2,2′-Biquinolines as test pilots for tuning the colour emission of luminescent mesomorphic silver(i) complexes

Article abstract of DOI:10.1039/c0dt01842b

The synthesis and characterization of a series of 2,2′-biquinolines differently substituted in the 4,4′-position and their corresponding silver(i) derivatives obtained through reaction with silver triflate in a 1:1 stoichiometric ratio are reported. In or

Full text of DOI:10.1039/c0dt01842b

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PAPER
2
,2¢-Biquinolines as test pilots for tuning the colour emission of luminescent
mesomorphic silver(I) complexes†
a
a,b
a
a
a,b
Daniela Pucci,* Alessandra Crispini, Mauro Ghedini, Elisabeta I. Szerb and Massimo La Deda
Received 29th December 2010, Accepted 7th March 2011
DOI: 10.1039/c0dt01842b
The synthesis and characterization of a series of 2,2¢-biquinolines differently substituted in the
4,4¢-position and their corresponding silver(I) derivatives obtained through reaction with silver triflate
in a 1 : 1 stoichiometric ratio are reported. In order to perform a systematic investigation on the role
played by the substituents on the coordination to the silver(I) centre, structural studies through single
crystal X-ray diffraction have been performed on two Ag(I) model complexes. Unlike their analogous
2,2¢-bipyridine ligands, the biquinolines have been found to behave only as chelated ligands towards the
silver(I) ion, irrespective of the substituents. The coordination sphere of the Ag(I) is filled by a solvent
molecule and, depending on the presence and nature of the substituents on the organic ligand, by an
oxygen atom coming from a coordinated triflate or from a carboxylic group of a symmetrically related
molecule, giving rise to neutral or ionic species. For the highest Ag(I) triflate homologues the presence
of long and flexible peripheral tails makes it possible to achieve liquid crystalline properties with
columnar organization whose high order is due to the large and rigid core. Moreover, the metal
coordination induces in all the Ag(I) species interesting emission properties both in solution and
condensed states, giving rise to blue or green emitters, depending on the nature of the substituents on
the biquinoline units.
Introduction
Ag(I) cations are attracting a great deal of attention due to the
high flexibility of the coordination numbers and geometries of
the corresponding complexes, above all when based on N-donor
Inorganic crystal engineering has been increasingly used over
recent years for generating a wide variety of molecular archi-
tectures and supramolecular arrangements, properly designed
for the development of innovative materials whose properties
and functionalities are controlled through the choice of simple
12
pyridyl ligands.
In this context we have been recently involved in the study of 4,4¢-
substituted-2,2¢-bipyridines whose great coordination versatility
allowed us to tune, in dependence of the counterion and of
the substituents used, the electroneutrality, the topology, the
supramolecular architectures as well the various properties in
1–6
and suitable building-blocks. The proper control of the self-
organizing process is critical for the synthesis of dynamically
functional soft materials such as liquid crystals, for which the
right combination of specific intermolecular interactions, nano-
segregation and molecular shape represents the key point for their
13
a series of silver(I) derivatives. Indeed, by selecting proper
parameters (coordinating ability of the anion of the silver salt,
substituents on the 2,2¢-bipyridine ligand, ligand-to-metal stoi-
chiometric ratio) we have been able to drive the supramolecular
self-assembly for inducing argentophilic and/or microsegregation
7–10
synthesis. The overall structure is predominantly controlled by
the nature of the transition metal ion and the organic ligand
chosen, but the network topology and the subsequent physical
and optical properties are affected by non covalent interactions,
responsible for the onset of liquid crystalline properties, in silver(I)
14–18
derivatives.
Here we are reporting an extension of our work
1
0
including, in the case of d metal ions, the metallophilic one
in which we have investigated the effect of the presence of
a larger and more rigid p system introduced on the organic
framework (by using 2,2¢-biquinolines ligands), exerted on both
the supramolecular organization and the thermal behaviour of a
series of triflate Ag(I) complexes. For this class of oligopyridines,
the presence of two donor atoms and the flexibility of the two
quinoline units linked together by a single C–C bond provide the
potential for coordinating to metal ions in a variety of modes.
The increased aromatic/aliphatic ratio in the biquinoline Ag(I)
derivatives should however preserve the proper phase segregation
helpful in the formation of liquid-crystalline structures. At the
11
(
aurophilicity). In particular, coordination polymers based on
a
Centro di Eccellenza CEMIF.CAL-LASCAMM, CR-INSTM Unit a` della
Calabria, Dipartimento di Chimica, Universit a` della Calabria, Via P. Bucci
Cubo 14C, Italy. E-mail: d.pucci@unical.it; Fax: +39 0984 492066
b
Centro di Eccellenza CEMIF.CAL-LASCAMM, CR-INSTM Unit a` della
Calabria, Dipartimento di Chimica, Dipartimento di Scienze Farmaceutiche,
Universit a` della Calabria, Edificio Polifunzionale, Italy
†
Electronic supplementary information (ESI) available. CCDC reference
numbers 805766 (1) and 805767 (2). For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt01842b
4
614 | Dalton Trans., 2011, 40, 4614–4622
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3
same time, fluorescence emission properties of the biquinoline
of L has been performed through the reaction between I and
thionyl chloride, followed by the coupling of the resulting acid
chloride with the hexadecyl alcohol. Finally, the reaction between
19
chromophores should expand the applicability of the Ag(I)
complexes leading them to be able to tune the photoluminescent
properties using phase transitions induced by thermal treatment.
Thus we have designed a series of 2,2¢-biquinolines to use as
building blocks for the formation of silver(I) complexes through
reaction with the moderately coordinating triflate anion in a 1 : 1
ratio (Fig. 1). The influence of the presence/absence and nature
of substituents in the p,p¢ positions with respect to the nitrogen
atoms of the ligands on the structure and functional properties
of the resulting Ag(I) compounds will be discussed and compared
with those of analogous 2,2¢-bipyridine-based derivatives.
2
L and the 3,4,5-tridodecyloxy benzoic acid through a DCC–
4
2
PPY esterification afforded L in a two step procedure: L was
reduced to 4,4¢-bis(hydroxymethyl)-2,2¢-biquinoline with NaBH
4
,
and subsequently reacted with 3,4,5-tridodecyloxy benzoic acid
through a DCC–PPY esterification.
