
acceptor moiety.
The hesitant selectivity trend towards Pb2+ found for L3
is fully developed when using L4. This ligand contains the
largest macrocyclic cavity that is able to accommodate a
large cation such as Pb2+ (anionic radius 1.19 Å).[21] In fact,
the addition of equimolar quantities of Pb2+ to solutions of
L4 in acetonitrile induced the apparition of blueshifted
bands at 526 and 430 nm together with an important re-
duction in the absorbance intensity (see Figure 3). This
strongly suggests strong coordination with the lone pair of
the nitrogen atom imbedded in the macrocycle. Least-
squares treatment of the titration profiles allowed us to de-
termine a logarithm of the stability constant of 6.17Ϯ0.05
for the formation of the [Pb(L4)]2+ complex. It has to be
noted that Pb2+ cation does not interact with L1 and L2
receptors. Apart from this distinct response towards Pb2+
cation, the presence of Hg2+ induced a similar behaviour
to that found for receptors L1, L2 and L3. From titration
experiments a logarithm of the stability constant of
5.33Ϯ0.02 for the formation of the [Hg(L4)]2+ complex was
determined.
Figure 2. UV/Vis behaviour of receptor L1 in acetonitrile (C =
5.0ϫ10–5 moldm–3) in the presence of 1 equiv. of certain metal cat-
ions.
The response presented by solutions of L2 upon addition
of equimolar quantities of metal cations was quite similar
to that observed for L1 (i.e., the Hg2+ metal cation coordi-
nated the acceptor moiety and induced the apparition of
two bands at 623 and 590 nm), whereas Fe3+ induced a hy-
pochromic and blueshift from 574 to 568 nm and the devel-
opment of a shoulder at 490 nm. The presence of other cat-
ions (i.e., Ni2+, Zn2+ and Cd2+) induced negligible changes
in the visible spectrum of L2. The presence of isosbestic
points in the titration studies of L2 with Hg2+ suggest the
formation of well-defined 1:1 complexes with logK =
4.79Ϯ0.02 (see Table 3). Fe3+ gave more complicated ti-
tration patterns indicative of the formation of different co-
ordination complexes.
Interestingly, receptors L3 and especially L4 behave dif-
ferently in the sense that the inclusion of large crowns in-
duces a change in selectivity trend when compared with L1.
Receptors L3 and L4 contain one and two more oxygen
atoms and one and two more ethylene bridges than the
macrocycle in L2. For L3, the most significant feature was
a hypochromic effect observed in the presence of Pb2+ that
could be ascribed to a weak interaction with the nitrogen
atom of the macrocyclic moiety. A similar reduction in the
intensity of the absorption band was found for L3 in the
Figure 3. UV/Vis behaviour of receptor L4 in acetonitrile (C =
2.0ϫ10–5 moldm–3) in the presence of 1 equiv. of certain metal cat-
ions.
Remarkably, L5 behaves very differently to L1–L4 and
presence of Fe3+. The lack of isosbestic points and the exis- shows a selective response to Hg2+ due to the presence of
tence of complex titration patterns found for Fe3+ and Pb2+ sulfur atoms in the crown. In fact, several examples of chro-
precluded the determination of the stability constants. Ad- mogenic and fluorogenic receptors functionalized with
dition of Hg2+ to solutions of L3 resulted in similar behav- macrocycles that contain two or more than two S atoms in
iour to that found for L1 and L2 (i.e., the shift of the 575 nm its structure that selectively recognize Hg2+ cations have
absorption band of the ligand to 622 nm and the appear- been described.[22] In particular, the macocycle 6 has been
ance of a new band at 589 nm). From titration studies a reported by us and others to selectively coordinate Hg2+
logarithm of the stability constant of 5.20Ϯ0.2 for the for- over other transition-metal cations.[23] The presence in this
mation of the [Hg(L3)]2+ complex was obtained. As in the macrocycle of two sulfur atoms close to the aniline nitrogen
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Chromogenic Cation Sensors
atom has the ability to strongly shield the site against com- Hg2+ cation with the macrocyclic subunit in L6, poor inter-
plexation with nonthiophilic cations. Solutions of L5 in ace- actions with the lone pair and a poor spectral response.
