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Spectroscopic Properties of Zn(Salphenazine) Complexes and their
Application in Small Molecule Organic Solar Cells
Giovanni Salassa,a James W. Ryan,a Eduardo C. Escudero-Adán,a and Arjan W. Kleij*a,b
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Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
A new family of salphen based complexes, viz. Zn(salphenazine)s, has been prepared and is characterized
by a larger π-surface compared to previously reported Zn(salphen) complexes. The spectroscopic
properties of these Zn(salphenazine)s have been studied in detail using UV-Vis and fluorescence
spectroscopy, and further investigated by computational methods. The first application of a
Zn(salphenazine) complex in a small molecule organic solar cell (smOSC) is presented showing the
potential of salphenazine systems in this area.

Introduction

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Organic solar cells (OSCs) have recently attracted considerable
attention as low-cost renewable energy sources. OSCs, due to the
inherent electrostatic properties of organic semiconductors, rely on
the use of a donor/acceptor interface to provide sufficient free
energy to separate the photo-generated charges, which are bound
together by a strong Coloumbic attraction. Fullerenes have been by
far the most utilised and efficient electron acceptors,1 however a
range of donor materials have been shown to produce efficient
devices.2 Polymeric donor materials, have led the way until
recently, with efficiencies as high as 10.6% for a tandem device
having been demonstrated.3 However, small molecule donors have
made drastic improvements over the past 5-6 years, with devices
now close to 9% for a single junction4 as well as certified tandem
solar cells now at a record 12%.5
Small molecules have rapidly evolved as alternatives in this
field due to numerous advantages: their straightforward (modular)
synthesis and purification, less batch-to-batch variation properties,
their intrinsic mono-dispersity and low cost.6 In the exploration of
novel suitable small molecule donors, various systems have been
examined including oligoacenes,7 oligothiophenes,8 boron
dipyrromethenes,9 diketopyrrolopyrroles,10 phthalocyanines,11
merocyanines,12 squaraines,13 porphyrins14
and
mixed
porphyrin/phthalocyanine scaffolds (Fig. 1).15 These latter
structures (porphyrins) have shown to possess highly interesting
spectroscopic properties due to their unique macrocyclic and
conjugated arrangement. Also, considering the fine-tuning of these
properties there is a vast amount of literature that shows that a wide
range of substituted porphyrins can be accessed with easy
variations possible at the meso positions of the scaffold. The
presence of a metal ion may also be useful to further tune the
spectroscopic behaviour, and additionally the Zn(II) family of
porphyrins has been frequently used for the creation of
supramolecular structures displaying unusual photochemical
features.15

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2 | Dalton Trans., 2013], 42, 00–00

Fig. 1 Some examples of small molecules used in solar cell applications,
and schematic structures of a metallo-salphenazine and -salphen.

The application of Schiff base complexes in photovoltaics has
been very limited to date,16 even though Schiff base ligands, and
more particularly salen systems, are easily prepared and
structurally modified; this intrinsic feature has been demonstrated
to be useful in the development and optimization of metal catalysts
for highly enantio-selective organic transformations.17
Nonetheless, in the last few years an increasing interest has been
noted in the spectroscopic properties of salphen ligands (Fig. 1)18
and new interesting applications in field of photo-functional
materials have appeared.17 Che and co-workers reported the
application of Pt(salphen) complexes in high-performance
OLEDs, and they have shown the importance of the π-conjugation
in these salphens.20 In this study, we present the synthesis and a
detailed study of the spectroscopic properties of a (relatively) new
type of Zn(salphen) complex having a phenazine moiety in the
backbone (i.e., a salphenazine complex, Fig. 1).21 This alternative
This journal is © The Royal Society of Chemistry 2013

salen scaffold with a more extended π-conjugated structure
compared to typical salphen ligands is shown herein to be an
attractive candidate for the development of new smOSC.

Results and Discussion
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Synthesis
Zn(salphenazine) complexes have been synthesized through a one
pot reaction between 2,3-diaminophenazine A, substituted
salicylaldehydes B and Zn(OAc)2·2H2O as templating agent (see
Experimental section and Scheme 1). Since 2,3-diaminophenazine
A is relatively insoluble in a wide range of solvents, the reaction
was performed in a minimum amount of DMSO at 100ºC. This
approach allows maintaining all the reagents and intermediates in
solution while the product mostly precipitates after a few hours (in
some cases addition of MeOH is needed to obtain the precipitate).
Subsequent filtration gave salphenazine complexes 1-7 in fairly
good yield (60−73%) and purity; in the case of 1 and 5, however,
the isolated yields were lower (10%) as a result of their higher
solubility in MeOH.
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Scheme 2 Synthesis of salphenazine complex 8 and the salphenazine
cluster complex 9 from precursor A and the required salicylaldehyde
derivatives.

Structural analysis

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Scheme 1 Synthesis of salphenazine complexes 1-7 from precursors A
and B.

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With the aim of preparing a Zn complex with a more extensive
π-conjugated structure, the synthesis of complex 8 (Scheme 2) has
been successfully achieved by applying the synthetic strategy
described above using two equivalents of 2-hydroxy-1naphthaldehyde. Furthermore, by using a previously reported
methodology22 an octanuclear, Zn8 cluster complex 9 characterized
by the presence of four salphenazine scaffolds has also been
prepared (23% yield) using 2,3-dihydroxy-benzaldehyde, 2,3diaminophenazine A and Zn(OAc)2·2H2O (Scheme 2).

