Synthesis, crystal structure and characterization of a new zinc phthalocyanine complex

Article abstract of DOI:10.1016/j.molstruc.2006.05.030

A new complex [ZnPc(H₂O)]·2DMF (1), where Pc = phthalocyanine and DMF = N,N-dimethylformamide, has been synthesized and its crystal has been determined by single-crystal X-ray diffraction method. The compound crystallizes in the triclinic space group P - 1. The lattice parameters are a = 11.668(5) A?, b = 12.186(5) A?, c = 13.939(6) A?, α = 78.697(7)°, β = 88.045 (7)°, γ = 62.949(7)°, V = 1727.4(12) A?³ and Z = 2. The Zn(II) ion is five-coordinated by four nitrogen atoms from Pc ligands and one oxygen atom from one water molecule. Notably, there are strong π-π interactions between Pc ligands, leading to 1D superamolecular structure. Moreover, the elemental analyses, FT-IR, UV-vis and Fluorescence spectra for this complex were also determined.

Full text of DOI:10.1016/j.molstruc.2006.05.030

Journal of Molecular Structure 827 (2007) 149–154
www.elsevier.com/locate/molstruc
Synthesis, crystal structure and characterization of a new
zinc phthalocyanine complex
*
Li-Ying Cui, Jin Yang, Qiang Fu , Bao-Zhong Zhao, Lei Tian, Hai-Ling Yu
Department of Chemistry, Northeast Normal University, Changchun 130024, People’s Republic of China
Received 13 January 2006; received in revised form 13 April 2006; accepted 14 May 2006
Available online 27 June 2006
Abstract
A new complex [ZnPc(H2O)]Æ2DMF (1), where Pc = phthalocyanine and DMF = N,N-dimethylformamide, has been synthesized and
its crystal has been determined by single-crystal X-ray diffraction method. The compound crystallizes in the triclinic space group P À 1.
˚
˚
˚
The lattice parameters are a = 11.668(5) A, b = 12.186(5) A, c = 13.939(6) A, a = 78.697(7)ꢀ, b = 88.045 (7)ꢀ, c = 62.949(7)ꢀ,
3
˚
V = 1727.4(12) A and Z = 2. The Zn(II) ion is five-coordinated by four nitrogen atoms from Pc ligands and one oxygen atom from
one water molecule. Notably, there are strong p–p interactions between Pc ligands, leading to 1D superamolecular structure. Moreover,
the elemental analyses, FT-IR, UV–vis and Fluorescence spectra for this complex were also determined.
ꢁ 2006 Elsevier B.V. All rights reserved.
Keywords: ZnPc; Crystal structure; FT-IR; UV–vis; Fluorescence
1. Introduction
(MCPL), absorption and magnetic circular dichroism
(MCD) spectra. Thus, the syntheses of new ZnPc and its
derivative materials are of intensive importance. In this
paper a new compound [ZnPc(H2O)]Æ2DMF (1) was pre-
sented, and the FT-IR, UV–vis and fluorescence spectra
were also applied to characterize this complex.
Since the firstly reported paper by Braun and Tcherniac
about phthalocyanine, there has been extensive interest in
phthalocyanine and its derivatives, and the search for
new phthalocyanines is one of the fundamental studies
[1]. It is well known that the phthalocyanines are P-type
semiconductor characterised by high thermal and chemical
stability. They also exhibit interesting optical, electrical,
magnetic and catalytic properties, and are widely applied
to many fields such as dyes [2], chemical sensors [3], electro-
chromism [4], batteries [5] and photodynamic therapy
(PDT) [6].
On the other hand, the metal complexes containing
phthalocyanine were the field of many studies and particu-
larly over the recent years. Among phthalocyanine com-
plexes the ZnPc derivatives are particularly interesting
owing to their unique photosensitizing properties for
PDT [7–9], magnetic circularly polarized luminescence
2. Experiment
2.1. Preparation
Traditionally, metal phthalocyanine complexes were
prepared in the high-boiling solvents such as 1-chloronaph-
thalene, nitrobenzene, and 1,2-dichlorobenzene. However,
the [ZnPc(H2O)]Æ2DMF (1) was directly synthesized in
our laboratory through anhydride method [10]. A mixture
of phthalic anhydride, zinc dichloride, urea and ammoni-
um molybdate was stirred for about 1 h at room tempera-
ture, sealed in a 23-ml Teflon-lined stainless steel autoclave
and heated at 200 ꢀC for 3 days under autogenous pressure.
After washed with diluted HCl solution, the product was
placed in a Soxhlet extractor and extracted for 24 h. The
dark green single crystals of [ZnPc(H2O)]Æ2DMF (1) suit-
*
Corresponding author. Tel.: +86 431 5099551; fax: +86 431 5098768.
E-mail address: fqiang@nenu.edu.cn (Q. Fu).
0022-2860/$ - see front matter ꢁ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.05.030