tonitrile show a charge-transfer band at 575 nm. Addition Neither of the other cations tested induced significant
of equimolar amounts of Hg2+ induced a pronounced blue- changes in the visible spectrum of L6.
shift of the band to 406 nm with a colour change from blue
To get a better insight into the chromophoric nature in
to pale yellow (see Figure 4). This blueshift together with a the presence of metal cations, the interaction of Hg2+ with
high hypochromic effect is indicative of Hg2+ coordination compound L1 in two different coordination modes was
within the macrocyclic subunit. This strong coordination studied theoretically by using DFT quantum mechanical
with the crown was reflected in the high stability constant calculations. As carried out before for protonations, the en-
(logK = 7.63Ϯ0.09) for the formation of [Hg(L5)]2+ com- ergies of the electronic transitions for the different com-
plex calculated from titration profiles. This behaviour is plexes were obtained from calculations based on the time-
clearly different to those shown by receptors L1–L4. The dependent (TD) formalism. As we have seen, the metals
presence of the two S atoms in the macrocycle also induces studied and the protons have a similar electronic effect
a different behaviour in receptor L5 in the presence of the when binding a given ligand. Both metal and protons ac-
Fe3+ in the sense that, in this case, preferential coordination cept electronic density that results in changes in the energies
with the thiazolylazo moiety occurs. This was reflected in a of HOMO and LUMO orbitals, therefore they have direct
slight redshift of the absorption band that was observed consequences on the energy of the ICLT band. In the inter-
upon addition of Fe3+ to solutions of L5. Titration profiles action of the model compound L1 with Hg2+, two coordi-
of receptor L5 with Fe3+ showed clear isosbestic points and nation complexes were studied. In one model the Hg+2 cat-
least-squares treatment of the titration profiles indicated the ion was coordinated by the N2 and N4 atoms of L1,
formation of 1:1 complexes and a logarithm of the stability whereas in the second model the Hg+2 cation coordinated
constant of 4.27Ϯ0.08 for the formation of complex the aniline N1. In the theoretical calculations the remaining
[Fe(L5)]3+ was calculated. As can be seen in Figure 4, recep- positions of the coordination sphere of Hg2+ (tetrahedral
tor L5 acts as a selective chromogenic chemosensor for geometry) were occupied by solvent (acetonitrile) mole-
Hg2+ cation.
cules. TD calculations for the chelation by coordination in
N2 and N4 predict moderate and intense ILCT electronic
transitions at 613 and 576 nm that are very close to those
experimentally observed (610 and 578 nm) for complexes of
Hg2+ with ligands from L1, L2, L3, L4 and L6. Moreover,
TD calculations for the complex with the Hg2+ coordina-
tion at the aniline anticipated the appearance of a band at
407 nm. This result is in very good agreement with that
found for the interaction of Hg2+ with L5 that resulted in
and electronic transition at 406 nm.
Conclusion
In summary, we have prepared and characterized a fam-
ily of dyes (L1–L6) that contain a thiazolylazo group as sig-
nalling subunit and several macrocyclic cavities with dif-
ferent ring sizes and type and number of heteroatoms as
binding sites. Solutions of receptors L1–L6 in acetonitrile
showed absorption bands in the 554–577 nm range with
typical molar absorption coefficients that ranged from
Figure 4. UV/Vis behaviour of receptor L5 in acetonitrile (C =
5.0ϫ10–5 moldm–3) in the presence of 1 equiv. of certain metal cat-
ions.