All the ligands were characterized by elemental analyses, IR,
H NMR and UV-vis spectroscopies (Experimental Section)
1
confirming the structure proposed in Fig. 1.
n
The reaction between the L ligands and silver triflate (AgOTf),
performed in a 1 : 1 ratio for 12 h in chloroform solution
(
Experimental Section), led to yellowish air stable solids, 1–4,
separated in good yields (60–90%).
For all Ag(I) complexes, characterized by elemental analyses,
1
IR, H NMR and UV-vis spectroscopies (Experimental Section),
only the 1 : 1 ligand-to-metal ratio products have been isolated,
while the same synthetic pathway followed using a series of anal-
ogous 2,2¢-bipyridine ligands afforded the formation of products
with different stoichiometries (1 : 1, 2 : 1 or 3 : 2 for a 1 : 1 ligand-
13,17–18
to-metal ratio) despite the initial proportion used.
Moreover,
in the case of the bipyridines reported previously, the presence
and the nature of substituents in 4,4¢ positions was found to
drive both their coordination mode (monochelated or bridged)
and the participation of the triflate anion to the coordination, in
determining the fulfilling of the coordination sphere of the Ag(I)
ion. Therefore structural analyses of the model Ag(I) biquinoline
derivatives 1 and 2 have been performed in the solid state in
order to clarify their effective molecular structure. The main
structural feature highlighted by the X-ray single-crystal structures
of complexes 1 and 2 is the exclusive chelated coordination mode
of the biquinoline to the silver ion, despite their substitution
Fig. 1 Chemical structure, synthesis and related proton numbering
scheme of ligands L –L .
1
4
(
Fig. 2).
Results and discussion
Synthesis and structural studies
In order to perform a systematic investigation on the role played
by the substituents of the biquinoline ligands in the coordination
of the silver(I) centre and in the supramolecular architectures of
1
the metal derivatives, four types of ligands have been used (L –
4
1
L in Fig. 1). Starting from the unsubstituted L and the 4,4¢-
2
bis(methoxycarbonyl)-2,2¢-biquinoline L (chosen as model lig-
ands in the construction of small dimensional model complexes),
3
4
Fig. 2 Perspective view of the asymmetric unit content of 1 (a) and 2 (b)
with atomic numbering scheme (ellipsoids at the 40% level).
two promesogenic biquinolines (L –L ) have been designed for
promoting nano-segregation and intermolecular interactions in
the corresponding triflate silver(I) derivatives. Long aliphatic
chains have been introduced through an electron withdraw-
However, the presence of the carboxylic substituents on the
2
ing link in the 4,4¢-bis(hexadecyloxycarbonyl)-2,2¢-biquinoline
organic ligand L is responsible for a difference in the coordination
3
L
and a long polycatenar system was grafted on a further
sphere of the silver ion. In the case of complex 1, one water
molecule and the oxygen atom of one triflate anion are coordinated
to Ag(I), with the generation of a neutral unit molecule (Fig. 2a).
The proximity of the two ligands is such that there is a short
aromatic ring through the weakly electron donating methylene
group, in the 4,4¢-bis[3,4,5-tri(dodecyloxy)benzoyloxymethyl]-
4
2
,2¢-biquinoline L ligand.
2
4
˚
The synthetic strategy used for the synthesis of L –L is based on
distance between the O(2) and O(4) atoms (O ◊ ◊ ◊ O, 2.847(7) A),
the commercially available 2,2¢-biquinoline-4,4¢-dicarboxylic acid
which may give rise to an intramolecular hydrogen bond. However,
the best calculated positions for the hydrogen atoms bound to
the oxygen water molecule do not seem to fulfil the geometrical
(
I) (Fig. 1). In particular, the Fischer esterification of the precursor
2
I with methanol gave rise directly to ligand L . The preparation
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parameters characteristic for a significant hydrogen bond [O(4)–
Table 1 Phase transition data of complexes 3–4
◦
˚
H(4b) ◊ ◊ ◊ O(2) 2.25 A, O–H ◊ ◊ ◊ O, 126 ].
a
◦
b
DH/kJ mol-1
Complex
Transition
T/ C
The asymmetric unit of complex 2 is given by a silver cation
and a triflate anion non interacting to each other. The silver
ion, in a pseudotetra-coordination geometry, is bound to two
3
[
Ag(L )(OTf)], 3
Cr–Col
L
146.8
166.6
159.1
135.0
72.9
102.3
86.2
34.7
13.3
15.7
39.2
0.73
34.2
30.6
Col –I
L
2
I–ColL
nitrogen atoms of the chelating L ligand, a water molecule and
L
Col –Cr
the oxygen atom belonging to the methoxycarbonyl substituent of
4
[
Ag(L )](OTf), 4
Cr–Colobp
Colobp–I
I–Colobp
i
˚
a symmetrically related molecule [Ag–O(2) = 2.699(2) A, i = 2-x,
1-y, -z] (Fig. 2b).
In both cases, the crystal packing is characterized by the
a
L
Cr: crystal; Col : lamello-columnar; Colobp plastic columnar oblique
b
presence of strong associations between the extended aromatic
ligands through p–p aromatic stacking interactions and the
formation of columns (Fig. 3), characterized by short interplanar
lattice; I: isotropic liquid. Onset peaks, second heating–cooling cycle.
˚
2
distances of about 3.4 A and indicative of the overlap of the
aromatic rings.
respectively, for 3 and 4 the intermediate values of 25 and 30 cm
X
or ionic species.
molecule of water at 95 C was detected by the TGA analyses (see
20
-
1
-1
mol are not conclusive to clearly distinguish between neutral
21–22
In the solid state for 1 and 2 a loss of one
◦
ESI), while complexes 3 and 4 do not show any water content
◦
with any weight loss until 250 C, where the decomposition starts.
Therefore we can hypothesize that the coordination sphere of
the Ag(I) ion is completed with the coordination of the triflate
ion (such as in complex 1) and the interaction with an oxygen
atom coming from the carboxylic group and/or an anion of
a symmetrically related molecule (such as in complex 2). Both
complexes 3 and 4 can be neutral in nature in the solid state but
undergo a partial dissociation of the coordinated triflate ion in
solution.
Fig. 3 Crystal packing views of 1 in (a) and 2 in (b) showing the formation
of columns with intracolumnar p–p aromatic stacking interactions.
