Synthesis and photochemical behaviour of novel uranyl-salophen complexes bearing anthracenyl side arms

Article abstract of DOI:10.1080/10610278.2012.752089

In this paper, we report the synthesis and physico-chemical investigation of two uranyl-salophen receptors, bearing either one or two anthracenyl moieties appended to the salophen skeleton. Despite the presence of the anthracenyl fluorophores, no fluorescence emission was detected. Photophysical data and cyclic voltammetric experiments show that photoinduced electron transfer from the anthracene-localised first singlet excited state to the metal centre is strongly exergonic, thus suggesting that this is the main fluorescence quenching mechanism in these complexes. The investigated compounds are photoreactive upon UV irradiation, yielding either anthracene photooxidation or photodimerisation products depending on the specific complex and the experimental conditions.

Full text of DOI:10.1080/10610278.2012.752089

This article was downloaded by: [University of New Hampshire]
On: 16 February 2013, At: 18:30
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Supramolecular Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/gsch20
Synthesis and photochemical behaviour of novel
uranyl–salophen complexes bearing anthracenyl side
arms
Francesco Yafteh Mihan a , Silvia Bartocci a , Alberto Credi b , Serena Silvi b & Antonella
Dalla Cort a
a Department of Chemistry and IMC-CNR, Università La Sapienza, Piazzale Aldo Moro 5,
00185, Roma, Italy
b Photochemical Nanosciences Laboratory and Center for the Chemical Conversion of Solar
Energy (SolarChem), Dipartimento di Chimica ‘Giacomo Ciamician’, Università di Bologna,
via Selmi 2, 40126, Bologna, Italy
Version of record first published: 17 Dec 2012.
To cite this article: Francesco Yafteh Mihan , Silvia Bartocci , Alberto Credi , Serena Silvi & Antonella Dalla Cort (2013):
Synthesis and photochemical behaviour of novel uranyl–salophen complexes bearing anthracenyl side arms, Supramolecular
Chemistry, 25:2, 109-115
To link to this article: http://dx.doi.org/10.1080/10610278.2012.752089
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to
anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation that the contents
will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should
be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,
proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in
connection with or arising out of the use of this material.

Supramolecular Chemistry
Vol. 25, No. 2, February 2013, 109–115
Synthesis and photochemical behaviour of novel uranyl–salophen complexes bearing
anthracenyl side arms†
Francesco Yafteh Mihana, Silvia Bartoccia, Alberto Credib*, Serena Silvib* and Antonella Dalla Corta*
a
b
Department of Chemistry and IMC-CNR, Universita La Sapienza, Piazzale Aldo Moro 5, 00185 Roma, Italy; Photochemical
`
Nanosciences Laboratory and Center for the Chemical Conversion of Solar Energy (SolarChem), Dipartimento di Chimica ‘Giacomo
`
Ciamician’, Universita di Bologna, via Selmi 2, 40126 Bologna, Italy
(Received 13 August 2012; final version received 19 November 2012)
In this paper, we report the synthesis and physico-chemical investigation of two uranyl–salophen receptors, bearing either
one or two anthracenyl moieties appended to the salophen skeleton. Despite the presence of the anthracenyl fluorophores, no
fluorescence emission was detected. Photophysical data and cyclic voltammetric experiments show that photoinduced
electron transfer from the anthracene-localised first singlet excited state to the metal centre is strongly exergonic, thus
suggesting that this is the main fluorescence quenching mechanism in these complexes. The investigated compounds are
photoreactive upon UV irradiation, yielding either anthracene photooxidation or photodimerisation products depending on
the specific complex and the experimental conditions.
Keywords: uranyl–salophen complexes; anthracenyl fluorophore; PET; cyclic voltammetry
Introduction
occupying four of the five equatorial coordination sites
(Figure 1).
The condensation reaction between aldehydes and amines
to give imines was firstly reported by Schiff (1) in 1864.