The change in the position of the S atoms in the macro- 20000 to 32000 m–1 cm–1. In these spectroscopic studies that
cycle between L5 and L6 induced a remarkable change in involved protons, from the point of view of chemical ad-
the coordination behaviour of the latter. In this case, upon dressability, ligands L1–L6 possess four potential proton-
addition of one equivalent of Hg2+, the charge-transfer ation sites (i.e., the aniline nitrogen, the two nitrogen atoms
band at 560 nm was shifted to 570 nm and a broad shoulder from the azo moiety and the thiazole ring). From experi-
1
appeared at 650 nm. Also a band at 375 nm was observed. mental H NMR spectroscopy data and theoretical studies
The presence of these bands at longer and lower wave- carried out using DFT quantum mechanical calculations on
lengths seems to be indicative of the simultaneous forma- the model ligand L1, it was found that hypsochromic shifts
tion of metal–aniline and metal–thiazolylazo complexes, al- were related to protonation at the aniline nitrogen, whereas
though from the intensities of the bands, the formation of bathochromic shifts dealt with coordination at the nitrogen
the thiazolylazo complexes appeared to be predominant. of the azo moiety that is closer to the aniline group. A sim-
The remote position of the sulfur atoms with respect to the ilar behaviour (hypsochromic and bathochromic shifts)
nitrogen in the macrocycle induced, upon coordination of were observed in solutions of L1–L6 in acetonitrile in the
Eur. J. Inorg. Chem. 2012, 76–84
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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81

R. Martínez-Máñez et al.
FULL PAPER
lated as a dark blue solid; yield 60%. 1H NMR (300 MHz, [D6]-
DMSO): δ = 3.20 [s, 6 H, N-(CH3)2], 6.77 (d, 2 H, C6H4), 7.91 (d,
2 H, C6H4), 8.58 (s, 1 H, thiazole) ppm. 13C{1H} NMR (75 MHz,
CDCl3): δ = 40.3, 112.7, 143.1, 143.8, 147.0, 154.2, 181.4 ppm.
HRMS calcd. for C11H11N5O2S 207.0633; found 207.0689.
presence of the metal cations Fe3+, Ni2+, Zn2+, Cd2+, Pb2+
and Hg2+. Additionally, a remarkable selective chromogenic
response for L4 in the presence of Pb2+ and for L5 in the
presence of Hg2+ was observed. Finally, the experimental
chromogenic data found for L1–L6 in the presence of Hg2+
cation was studied more in detail by using DFT calcula-
tions. Two different coordination modes were selected: co-
ordination of the Hg2+ cation with the aniline that induced
a hypsochromic shift and coordination of Hg2+ by two ni-
trogen atoms from the thiazolylazo group that resulted in
a bathochromic shift. The calculations were in very good
agreement with the experimental results.
Synthesis of L2: In a round-bottomed flask, compound 1 (100 mg,
0.69 mmol) was dissolved in a mixture (5 mL) of acetic acid and
water (5:1 v/v). The crude material was cooled with an ice bath.
Then NaNO2 (47.6 mg, 0.69 mmol) dissolved in water (1.5 mL) was
added. After 10 min, macrocycle 3 (158 mg, 0.63 mmol) dissolved
in HCl/water (5:1 v/v, 5 mL) was added dropwise to the crude reac-
tion mixture. Then the crude mixture was allowed to react for
30 min in an ice bath and for 60 min at room temperature. The
crude reaction mixture was extracted with CH2Cl2 and the organic
phase washed with aqueous NaHCO3 solution. The crude reaction
mixture was purified with column chromatography by employing
aluminium oxide as the stationary phase and CH2Cl2/CH3CN (9:1
v/v) as eluent. The final receptor L2 (102.5 mg, 0.25 mmol) was
isolated as a dark blue solid; yield 40%. 1H NMR (300 MHz, [D6]-
DMSO): δ = 3.65 (s, 8 H, O-CH2-O), 3.76 (t, 4 H, N-CH2-O), 3.80
(t, 4 H, O-CH2-O), 6.78 (d, 2 H, C6H4), 7.91 (d, 2 H, C6H4), 8.58
(s, 1 H, thiazole) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 53.5,
70.0, 70.4, 71.3, 112.7, 143.1, 143.8, 147.0, 154.2, 181.4 ppm.
HRMS calcd. for C17H21N5O5S 407.1263; found 407.1275.
Synthesis of L3: In a round-bottomed flask, compound 1 (100 mg,
0.69 mmol) was dissolved in a mixture (5 mL) of acetic acid and
water (5:1 v/v). The crude material was cooled with an ice bath.