Thermal properties
Within the columns the strong vicinity of the two molecular
units is reinforced by the presence of hydrogen bonds between
the coordinated water molecules and the coordinated in 1 and
non-coordinated in 2 triflate anions [O(4)–H(4A) ◊ ◊ ◊ O(3) (x, y,
The thermal properties of the Ag(I) complexes 3 and 4 (Table
1
) based on the biquinolines bearing the longest promesogenic
3
4
substituents, L and L , respectively, were investigated by using
polarised optical microscopy (POM) and differential scanning
calorimetry (DSC) with the intention to establish possible analo-
gies with their analogous silver 2,2¢-bipyridine triflate derivatives.
Although none of the ligands L shows liquid crystalline proper-
◦
˚
˚
z-1), 2.11 A; O ◊ ◊ ◊ O, 2.858(8) A; O–H ◊ ◊ ◊ O, 144 for 1; O(1)–
˚
˚
H(1w) ◊ ◊ ◊ O(7) (x+1, y, z-1), 1.89 A; O ◊ ◊ ◊ O, 2.757(3) A; O–
17
◦
˚
H ◊ ◊ ◊ O, 157 , O(1)–H(2w) ◊ ◊ ◊ O(8) (x, y, z-1), 1.92 A; O ◊ ◊ ◊ O,
n
◦
˚
2
.809(3) A; O–H ◊ ◊ ◊ O, 171 for 2].
ties, an interesting thermal behaviour was induced upon com-
plexation. On POM both complexes 3 and 4 show rather fine
textures with a limited flowability when subject to stress, whose
identification was not unequivocal. In particular, 3 shows, on
both heating and cooling cycles (enantiotropically) an uncommon
birefringent texture (Fig. 4a) while for the polycatenar complex
In absence of structural studies performed on the highest
homologues 3 and 4, the definition of their molecular structure
has been based on analogies with complexes 1 and 2. In solution,
3
4
the success of the coordination of L and L to the Ag(I) ion
1
has been evidenced in the H NMR spectra of 3 and 4 from the
6
,6¢
7,7¢
upshift of the signals attributable to the H and H protons
with respect to the organic precursors. Moreover, in order to
define the neutral or ionic nature of complexes 3 and 4 (that is the
presence of a coordinated or non coordinated triflate per silver ion)
conductivity measurements have been performed in acetone and
dichloromethane solutions. In acetone all complexes behave as 1 : 1
4
, Maltese crosses appeared after annealing on cooling from the
isotropic melt, which developed in the fingerprint texture reported
in Fig. 4b.
2
-1
-1
electrolytes (168–180 cm X mol ), thus they undergo a complete
ionic dissociation in a polar medium and this can be attributed to
the lability of the moderate coordinating triflate group. Therefore
we have carried out conductivity measurements in an apolar and
non coordinating solvent such as dichloromethane. Even if this
solvent usually is not the best for conductivity measurements due
to its eventual ion-pairing effects, in these complexes the size
of the cation can avoid this limitation. Differently from model
compounds 1 and 2 for which the equivalent conductances in
Fig. 4 Polarized light optical photomicrograph of the textures exhibited
by complex 3, at 125 C on cooling (Plate a); by complex 4 at 71 C on
cooling (Plate b).
◦
◦
2
-1
-1
dichloromethane have been found to be 6 and 60 cm X mol
4
616 | Dalton Trans., 2011, 40, 4614–4622
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The nature of the phases was clarified by powder X-ray
diffraction experiments carried out at variable temperatures.
In the small angle range of the X-ray diffraction pattern of
◦
3
, recorded at 155 C on heating, three diffraction peaks with
reciprocal spacings in the ratio 1 : 2 : 3 and indexed as (001), (002)
and (003) are observed. These three peaks indicate the presence
of a very pronounced layered structure, with a repetition distance
˚
d of 31.9 A (Fig. 5). Two broad halos are observed in the wide-
L
˚
angle part, centred at 4.3 and 3.4 A, referred to as hch and h
corresponding to the liquid-like order of the molten chains (hch
and the stacking of the molecular cores (h
0
,
)
0
). These intermolecular
interactions are associated with a degree of columnar stacking
within the layers, driving towards the assignment of a highly
ordered lamello-columnar mesophase, Col .
L
Fig. 6 Proposed packing diagram for the Col
L
phase of 3 showing
(
a) the layered repetition of columns and (b) the monoclinic columnar
organization within the layers.
To investigate the structure of the phase in complex 4, the
◦
X-ray powder pattern was recorded at 30 C on cooling (Fig.
7
). A set of several peaks was observed in the small and middle
angle region of the powder pattern and successfully indexed as a
two-dimensional oblique lattice with lattice parameters a = 42.1
◦
˚
˚
A, b = 35.8 A and g = 112.3 (see ESI). This is in agreement with
the formation of a columnar structure with the resulting columns
packed into an oblique lattice (Fig. 8). The plastic nature of this
columnar phase is evident from the wide angle region of the X-ray
2
5,26
powder pattern (see ESI).
Indeed, a relatively intense and sharp
˚
reflection at 4.4 A (indexed as the (001) reflection) under the broad
halo hch reveals additional intracolumnar periodicity and indicates
a degree of three-dimensional order of the molecules within the
columns. Furthermore, the stack of the molecules is reinforced by
◦
p–p stacking interactions, as confirmed by the broad h reflection
centred at 3.6 A.
0
Fig. 5 X-ray powder diffraction pattern of complex 3 at 155 C on
heating; the middle and wide angle regions of the powder pattern in (a)
and subtracted background in (b).
˚
The other diffraction peaks, observed in the middle angle region
of the spectra, reflect the organization of 3 within each layer. These
peaks can be indexed on a two-dimensional monoclinic lattice with
˚
˚
parameters a = 9.79 A, b = 8.96 A, and an angle g between the two
◦
directions of about 86 (see ESI for indexing and Fig. 6).
For complex 4, the enhancement of the aliphatic periphery
4
grafted around the poly-branched biquinoline ligand L is ac-
companied by a visible change of thermal behaviour of the
corresponding silver(I) derivative. The difference in the molecular
anisotropy and the volume of the two silver(I) compounds changes
◦
their phase stability, lowering by 60 C the clearing temperature
of 4 with respect to 3. Moreover, the high viscosity and the texture
developed on POM, the relatively high enthalpy transition value
at the isotropization, could be indicative of the formation of a
23
high ordered columnar phase. Since columnar ordered phases
prove to be the closest relation to crystalline structures, they are
often considered and defined as “soft crystals” instead of liquid-
crystalline systems. Moreover, when the sample can be sheared
easily, as in this case, unlike other three-dimensionally ordered
◦
phases, the definition of plastic columnar phase (Col
p
) is also
Fig. 7 X-ray powder diffraction pattern of complex 4 at 30 C on cooling;
24
applied.
the middle and wide angle regions of the powder pattern in the inset.