From that time, such derivatives have been extensively
used for a wide range of applications. Well-designed
Schiff bases are known to behave as privileged ligands (2),
able to stabilise different metals in various oxidation
states, controlling their performances and tuning their
properties. For instance, N,N0-bis(salicylaldehyde)-1,2-
phenylenediimino (salophen) compounds deriving from
the condensation of 1,2-phenylenediamine with two equiv.
of salicylaldehydes are quite popular ligands in coordi-
nation chemistry as they form stable complexes with
several transition and main group metals. In recent years,
these metal complexes have emerged as antitumoural (3),
antiviral and antibacterial agents (4), as building blocks in
the formation of supramolecular assemblies (5), in the
design of ion-selective membranes and ion-pair receptors
(6), as sensors (7), and in the development of new
materials showing nonlinear optical properties (8).
Hence, the fifth equatorial position is still available for
coordination with monodentate ligands, e.g. enones and
ketones (10), or anions such as halides (11), carboxylates,
phosphates and nucleotides. Uranyl–salophen complexes
can thus be regarded as strong Lewis acids capable of
recognising hard Lewis bases, not only in organic solvents
but, if properly derivatised, also in a more competitive
solvent such as water (12). NMR and UV–vis absorption
spectroscopies are commonly employed to measure the
binding strength between such complexes and given
guests, demonstrating that in many instances they behave
as highly efficient and selective molecular receptors. In the
last three decades, however, the supramolecular commu-
nity has dedicated great attention to the development of
receptors capable of generating changes in the fluor-
escence spectra upon guest recognition (13–15), expe-
cially when dealing with anion sensing (16). Because of its
simplicity and high sensitivity, fluorescence spectroscopy
is a particularly attractive technique for analytical
applications, and is highly recommended particularly for
trace detection. Unfortunately, simple uranyl–salophen
complexes do not show fluorescence emission properties
(17). A feasible route to obtain fluorescent chemosensors
based on this kind of receptors consists, therefore, in the
Among the metal centres that form robust, electrically
neutral complexes with salophen ligands is the hexavalent
uranyl ion, UO22þ. It is well known that uranyl exhibits a
preference for a pentagonal bipyramidal coordination
geometry (9) with the two metal-bound oxygen atoms in
the apical positions and the salophen N2O2 donor atoms
*Corresponding authors. Emails: alberto.credi@unibo.it; antonella.dallacort@uniroma1.it; serena.silvi@unibo.it
†Dedicated to Professor A.P. de Silva for his 60th birthday.
ISSN 1061-0278 print/ISSN 1029-0478 online
q 2013 Taylor & Francis
http://dx.doi.org/10.1080/10610278.2012.752089
http://www.tandfonline.com

110
F.Y. Mihan et al.
solution of BBr3 in dichloromethane at room temperature.
Formylation, performed on phenol 4, led to 3-(anthracen-
9-yl)-2-hydroxybenzaldehyde, 5. The reaction is regiose-
lective, affording the ortho derivative, thanks to the
formation of an MgClþ chelating intermediate (19), and is
performed in two steps: acid–base reaction of the phenol
with 1 equiv. of EtMgBr, followed by the addition of
MgCl2, Et3N and paraformaldehyde.
The final complexes 1 and 2 were directly synthesised
by statistical condensation of an equimolar mixture of
aldehyde 5, salicylaldehyde and o-phenylendiamine in the
presence of a slight excess of UO2(OAc)2·2H2O as
templating and metallating reagent. After chromatog-
raphy, the pure compounds precipitated as bright orange
solids.
Figure 1. Chemical structure of the host–guest complex
between a uranyl–salophen derivative and a guest, G.
incorporation of fluorescent fragments within the basic
skeleton of the receptor.
The general design of a good fluorescent chemosensor
relies on an efficient mechanism for either quenching
or reviving the fluorescence upon recognition of the
substrate (13, 14). A series of receptors utilising
photoinduced electron transfer (PET) (20), intramolecular
charge transfer (21), excited-state proton transfer (22),
excimer/exciplex formation, competitive binding (23) and
metal-to-ligand charge transfer (24) as mechanisms to
transduce the binding event into a luminescence change
have been reported in the literature (25). Among the
mechanisms listed above, PET is often exploited for the
construction of sensors, because the thermodynamic and
kinetic aspects of this phenomenon can be reliably
rationalised and hence predicted (26), and a large amount
of literature data is available on PET processes in
In this paper, we report the synthesis of two novel
uranyl–salophen complexes (Scheme 1) bearing either
one (1) or two (2) anthracenyl fluorogenic moieties
appended to the salophen framework, and describe their
photochemical and electrochemical properties.