Then NaNO2 (47.6 mg, 0.69 mmol) dissolved in water (1.5 mL) was
added. After 10 min, macrocycle 4 (186 mg, 0.63 mmol) dissolved
in HCl/water (5:1 v/v, 5 mL) was added dropwise to the crude reac-
tion mixture. Then the crude mixture was allowed to react for
30 min in an ice bath and for 60 min at room temperature. The
crude reaction mixture was extracted with CH2Cl2 and the organic
phase washed with aqueous NaHCO3 solution. The crude reaction
mixture was purified with column chromatography by employing
aluminium oxide as the stationary phase and CH2Cl2/CH3CN (9:1
v/v) as eluent. The final receptor L3 (117 mg, 0.26 mmol) was iso-
lated as a dark blue solid; yield 41%. 1H NMR (300 MHz, [D6]-
DMSO): δ = 3.65 (s, 4 H, O-CH2-O), 3.68 (m, 12 H, O-CH2-O and
N-CH2-O), 3.83 (t, 4 H, O-CH2-O), 6.79 (d, 2 H, C6H4), 7.89 (d,
2 H, C6H4), 8.56 (s, 1 H, thiazole) ppm. 13C{1H} NMR (75 MHz,
CDCl3): δ = 53.1, 68.3, 70.1, 70.5, 71.3, 112.9, 142.8, 143.6, 147.2,
154.1, 181.7 ppm. HRMS calcd. for C19H25N5O6S 451.1526; found
451.1511.
Experimental Section
General Remarks: All commercially available reagents were used
without further purification. Air-/water-sensitive reactions were
performed in flame-dried glassware under argon. Acetonitrile was
dried with CaH2 and distilled prior to use.
Physical Measurements: Metal cations (Cd2+, Fe3+, Hg2+, Ni2+
,
Pb2+ and Zn2+ as perchlorate or triflate salts) were used to obtain
solutions of approximate concentration of 5.0ϫ10–3 moldm–3 in
acetonitrile. Protonation studies were carried out with solutions of
perchloric acid in acetonitrile. Photophysical studies of the behav-
iour of solutions of all the ligands in acetonitrile in the presence of
the metal cations cited above and protons were carried out. The
UV/Vis behaviour was studied with a Perkin–Elmer Lambda 35
spectrometer. The concentration of ligands used in the UV/Vis
measurements was around 5.0ϫ10–5 moldm–3 in acetonitrile. UV/
Vis spectra were recorded in the presence of equimolar quantities
of all the ligands and the corresponding metal cations.
The 1H and 13C NMR spectra were recorded with a Varian–Gemini
spectrometer. Chemical shifts are reported in ppm downfield from
the TMS signal. Spectra taken in CDCl3 were referenced to residual
1
CHCl3. H NMR spectroscopic studies in the presence of increas-
ing quantities of protons were also carried out. For these proton-
ation studies, the correspondent receptor (concentration of around
1.0ϫ10–2 moldm–3) were dissolved in deuterated acetonitrile and
then titrated with perchloric acid.
Synthetic Procedures: The synthesis of macrocyclic subunits 3–7
were previously published.[24] The synthesis of receptors L1 and L3
was also previously published.[14,12]
Synthesis of L4: In a round-bottomed flask, compound 1 (100 mg,
0.69 mmol) was dissolved in a mixture (5 mL) of acetic acid and
water (5:1 v/v). The crude material was cooled with an ice bath.
Then NaNO2 (47.6 mg, 0.69 mmol) dissolved in water (1.5 mL) was
added. After 10 min, macrocycle 5 (213.6 mg, 0.63 mmol) dissolved
in HCl/water (5:1 v/v, 5 mL) was added dropwise to the crude reac-
tion mixture. Then the crude mixture was allowed to react for
30 min in an ice bath and for 60 min at room temperature. The
crude reaction mixture was extracted with CH2Cl2 and the organic
phase washed with aqueous NaHCO3 solution. The crude reaction
mixture was purified with column chromatography by employing
aluminium oxide as the stationary phase and CH2Cl2/CH3CN (9:1
v/v) as eluent. The final receptor L4 (139 mg, 0.28 mmol) was iso-
lated as a dark blue solid; yield 45%. 1H NMR (300 MHz, [D6]-
DMSO): δ = 3.71–3.85 (m, 24 H, O-CH2-O and N-CH2-O), 6.80
(d, 2 H, C6H4), 7.93 (d, 2 H, C6H4), 8.60 (s, 1 H, thiazole) ppm.