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Single crystals suitable for X-ray analysis were obtained by
dissolving complex 1 and 5 in hot DMSO (Fig. 2; see also
Experimental Section). Similar to previously reported X-ray
structures of Zn(salphen) complexes,23 the Zn ion is slightly tilted
from the N2O2 binding pocket of the salphen ligand. The axial
coordination site in both structures is occupied by a solvent
molecule (DMSO) due to the high Lewis acidity of Zn(salphen)s.
In order to get more structural information for the structure of
complex 9, its DFT-minimized structure was computed (see the
Experimental Section) using previously reported X-ray structures
of similar Zn(salphen) clusters as a starting point.20 The computed
structure (Fig. 3) shows the assembly of four salphenazine units
positioned in a pseudo tetrahedral structure with every vertex
ending with a phenazine moiety: the latter are thus pointing
outward. Four of the in total eight Zn ions are situated in the N2O2
pockets (represented in orange in Fig. 3) having an axial H2O
ligand associated. The other four “internal” Zn ions (represented in
purple in Fig. 3, see also ESI) are surrounded by five O-atom
donors, two of which belong to the same salphenazine unit and the
other three form 2-phenoxo bridges between two Zn ions of
adjacent salphenazine units.
Spectroscopic properties of Zn(salphenazines)
Typical Zn(salphen)s are generally characterized by two
absorption bands in their UV-Vis spectra (200600 nm region), a
first one around 400 nm and a second one around 300 nm (i.e.,
black trace of compound 10 in Fig. 4). These two bands are
influenced by the substituents present in the salphen scaffold;
especially the role of the phenyl ring in backbone of the salphen
ligand is important. When the latter is substituted with a pyridine
ring (designated as “salpyr” complex 11), for example, an increase
in the extinction coefficient ε occurs combined with a slight redshift (see red trace in Fig. 4). Inspired by this characteristic change
in the UV-Vis, a further modification of the backbone motif was
Dalton Trans., 2013, 42, 00–00 | 3

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realized and a phenazine scaffold was then selected for its presence
in many natural dyes.24 As shown in Figure 4, the phenazine
contribution to the electronic properties of complex 1 results in a
red-shift of 100 nm and a 50% increase of the ε of the lower energy
band (max = 516 nm) compared to salphen complex 10 (max  420
nm). Meanwhile the second absorption band (max  380 nm) of 1
undergoes in a blue-shift compared to 10 (max  420 nm, see ESI
for more detail).

N

N
N
Zn N

O

O
Zn

Zn

Zn

O

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Fig. 2 Displacement ellipsoid plots at 50% probability level of complex 1
(top) and 5 (bottom). Selected bond lengths (Å) and angles (º) for
complex 1·DMSO: N(1)-Zn(1)= 2.0928 Å, N(2)-Zn(1) = 2.0537 Å, O(1)Zn(1) = 1.9788 Å, O(2)-Zn(1) = 1.9570 Å, Zn(1)-O(1D) = 2.0862 Å;
O(2)-Zn(1)-N(1) = 153.48º, O(1)-Zn(1)-N(1) = 89.13º, O(2)-Zn(1)-O(1D)
= 103.47º; Selected data for 5·DMSO: N(1)-Zn(1)= 2.0717 Å, N(4)-Zn(1)
= 2.0765 Å, O(1)-Zn(1) = 1.9554 Å, O(2)-Zn(1) = 1.9807 Å, Zn(1)-O(3)
= 2.0658 Å; O(2)-Zn(1)-N(4) = 158.04º, O(2)-Zn(1)-N(4) = 88.22º, O(1)Zn(1)-O(3) = 102.45º.

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Zn
O

Fig. 3 DFT calculated structure for 9·(H2O)4, the orange and the purple
spheres represent the Zn ions respectively inside the N2O2 and the O4
coordination pockets. For simplicity, only a partial numberings scheme is
shown here. Further snapshots of the structure are presented in the ESI†.

Fig. 4 UV-Vis comparison between Zn(salphen) derivative 10 (black
trace), Zn(salpyr) complex 11 (red trace) and Zn(salphenazine) 1 (blue
trace) in THF at a concentration of 1 × 10-5 M.

A detailed study toward the spectroscopic properties of
Zn(salphenazine) complexes has been carried out using
Zn(salphenazine) 1 as model compound due to its higher solubility
compared to 2-9. Furthermore, the presence of four tert-butyl
groups highly reduces the possibility of formation of dimeric
species, which can affect the absorption and emission properties.
The UV-Vis spectrum of 1 only slightly changes upon variation of
the solvent (Fig. S1, see ESI), and this suggest that the type of
electronic transitions that are involved have π-π* character rather
than charge transfer (CT) character. Figure 5 shows the UV-Vis
absorption and emission spectra of 1 in THF, which provides the
highest ε value among all the solvents tested. In the absorption
spectra five main bands are observed, two in the visible region (λ
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= 384 nm and λ = 516 nm) and three in the near-UV (λmax = 231
nm, λmax = 257 nm and λmax = 328 nm). Upon excitation of the
lowest energy band (λ = 516 nm), an appreciable emission band at
λ = 624 nm is observed being lower in intensity if the wavelength
of excitation is varied to other values.

groups such as present in Zn(salphenazines) as heterocyclic
synthons have shown interesting results in heterojunction solar
cells.25
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Fig. 6 UV-Vis comparison between Zn(salphenazine) complexes 1, 8 and
8 in THF at a concentration of 1 × 10-5 M.

Fig. 5 Absorption and emission spectra of 1 in dry THF at 1.76 × 10-5 M.
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By comparing the UV-Vis spectra of complexes 1-9, the role of
the substituents in the salphenazine ligand has been evaluated (see
also ESI Figures S2 and S3). In the case of tetra-substituted 1, the
two bands in the visible region are at slightly lower energy (λ =
15 nm) compared to the bands from the di-substituted complex 5
(Fig. S2). The two additional tert-butyl groups in the 5- and 5ʹpositions of the salphenazine scaffold bring about an additional
positive inductive effect that would further destabilize the π ground
state in 1. Halogens are controversial substituents, since they
produce a negative inducting effect and a positive resonance effect.
As suggested by TD-DFT calculations (see next section) the
resonance effect seems to have a stronger influence on the
salphenazine scaffold causing a destabilization of the π* exited
states. This results in a blue-shift of around 31 nm for 2-4 (Fig. S2).
Complexes 5-7, due to the presence of only two substituents (3and 3ʹ-position in the ligand backbone), are less influenced by the
electron-donating and electron-withdrawing groups but show
similar effects (see Fig. S3, ESI†).
In order to obtain systems with increased absorbance towards
the near IR, two modified synthetic strategies were applied (see
Scheme 2). The preparation of a Zn(salphenazine) complex with a
more extended π-conjugated system compared to salphenazine
complex 1 (i.e, Zn(salphenazine) 8) was carried out; instead of
having two substituted phenyl rings (derived from the
salicylaldehyde precursor), complex 8 is characterized by the
presence of two naphthyl groups.
The enhancement of the π-conjugation, however, results only in
a small improvement of the absorption properties (Fig. 6); a slight
red-shift of 8 nm was observed while maintaining a similar value
of ε compared to complex 1. This suggests that simple extension
of the π-conjugation (i.e., the change from phenyl to naphthyl side
groups) does not substantially improve the spectroscopic
properties required for an effective application thereof in OSC.
Thus, in order to obtain good smOSC candidates the attention was
then focused on multinuclear Zn(salen)s with heteroaryl bridging
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A second synthetic strategy was considered in order to interconnect
multiple chromophores; this was successfully achieved in the
preparation of the octanuclear Zn-cluster complex 9 incorporating
four Zn(salphenazine) units. As shown in Figure 7, the absorption
spectra of 9, in comparison with 1, is characterized by a 70%
increase in the ε value for the band in the visible range. However,
the absorption maximum located at 413 nm (100 nm towards the
blue with respect to complex 1) does not make complex 9 suitable
for OSC applications.
As previously mentioned, porphyrins and their metal complexes
have demonstrated to be good candidates in the preparation of
devices for DSC and OSC. Therefore, a comparison between the
newly developed Zn(salphenazine) systems and a Zn(porphyrin)
would be useful. In Figure 7 the comparison between
Zn(salphenazine) complex 1 and Zn(porphyrin) complex 12 is
reported. Zn(porphyrin) 12 shows a typical Soret band (at  = 424
nm) with a ε value of an order of magnitude higher than 1. On the
contrary, complex 1 has an absorption spectrum that covers a wider
range of accessible wavelengths. These spectroscopic properties
combined with the easy synthesis/functionalization demonstrate
that the salphenazine scaffold could be a potential alternative to
porphyrins and its derivatives.