150
L.-Y. Cui et al. / Journal of Molecular Structure 827 (2007) 149–154
able for X-ray analysis were obtained by slow evaporation
of air-exposed DMF solution at room temperature, and the
same complex [ZnPc(H2O)]Æ2DMF is also obtained after
the complex is re-crystallized from DMF. At the same time
many other methods are applied to crystallize commercial
zinc phthalocyanine (ZnPc) from DMF containing small
amount of water, but no compound (powder or crystal)
was in agreement with our title compound. So the
ZnPc(H2O) framework may be formed in the process of
synthesis before ZnPc(H2O) was dissolved in DMF. Calc.
for C38H32N10O3Zn: C, 61.50; H, 4.35; N, 18.87%. Found:
C, 61.70; H, 4.42; N, 18.65%.
ter using KBr pellets. The UV–visible spectra (200–
1000 nm) were measured in DMF solution on a Varian
Cary 500 UV-Vis-NIR scan spectrophotometer. The fluo-
rescence spectrum was determined on a Cary Eclipse fluo-
rometer. Elemental analyses for C, H and N were
performed on a Perkin-Elmer 2400 CHN elemental
analyzer.
3. Results and discussion
3.1. Crystal structure of [ZnPc(H2O)]Æ2DMF (1)
Selected bond distances and angles are given in Table 2.
The structure of [ZnPc(H2O)]Æ2DMF (1) is shown in Fig. 1.
The compound (1) consists of one ZnPc, one water mole-
cule and two DMF molecules. The central Zn(II) ion is
five-coordinated by four nitrogen atoms from Pc ligand
and one oxygen atom from water molecule. The Zn(II)
atom orbitals in this coordination environment assume
the sp2d2 hybridisation. The ZnAN distances range from
2.2. X-ray data collection
Crystallographic data of compound 1 were collected on
a Bruker–Apex Smart CCD diffractometer equipped with a
normal-focus, 2.4 kW X-ray source (graphite-monochro-
˚
mated MoAKa radiation with k = 0.71073 A) operating
at 50 kV and 40 mA with increasing x (width of 0.3ꢀ and
exposure time 30 s per frame). All the structures were
solved by direct methods using the program SHELXS-97
and refined by full-matrix least-squares techniques against
F2 using the SHELXTL-97 crystallographic software pack-
age [11]. All non-hydrogen atoms were easily found from
the difference Fourier map and refined anisotropically,
whereas the hydrogen atoms of the organic molecules were
placed by geometrical considerations and were added to
the structure factor calculation. The detailed crystallo-
graphic data and structure refinement parameters for 1
are summarized in Table 1.
˚
2.024(2) to 2.014(2) A, and the axial ZnAO (OW1) bond
˚
distance is 2.077(2) A which is much shorter than that in