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Table 2 Photophysical data of ligands and complexes
Em, lmax/nm
complex
CH
2
Cl
2
solution (U)
powder sample
mesophase
1
L
410 (0.010)
448 (0.035)
452 (0.010)
425 (0.015)
478 (0.006)
525(0.040)
525(0.016)
453 (0.022)
415
460
460
430
519
556
560
490
2
L
3
L
L
1
2
3
4
4
—
—
560
460
Fig. 8 Proposed packing diagram for the Colobp. phase of 4 showing the
repetition of ordered columns packed into an oblique lattice.
structure and show a weakening of the low-energy absorption band
due to the quinoline co-planarity defeat that reduces the oscillator
strength of the ILCT between the two quinoline moieties.
Moreover, on cooling from the isotropic liquid, complex 4
does not crystallize but solidifies into a glassy state retaining the
structure of the mesophase. All of these findings point towards the
assignment of a plastic columnar phase with an oblique symmetry,
28
The complexation forces all the molecules into a rigid and
planar cis conformation, regardless of the stabilization effect
induced by the electronic delocalization; so the dichloromethane
solution absorption spectra of the silver(I) complexes 1–4 are all
Colobp
.
Comparing the behaviour of 3 with that reported for the
1
0
17
vibrationally structured. The d metal co-ordination does not
influence the electronic transitions already active in the ligands,
and the spectral features of all complexes are unvaried with respect
to those of the corresponding ligands, showing a bathochromic
shift only.
analogous silver 2,2¢-bipyridine triflate derivative, it seems that
the change of the oligopyridine, although causing a drastic change
in the coordination mode and the global molecular shape, does not
affect the lamello-columnar nature of the mesophases formed.
However, in the case of the polycatenar substituted biquinoline
derivative 4, the increased number of terminal chains drives to a
pure highly ordered columnar arrangement.
As regards the luminescence, all the ligands in dichloromethane
solution and in the solid state emit, irrespective of the wavelength
excitation (Table 2). Both the unsubstituted and polycatenar
1
4
ligands, L and L emit in the violet region while the reduced
Photophysical properties
rigidity achieved with the presence of the esteric substituents
2
3
The photophysical behaviour of the chromophore 2,2¢-
biquinolines and the corresponding Ag(I) derivatives has been
investigated both in solution and in their condensed states (ESI).
in L and L shifts the emission maxima towards the blue
region.
The luminescence of complexes 1–4, which is due to the metal-
perturbed ILCT state de-excitation, is strongly red-shifted in
solution (about 100 nm) with respect to that of the corresponding
biquinoline precursors (Table 2). Therefore complexes 1 and 4 emit
in the blue region while 2 and 3 behave as green emitters.
Solid samples of 1–4 complexes show a remarkable lumines-
cence, having the same origin of the compounds in solution, but
the maxima are red-shifted with respect to the corresponding
spectra recorded in solution. This behaviour is attributed to
the intermolecular interactions existing in the condensed phase,
allowing a certain degree of electronic delocalization. Comparing
the spectral shift amount within complexes 1–4, it is possible to
note that in 1 the shift of the emission maximum from 478 nm in
solution to 519 nm in the solid state is more relevant with respect
to the other complexes, raising, in terms of energy, the value of
1
4
In the room temperature absorption spectra of L –L recorded
in dichloromethane solution three groups of bands are detected
(
see ESI), all originating from p–p* transitions on the aromatic
rings of the 2,2¢-biquinoline: an intense band (maximum spanning
in the 250–290 nm range, depending on the compound considered)
originating from an excitation on the pyridyl ring of the quinoline
ligand; a series of medium-intensity bands (in the 290–350 nm
range) due to vibronic components of an intraligand charge-
transfer (ILCT) from the pyridyl to the phenyl ring of the quinoline
unit, and a weak band (in the 350–390 nm range) attributed to an
ILCT from the pyridyl ring of a quinoline moiety towards the
26–27
phenyl ring of another quinoline.
By comparing the absorption spectra of the ligands, it can be
1
noted that the spectrum of the unsubstituted biquinoline L is
4
-1
substantially the same as that of L , both being characterized by
1653 cm . Therefore this compound changes from blue to green
a vibrational structure which indicates an accentuated molecular
emitter by passing from the solution to the solid state, while
the other complexes in solid retain a green (2 and 3) or a blue
emission (4) like in solution. This effect is directly related to
the enhancement of vibrational motions in the solid state of
complexes 2–4, due to the presence of mobile substituents on
the biquinoline ligand, when compared to complex 1. Since in
solution vibrational motions are relevant, in the solid phase of
complex 1 the vibrational losses are very low in absence of mobile
substituents.
2
rigidity in solution; this feature is absent in the spectra of L and
3
1
4
L . In L and L a great stabilization derives from an extended
electronic delocalization on both the quinoline rings, which forces
the molecule into a rigid and planar trans conformation. In
contrast, the introduction of electron-withdrawing substituents,
such as esteric groups, directly connected to the phenyl rings
2
3
of L and L (the length of the alkoxy chains is irrelevant to
the electronic properties) reduces the delocalization and allows
a degree of torsion around the s-bond connecting the quinolinic
Moreover, the luminescent properties of complexes 3 and 4 are
kept in their mesophases. Indeed, maxima centred at 560 and
2
3
moieties. Therefore the spectra of L and L lose the vibrational
4
618 | Dalton Trans., 2011, 40, 4614–4622
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3
0,31
4
60 nm, respectively, are detected. These values are very similar to
thetic route reported previously in the literature was followed.
1
those of their solid samples, proving the small differences existing
between the intermolecular interactions responsible for the two
aggregation states.
H NMR spectra were acquired on a Bruker Avance DRX-300
spectrometer in CDCl solution, with TMS as internal standard.