Results and discussion
Compounds 1 and 2 were synthesised according to
Scheme 1. Briefly, 3-methoxyphenylboronic acid and 9-
bromoanthracene were used as starting materials for the
synthesis of aldehyde 5. By following the published
procedures (18), intermediate 4 was obtained by standard
Suzuki coupling followed by demethylation with a
Br
OH OCH3
B
OCH3
Pd(PPh3)3
HO
+
K2CO3
Toluene/MeOH
3
BBr3
CH2Cl2
dry
i) EtMgBr
ii) CH2O, Et3N, MgCl2
OH
O
OH
THF dry, 75°C
5
4
N
O
N
UO2
N
O
N
UO2
O
OH
O
OH
UO2(OAc)2 · 2H2O
+
O
O
CHCl3/MeOH
reflux
+
NH3
H2N
5
1
2
Scheme 1. Synthetic route to uranyl–salophen complexes 1 and 2.

Supramolecular Chemistry
111
multicomponent molecular systems (13, 20, 27–29). This
was also the idea behind the development of our systems:
we thought that the presence of the anthracenyl fragments
in the ortho position with respect to the phenolic oxygen,
i.e. proximal to the incoming guest, could eventually
maximise the fluorescence sensing response.
literature for the one-electron reduction of the uranyl
dication in salophen complexes (32). The process observed
in the positive potential region is assigned to the
monoelectronic oxidation of the anthracenyl units.
These data, together with the energy of the first singlet
excited state (S1) of the anthracenyl chromophore, suggest
that an intramolecular PET process from the anthracenyl
S1 state to the metal centre may occur in our complexes
(Equation (1)):
Unfortunately, despite the presence of the fluorescent
units, both 1 and 2 resulted to be not luminescent both in
chloroform solution at room temperature and in a solvent
glass matrix at 77 K. Only a very weak fluorescence band
at around 500 nm was detected and ascribed to a residual
emission of the bound salophen ligand (30). We, therefore,
decided to perform photochemical and electrochemical
experiments in order to investigate the interplay between
the various subunits of our systems, and eventually
understand their luminescence.
AntðS Þ þ UVI 2 Sal ! Ant·þ þ UV 2 Sal: ð1Þ
The overall free energy change associated with the
PET (DG8PET) can be estimated by Equation (2):
*
1
ꢂ
ꢀ
ꢁ
ꢀ
ꢁꢃ
Dþ
D
A
A2
DG8PET ø E8
2 E8
2 E020
;
ð2Þ
We know from the work of Kunkler and Vogler (17)
that the lack of fluorescence in simple uranyl–salophen
complexes is due to the occurrence of a ligand-to-metal
charge-transfer (LMCT) process involving lower energy
salophen22 states. They reported that an analogous
intermolecular quenching mechanism can take place
between uranyl salts and suitable electron donors present
in solution (31). An intramolecular version of such an
LMCT phenomenon may indeed happen also in our
systems, which contain anthracenyl moieties potentially
capable of playing the role of electron donors. To verify
this hypothesis, we analysed the electrochemical beha-
viour of compounds 1 and 2 in chloroform solution. Cyclic
voltammetry measurements showed that in both com-
plexes, a quasi-reversible reduction process at 21.5 V
versus ferrocene (Fc) occurs (Figure 2), while an
irreversible oxidation process at potential higher than
þ0.6 V versus Fc is observed.
in which E8(Dþ/D) and E8(A/A2) are the redox potentials
for oxidation of the donor (anthracenyl unit) and reduction
of the acceptor (uranyl–salophen moiety), respectively,
and E0–0 is the energy of the excited state involved in the
reaction (the S1 level of the anthracenyl unit, about 3.3 eV)
(33). On the basis of the redox potentials we have found, a
DG 8PET value of ca. 21.2 eV can be estimated. Therefore,
a PET process involving the anthracenyl pendant units and
the metal centre is thermodynamically feasible, consider-
ing also the close proximity of these moieties, and PET is
most likely the cause of the very efficient fluorescence
quenching of the anthracene substituents in 1 and 2. A
further experimental evidence in support of the intramo-
lecular quenching mechanism comes from the emission
spectra of 1 and 2 recorded in CHCl3 after the addition of a
small amount of triflic acid which catalyses and promotes
the hydrolysis of the imine bond. The rupture of the imine
bond causes the detachment of the anthracenyl unit (as the
corresponding salicylaldehyde) from the metal–salophen
The reduction process found for 1 and 2 takes place at
a potential value consistent with that reported in the
Figure 2. Cyclic voltammetric scans upon reduction of (a) 1 (6.8 £ 1024 M) and (b) 2 (5.3 £ 1024 M). Conditions: argon purged CHCl3,
0.067 M tetrabutylammonium hexafluorophosphate, scan rate 200 mV/s. The wave at around þ0.4 V is that of Fc used as an internal
standard.