Dalton Trans., 2013, 42, 00–00 | 5

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Fig. 7 UV-Vis comparison between salphenazine complex 1 and
Zn(porphyrin) 12 in THF at a concentration of 1 × 10-5 M.
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C
Transition 2
Energy = 2.43 eV (511 nm)
 = 0.54; H-1LUMO (97%)

TD-DFT analysis of Zn(salphenazine)s
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TD-DFT was employed for calculating 80 singlet excited states
starting from the gas-phase optimized geometry of 1 and 3 with a
THF molecule coordinated in the axial position. Experimental and
theoretical absorption spectra of complex 1 and 3 in THF are
reported in Figure 9 together with the electron density difference
maps (EDDMs)26 of the major electronic transitions of the lowest
energy band. The solvent effect was taken into account with the
CPCM method. A very good agreement between the experimental
and simulated UV-Vis spectra was observed for 1; the three bands
shown in the experimental spectrum are blue-shifted only by 5 nm
in the DFT calculated UV-Vis trace. Despite this excellent
agreement, TD-DFT significantly overestimates the extinction
coefficient of the two highest energy bands. The lowest energy
band is formed by two electronic transitions: the first one at  =
534 nm (2.32 eV) with small oscillator strength (0.035) and the
second one at  = 511 nm (2.43 eV) with oscillator strength of 0.54.
Both transitions are shown to have a π-π* character with no
contribution from the metal centre, in particular the electron
density migrates from the two phenyl side groups towards the
salphenazine backbone as represented in the EDDM of the major
transition 2 (Fig. 8A, at the right).

D
Transition 2
Energy = 2.64 eV (467 nm)
 = 0.64; H-1LUMO (96%)

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Fig. 8 Calculated (blue and green lines) and experimental (black dotted
lines) absorption spectra of 1 (A) and 3 (B) in THF. The excited states are
shown as vertical bars and the transition 2 for complex 1 (C) and
complex 3 (D) is represented below with electron density difference maps
(EDDMs, the electron density migrates from the violet to the blue lobes).
Energy values, oscillator strength values and major orbital contributions
are reported beside the EDDMs.

The other two bands at higher energy (at  = 389 nm and 326 nm,
respectively) are also based on π-π* transitions (see EDDMs of
transition 7, 13 and 14 in the ESI†), and this is in line with the
observations done in the UV-Vis experiments carried out in
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different solvents (see Fig. S1, ESI). In the case of
Zn(salphenazine) complex 3 the computed spectrum is in
reasonable agreement with the experimental one, and a blue-shift
of 15 nm of the lowest energy band is now observed. Through
analysis of the type of transition involved in the UV-Vis spectrum
of 3, similar π-π* excited states were found as observed for
Zn(salphenazine) complex 1 (EDDM in Fig. 8B). In order to
understand the 44 nm blue-shift of the lowest energy band caused
by the substitution of the four tert-butyl groups in 1 with four Cl
atoms present in 3, frontier molecular orbital (FMO) analysis has
been carried out. Figure 9 shows that the Cl substituents
significantly destabilize the lowest unoccupied molecular orbital
(LUMO) in 3 and also cause a slight destabilization of the H-1.
This behaviour may be ascribed to the resonance effect of the ion
pairs of the chlorine atoms, which destabilize the frontier MO. The
latter results in the enhancement of the energy difference between
H-1 and LUMO of 3 and thus a relative shift towards the blue of
the lowest energy band compared with complex 1.

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Table 1 Thermal degradation (Td) data for complexes 1-7.
Complex

R1

R2

Td (ºC)

1
2
3
4
5
6
7

tBu
F
Cl
Br
H
H
H

tBu
F
Cl
Br
tBu
allyl
Br

470
520
480
410
440
480
440

Preparation of a smOSC based on Zn(salphenazine) 1

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Fig. 9 Relative energy diagram of the frontier molecular orbitals for 1 (on
the left) and 3 (on the right). The zero is set on the HOMO energy. Note
that the Cl-atoms in complex 3 are shown in light green.
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Thermal stability of Zn(salphenazine)s

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The thermal stability of Zn(salphenazine) complexes 1-7 has been
examined by thermogravimetric analysis (TGA) under a nitrogen
atmosphere (Table 1). All complexes show high thermal stability,
the decomposition temperature ranges from 410ºC (for complex 4)
to 520ºC (for complex 2). Comparing the di-substituted complexes
5 and 7 with the tetra-substituted complexes 1 and 4, a higher
thermal stability for the di-substituted systems was observed. In
the case of complexes 1-4 (tetra-substituted ones), replacing the R1
and R2 substituent from Br to tBu, Cl or F leads to a significant
increase in the decomposition temperature (Td) from 410ºC to up
to 520ºC. No glass transition temperature (Tg) was observed in the
differential scanning calorimetric experiments (DSC) done for
complexes 1-7.