3
Infrared spectra were recorded with a Spectrum One FT-IR
Perkin-Elmer spectrometer. Elemental analyses were performed
with a Perkin-Elmer 2400 microanalyzer by the Microanalytical
Laboratory at the University of Calabria. Conductivity measure-
ments were performed in dichloromethane and acetone, with
an InoLab Cond Level 1-720 conductometer equipped with a
LR 325/001 immersion cell. The transition temperatures and
enthalpies were measured on a Perkin-Elmer Pyris1 Differen-
tial Scanning Calorimeter with a heating and cooling rate of
Conclusions
The use of 2,2¢-biquinoline ligands in the coordination of silver(I)
ion has proven to be a good strategy for the generation of a
series of mononuclear silver(I) complexes starting from silver
triflate in a 1 : 1 metal-to-ligand stoichiometric ratio. Unlike
their analogous bipyridine-based Ag(I) complexes, the enlarged
aromatic portion of the 2,2¢-biquinolines pushes them to coor-
dinate in an exclusive chelating mode to the silver(I) ion. The
presence of appropriate terminal tail lengths on the biquinolines
allows the existence in the corresponding Ag(I) derivatives, 3
and 4, of intermolecular interactions and micro-segregation able
to induce liquid crystalline behaviour. However, while in the
case of 3 the lamello-columnar nature of the mesophase is
retained, changing the oligopyridine from 2,2¢-bipyridine to 2,2¢-
◦
-1
1
0 C min . The apparatus was calibrated with indium. Three
17
heating/cooling cycles were performed on each sample. Thermo-
gravimetry (TGA) measurements were performed on a Perkin-
Elmer TGA6 Thermogravimetric Analyser, with a heating rate
of 10 C min . Spectrofluorimetric grade solvents were used for
the photophysical investigations in solution, at room temperature.
A Perkin-Elmer Lambda 900 spectrophotometer was employed
to obtain the absorption spectra. Steady-state emission spectra
were recorded on a HORIBA Jobin-Yvon Fluorolog-3 FL3-211
spectrometer equipped with a 450 W xenon arc lamp, double-
grating excitation and single-grating emission monochromators
◦
-1
17
biquinoline ligand, for the polycatenar derivative 4, the increased
aromatic flat portion of the core induces the formation of a
highly ordered (plastic) columnar arrangement with an oblique
symmetry.
-
1
(
2.1 nm mm dispersion; 1200 grooves/mm), and a Hamamatsu
R928 photomultiplier tube. Emission and excitation spectra were
corrected for source intensity (lamp and grating) and emission
spectral response (detector and grating) by standard correction
curves. Emission quantum yields were determined using the
Moreover, the biquinoline chromophores as nitrogen ligands
promote in their silver(I) derivatives, luminescence properties
completely absent in the similar bipyridine-based Ag(I) complexes.
Therefore complexes 1–4 emit in the blue or green region
depending on both the aggregation state and the substituents
on the biquinoline fragment. In particular, the introduction of
substituents on the biquinoline ligands plays an important role
in the modulation of the emission colours. The induction of a
certain degree of molecular motion is able to reduce the shift
of the emission maximum on going from the solution to the
solid state in the case of complexes 2–4. Therefore, only the
unsubstituted complex 1 changes from green to blue emitter
by passing from the solution to the solid state, while the other
complexes retain a green (2 and 3) or a blue emission (4) like in
solution. Moreover, complexes 3 and 4 preserve the luminescence
properties also in their mesophases. Due to this invariance of
the photophysical properties on moving towards a soft type of
aggregation state, it is possible to tune the emission colours of
these systems simply by introducing changes at a molecular level,
such as the presence of different substituents on the aromatic
core.
32
optically dilute method on aerated solutions of which absorbance
at excitation wavelengths was < 0.1; Ru(bipy) Cl (bipy = 2,2¢-
bipyridine) in water (U = 0.028) or 9,10-diphenylanthracene in
3
2
33
34
cyclohexane (U = 0.96) were used as standards. Luminescence
spectra from powder samples and from mesophase have been
obtained placing the powder between two quartz plates, in such
a position that the luminescence could be measured in reflection
mode, in front-face arrangement to reduce the scattered light.
To reach the mesophase, the two quartz plates were heated in
the sample compartment of the spectrofluorimeter by means
of a customized hot stage realized by CaLCTec s.r.l. (Rende,
Italy).
The experimental uncertainty on the molar extinction coef-
ficients is 10%, while that on the emission quantum yields is
10%. The examined compounds are fairly stable in solution, as
demonstrated by the constancy of their absorption spectra over a
week.
This type of self-organized anisotropic soft materials has a
great potential in a wide variety of fields of advanced tech-
nology preserving the same emission properties shown at room
temperature.
Powder X-ray diffraction
The powder X-ray diffraction patterns of 3 and 4 at variable
temperature were obtained using a Bruker AXS General Area
Detector Diffraction System (D8 Discover with GADDS) with
Experimental section
˚
Cu-Ka radiation (l = 1.54056 A). Measurements were performed
Materials and measurements
by placing samples in Lindemann capillary tubes with an inner
diameter of 0.05 mm. The highly sensitive area detector was
placed at a distance of 20 cm from the sample (2q detector placed
at 14 ) and equipped with a CalCTec (Italy) heating stage. The
samples were heated at a rate of 5.0 C min to the appropriate
temperature.
Silver triflate (AgOTf) and 2,2¢-biquinoline-4,4¢-dicarboxylic acid
were purchased from Aldrich and used as received. L was
2
◦
obtained through a small modification of a procedure reported in
29
◦
-1
the literature. For the synthesis of the bicatenar 2,2¢-biquinoline
3
4
ligand (L ) and the hexacatenar 2,2¢-biquinoline ligand (L ), a syn-
This journal is © The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 4614–4622 | 4619

View Online
◦
Table 3 Details of data collection and structure refinements for com-
plexes 1 and 2
Yield 95%. M. p. 288 C. Anal. Calcd. for C H N O (372.37):
2
2
16
2
4
1
C, 70.96; H, 4.33; N, 7.52; Found: C, 70.83; H, 4.35; N, 7.45. H
3
NMR (300 MHz, CDCl ): d 9.33 (2H, s, H3); 8.82 (2H, d, J = 8.4
3
3
1
2
3
Hz, H8); 8.43 (2H, d, J = 8.4 Hz, H5); 7.83 (2H, dt, J = 7.7 Hz,
4
3
4
Formula
Mr
Crystal size/mm
Crystal system
C
531.25
0.22 ¥ 0.15 ¥ 0.12
Monoclinic
19
H
14AgF
3
N
2
O
4
S
C
647.32
0.35 ¥ 0.22 ¥ 0.18
Triclinic
23
H
18AgF
3
N
2
O
8
S
J = 1.5 Hz, H7); 7.70 (2H, dt, J = 7.8 Hz, J = 1.4 Hz, H6); 4.13
-1
(s, 6H, COOCH
3
); IR (KBr): u
C
O
1733 cm .