112
F.Y. Mihan et al.
Figure 3. Absorption spectral changes observed upon exhaustive UV irradiation of (a) 2 (5.6 £ 1025 M) in air-equilibrated CHCl3 (left;
total irradiation time, 220 min) and of (b) 2 (1.1 £ 1025 M) in carefully deoxygenated CHCl3 (right; total irradiation time, 90 min).
moiety, resulting in the appearance of the typical
structured fluorescence band of anthracene.
The loss of the structured absorption band in the 300–
400 nm region observed upon irradiation of an air-
equilibrated solution indicates that 2 undergoes the
anthracene photooxidation reaction. Qualitatively similar
spectral changes were detected also upon irradiation of 2 in
an oxygen-free solution. Since the oxidation reaction
cannot occur under these conditions, the disappearance of
the anthracene absorption band has to be ascribed to a
photodimerisation process. Intermolecular dimerisation,
however, can be ruled out because of the short lifetime of
the S1 excited state (a few nanoseconds for anthracene, but
in our case it may be much shorter because of the PET
quenching process) and the low concentration of the
compound. Therefore, we believe that UVirradiation of 2 in
the absence of oxygen causes the intramolecular dimerisa-
tion of the two anthracenyl pendant units. To confirm this
hypothesis, similar irradiation experiments were performed
with complex 1 that has only one anthracenyl pendant unit.
The corresponding absorption changes (Figure 4) indicate
that for this compound, the decrease in the anthracene
absorption band takes place only in an air-equilibrated
solution because of the photooxidation process. No
absorption changes could be detected upon irradiation of
1 in oxygen-free solution even after 50 min of continuous
irradiations, suggesting that anthracene photodimerisation
It is well known that anthracene derivatives undergo
photochemical reactions upon UV (S1) excitation (34, 35).
Specifically, UV irradiation in solution in the presence of
oxygen affords oxidation products (usually, the bridged
1,10-endoperoxide) because singlet oxygen produced by
photosensitisation from the lowest triplet state of
anthracene reacts with the anthracene itself. Conversely,
in oxygen-free solutions photooxidation reactions are
prevented and, if the anthracene concentration is high
enough, photodimerisation can take place via the S1 state
(34, 35). Both photooxidation and photodimerisation
reactions cause a decrease in the structured absorption
band between 300 and 400 nm region, as a result of the
disruption of the anthracene aromatic system.
The above experiments indicate that in our complexes
the anthracene S1 state is strongly quenched; to investigate
whether this excited state can still evolve along a reactive
path, we subjected solutions of 1 and 2 to UV irradiation in
the presence and absence of oxygen. Chloroform solutions
of 2 in the concentration range of 1025 M were irradiated
using a cut-off filter at 350 nm, under continuous stirring,
both in aerated and disaerated conditions; the correspond-
ing UV–vis absorption changes are reported in Figure 3.
Figure 4. Absorption spectral changes observed upon exhaustive UV irradiation of (a) 1 (7.1 £ 1025 M) in air-equilibrated CHCl3 (left;
total irradiation time, 300 min) and of (b) 1 (4.7 £ 1025 M) in carefully deoxygenated CHCl3 (right; total irradiation time, 50 min).

Supramolecular Chemistry
113
does not occur. These observations strongly indicate that
the photoreaction observed for compound 2 in deoxyge-
nated conditions is in fact the intramolecular dimerisation
of the two anthracenyl units.
employed as the solvent, and the sample concentration was
on the order of 5 £ 1024 M, and tetrabutylammonium
hexafluorophosphate (0.067 M) was the supporting elec-
trolyte. The reversible oxidation wave of Fc
(E1/2 ¼ þ0.51 V versus SCE) (36) was employed as an
internal reference for the potential measurements.