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EHOMO = (1.4  0.1) × (qVcv)  (4.6  0.08) eV
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This journal is © The Royal Society of Chemistry 2013

Zn(salphenazine) complex 1 has the highest solubility among all
the compounds reported herein and has relative good thermal
stability (vide infra). At the same time, the spectroscopic properties
of 1 display optimal characteristics to be donors in the production
of relatively efficient smOSC and therefore this complex was
selected for the preparation of a photovoltaic device.
One of the most important requisites for the correct operation of
an OSC and the production of a photocurrent is the establishment
of an adequate energy gap between the LUMO of the donor (i.e,
Zn(salphenazine) complex 1) and the acceptor (C60) LUMO. The
photogenerated electron–hole pair (exciton) is bound by a
Coulombic force, which is of the order of 0.3 eV.27 In order to
successfully separate the charges, the general process requires
excitons to travel to the donor–acceptor interface where the
difference in donor and acceptor LUMO levels must exceed the
Coulombic attraction force (ELUMO > 0.3 eV). Energy values of
the HOMO and LUMO for complex 1 have thus been calculated
using differential pulse voltammetry (DPV), and absorption and
emission spectroscopy. DPV of 1 was recorded in degassed
acetonitrile (ACN) with 0.1 M tetrabutylammonium
hexafluorophosphate (TBAP) as supporting electrolyte and all the
potentials were referenced to the ferrocenyl/ferrocene (Fc+/Fc)
couple. Two reversible, anodic waves (confirmed by cyclic
voltammetry, see ESI†) with Eox at 0.852 V and 1.01 V were
observed; both of them are attributed to the oxidation of the
salphenazine ligand (Fig. 10A).
To determine the energy level of the HOMO, the following
equation28 was used (eq. 1)
(eq. 1)

where VCV corresponds to EOX of complex 1. The HOMO level of
1 was estimated to be −5.27 eV. From the intersection point
between the normalized absorption and emission curves it is
possible to extract the energy gap between HOMO and LUMO and
consequently obtain the LUMO energy value of complex 1. Figure
10B shows that the intersection point is at 560 nm, which
corresponds to 2.21 eV (in good agreement with the DFT
Dalton Trans., 2013, 42, 00–00 | 7

calculated value, vide infra) and the LUMO level is −3.05 eV. By
comparison with the LUMO value of C60 (−3.5 eV)29 an OSC
device based on complex 1 would display an acceptable ELUMO
between donor and acceptor.

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10

Here, VOC stands for the open-circuit voltage, JSC is the current
density at short-circuit and Pin is the incident power of the lamp.
While this efficiency is not yet competitive compared to known
systems,7-14 it nonetheless demonstrates the potential of this new
class of compounds. In particular, the V OC of the device was 0.65
V, which is acceptable but can be improved through modification
of the HOMO level of donor. The FF was low due to the
aforementioned high series resistance together with a strong
voltage dependent current generation. In order to improve the FF,
directly evaporating complex 1 could be a good strategy compared
with the solution-process approach. The biggest limitation of the
device was the JSC, which was very low; the reason for this
behavior is the modest extinction coefficient ε value of 1 together
with the thin nature of the film employed. Increasing the thickness
of the donor layer will improve absorption but due to the apparent
low exciton-diffusion length, further improvements in JSC are not
possible. Thus a better design at the molecular level is needed to
reduce the overlap between donor and acceptor moieties (extend
π-conjugation) and to increase the ε value of the donor molecules.

Fig. 10 (A) Differential pulse voltammetry for 1 vs Fc+/Fc recorded in
degassed ACN. (B) Normalized absorption (blue) and emission (light
blue) spectra in ACN.
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The devices were fabricated by spin coating a 1 mg/ml solution of
Zn(salphenazine) 1 directly onto UV/O3 treated indium tin oxide
(ITO) (2000 rpm, 1min, ~ 10 nm thick), followed by the
evaporation of C60 (40 nm), BCP (10 nm), and Al (100 nm), with
devices having an active area of 0.09 cm2. The device was studied
in the dark and under standard conditions (A.M 1.5 G solar
spectrum, 100 mW cm-2), and the current-voltage curves (J-V
curve) of the 1:C60 device are reported in Figure 12. The dark curve
showed typical behaviour, with very low current in negative bias,
with current being generated under forward bias at 0.5 V. From the
dark curve we calculated the shunt resistance at short circuit to be
2 x 106 ohm cm2, and the series resistance at high forward bias to
be 6.7 ohm cm2. The value of the shunt resistance is relatively
high, which suggests that the leakage current is not too significant,
even without an electron blocking layer. The series resistance on
the other hand is rather high and contributes to the low fill factor
(FF) of the devices. Under 1 Sun conditions the device recorded a
power conversion efficiency (PCE) of 0.35%, which is calculated
using the following equation (eq. 2):
PCE = (VOC × JSC × FF) / Pin

8 | Dalton Trans., 2013], 42, 00–00

(eq. 2)

Fig. 11 J-V curve for the devices comprising of ITO/1/C60/BCP/Al.

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An approach to improve the photocurrent and the relative
efficiency of this complex would be to utilize a bulk heterojunction
architecture,14a which maximizes the interfacial area between
donor and acceptor as well as allowing thicker films to be
employed. A possible advantage of Zn(salphen) complexes in this
regard is their ability to self-assemble creating well-ordered large
domains which would ideally be surrounded by an acceptormatrix.30

Conclusions

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In summary, a new class of Zn(II) Schiff base complexes
incorporating a phenazine unit in the backbone has been
developed.
Salphenazine
complexes
show
interesting
spectroscopic properties compared to typical salen and salphen
complexes while remaining easily synthesized and tuneable. From
the experimental and theoretical UV-Vis data the absorption bands
have been assigned to π-π* transitions which are directly
influenced by the type of substituents present in the salphenazine
scaffold. Therefore, by a judicious choice of these groups, it is

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possible to obtain systems with desired spectroscopic properties.
Zn(salphenazine) complexes have also shown to have potential
application in smOSCs due to their high stability and adequate
electronic properties against the acceptor C60. Even though the
efficiency of the device is not competitive yet, Zn(salphenazine)s
show the synthetic potential for significant improvement based on
the modular construction of these photo-active complexes.