¯
Space group
P2
1
/c
P1
Synthesis of 4,4¢-bis(hexadecyloxycarbonyl)-2,2¢-biquinoline,
a/A˚
13.5936(7)
20.5452(12)
7.1974(4)
90
7.2305(16)
12.765(3)
13.307(3)
83.416(10)
81.940(10)
86.948(10)
1207.2(4)
2
3
ligand L
b/A˚
c/A˚
◦
A mixture of the commercially available 2,2¢-biquinoline-4,4¢-
dicarboxylic acid (1.0 g, 2.904 mmol) and thionyl chloride
(70 mL) was refluxed under nitrogen atmosphere until a clear
yellow solution was obtained. The excess of thionyl chloride was
then removed and the residue dried under vacuum for 2 h. The
acid chloride was suspended in toluene (50 mL) and treated with a
small excess of 1-hexadecanol (1.690 g, 6.970 mmol). The mixture
was heated at reflux until a weakly pink solution was obtained
a ( )
◦
b ( )
98.058(3)
90
1990.27(19)
4
1.773
1.174
◦
g ( )
V/A˚
3
Z
-3
r calcd [g cm ]
1.781
0.998
1.55–28.28
23 305
-
1
m/cm
◦
q range [ ]
data collected
1.51–27.98
19 398
unique data, Rint
obs. data [I > 2s(I)]
no. parameters
4774, 0.0279
2931
271
0.0519
0.1653
1.061
5904, 0.0263
4602
343
0.0331
0.0867
(
18 h). Then the temperature was cooled to room temperature,
the solvent evaporated, chloroform was added and the mixture
was washed with saturated sodium hydrogen carbonate solution
and three times with water. The pure product was obtained after
recrystallisation from CHCl
01 C. Anal. Calcd. for C52
R
1
[obs. data]
[all data]
wR
2
GOF
1.027
3
–MeOH (2.07 g, yield 90%). M. p.
(793.17): C, 78.74; H, 9.66;
◦
1
H
76
N
2
O
4
X-ray crystallography
1
N, 3.53; Found: C, 78.51; H, 9.29; N, 3.85. H NMR (300 MHz,
3
CDCl ): d 9.31 (2H, s, H3); 8.79 (2H, d, J = 8.6 Hz, H8); 8.32
3 3
3
X-ray data for 1 and 2 were collected at room temperature on
a Bruker-Nonius X8 Apex CCD area detector equipped with
graphite monochromator and Mo-Ka radiation (l = 0.71073
(
2H, d, J = 8.3 Hz, H5); 7.82 (2H, t, J = 7.7 Hz, H7); 7.69 (2H,
3
3
t, J = 7.7 Hz, H6); 4.53 (t, 4H, J = 6.7 Hz, OCH ); 1.92 (m, 4H,
2
3
3
5
OCH
Hz, CH
2
CH
2
); 1.37 (overlapped peaks, 52H); 0.87 (t, 6H, J = 6.8
˚
A). Data were processed through the SAINT reduction and
-
1
36
3
); IR (KBr): u
C
O
1724 cm .
SADABS absorption software. The structures were solved
by standard Patterson methods through the SHELXTL-NT
37
structure determination package and refined by full-matrix least-
squares based on F . In general, all non-hydrogen atoms were
Synthesis of 4,4¢-bis[3,4,5-tri(dodecyloxy)benzoyloxymethyl)]-
2,2¢-biquinoline, ligand L
2
4
refined anisotropically and hydrogen atoms were included as
idealized atoms riding on the respective carbon atoms with C–
H bond lengths appropriate to the carbon atom hybridization.
Hydrogen atoms of the co-ordinated water molecules have been
included in calculated positions in 1, and detected in the difference
Fourier map and then their position included in the refinement in
2
To a suspension of ligand L (1.7 g, 4.5 mmol) in ethanol
(
130 mL) was added slowly an excess of NaBH
mol) and the reaction mixture was refluxed for 5 h. Subsequently,
to the yellow solution obtained saturated NH Cl solution (90 mL)
was added slowly. The white precipitate formed was filtered out,
washed with water, dried and used without further purifications
in the next step (4,4¢-bis(hydroxymethyl)-2,2¢-biquinoline, yield
3%). 3,4,5-Tridodecyloxy benzoic acid (1.0 g, 1.481 mmol), 4,4¢-
bis(hydroxymethyl)-2,2¢-biquinoline (0.213 g, 0.673 mmol) and 4-
pyrrolidinopyridine (Ppy, 0.100 g, 0.673 mmol) were dissolved in
the minimum volume of dry CH
4
(4.14 g, 0.110
4
2
. In both cases restraining bond distances and angles have been
used.
Details of data and structure refinements are given in Table
. CCDC 805766 (1) and 805767 (2) contain the supplementary
8
3
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
2
Cl
2
under nitrogen atmosphere.
◦
The temperature was then cooled down to 0 C. After 20 min,
N,N¢-dicyclohexylcarbodiimide (0.306 g, 1.481 mmol) dissolved
2
in the minimum volume of dry CH
reaction mixture was stirred at room temperature and under N
for five days. The white precipitate formed was then eliminated by
2
Cl was added dropwise. The
2
Synthesis of 4,4¢-bis(methoxycarbonyl)-2,2¢-biquinoline, ligand L
2
2
L was obtained through a Fischer esterification with methanol, in
presence of H
2
SO
4
, starting from the commercially available 2,2¢-
filtration and the pure ligand was isolated after recrystallisation
◦
biquinoline-4,4¢-dicarboxylic acid. In particular, the dicarboxylic
from CHCl
3
–MeOH (0.990 g, yield 41%). M. p. 115 C. Anal.
acid (2.0 g, 5.808 mmol) was suspended in 300 mL MeOH and
Calcd. for C106
H
168
N
2
O
10 (1630.48): C, 78.08; H, 10.39; N, 1.72;
1
4
0 mL of H
2
SO
4
was added slowly. The reaction mixture was
Found: C, 78.59; H, 10.40; N, 2.01. H NMR (300 MHz, CDCl
3
):
3
then heated to reflux and stirred until the total solubilisation
of the suspension. Then the yellowish solution was cooled to
room temperature, the solvent evaporated and slowly a saturated
solution of NaOH was added until pH 9. The white precipitate
formed was filtered out, washed with water and MeOH and dried.
d 9.03 (2H, s, H3); 8.25 (2H, d, J = 8.4 Hz, H8); 8.11 (2H, d,
3
3
3
J = 8.2 Hz, H5); 7.79 (2H, t, J = 7.6 Hz, H7); 7.65 (2H, t, J =
7.6 Hz, H6); 7.38 (s, 4H, b-H2); 5.90 (s, 4H, CH OOC); 4.03 (m,
2
12H, OCH
2
); 1.77 (m, 12H, OCH
2
CH
2
); 1.35 (overlapped peaks,
3
-1
108H); 0.87 (t, 18H, J = 6.3 Hz, CH
3
); IR (KBr): u
C
O
1714 cm .