Conclusions
We have described the synthesis of two new uranyl–
salophen complexes, 1 and 2, bearing, respectively, one
and two anthracenyl units appended to the ligand skeleton.
The absence of fluorescence emission in the two
derivatives, despite the presence of the anthracenyl
fluorophore, is most likely due to a PET process from
the lowest singlet excited state of the anthracenyl unit to
the metal centre. The redox potentials measured for 1 and
2 by cyclic voltammetry are indeed in agreement with such
an interpretation. Although the anthracenyl unit in the
investigated complexes is strongly quenched by PET, it is
still capable of exhibiting the typical light-induced
reactions of anthracene in solution, namely photo-
oxidation and photodimerisation. Both 1 and 2 undergo
photo-oxidation when irradiated in the UV in an air-
equilibrated solution, whereas only 2, which bears two
anthracenyl units, is photoreactive upon UV irradiation in
the absence of oxygen. We therefore inferred that such a
photoreaction is the intramolecular dimerisation of the two
anthracenyl units, which is obviously impossible in
compound 1. In principle, such a process could be used
as a tool to control the access of guests to the free
coordination site on the uranyl moiety. Further studies in
this direction are underway in our laboratories.
Photochemical reactions
Photochemical reactions were performed by irradiation
with a Xenon lamp projector using a cut-off filter at
350 nm. Deoxygenation was performed by five freeze–
pump–thaw cycles. The reactions were monitored by
UV–vis absorption spectrophotometry using a Perkin-
Elmer l18 spectrophotometer.
9-(20-Methoxyphenyl)anthracene (3). Under argon atmos-
phere,
a solution of 9-bromoanthracene (3.00 g,
11.7 mmol) and Pd(PPh3)4 (130 mg, 0.117 mmol) in
40 ml of toluene was added to a solution of 2-
methoxyphenylboronic acid (2.13 g, 11.4 mmol) in 35 ml
of ethanol absolute followed by addition of K2CO3 (2.40 g,
17.4 mmol). The mixture was stirred and heated to reflux
for 20 h under inert atmosphere, and then allowed to cool
to room temperature. Then 90 ml of 0.5 M NaOH solution
was added to the reaction mixture, which was extracted
with CH2Cl2 (two portions of 90 ml). The organic phases
were combined, dried over anhydrous MgSO4 and filtered.
After flash chromatographic purification on a silica gel
(petroleum ether 40–708C: CH2Cl2, 9:1), 3.55 g of product
1
was obtained as an off-white solid. Yield 76%. H NMR
Experimental
(300 MHz, CDCl3) d: 8.47 (s, 1H), 8.02 (d, 2H,
J ¼ 8.4 Hz), 7.61–7.49 (m, 3H), 7.46–7.43 (m, 2H),
7.42–7.29 (m, 2H), 7.15 (t, 2H, J ¼ 8.4 Hz), 3.60 (s, 3H).
General methods and materials
1H NMR spectra were recorded on a Bruker AC-200 and
AC-300 MHz. High-resolution mass spectra (HR-MS)
were performed by an ESI-TOF spectrometer. Salicylal-
dehyde, 2-methoxyphenylboronic acid, 9-bromoanthra-
cene, EtMgBr solution in hexane and the BBr3 solution in
CH2Cl2 were purchased from Aldrich Co. (Milan, Italy)
Anhydrous MgCl2 and K2CO3 were obtained by Fluka Co
(Milan, Italy). Other reagents were of analytical grade and
were used without further purification. Solvents and
solutions used in the Suzuki coupling have been degassed
for 30 min by Argon bubbling.
9-(20-Hydroxyphenyl)anthracene (4). Under argon atmos-
phere in a dry flask, a solution of BBr3 (1.0 M in CH2Cl2)
(18 ml, 18 mmol) was added dropwise over a period of
20 min to a stirring solution of 3 (1.05 g, 3.68 mmol)
dissolved in 50 ml of CH2Cl2 and cooled in an ice bath.