13C{1H} NMR (75 MHz, CDCl3): δ = 51.2, 68.4, 70.7, 70.9, 113.0,
143.5, 144.2, 147.6, 153.9, 183.5 ppm. HRMS calcd. for
C21H29N5O7S 495.1788; found 495.1769.
General Procedure for the Synthesis of Thiazolylazo Derivatives L1–
L6: Compound 1 was diazotated with NaNO2 and HCl and sub-
sequently treated with 2 or the corresponding phenyl macrocycle
(3–7) dissolved in water solutions that contained acetic acid to give
the correspondent receptors L1–L6 as blue solids.
Synthesis of L1: In a round-bottomed flask, compound 1 (1320 mg,
9.1 mmol) was dissolved in a mixture (50 mL) of acetic acid and
water (5:1 v/v). The crude material was cooled with an ice bath.
Then NaNO2 (628 mg, 9.1 mmol) dissolved in water (15 mL) was
added. After 10 min, compound 2 (1000 mg, 8.26 mmol) dissolved
in HCl/water (5:1 v/v, 50 mL) was added dropwise to the crude
reaction mixture. Then the crude mixture was allowed to react for
30 min in an ice bath and for 60 min at room temperature. The
crude reaction mixture was extracted with CH2Cl2 and the organic
phase washed with aqueous NaHCO3 solution. The crude reaction
mixture was purified with column chromatography by employing
aluminium oxide as the stationary phase and CH2Cl2/CH3CN (9:1
v/v) as eluent. The final receptor L1 (1373 mg, 4.96 mmol) was iso-
82
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 76–84

Chromogenic Cation Sensors
Synthesis of L5: In a round-bottomed flask, compound 1 (100 mg,
0.69 mmol) was dissolved in a mixture (5 mL) of acetic acid and
water (5:1 v/v). The crude material was cooled with an ice bath.
Then NaNO2 (47.6 mg, 0.69 mmol) dissolved in water (1.5 mL) was
added. After 10 min, macrocycle 6 (206 mg, 0.63 mmol) dissolved
in HCl/water (5:1 v/v, 5 mL) was added dropwise to the crude reac-
tion mixture. Then the crude mixture was allowed to react for
30 min in an ice bath and for 60 min at room temperature. The
crude reaction mixture was extracted with CH2Cl2 and the organic
phase washed with aqueous NaHCO3 solution. The crude reaction
mixture was purified with column chromatography by employing
aluminium oxide as the stationary phase and CH2Cl2/CH3CN (9:1
v/v) as eluent. The final receptor L5 (145 mg, 0.3 mmol) was iso-
lated as a dark blue solid; yield 48%. 1H NMR (300 MHz, [D6]-
DMSO): δ = 2.76 (t, 4 H, S-CH2-S), 2.93 (t, 4 H, S-CH2-S), 3.63
(s, 4 H, O-CH2-O), 3.80 (m, 8 H, S-CH2-N, O-CH2-O), 6.78 (d, 2
H, C6H4), 7.92 (d, 2 H, C6H4), 8.60 (s, 1 H, thiazole) ppm. 13C{1H}
NMR (75 MHz, CDCl3): δ = 29.6, 31.7, 52.4, 70.8, 74.4, 112.4,
143.5, 144.5, 147.6, 154.7, 182.1 ppm. HRMS calcd. for
C19H25N5O4S3 483.1069; found 483.1075.
Synthesis of L6: In a round-bottomed flask, compound 1 (100 mg,
0.69 mmol) was dissolved in a mixture (5 mL) of acetic acid and
water (5:1 v/v). The crude material was cooled with an ice bath.