4
620 | Dalton Trans., 2011, 40, 4614–4622
This journal is © The Royal Society of Chemistry 2011

View Online
-
1
-1
-5
-1
2
General procedure for the synthesis of silver(I) complexes 1–4
cm , uOTf 1220 cm ; K (C
X
M
= 1.6 ¥ 10 mol L , CH
2
Cl
2
) = 30 cm
-
1
-1
mol .
The synthesis of the complexes 1–4 was carried out starting from
n
the appropriate L ligand in a 1 : 1 ratio with silver triflate. The
reaction mixture in chloroform was heated to reflux and stirred
for 12 h, under nitrogen atmosphere and in vessel protected by
light.
Acknowledgements
Financial support received from the Ministero dell’Istruzione,
dell’Universit a` e della Ricerca (MIUR) through the Centro di
Eccellenza CEMIF.CAL (CLAB01TYEF) and from the Italian
PRIN funding no. 2006038447 is gratefully acknowledged.
Synthesis of complex 1
The yellowish precipitate formed after 12 h of reaction is filtered
◦
out and washed with ethylic ether (yield 68%). M. p. 257 C. Anal.
Notes and references
Calcd. for C19
H
14AgF
3
N
2
O S (531.25): C, 42.96; H, 2.66; N, 5.27;
4
1
Found: C, 42.90; H, 2.65; N, 5.26. H NMR (300 MHz, CDCl
3
):
d 8.87 (2H, d, J = 8.6 Hz, H3); 8.34 (2H, d, J = 8.6 Hz, H8); 8.25
1
A. J. Blake, N. R. Champness, P. Hubberstey, W. S. Li, M. A. Withersby
and M. Schr o¨ der, Coord. Chem. Rev., 1999, 183, 117.
3
3
3
3
2 L. E. Depero and M. L. Curri, Curr. Opin. Solid State Mater. Sci., 2004,
(
2H, d, J = 8.6 Hz, H4); 7.90 (2H, d, J = 7.9 Hz, H5); 7.77 (2H,
3 3
8
, 103.
t, J = 7.3 Hz, H7); 7.59 (2H, t, J = 7.3 Hz, H6); IR (KBr): uOTf
3
M. Ruben, J. Rojo, F. J. R. Salguero, L. H. Uppadine and J. M. Lehn,
-
1
-4
-1
2
-1
-1
1
381 cm ; K (C
M
-
= 2.6 ¥ 10 mol L , CH
2
Cl
2
2
) = 6 cm X mol ;
Angew. Chem., Int. Ed., 2004, 43, 3644.
5
-1
-1
-1
4 G. F. Swiegers and T. J. Malefetse, Chem. Rev., 2000, 100,
K (C = 5.7 ¥ 10 mol L , acetone) = 186 cm X mol .
M
3
483.
5
6
D. Maspoch, D. Ruiz-Molinaa and J. Veciana, Chem. Soc. Rev., 2007,
Synthesis of complex 2
36, 770.
Y. Yan and J. Huang, Coord. Chem. Rev., 2010, 254, 1072.
The yellowish precipitate formed after 12 h of reaction is filtered
out and washed with ethylic ether. The pure product was recovered
from the solution by evaporating the solvent (yield 86%). M. p.
7 J. W. Goodby, I. M. Saez, S. J. Cowling, V. Gortz, M. Draper, A. W.
Hall, S. Sia, G. Cosquer, S. E. Lee and E. P. Raynes, Angew. Chem., Int.
Ed., 2008, 47, 2754.
8
P. Palffy-Muorhay, W. Cao, M. Moreira, B. Taheri and A. Munoz,
◦
2
2
64 C. Anal. Calcd. for C23
H
18AgF
3
N
2
O
8
S (647.33): C, 42.67; H,
Philos. Trans. R. Soc. London, Ser. A, 2006, 364, 2747.
9 D. W. Bruce, J. W. Goodby, J. R. Sambles and H. J. Coles, Philos. Trans.
R. Soc. London, Ser. A, 2006, 364, 2567.
0 T. Kato, Chem. Commun., 2009, 729.
1 M. J. Katz, K. Sakaib and D. B. Leznof, Chem. Soc. Rev., 2008, 37,
1884.
1
.80; N, 4.33; Found: C, 42.35; H, 2.70; N, 4.24. H NMR (300
MHz, (CD
.37 (2H, d, J = 8.4 Hz, H5); 7.80 (2H, t, J = 7.8 Hz, H7); 7.71
2H, t, J = 7.0 Hz, H6); 4.19 (6H, s, COOCH
726 cm , uOTf 1225 cm ; K (C
1 cm X mol ; K (C
3
3
)
2
CO): d 9.34 (2H, s, H3); 8.77 (2H, d, J = 8.8 Hz, H8);
1
1
3
3
8
(
1
6
X
3
3
); IR (KBr): u
C O
-
1
-1
-5
-1
12 A. N. Khlobystov, A. J. Blake, N. R. Champness, D. A. Lemenovskii,
M
= 3.7 ¥ 10 mol L , CH
2
Cl ) =
2
A. G. Majouga, N. V. Zyk and M. Schr o¨ der, Coord. Chem. Rev., 2001,
2
-1
-1
-4
-1
2
M
= 1.4 ¥ 10 mol L , acetone) = 168 cm
2
22, 155.
-
1
-1
mol .
13 D. Pucci, A. Bellusci, A. Crispini, M. La Deda, M. Ghedini and E. I.
Szerb, Cryst. Growth Des., 2008, 8, 3114.
4 D. Pucci, G. Barberio, A. Bellusci, A. Crispini, M. La Deda, M. Ghedini
and E. I. Szerb, Eur. J. Inorg. Chem., 2005, 2457.