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Device fabrication

Experimental
General comments
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All chemicals were commercial available and were used as
received. 1H NMR and 13C{1H} NMR spectra were recorded on
Bruker Avance 400 MHz Ultrashield NMR spectrometers at 297
K. Chemical shifts are reported in ppm relative to tetramethylsilane
(δ = 0 ppm) as an internal standard. Mass analyses were carried out
by the Mass Spectrometry Unit at the Institute of Chemical
Research of Catalonia (ICIQ, Spain) using either DCTB (trans-2[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]-malononitrile)
or pyrene as matrix. Crystallographic analyses were also
performed at ICIQ by the X-ray crystallographic unit. Elemental
analyses were determined by the Elemental Analysis Unit of the
University of Santiago de Compostela, Spain. UV-Vis spectra
were acquired on a Shimadzu UV-1800 spectrophotometer.
Fluorescence spectroscopy was performed on an AMINCO
Bowman series 2 luminescence spectrometer. Acetonitrile, N,Ndimethylformamide (DMF), tetrahydrofuran (THF) and toluene
used for UV-Vis and the DPV experiment were dried by using a
solvent purification system (SPS) from Innovative Technology.
The complexes 10,23a 1131 and 1232 were prepared using previously
reported procedures. For all complexes that contain solvent
impurities in the microanalysis samples, copies of the 1H NMR
spectra are presented in the ESI†.

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All calculations were performed with the Gaussian 09 (G09)
program package33 employing the DFT method with Becke's threeparameter hybrid functional34 and Lee−Yang−Parr’s gradientcorrected correlation functional (B3LYP).35 The LanL2DZ basis
set36 and effective core potential were used for the Zn atom, and
the split-valence 6-311G** basis set37 was applied for all other
atoms. Geometry optimizations of the complexes were performed
without any constraint, and the nature of all stationary points was
confirmed by normal-mode analysis. Non-equilibrium TDDFT38
calculations produced singlet excited states employing the DFT
method with the hybrid functional of Truhlar and Zhao (M06), 39
using the conductor like polarizable continuum model method
(CPCM)40 with THF as solvent. Eighty singlet excited states were
determined starting from optimized geometries of 1 and 3.
Electronic distributions and localizations of the singlet excited
states were visualized using the electron density difference maps
(EDDMs).41 GaussSum 2.2542 was used for singlet EDDMs
calculations and for simulation of the electronic spectra.

Syntheses

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Differential pulse voltammetry
110

55

Differential pulse voltammetry (DPV) experiments were carried
out using a CH Instruments 660c Electrochemical Workstation,
This journal is © The Royal Society of Chemistry 2013

Devices were prepared on ITO substrates (5 ohm/square, Psiotech
Ltd. U.K.). The substrates were cleaned by sonicating, firstly in
acetone, followed by two cycles of sonication in 2-propanol, and
then treated with UV/O3 for 20 min. Thin films of the
Zn(salphenazine) donor 1 were prepared by spin-coating a 1 mg/ml
solution of the donor in CHCl3 (filtered using a PTFE membrane,
pore size = 0.2 μm) at a rate of 2000 rpm for 1 minute.
Subsequently, the films were transferred to an evaporation
chamber where the C60 (40 nm, MER Corp., 99.9%),
bathocuproine BCP (8 nm, Sigma Aldrich), and Al (100 nm, Sigma
Aldrich) were deposited at a base pressure of 1 × 10-6 mbar. Device
J-V curves were recorded using a 150 W solar simulator (Abet
Technologies) at 1 sun conditions (AM 1.5 G, 100 mW/cm2).

75

DFT calculations

35

with a standard three-electrode setup utilizing a Pt disc working
electrode, Pt wire working electrode and SCE reference electrode.
A 0.1 M solution of tetrabutylammonium phosphate in DMSO was
used as the background electrolyte. Cyclic voltammetry
experiments were run under similar conditions.

Zn(salphenazine) complex (1): 2,3-diaminophenazine (103 mg,
0.49 mmol) was dissolved in DMSO (2 mL) and the mixture was
heated to 95ºC in order to dissolve the reagent. While stirring, to
the heated solution was added a methanol solution (2 mL) of 3,5tert-butyl-2-hydroxybenzaldehyde (230 mg, 0.75 mmol) and a
methanol solution (1 mL) of Zn(OAc)2·H2O (88 mg, 0.40 mmol).
The solution was stirred for 18 h at 95ºC, subsequently cooled to
room temperature and the precipitate which had formed was
filtered off, washed with methanol and dried under vacuum to yield
a dark brown powder (44 mg, 12 %). 1H NMR (400 MHz, DMSOd6): δ = 9.41 (s, 2H; CH=N), 8.64 (s, 2H; ArH), 8.18-8.20 (m, 2H;
ArH), 7.87-7.93 (m, 2H; ArH), 7.41 (d, 2H, 4JHH = 2.7 Hz; ArH),
7.39 (d, 2H, 4JHH = 2.7 Hz; ArH), 1.51 (s, 9H; tBu), 1.32 (s, 9H;
tBu); Due to the low solubility of 1 a proper 13C NMR analysis was
not possible; MALDI(+): m/z = 704.5 [M]+ (calcd. 704.31); UVVis (c = 0.25 mg in 20 mL THF): λmax (ε) = 231 nm (43107 mol1·m3·cm-1), λ
-1
3
-1
max (ε) = 257 nm (42508 mol ·m ·cm ), λmax (ε) = 328
-1
3
-1
nm (37445 mol ·m ·cm ), λmax (ε) = 384 nm (28709 mol-1·m3·cm1), λ
-1
3
-1
max (ε) = 516 nm (34357 mol ·m ·cm ); elemental analysis
calcd. (%) for C42H48N4O2Zn·2H2O: C 68.80, H 7.01, N 7.64;
found: C 68.82, H 7.27, N 7.55.
Zn(salphenazine) complex (2): This compound was prepared in
a similar manner to complex 1 using 2,3-diaminophenazine (108
mg, 0.51 mmol), 3,5-difluorosalicylaldehyde (162 mg, 1.03 mmol)
and Zn(OAc)2·H2O (116 mg, 0.53 mmol). After cooling to room
temperature the complex was precipitated by further addition of
methanol to yield a red powder (185 mg, 66 %). 1H NMR (400
MHz, DMSO-d6): δ = 9.37 (s, 2H; CH=N), 8.66 (s, 2H; ArH), 8.238.25 (m, 2H; ArH), 7.96-7.98 (m, 2H; ArH), 7.34-7.40 (m, 2H;
ArH), 7.24-7.27 (m, 2H; ArH); 19F NMR (400 MHz, DMSO-d6): δ
= 129.96 (d, 2F, 3JHF = 11.4 Hz; ArF), 130.66 (dd, 2F, 3JHF = 8.8
Hz, 3JHF = 8.8 Hz; ArF); Due to the low solubility of 2 a proper 13C
NMR analysis was not possible; MALDI(+): m/z = 552.1 [M]+
(calcd. 552.02), 1108.2 [2M]+ (calcd. 1108.3); UV-Vis (c = 0.25
mg in 20 mL THF): λmax (ε) = 277 nm (74112 mol-1·m3·cm-1), λmax
Dalton Trans., 2013, 42, 00–00 | 9