Then NaNO2 (47.6 mg, 0.69 mmol) dissolved in water (1.5 mL) was
added. After 10 min, macrocycle 7 (206 mg, 0.63 mmol) dissolved
in HCl/water (5:1 v/v, 5 mL) was added dropwise to the crude reac-
tion mixture. Then the crude mixture was allowed to react for
30 min in an ice bath and for 60 min at room temperature. The
crude reaction mixture was extracted with CH2Cl2 and the organic
phase washed with aqueous NaHCO3 solution. The crude reaction
mixture was purified with column chromatography by employing
aluminium oxide as the stationary phase and CH2Cl2/CH3CN (9:1
v/v) as eluent. The final receptor L6 (121 mg, 0.25 mmol) was iso-
lated as a dark blue solid; yield 40%. 1H NMR (300 MHz, [D6]-
DMSO): δ = 2.80 (t, 4 H, S-CH2-S), 2.91 (t, 4 H, S-CH2-S), 3.73
(s, 4 H, O-CH2-O), 3.87 (m, 8 H, S-CH2-N, O-CH2-O), 6.77 (d, 2
H, C6H4), 7.93 (d, 2 H, C6H4), 8.59 (s, 1 H, thiazole) ppm. 13C{1H}
NMR (75 MHz, CDCl3): δ = 31.8, 33.0, 51.6, 70.5, 72.7, 112.4,
142.7, 143.8, 147.3, 154.7, 182.3 ppm. HRMS calcd. for
C19H25N5O4S3 483.1069; found 483.1057.
CTQ2010-15364, Molecular Nanoscience (Consolider Ingenio
CSD2007-00010) and Generalitat Valenciana (PROMETEO/2009/
016 and PROMETEO/2009/108) is gratefully acknowledged.
[1] a) L. Fabbrizzi, A. Poggi, Chem. Soc. Rev. 1995, 24, 197–202;
b) R. A. Bissell, A. P. de Silva, H. Q. N. Gunaratne, P. L. M.
Lynch, G. E. M. Maguire, K. R. A. S. Sandanayake, Chem.
Soc. Rev. 1992, 21, 187–195.
[2] J. P. Dix, F. Vögtle, Angew. Chem. 1978, 90, 893; Angew. Chem.
Int. Ed. Engl. 1978, 17, 857–859.
[3] a) R. Martínez-Máñez, F. Sancenón, Chem. Rev. 2003, 103,
4419–4476; b) P. D. Beer, P. A. Gale, Angew. Chem. 2001, 113,
502; Angew. Chem. Int. Ed. 2001, 40, 486–516.
[4] a) B. Valeur, I. Leray, Coord. Chem. Rev. 2000, 205, 3–40; b)
A. W. Czarnik, Acc. Chem. Res. 1994, 27, 302–308; c) K. Rur-
ack, U. Resch-Genger, Chem. Soc. Rev. 2002, 31, 116–127.
[5] a) A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson,
A. J. M. Huxley, C. P. McCoy, J. T. Rademacher, T. E. Rice,
Chem. Rev. 1997, 97, 1515–1566; b) K. Rurack, Spectrochim.
Acta Part A 2001, 57, 2161–2195.
[6] a) H. G. Löhr, F. Vögtle, Acc. Chem. Res. 1985, 18, 65–72; b)
M. Takagi, K. Ueno, Top. Curr. Chem. 1984, 121, 39–65.
[7] See, for example: a) J. V. Ros-Lis, R. Martínez-Máñez, F. San-
cenón, J. Soto, K. Rurack, H. Weißhoff, Eur. J. Org. Chem.
2007, 2449–2458; b) Y.-J. Chen, W.-S. Chung, Eur. J. Org.
Chem. 2009, 4770–4776; c) H. G. Lee, J.-E. Lee, K. S. Choi,
Inorg. Chem. Commun. 2006, 9, 582–585; d) P. Mahato, A.
Ghosh, S. Saha, S. Mishra, S. K. Mishra, A. Das, Inorg. Chem.
2010, 49, 11485–11492.
[8] a) H. R. Hovind, Analyst 1975, 100, 769–796; b) V. A. Lemos,
E. S. Santos, M. S. Santos, R. T. Yamaki, Microchim. Acta
2007, 158, 189–204.
[9] a) M. M. Saeed, S. Z. Bajwa, M. S. Ansari, R. Ahmed, Ra-
diochim. Acta 2005, 93, 177–185; b) A. M. Starvin, P. T. Rao,
J. Hazard. Mater. 2004, 113, 75–79.
[10] a) M. Wang, J.-M. Lin, F. Qu, X. Shan, Z. Chen, J. Cromato-
graph. A 2004, 1029, 249–254; b) I. Takase, A. S. Luna, R.
Calixto de Campos, Talanta 2003, 61, 597–602; c) A. S. Amin,
Anal. Lett. 2001, 34, 163–176.