˚
ZnPc(H2O) complex (the ZnAO bond distance is 2.20 A)
[12]. In compound (1) the CAN bonds are typical conjugat-
ed p-electron systems and their distances are similar to
those observed in other phthalocyanine structures [13–
15]. Notably, the Zn(II) atom is at an inversion center,
and the distance between the Zn(II) atom and the least-
square plane defined by N1AN4 toward the water molecule
˚
is about 0.38 A.
The water molecule and the DMF molecules are all
potential hydrogen-bonding sites. The hydrogen-bonding
interactions occur between OW1 and two DMF molecules,
where the OW1 water molecule acts as the hydrogen donor,
whereas the DMF molecules only play a role of hydrogen
2.3. Physical measurements
The FT-IR spectra were recorded in the range 400–
4000 cmÀ1 on an Alpha Centaurt FT-IR spectrophotome-
acceptors. The distances of OW1Á Á ÁO1 and OW1Á Á ÁO2#1
#1
˚
˚
(
1 À x,1 À y,1 À z) are 2.722(3) A and 2.687(3) A,
Table 1
respectively. The angles of OW1Á Á ÁHW12Á Á ÁO1 and
OW1Á Á ÁHW11ÆÆO2#1 are 175(3)ꢀ and 166(4)ꢀ, respectively.
These hydrogen-bonded data are in good agreement with
those in the reported compounds [16].
Crystallographic data and final refinement parameters for
[ZnPc(H2O)]Æ2DMF (1)
Chemical formula
C32H18N8OZn
Molecular weight
Temperature (K)
Crystal system
Space group
742.11
293(2)
Triclinic
P-1
In Fig. 2, the compound (1) is stacked in a herringbone
fashion along crystallographic b axis. As one of important
types of supramolecular forces, pÁ Á Áp stacking shows a spe-
cific structural requirement for substrate recognition or the
arrangement of complicated architectures. In complex (1),
strong intermolecular pÁ Á Áp stacking is present. One is
formed between two Pc ligands (labeled a, centroid-to-cen-
˚
˚
a (A)
11.668(5) A
˚
˚
b (A)
12.186(5) A
˚
˚
c (A)
13.939(6) A
a (ꢀ)
b (ꢀ)
78.697(7)
88.045(7)
62.949(7)
1727.4(12)
2
˚
troid distances: 3.48 A) and the other between two Pc
c (ꢀ)
V (A)
3
˚
˚
ligands (labeled b, centroid-to-centroid distances: 3.62 A).
Z
The a-type pÁ Á Áp interactions link the (1) to form dimer,
which is further connected through the b-type pÁ Á Áp inter-
actions, resulting in an infinite 1D superamolecular chain
(Scheme 1 and Fig. 3).
The average distances and angles of various Zn(II) por-
phyrin derivatives including ZnPcCl [17], ZnTPP(H2O)
(TPP = tetraphenylporphine) [18], (n-hexyl)ZnPc [19] and
F(000)
768
1.427
Dcalc (g cmÀ3
)
Reflections collected
Reflections observed
R [I > 2r(I)]
wR [I > 2r(I)]
Goodness-of-fit
10,829
7661
0.0514
0.0871
0.924