5 D. Pucci, G. Barberio, A. Bellusci, A. Crispini, M. Ghedini and E. I.
Szerb, Mol. Cryst. Liq. Cryst., 2005, 441, 251.
16 D. Pucci, G. Barberio, A. Bellusci, A. Crispini, B. Donnio, L. Giorgini,
1
1
Synthesis of complex 3
After 12 h of reaction, the reaction mixture was filtered through
celite and the pure product was obtained after recrystallisation
M. Ghedini, M. La Deda and E. I. Szerb, Chem.–Eur. J., 2006, 12,
from CHCl
3
–Et
2
O as a yellowish solid (yield 88%). Anal. Calcd.
S (1050.11): C, 60.62; H, 7.29; N, 2.66; Found:
6
738.
for C53
H
76AgF
3
N
2
O
7
1
7 A. Bellusci, M. Ghedini, L. Giorgini, F. Gozzo, E. I. Szerb, A. Crispini
and D. Pucci, Dalton Trans., 2009, 7381.
18 C. Pettinari, N. Masciocchi, L. Pandolfo and D. Pucci, Chem.–Eur. J.,
2010, 16, 1106.
9 J. W. Ye, P. Zhang, K. Q. Ye, H. Y. Zhang, S. M. Jiang, L. Ye, G. D.
Yang and Y. Wang, J. Solid State Chem., 2006, 179, 438.
20 C. Janiak, J. Chem. Soc., Dalton Trans., 2000, 3885.
21 W. J. Geary, Coord. Chem. Rev., 1971, 7, 81.
1
C, 60.55; H, 7.11; N, 2.44. H NMR (300 MHz, CDCl
3
): d 9.31
3
4
(
2H, s, H3); 8.79 (2H, dd, J = 8.6 Hz, J = 1.4 Hz, H8); 8.32 (2H,
3
3
d, J = 8.3 Hz, H5); 7.82 (2H, t, J = 7.7 Hz, H7); 7.69 (2H, t,
1
3
3
J = 7.7 Hz, H6); 4.53 (4H, t, J = 6.7 Hz, OCH
2
); 1.92 (4H, m,
3
OCH
2
CH
2
); 1.35 (52H, overlapped peaks); 0.87 (6H, t, J = 6.8
-
1
-1
Hz, CH
3
); IR (KBr): u
C
O
1723 cm , uOTf 1358 cm ; K (C = 3.0
M
-5
2
2 W. H. Lee and R. J. Wheaton, J. Chem. Soc., Faraday Trans. 2, 1979,
5, 1128.
23 U. Beginn, Prog. Polym. Sci., 2003, 28, 1049.
-
5
-1
2
-1
-1
¥
10 mol L , CH
2
Cl
2
) = 25 cm X mol ; K (C = 5.7 ¥ 10 mol
M
7
-
1
2
-1
-1
L , acetone) = 180 cm X mol .
2
4 S. Chandrasekhar, S. K. Prasad, D. S. S. Rao and V. S. K. Balagurusamy,
Proc. Indian Acad. Sci., Sect. A, 2002, 68, 175.
Synthesis of complex 4
2
5 J. Simmerer, B. Gl u¨ sen, W. Paulus, A. Kettner, P. Schuhmacher, D.
Adam, K.-H. Etzbach, K. Siemensmeyer, J. H. Wendorff, H. Ringsdor
and D. Haarer, Adv. Mater., 1996, 8, 815.
After 12 h of reaction, the reaction mixture was filtered through
celite and the pure product was obtained after recrystallisation
26 I. Tomatsu, C. F. C. Fiti e´ , D. Byelov, W. H. de Jeu, P. C. M. M.
Magusin, M. Wubbenhorst and R. P. Sijbesma, J. Phys. Chem. B, 2009,
from CHCl /hexane as a white solid (yield 93%). Anal. Calcd. for
3
1
13, 14158; M. Maestri, D. Sandrini, V. Balzani, A. Von Zelewsky,
C
107
H
168AgF
3
N
2
O
13S (1887.41): C, 68.09; H, 8.97; N, 1.48; Found:
C. Deuschel-Cornioley and P. Jolliet, Helv. Chim. Acta, 1988, 71,
1
C, 68.28; H, 9.19; N, 1.61. H NMR (300 MHz, CDCl
3
): d 8.95
1053.
3
(
(
2H, s, H3); 8.24 (2H, d, J = 8.1 Hz, H8); 8.07 (2H, m, H5); 7.60
2H, m, H6, H7); 7.35 (2H, s, b-H2); 6.02 (4H, s, CH OOC);
.01 (4H, m, OCH ); 1.72 (12H, m, OCH CH ); 1.35 (108H,
overlapped peaks); 0.87 (18H, m, CH ). IR (KBr): u 1717
27 B. Benali, M. Fadouach, B. Kabouchi, C. Cazeau-Bubroca and G.
Nouchi, J. Mol. Liq., 1999, 81, 159 and ref. cit. therein.
8 C. H. Chen and J. Shi, Coord. Chem. Rev., 1998, 171, 161.
9 C. Klein, E. Graf, M. W. Hosseini, G. Mislin and A. De Cian,
Tetrahedron Lett., 2000, 41, 9043.
2
2
2
4
2
2
2
3
C O
This journal is © The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 4614–4622 | 4621

View Online
3
3
3
3
0 G. Barberio, A. Bellusci, A. Crispini, M. Ghedini, A. Golemme, P. Prus
and D. Pucci, Eur. J. Inorg. Chem., 2005, 181.
34 W. R. Ware and W. Rothman, Chem. Phys. Lett., 1976, 39, 449.
35 SAINT, Version 6.45 Copyright 2003, Bruker Analytical X-ray Systems
1 D. Pucci, G. Barberio, A. Crispini and M. Ghedini, Mol. Cryst. Liq.
Cryst., 2003, 395, 155.
Inc.
36 G. M. Sheldrick, SADABS, Version 2.10, Bruker AXS Inc., Madison,
2 J. N. Demas and G. A. Crosby, J. Phys. Chem., 1971, 75,
WI, USA, 2003.
9
91.
37 SHELXTL-NT, Version 5.1 Copyright 1999, Bruker Analytical X-ray
3 K. Nakamaru, Bull. Chem. Soc. Jpn., 1982, 55, 2697.
Systems Inc.
4
622 | Dalton Trans., 2011, 40, 4614–4622
This journal is © The Royal Society of Chemistry 2011