[11] a) M. Moragues, R. Martínez-Máñez, F. Sancenón, Chem. Soc.
Rev. 2011, 40, 2593–2643; b) R. Martínez-Máñez, F. Sancenón,
M. Hecht, M. Biyical, K. Rurack, Anal. Bioanal. Chem. 2011,
399, 55–74; c) R. Martínez-Máñez, J. Soto, J. M. Lloris, T.
Pardo, Trends Inorg. Chem. 1998, 5, 183–203.
[12] J. P. Dix, F. Vögtle, Angew. Chem. 1978, 90, 893–894.
[13] a) J. E. Richman, T. J. Atkins, J. Am. Chem. Soc. 1974, 96,
2268–2270; b) T. J. Atkins, J. E. Richman, W. F. Oettle, Org.
Synth. 1978, 58, 86–95; c) K. E. Krakowiak, J. S. Bradshaw,
D. J. Zamecka-Krakowiak, Chem. Rev. 1989, 89, 929–972.
[14] a) K. Higashino, T. Nakaya, E. Ishiguro, J. Photochem. Pho-
tobiol. A: Chem. 1994, 79, 81–88; b) H. Mustroph, J. Epperlein,
Z. Chem. 1983, 23, 298–299.
[15] J. V. Ros-Lis, R. Martínez-Máñez, F. Sancenón, J. Soto, M.
Spieles, K. Rurack, Chem. Eur. J. 2008, 14, 10101–10114.
[16] a) L. Forlani, P. De Maria, A. Fini, J. Chem. Soc. Perkin Trans.
2 1980, 1156–1158; b) P. Haake, L. P. Bausher, J. Phys. Chem.
1968, 72, 2213–2217.
[17] a) E. Sawicki, J. Org. Chem. 1957, 22, 365–367; b) O. Siiman,
A. Lepp, J. Phys. Chem. 1984, 88, 2641–2650; c) H. Wada, O.
Nakazawa, G. Nakagawa, Talanta 1974, 21, 97–102; d) I. I.
Pogoida, P. P. Kish, Org. Reakt. Anal. 1976, 2, 102–104.
[18] Critical Stability Cosntants (Eds.: R. M. Smith, A. E. Martell),
Plenum, New York, Vol. 2, 1974.
[19] B. García-Acosta, R. Martínez-Máñez, F. Sancenón, J. Soto,
K. Rurack, M. Spieles, E. García-Breijo, L. Gil, Inorg. Chem.
2007, 46, 3123–3135.
Computational Details: Calculations were performed with the
Gaussian 09 package using the B3LYP functional and the qua-
dratic convergence approach.[25] Double-ζ all-electron basis sets
proposed by Ahlrichs et al. were used for all atoms except for the
mercury atom, for which valence double-ζ proposed by Dunning
and Huzinaga and Los Alamos electron core pseudopotential were
used.[26] Molecular geometries were optimized for the used mole-
cules. To optimize the computational time, the organic skeleton
involved in the studied charge-transfer band – formed by aniline,
azo and thiazole groups – was frozen in metallic complexes. Ener-
gies and oscillator strengths of the electronic transitions were ob-
tained from calculations based on the time-dependent formal-
ism.[27] In such cases, a polarizable continuum model (PCM) with
the parameters that correspond to the acetonitrile was used to sim-
ulate the electronic effects of the solvent.[28]
Supporting Information (see footnote on the first page of this arti-
1
cle): H NMR and UV/Vis titrations.
Acknowledgments
[20] HyperChem. 6.03 Molecular Modeling System, Hypercube Inc,
Gainesville, Florida, USA, 2000.
[21] See, for example: a) K. Tsubaki, D. Tanima, Y. Kuroda, K.
Fuji, T. Kawabata, Org. Lett. 2006, 8, 5797–5800; b) H. J. Kim,
Financial support by the Spanish Ministerio de Ciencia e Innova-
ción (MICINN) through projects MAT2009-14564-C04-01,
Eur. J. Inorg. Chem. 2012, 76–84
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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83

R. Martínez-Máñez et al.
S. H. Kim, J. H. Kim, L. N. Ahn, J. H. Lee, C.-H. Lee, J. S. [24] D. Jiménez, R. Martínez-Máñez, F. Sancenón, J. V. Ros-Lis, J.