L.-Y. Cui et al. / Journal of Molecular Structure 827 (2007) 149–154
151
Table 2
˚
Selected bond length (A) and angles (ꢀ) for [ZnPc(H2O)]Æ2DMF (1)
Bond lengths
Zn(1)AN(1)
Zn(1)AN(3)
2.024(2)
2.014(2)
N(1)AC(1)
N(2)AC(9)
N(3)AC(24)
1.363(3)
1.366(4)
1.364(4)
N(4)AC(25)
N(5)AC(8)
N(6)AC(16)
1.363(3)
1.330(3)
1.343(4)
N(7)AC(24)
N(8)AC(1)
C(2)AC(1)
C(10)AC(9)
C(18)AC(17)
C(26)AC(25)
C(2)AC(7)
1.336(3)
1.329(4)
1.469(4)
1.463(4)
1.457(4)
1.449(4)
1.385(4)
1.393(4)
C(18)AC(23)
Fig. 1. ORTEP view of [ZnPc(H2O)]Æ2DMF (1).
Zn(1)AOW(1)
Zn(1)AN(2)
Zn(1)AN(4)
2.077(2)
2.018(2)
2.020(2)
˚
and (n-hexyl)ZnPc are 2.35, 2.20 and 2.17 A, respectively.
It is can be seen that the ZnAO (water) bond distance
N(1)AC(8)
N(2)AC(16)
N(3)AC(17)
1.367(4)
1.369(3)
1.367(3)
˚
(2.077 A) for our compound [ZnPc(H2O)]Æ2DMF (1) is
the shortest among others. The ZnANp distance of
N(4)AC(32)
N(5)AC(9)
N(6)AC(17)
1.365(3)
1.335(3)
1.335(3)
˚
2.019(2) A for [ZnPc(H2O)]Æ2DMF (1) is very close to that
˚
of ZnPc(1.980 A), and shorter than those of other three
complexes. This indicates that Zn(II) atom in compound
ZnPc is almost coplanar in the absence of axial ligand. In
contrast to the NpACa values of ZnPc, ZnPcCl and (n-hex-
yl)ZnPc the corresponding values of [ZnPc(H2O)]Æ2DMF
(1) are obviously nearer to that of ZnPc, and somewhat dif-
ferent from those of ZnPcCl and (n-hexyl)ZnPc. In the
same manner considering the value of CaANb, CaACb
and CbACb, respectively, the same consequence can be
obtained. Thus it also indicates that the axial water mole-
cule has less influence on Pc ring than the axial ligand
ClÀ ion and n-hexyl group.
N(7)AC(25)
N(8)AC(32)
C(7)AC(8)
C(15)AC(16)
C(23)AC(24)
C(31)AC(32)
C(10)AC(15)
C(26)AC(31)
1.339(3)
1.337(3)
1.470(4)
1.452(4)
1.459(4)
1.458(4)
1.401(4)
1.399(4)
Bond angles
N(2)AZn(1)AN(1)
N(3)AZn(1)AN(2)
N(4)AZn(1)AN(1)
N(1)AZn(1)AOW(1)
N(3)AZn(1)AOW(1)
C(1)AN(1)AC(8)
C(24)AN(3)AC(17)
C(8)AN(5)AC(9)
C(24)AN(7)AC(25)
N(3)AZn(1)AN(1)
N(3)AZn(1)AN(4)
N(4)AZn(1)AN(2)
N(2)AZn(1)AOW(1)
N(4)AZn(1)AOW(1)
C(9)AN(2)AC(16)
C(25)AN(4)AC(32)
C(17)AN(6)AC(16)
C(1)AN(8)AC(32)
87.94(10)
88.20(10)
87.84(9)
101.66(9)
98.90(9)
109.5(2)
108.6(2)
123.4(3)
123.3(3)
159.42(9)
88.03(9)
157.50(9)
98.24(10)
104.26(10)
108.8(2)
108.8(2)
123.6(2)
123.6(2)
3.2. Characterization
In the IR spectrum, the compound (1) has absorption at
888, 1062, 1286 cmÀ1 as well as in the 1410–1486 cmÀ1
region, corresponding to the presence of ZnPc (Fig. 4)
[21]. The IR spectrum also showed strong bands at 3432
and 3051 cmÀ1 that can be attributed to the OAH stretch-
ing of the water and CAH stretching mode for the phenyl
ring, respectively [12]. The strong peak at 1456 cmÀ1 is
assigned to ms(ACNAC@CA) groups. The two peaks at
776 and 727 cmÀ1 are attributed to the CAH vibrations
[22]. These features could be completely confirmed by the
single crystal X-ray diffraction study.
The UV–visible spectrum in DMF indicates the Soret
band at 331 nm and Q band at 669 nm, which are the typ-
ical bands characteristic of ZnPc (Fig. 5a). In contrast with
the corresponding bands of ZnPc (340 and 670 nm)
(Fig. 5b), a slight blue shift occurs in our compound (1)
[23]. The blue shift of the 340–331 nm most probably
ZnPc(H2O), and ZnPc [20] are shown in Table 3. Ct is the
center of the square formed by the four central nitrogen
atoms. Ca and Cb represent a- and b-carbon atoms of a
pyrrole unit, respectively. Np and Nb represent a pyrrole
nitrogen atom and an azamethine atom, respectively. The
comparable values observed for ZnPcCl, ZnTPP(H2O)