Once the addition was complete, the mixture was stirred
for an additional hour at room temperature. While cooling
with an ice bath, the reaction was quenched with 100 ml of
H2O, and the mixture was extracted with two portions of
50 ml of CH2Cl2. The combined organic phases were dried
over MgSO4 and filtered, and the solvent was removed
under reduced pressure to give the crude product. After
recrystallisation from hot toluene, 0.890 g of yellow
crystals was obtained with a yield of 94%. GC–MS m/z
(þ) 270 (M, 100%). 1H NMR (300 MHz, CDCl3): 8.62 (s,
1H), 8.75 (d, 2H, J ¼ 8.4 Hz), 7.68–7.65 (m, 2H), 7.52–
7.37 (m, 6H), 7.18–7.01 (m, 2H), 4.53 (s, 1H).
Cyclic voltammetry
Cyclic voltammetric experiments were performed with an
Autolab 30 multipurpose equipment interfaced to a PC,
using a three electrode cell composed of a glassy carbon
working electrode, a platinum spiral counter electrode and
a pseudo-reference silver electrode. Spectrophotometric
grade chloroform, deoxygenated by argon bubbling, was

114
F.Y. Mihan et al.
1
Complex 2. H NMR (300 MHz, CDCl3) d: 9.49 (s, 2H),
3-(Anthracen-9-yl)-2-hydroxybenzaldehyde (5). In a two-
necked flask, previously flamed under flux of argon, 6 ml
of dry tetrahydrofuran (THF) freshly distilled on sodium
and phenol 4 (234 mg, 0.856 mmol) was added. Then
EtMgBr (0.285 ml, 0.856 mmol) was slowly added. The
mixture was stirred for 45 min and then paraformaldehyde
(570 mg, 18.98 mmol) and anhydrous MgCl2 (187 mg,
1.96 mmol) were added. The reaction mixture was stirred
at 758C for 4 h. Then, AcOEt (50 ml) was added to
the mixture and the organic phase was washed with
three portions of 1 M (40 ml) HCl. The organic phase was
then washed once with saturated NaCl solution and twice
with portions of 50 ml of water. The organic phase was
dried over anhydrous Na2SO4. The crude product was
purified by chromatographic column on flash silica gel
(CHCl3:petroleum ether (40–708C), 4:6). One hundred
and nineteen milligrams of pure product as bright yellow
solid have been obtained with a yield of 46%. GC–MS m/z
(þ) 298 (M, 100%). 1H NMR (300 MHz, CDCl3) d: 11.15
(s, 1H), 10.07 (s, 1H), 8.54 (s, 1H), 8.06 (dd, 2H, J ¼ 6 Hz,
J ¼ 1.8 Hz), 7.78 (dd, 1H, J ¼ 7.8 Hz, J ¼ 1.8 Hz), 7.62–
7.56 (m, 3 H), 7.50–7.20 (m, 6H). 13C NMR (75 MHz,
CDCl3) d: 196.39, 140.00, 133.59, 131.16, 130.02, 128.39,
127.21, 125.75, 125.51, 124.89, 119.62 ppm. MS-ESI-
TOF for C21H14NaO2 calcd 321.0886, found
321.0877 m/z þ.
8.43 (s, 2H), 8.01 (d, 4H, J ¼ 8.7 Hz), 7.83–7.79 (m, 3H),
7.70 (d, 4H, J ¼ 1.8 Hz), 7.70–7.53 (m, 4H), 7.53–7.39
(m, 6H), 7.13–6.93 (m, 6H). 13C NMR (50 MHz, CDCl3)
d: 165.47, 138.89, 135.42, 131.04, 130.28, 128.69, 128.04,
127.01, 126.10, 125.00, 124.97, 124.05, 119.54,
117.43 ppm. MS-ESI-TOF for C48H30N2O4NaU calcd
959.2611, found 959.2617 m/z þ.
Acknowledgement
`
We thank the Ministero dell’Istruzione, Universita e Ricerca
(PRIN 2008), for financial support.
References
(1) Schiff, H. Liebigs. Ann. Chem. Suppl. 1864, 3, 343–345.
(2) Cozzi, P.G. Chem. Soc. Rev. 2004, 33, 410–421.
(3) Campbell, N.H.; Abd Karim, N.H.; Parkinson, G.N.;
Gunaratnam, M.; Petrucci, V.; Todd, A.K.; Vilar, R.;
Neidle, S. J. Med. Chem. 2012, 55, 209–222.