5

(ε) = 365 nm (15685 mol-1·m3·cm-1), λmax (ε) = 483 nm (22177 mol1·m3·cm-1);
elemental
analysis
calcd.
(%)
for
C26H12F4N4O2Zn·MeOH·2/3DMSO: C 52.37, H 2.82, N 9.05, S
3.45; found: C 52.29, H 2.94, N 8.90, S 3.47. The presence of
DMSO and MeOH in the microanalysis sample was also supported
by 1H NMR.

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55

Zn(salphenazine) complex (3): This compound was prepared in
a similar manner to complex 1 using 2,3-diaminophenazine (93.4
mg, 0.44 mmol), 3,5-dichlorosalicylaldehyde (178 mg, 0.93 mmol)
and Zn(OAc)2·H2O (109 mg, 0.5 mmol). After cooling to room
temperature the complex was precipitated by addition of extra
methanol to yield an orange powder (200 mg, 73 %). 1H NMR (400
MHz, DMSO-d6): δ = 9.34 (s, 2H; CH=N), 8.64 (s, 2H; ArH), 8.238.25 (m, 2H; ArH), 7.95-7.98 (m, 2H; ArH), 7.64 (d, 2H, 4JHH =
2.9 Hz; ArH), 7.62 (d, 2H, 4JHH = 2.9 Hz; ArH); Complex 3 was
too insoluble for a proper 13C NMR analysis; MALDI(+): m/z =
617.8 [M]+ (calcd. 617.9), 1237.6 [2M]+ (calcd. 1237.79); UV-Vis
(c = 0.25 mg in 20 mL THF): λmax (ε) = 256 nm (45424 mol1·m3·cm-1), λ
-1
3
-1
max (ε) = 316 nm (31863 mol ·m ·cm ), λmax (ε) = 366
-1·m3·cm-1), λ
-1
3
nm (20328 mol
max (ε) = 484 nm (30383 mol ·m ·cm
1); elemental analysis calcd. (%) for C H N O Zn·H O·DMSO:
42 48 4 2
2
C 46.99, H 2.82, N 7.83; found: C 46.40, H 2.27, N 7.50. The
presence of DMSO in the microanalysis sample was also supported
by 1H NMR analysis.
Zn(salphenazine) complex (4): This compound was prepared in
a similar manner to 1 using 2,3-diaminophenazine (107 mg, 0.51
mmol), 3,5-dibromosalicylaldehyde (285 mg, 1.02 mmol) and
Zn(OAc)2·H2O (132 mg, 0.60 mmol). After cooling to room
temperature the complex was precipitated by addition of extra
methanol to yield a dark orange powder (295 mg, 73 %). 1H NMR
(400 MHz, DMSO-d6): δ = 9.32 (s, 2H; CH=N), 8.63 (s, 2H; ArH),
8.22-8.25 (m, 2H; ArH), 7.95-7.97 (m, 2H; ArH), 7.84 (d, 2H, 4JHH
= 2.5 Hz; ArH), 7.62 (d, 2H, 4JHH = 2.5 Hz; ArH); Complex was
too insoluble for a proper 13C NMR analysis; MALDI(+): m/z =
797.8 [M]+ (calcd. 797.69), 1595.4 [2M] + (calcd. 1595.38); UVVis (c = 0.25 mg in 20 mL THF): λmax (ε) = 233 nm (47110 mol1·m3·cm-1), λ
-1
3
-1
max (ε) = 256 nm (61100 mol ·m ·cm ), λmax (ε) = 317
-1·m3·cm-1), λ
-1
3
nm (37110 mol
max (ε) = 368 nm (24770 mol ·m ·cm
1), λ
-1·m3·cm-1); elemental analysis
max (ε) = 485 nm (34220 mol
calcd. (%) for C26H12Br4N4O2Zn: C 39.16, H 1.52, N 7.03; found:
C 39.19, H 1.74, N 6.93.
Zn(salphenazine) complex (5): This compound was prepared in
a similar manner to complex 1 using 2,3-diaminophenazine (108
mg, 0.51 mmol), 3-tert-butyl-2-hydroxybenzaldehyde (183 mg,
1.03 mmol) and Zn(OAc)2·H2O (114 mg, 0.52 mmol). After
cooling to room temperature the complex was precipitated by
further addition of methanol to yield a dark brown powder (62 mg,
20 %). 1H NMR (400 MHz, DMSO-d6): δ = 9.35 (s, 2H; CH=N),
8.61 (s, 2H; ArH), 8.20-8.22 (m, 2H; ArH), 7.92-7.94 (m, 2H;
ArH), 7.42 (d, 2H, 3JHH = 7.8 Hz, 4JHH = 1.7 Hz; ArH), 7.30 (d, 2H,
3J
4
3
3
HH = 7.8 Hz, JHH = 1.7 Hz; ArH), 6.52 (dd, 2H, JHH = 7.8, JHH
= 7.8 Hz, ArH), 1.49 (s, 9H; tBu); Complex 5 was too insoluble for
a proper 13C NMR analysis; MALDI(+): m/z = 592.3 [M]+ (calcd.
592.18); UV-Vis (c = 0.22 mg in 20 mL THF): λmax (ε) = 228 nm
(32067 mol-1·m3·cm-1), λmax (ε) = 255 nm (36994 mol-1·m3·cm-1),