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L.-Y. Cui et al. / Journal of Molecular Structure 827 (2007) 149–154
Fig. 2. The crystal structure viewed along the b axis.
Scheme 1. Schematic representation of the pÁ Á Áp interactions between the Pc ligands of compound (1).
Fig. 3. The packing structure of compound (1).
resulted from the remaining water molecule because the
water molecules usually show stronger coordination ability
than the DMF molecules for Zn(II) ions and the interac-
tion between the Zn(II) ion and the coordinating water
molecule slightly affects the electron distribution of ZnPc.
The Soret band corresponds to the excitation between the
1a2u(p) and the 1eg(p*) states. The Q-band is associated
with the excitation between the HOMO-A1g ground state
(a2 (p)) and the degenerate LUMO À (eg(p*))-the first
1u
excited singlet state, which has Eu symmetry from the
(a11ue1 ) configuration [24].
g
The emission spectra of compound (1) in DMF with dif-
ferent
concentrations
5.0 · 10À4 M,
3.0 · 10À4 M,
2.0 · 10À4 M, 1.5x10À4 M and 1x10À4 M were recorded at

L.-Y. Cui et al. / Journal of Molecular Structure 827 (2007) 149–154
153
Table 3
The average lengths (A) and angles (ꢀ) of characteristic bonds in ZnPc derivatives
˚
ZnPc
0
ZnPcCl
(H2O)ZnTPP
(n-Hexyl)ZnPc
[ZnPc(H2O)]Æ2DMF
CtAM
CtANp
MANp
MAL
0.59
1.95
2.034
2.35
1.380(8)
1.332(9)
1.474(9)
1.422(10)
0.19
2.04
2.05
2.20
1.38
1.42
1.43
1.37
105.4
125.9
O
0.48
2.00
2.06
2.17
1.38
1.34
1.47
1.43
109.3
124.5
N
0.38
1.98
1.980
2.019(2)
2.077(2)
1.366(3)
1.336(3)
1.452(4)
1.409(4)
108.9(2)
123.5(2)
O
NpACa
CaANb
CaACb
CbACb
\Ca Np Ca
\Nb
1.369(3)
1.333(3)
1.455(3)
1.400(3)
Ligand
Cl
Fig. 6. Emission spectra (kex = 550 nm) for compound (1) in DMF. The
concentrations of compound (1) are 5.0 · 10À4 M, 3.0 · 10À4 M,
2.0 · 10À4 M, 1.5 · 10À4M and 1 · 10À4 M from (1) to (5), respectively.
Fig. 4. FT-IR spectrum for compound (1).
at 743 nm (kex = 550 nm). Contrast to the emission wave-
length (678 and 745 nm) of compound ZnPc, the batho-
chromic shift (21 nm) and the corresponding blue shift
(2 nm) may be attributed to the presence of coordinated
water molecules for the compound (1) [23,25,26].
4. Conclusion
A new complex [ZnPc(H2O)]Æ2DMF (1) has been ratio-
nally synthesized through anhydride method. The Zn(II)
ion is five-coordinated by four nitrogen atoms from Pc
ligands and one oxygen atom from one water molecule.
The strong p–p interactions between Pc ligands result in
1D superamolecular structure. The FT-IR, UV–vis and
fluorescence spectra results are in good agreement with
the crystal structure. The systemic studies on related ZnPc
compounds are under way in our laboratory.
Fig. 5. Uv–vis absorption spectra for compound (1) (a) and ZnPc (b) in
DMF.
Acknowledgements
This work was supported by the application foundation
of Science and Technology office of Jilin Province (PR Chi-
na) (20010512) and the Ministry of Education of PR China.
room temperature after corrected for self-absorption,
respectively. As shown in Fig. 6, the compound (1) exhibits
two strong emission peaks that were about at 699 nm and

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L.-Y. Cui et al. / Journal of Molecular Structure 827 (2007) 149–154
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Appendix A. Supplementary data
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Additional material consisting of atomic coordinates,
anisotropic thermal parameters, a full list of bond lengths
and angles for the ZnPc(H2O) complex have been deposit-
ed with Cambridge Crystallographic Data Centre in CIF
format as supplementary publications No. CCDC
287273. Copies of this information may be obtained free
of charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44 1223 336033; e-mail:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.a-
c.uk). Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/
j.molstruc.2006.05.030.
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