FULL PAPER
Kim, Tetrahedron Lett. 2009, 50, 2782–2786; c) T. Ábalos, D.
Jiménez, M. Moragues, S. Royo, R. Martínez-Máñez, F. San-
cenón, J. Soto, A. M. Costero, M. Parra, S. Gil, Dalton Trans.
2010, 39, 3449–3459; d) M. Schmittel, H.-W. Lin, Angew.
Chem. 2007, 119, 911; Angew. Chem. Int. Ed. 2007, 46, 893–
896.
See, for example: a) E. M. Nolan, S. J. Lippard, Chem. Rev.
2008, 108, 3443–3480; b) X. Zhang, J. Huang, Chem. Commun.
2010, 46, 6042–6044; c) Q. Zhao, S. Liu, F. Li, T. Yi, C. Huang,
Dalton Trans. 2008, 3836–3840; d) S. Tatay, P. Gaviña, E. Coro-
nado, E. Palomares, Org. Lett. 2006, 8, 3857–3860; e) H. Lee,
S. S. Lee, Org. Lett. 2009, 11, 1393–1396; f) S. Yoon, E. W.
Miller, Q. He, P. H. Do, C. J. Chang, Angew. Chem. 2007, 119,
6778; Angew. Chem. Int. Ed. 2007, 46, 6658–6661; g) K. Rur-
ack, U. Resch-Genger, J. L. Bricks, M. Spieles, Chem. Commun.
2000, 2103–2104; h) C. S. Lim, D. W. Kang, Y. S. Tian, J. H.
Han, H. L. Hwang, B. R. Cho, Chem. Commun. 2010, 46,
2388–2390.
Soto, A. Benito, E. García-Breijo, Eur. J. Inorg. Chem. 2005,
2393–2403.
[25] a) A. D. Becke, Phys. Rev. A 1988, 38, 3098–3100; b) C. Lee,
W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785–789; c) A. D.
Becke, J. Chem. Phys. 1993, 98, 5648–5652.
[26] a) A. Schaefer, A. Horn, R. Ahlrichs, J. Chem. Phys. 1992, 97,
2571–2577; b) P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82,
270–283; c) M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Ba-
rone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H.
Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F. Ogli-
aro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N.
Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A.
Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N.
Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V.
Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Strat-
mann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski,
G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D.
Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski,
D. J. Fox, Gaussian 09, revision A01, Gaussian, Inc., Wall-
ingford CT, 2009.
[22]
[23] a) J. V. Ros-Lis, R. Martínez-Máñez, K. Rurack, F. Sancenón,
J. Soto, M. Spieles, Inorg. Chem. 2004, 43, 5183–5185; b) A. B.
Descalzo, R. Martínez-Máñez, R. Radeglia, K. Rurack, J.
Soto, J. Am. Chem. Soc. 2003, 125, 3418–3419; c) M. Yuan, Y.
Li, J. Li, C. Li, X. Liu, J. Lv, J. Xu, H. Liu, S. Wang, D. Zhu,
Org. Lett. 2007, 9, 2313–2316; d) M. Zhu, M. Yuan, X. Liu, J.
Xu, J. Lv, C. Huang, H. Liu, Y. Li, S. Wang, D. Zhu, Org. Lett.
2008, 10, 1481–1484; e) M. Tian, H. Ihmels, Chem. Commun.
2009, 3175–3177; f) M. Tian, H. Ihmels, K. Benner, Chem.
Commun. 2010, 46, 5719–5721; g) H. H. Wang, L. Xue, Y.-Y.
Qian, H. Jiang, Org. Lett. 2010, 12, 292–295; h) S. Atilgan, I.
Kutuk, T. Ozdemir, Tetrahedron Lett. 2010, 51, 892–894.
[27] M. E. Casida, C. Jamorski, K. C. Casida, D. R. Salahub, J.
Chem. Phys. 1998, 108, 4439–4449.
[28] J. Tomasi, B. Mennucci, R. Cammi, Chem. Rev. 2005, 105,
2999–3094.
Received: August 8, 2011
Published Online: November 22, 2011
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