10 | Dalton Trans., 2013], 42, 00–00

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115

λmax (ε) = 326 nm (33442 mol-1·m3·cm-1), λmax (ε) = 375 nm (26488
mol-1·m3·cm-1), λmax (ε) = 501 nm (36820 mol-1·m3·cm-1);
elemental
analysis
calcd.
(%)
for
C34H32N4O2Zn·½DMSO·½MeOH·H2O: C 63.91, H 5.89, N 8.40;
found: C 64.07, H 5.56, N 8.78. The presence of DMSO and
MeOH in the microanalysis sample was also supported by 1H
NMR.
Zn(salphenazine) complex (6): This compound was prepared in
a similar manner to complex 1 using 2,3-diaminophenazine (146
mg, 0.69 mmol), 3-allyl-salicylaldehyde (236 mg, 1.46 mmol) and
Zn(OAc)2·H2O (156 mg, 0.71 mmol). After cooling to room
temperature the complex was precipitated by addition of methanol
to yield a reddish brown powder (233 mg, 60 %). 1H NMR (500
MHz, DMSO-d6): δ = 9.28 (s, 2H; CH=N), 8.56 (s, 2H; ArH), 8.198.22 (m, 2H; ArH), 7.91-7.94 (m, 2H; ArH), 7.42 (d, 2H, 3JHH =
8.0 Hz, 4JHH = 1.7 Hz; ArH), 7.23 (d, 2H, 3JHH = 7.0 Hz, 4JHH = 1.8
Hz; ArH), 6.52 (d, 2H, 3JHH = 7.0, 3JHH = 8.0 Hz; ArH), 6.14-6.22
(m, 2H; allyl-H), 5.13-5.18 (m, 2H; allyl-H), 5.01-5.03 (m, 2H;
allyl-H), 3.44 (d, 4H, 3JHH = 6.8 Hz; allyl-H); Complex was too
insoluble for a proper 13C NMR analysis; MALDI(+): m/z = 560.1
[M]+ (calcd. 560.12), 1124.2 [2M]+ (calcd. 1124.23); UV-Vis (c =
0.25 mg in 20 mL THF): λmax (ε) = 224 nm (36150 mol-1·m3·cm-1),
λmax (ε) = 255 nm (44000 mol-1·m3·cm-1), λmax (ε) = 322 nm (31584
mol-1·m3·cm-1), λmax (ε) = 371 nm (23811 mol-1·m3·cm-1), λmax (ε)
= 491 nm (32830 mol-1·m3·cm-1); elemental analysis calcd. (%) for
C32H24N4O2Zn·MeOH·H2O: C 64.76, H 4.94, N 9.15; found: C
64.87, H 4.73, N 9.40. The presence of MeOH in the microanalysis
sample was also supported by 1H NMR.
Zn(salphenazine) complex (7): This compound was prepared in
a similar manner to complex 1 using 2,3-diaminophenazine (107
mg, 0.51mmol), 3-bromo-salicylaldehyde (215 mg, 1.07 mmol)
and Zn(OAc)2·H2O (132 mg, 0.60 mmol). After cooling to room
temperature the complex was precipitated by further addition of
methanol to yield an orange powder (146 mg, 45 %). 1H NMR (400
MHz, DMSO-d6): δ = 9.36 (s, 2H; CH=N), 8.66 (s, 2H; ArH), 8.228.25 (m, 2H; ArH), 7.95-7.97 (m, 2H; ArH), 7.75 (d, 2H, 3JHH =
7.6 Hz, 4JHH = 1.8 Hz; ArH), 7.61 (d, 2H, 3JHH = 7.6 Hz, 4JHH = 1.8
Hz; ArH), 6.53 (dd, 2H, 3JHH = 7.6 Hz, 3JHH = 7.6 Hz, ArH);
Complex 7 was too insoluble for a proper 13C NMR analysis;
MALDI(+): m/z = 639.9 [M]+ (calcd. 639.87), 1279.8 [2M]+
(calcd. 1279.75); UV-Vis (c = 0.25 mg in 20 mL, THF): λmax (ε) =
234 nm (34887 mol-1·m3·cm-1), λmax (ε) = 253 nm (42152 mol1·m3·cm-1), λ
-1
3
-1
max (ε) = 321 nm (33094 mol ·m ·cm ), λmax (ε) = 367
-1·m3·cm-1), λ
-1
3
nm (24573 mol
max (ε) = 482 nm (33632 mol ·m ·cm
1); elemental analysis calcd. (%) for C H Br N O Zn·H O: C
26 14
2 4 2
2
47.49, H 2.45, N 8.52; found: C 47.59, H 2.36, N 8.22.
Zn(salphenazine) complex (8): This compound was prepared in
a similar manner to complex 1 using 2,3-diaminophenazine (109
mg, 0.52 mmol), 2-hydroxy-1-naphthaldehyde (187 mg, 1.04
mmol) and Zn(OAc)2·H2O (119 mg, 0.54 mmol). After cooling to
room temperature the precipitate which formed, was filtered off
and washed with methanol to yield a brown powder (164 mg, 54
%). 1H NMR (500 MHz, DMSO-d6): δ = 10.05 (s, 2H; ArH), 8.76
(s, 2H; CH=N), 8.64 (d, 2H, 3JHH = 8.5 Hz; ArH), 8.22-8.24 (m,
2H; ArH), 7.92-7.94 (m, 2H; ArH), 7.88 (d, 2H, 3JHH = 9.3 Hz;

This journal is © The Royal Society of Chemistry 2013

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10

ArH), 7.74 (d, 2H, 3JHH = 7.9 Hz, 4JHH = 1.1 Hz; ArH), 7.54 (d, 2H,
3J
4
3
4
HH = 7.9 Hz, JHH = 1.2 Hz; ArH), 7.30 (d, 2H, JHH = 7.4, JHH =
1.1 Hz, ArH), 7.02 (d, 2H, 3JHH = 9.1 Hz; ArH); Complex 8 was
too insoluble for a proper 13C NMR analysis; MALDI(+): m/z =
580.3 [M]+ (calcd. 580.09); UV-Vis (c = 0.20 mg in 20 mL THF):
λmax (ε) = 248 nm (56802 mol-1·m3·cm-1), λmax (ε) = 322 nm (18520
mol-1·m3·cm-1), λmax (ε) = 356 nm (14414 mol-1·m3·cm-1), λmax (ε)
= 428 nm (23622 mol-1·m3·cm-1), λmax (ε) = 522 nm (33424 mol1·m3·cm-1);
elemental
analysis
calcd.
(%)
for
C34H20N4O2Zn·2H2O: 66.08, H 3.91, N 9.07; found: C 65.61, H
3.73, N 9.48.