(4) Hille, A.; Ott, I.; Kitanovic, A.; Kitanovic, I.; Alborzinia,
¨
¨
H.; Lederer, E.; Wolfl, S.; Metzler-Nolte, N.; Schafer, S.;
Sheldrick, W.S.; Bischof, C.; Schatzschneider, U.; Gust, R.
J. Bio. Inorg. Chem. 2009, 14, 711–725.
(5) Hui, J.K.H.; Zhen, J.; MacLachlan, M.J. Angew. Chem. Int.
Ed. 2007, 46, 7980–7983.
(6) Dalla Cort, A. In In Ion-Pair Receptors in Supramolecular
Chemistry: From Molecules to Nanomaterials. Steed, J.W.,
Gale, P.A., Eds.; Wiley: Chichester, 2012; pp. 1281–1308.
(7) Dalla Cort, A.; De Bernardin, P.; Forte, G.; Yafteh Mihan,
F. Chem. Soc. Rev. 2010, 39, 3863–3874.
(8) Di Bella, S. Chem. Soc. Rev. 2001, 30, 355–366.
(9) Engbersen, J.F.; Harkema, S.; Reinhoudt, D.N. J. Am.
Chem. Soc. 1992, 114, 9671–9673.
(10) Van Axel Castelli, V.; Dalla Cort, A.; Mandolini, L.; Pinto,
V.; Reinhoudt, D.N.; Ribaudo, F.; Sanna, C.; Schiaffino, L.;
Snellink-Rue¨l, B.H.M. Supramol. Chem. 2002, 14,
211–219.
(11) Cametti, M.; Nissinen, M.; Dalla Cort, A.; Mandolini, L.;
Rissanen, K. J. Am. Chem. Soc. 2007, 129, 3641–3648.
(12) Dalla Cort, A.; Forte, G.; Schiaffino, L. J. Org. Chem. 2011,
76, 7569–7572.
Complexes 1 and 2. 0.450 g (1.51 mmol) of aldehyde 5 was
dissolved in 20 ml of MeOH absolute. The mixture was
stirred and refluxed until dissolution of the solid, then
salicylaldehyde (158 ml, 1.51 mmol) and, after 2 min, 1,2-
diaminobenzene (0.158 g, 1.46 mmol) was added and the
solution was stirred for 20 min. After this, uranyl acetate
dihydrate (0.725 g, 1.71 mmol) was added. The reaction
mixture was then stirred and refluxed for 1 h 30 min. After
cooling at room temperature, the precipitated red solid was
filtered and then purified by chromatographic column in
flash silica gel using CHCl3 as eluent. From the column, two
fractions were collected containing, respectively, com-
plexes 1 and 2. Addition of acetone resulted in the
precipitation of the compounds that were isolated as orange
powders. Yields 27% (1) and 10% (2).
(13) de Silva, A.P.; Gunaratne, H.Q.N.; Gunnlaugsson, T.;
Huxley, A.J.M.; McCoy, C.P.; Rademacher, J.T.; Rice, T.E.
Chem. Rev. 1997, 97, 1515–1566.
(14) Prodi, L. New J. Chem. 2005, 29, 20–31.
(15) Credi, A. New J. Chem. 2012, 36, 1925–1930.
(16) Zapata, F.; Caballero, A.; White, N.G.; Claridge, T.D.W.;
Costa, P.J.; Felix, V.; Beer, P.D. J. Am. Chem. Soc. 2012,
134, 11533–11541; Sun, S.-S.; Lees, A.J. Coord. Chem.
Rev. 2002, 230, 171–192; Raad, F.S.; El-Ballouli A.O.;
Moustafa, R.M.; Al-Sayah, M.H.; Kaafarani, B.R. Tetra-
hedron 2010, 66, 2944–2952.
(17) Kunkler, H.; Vogler, A. Verlag Z. Naturforsh. 2002, 57b,
301–304.
(18) Flegel, M.; Lukeman, M.; Huck, L.; Wan, P. J. Am. Chem.
Soc. 2004, 126, 7890–7897.