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35

Zn8(salphenazine)4 cluster complex (9): 2,3-diaminophenazine
(90 mg, 0.42 mmol) was dissolved in DMSO (1.5 mL) and the
mixture was heated to 100ºC in order to dissolve the reagent. While
stirring, to the heated solution was added a DMSO solution (1 mL)
of 2,3-dihydroxy-benzaldehyde (130 mg, 0.94 mmol) and a
methanol solution (1 mL) of Zn(OAc)2·H2O (193 mg, 0.87 mmol).
The reaction mixture was stirred for 2 h at 100ºC, and subsequently
cooled to room temperature. A further amount of methanol was
added and the precipitate which formed was filtered off. The solid
that was obtained was recrystallized from hot DMF/pyridine to
yield a brown powder which was washed thoroughly with MeOH
and dried (59 mg, 23 %). 1H NMR (400 MHz, DMSO-d6): δ = 9.50
(s, 4H; CH=N), δ = 9.10 (s, 4H; CH=N), 8.87 (s, 4H; ArH), 8.62
(s, 4H; ArH), 8.24-8.27 (m, 8H; ArH), 7.94-8.10 (m, 8H; ArH),
6.97 (d, 4H, 3JHH = 7.3 Hz; ArH), 6.68 (d, 4H, 3JHH = 7.7 Hz; ArH),
6.55-6.59 (m, 8H; ArH), 6.43 (d, 4H, 3JHH = 7.6 Hz; ArH), 5.966.02 (m, 4H; ArH); Complex 9 was too insoluble for a proper 13C
NMR analysis; MALDI(+): m/z = 2308.1 [M]+ (calcd. 2308.83);
UV-Vis (c = 0.65 mg in 20 mL THF): λmax (ε) = 413 nm (94263
mol-1·m3·cm-1);
elemental
analysis
calcd.
(%)
for
C104H56N16O16Zn8·3pyr·3H2O·¼MeOH: C 54.59, H 3.04, N 10.17;
found: C 55.01, H 3.62, N 10.11. The presence of pyridine and
MeOH in the microanalysis sample was supported by 1H NMR.
Please note that these octanuclear structures usually retain four
water molecules (cf., Fig. 3)20a coordinating to the outer Zn
centres; the pyridine and MeOH molecules are thought to be
associated via H-bonding to the water ligands.

75

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Acknowledgements

90

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50

55

Crystallographic details for complex 1·3DMSO: C48H66N4O5S3Zn,
Mr = 940.60, triclinic, P-1, a = 9.8772(5) Å, b = 13.4186(6) Å, c =
19.0545(8) Å, α = 85.820(3)°, β = 75.934(2)°, γ = 85.146(2)°, V =
This journal is © The Royal Society of Chemistry 2013

This work was supported by ICIQ, ICREA and the Spanish
Ministerio de Economía y Competitividad (MINECO) through
project CTQ2011-27385 and an FPU fellowship for G.S. JWR
thanks ICIQ for his ICIQ Fellowship. We thank Dr Noemí Cabello,
Vanessa Martínez and Sofia Arnal for the mass spectrometric
studies.

Notes and references
a

X-ray crystallography
General: The measured crystals were stable under atmospheric
conditions; nevertheless they were treated under inert conditions
and were immersed in perfluoropoly-ether as a protecting oil for
manipulation. Data collection: measurements were made on a
Bruker-Nonius diffractometer equipped with an APPEX 2 4K
CCD area detector, an FR591 rotating anode with MoKα radiation,
Montel mirrors and a Kryoflex low temperature device (T = −173
°C). Full-sphere data collection was used with ω and φ scans.
Programs used: data collection Apex2 V2011.3 (Bruker-Nonius
2008), data reduction Saint+Version 7.60A (Bruker AXS 2008)
and absorption correction SADABS V. 2008–1 (2008). Structure
solution: SHELXTL version 6.10 (Sheldrick, 2000)43 was used.
Structure refinement: SHELXTL-97-UNIX VERSION.

Crystallographic details for complex 5·3DMSO: C40H50N4O5S3Zn,
Mr = 828.39, monoclinic, P2(1)/c, a = 16.9962(6) Å, b =
13.2017(5) Å, c = 18.0315(7) Å, α = 90°, β = 94.076(2)°, γ = 90°,
V = 4035.7(3) Å3, Z = 4, ρ = 1.363 mg·M−3, μ = 0.812 mm−1, λ =
0.71073 Å, T = 100(2) K, F(000) = 1744, crystal size = 0.40 × 0.15
× 0.02 mm, θ(min) = 1.20°, θ(max) = 36.36°, 73442 reflections
collected, 18952 reflections unique (Rint = 0.1023), GoF = 0.976,
R1 = 0.0551 and wR2 = 0.1025 [I > 2σ(I)], R1 = 0.1324 and wR2 =
0.1309 (all indices), min/max residual density = −0.708/0.717
[e·Å−3]. Completeness to θ(36.36°) = 0.966%. The structure has
been deposited at the CCDC with reference number 949797 and is
a bis-solvate; it contains two co-crystallized DMSO molecules
alongside one coordinating one. One of the co-crystallized DMSO
molecules is disordered over two positions with a relative
occupancy ratio of 77:23.

85

95

40

2437.36(19) Å3, Z = 2, ρ = 1.282 mg·M−3, μ = 0.680 mm−1, λ =
0.71073 Å, T = 100(2) K, F(000) = 1000, crystal size = 0.50 × 0.20
× 0.10 mm, θ(min) = 1.53°, θ(max) = 36.57°, 21580 reflections
collected, 21580 reflections unique (Rint = 0.0544), GoF = 1.028,
R1 = 0.0460 and wR2 = 0.1070 [I > 2σ(I)], R1 = 0.0783 and wR2 =
0.1221 (all indices), min/max residual density = −0.765/1.056
[e·Å−3]. Completeness to θ(36.57°) = 0.896%. The structure has
been deposited at the CCDC with reference number 949796 and is
a bis-solvate; it contains two co-crystallized DMSO molecules
alongside one coordinating one.

100

Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans
16, 43007 – Tarragona (Spain). E-mail: akleij@iciq.es; Fax: +34
977920224; Tel: +34 977920247.
b
Catalan Institute for Research and Advanced Studies (ICREA), Pg. Lluís
Companys 23, 08010, Barcelona, Spain.
† Electronic supplementary information (ESI) available: Further
experimental data, copies of relevant MS and NMR spectra of known and
new
compounds,
and
crystallographic
details.
See
DOI: 10.1039/b000000x/.
1

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