1
Complex 1. H NMR (300 MHz, CDCl3) d: 9.53 (s, 1H),
9.38 (s, 1H), 8.45 (s, 1H), 8.07 (d, 2H, J ¼ 8.4 Hz), 7.90–
7.78 (m, 3H), 7.70–7.50 (m, 5H), 7.38 (dd, 3H,
J ¼ 7.2 Hz), 7.2–7.1 (m, 2H), 7.17 (t, 1H, J ¼ 1.2 Hz),
6.98 (d, 1H, J ¼ 1.2 Hz), 6.81 (t, 1H, 1.2 Hz). 13C NMR
(75 MHz, CDCl3) d: 165.72, 165.63, 138, 136.25, 135.46,
135.08, 131.14, 130.38, 128.84, 138.73, 128.22, 126.98,
126.32, 125.25, 124.96, 121.17, 119.55, 117.96,
117.52 ppm. MS-ESI-TOF for C34H22N2O4NaU calcd
783.1985, found 783.1967 m/z þ.
(19) Hofsølkken, N.; Skattebøl, L. Acta Chem. Scand. 1999, 53,
258–262.
(20) Fabbrizzi, L.; Marcotte, N.; Stomeo, F.; Taglietti, A.
Angew. Chem. Int. Ed. 2002, 41, 3811–3814.

Supramolecular Chemistry
115
(21) Beer, P.D. Acc. Chem. Res. 1998, 31, 71–80.
(22) Gale, P.A.; Anzenbacher, Jr, P.; Sessler, J.L. Coord. Chem.
Rev. 2001, 222, 57–102.
(23) Leung, K.C.-F.; Nguyen, T.D.; Stoddart, J.F.; Zink, J.I.
Chem. Mater. 2006, 18, 5919–5928.
(24) Zhao, S.-B.; McCormick, T.; Wang, S. Inorg. Chem. 2007,
46, 10965–10967.
(25) Jiasheng, W.; Weimin, L.; Jiechao, G.; Hongyan, Z.;
Pengfei, W. Chem. Soc. Rev. 2011, 40, 3483–3495.
(26) Balzani, V., Ed. Electron Transfer in Chemistry; Wiley-
VCH: Weinheim, 2001.
(27) Fabbrizzi, L.; Gatti, F.; Pallavicini, P.; Parodi, L. New
J. Chem. 1998, 22, 1403–1407.
(28) Magri, D.C.; Brown, G.J.; McClean, G.D.; de Silva, A.P.
J. Am. Chem. Soc. 2006, 128, 4950–4951.
(29) de Silva, A.P.; Moody, T.S.; Wright, G.D. Analyst 2009,
134, 2385–2393.
(30) Shen, Y.Z.; Pan, Y.; Wang, L.Y.; Dong, G.; Jin, X.P.;
Huang, X.Y.; Hu, H. J. Organomet. Chem. 1999, 590,
242–247.
(31) Burrow, H.D.; Kemp, T.J. Chem. Soc. Rev. 1974, 3, 139–
165; Azenha, E.M.D.G.; Burrows, H.D.; Fermosinho, S.J.;
Miguel, Maria de Grac¸a M. J. Chem. Soc., Faraday Trans. 1
1989, 85, 2625–2634.
(32) Nocton, G.; Horeglad, P.; Vetere, V.; Pe’caut. J.; Dubois,
L.; Maldivi, P.; Eldstein, N.M. J. Am. Chem. Soc. 2010,
132, 495–508; Hardwick, H.C.; Royal, D.S.; Helliwell, M.;
Pope, S.J.A.; Ashton, L.; Goodacre, R.; Sharrad, C.A.
Dalton Trans. 2011, 40, 5939–5952.
(33) Gilbert, A.; Baggott, J. In Essentials of Molecular
Photochemistry; Blackwell Science Ltd: Oxford, 1991;
p 161.
(34) Turro, N.; Scaiano, J.C.; Ramamurthy, V. Modern
Molecular Photochemistry of Organic Molecules; Univer-
sity Science Books: Herndon, VA, 2008.
(35) (a) Bouas-Laurent, H.; Castellan, A.; Desvergne, J.-P.;
Lapouyade, R. Chem. Soc. Rev. 2000, 29, 43–55; (b) Bouas-
Laurent, H.; Castellain, A.; Desvergne, J.-P.; Lapouyade, R.
Chem. Soc. Rev. 2001, 30, 248–263.
(36) Dubois, D.; Moninot, G.; Kutner, W.; Jones, M.T.; Kadish,
K.M. J. Phys. Chem. 1992, 96, 7137–7145.