Synthesis, crystal structure and properties of the zinc complexes with unsymmetrical tridentate ligands

Article abstract of DOI:10.1016/S0022-2860(03)00240-0

Two complexes of zinc (II) with mixed-ligand, [Zn₂(phen)₂(HL¹)₂] (ClO₄)₂ (1) and [Zn₂(phen)₂(HL²)₂] (ClO₄)₂ (2) (H₂L¹=N-(2-hydroxybenzyl) ethanolamine and H₂L² = N-(2-hydroxybenzyl) propanolamine), and another zinc complex ZnL¹ (3) were synthesized and characterized by elemental analysis, IR spectra, thermal analysis, fluorescence and ¹H NMR. The crystal structure of (1) has a centrosymmetric di-phenoxo-bridged dizinc (II) core and each zinc center is laid in a slightly distorted trigonal bipyramidal geometry. A 2D supramolecular structure is formed approximately along bc plane in terms of the action of multiple N-H?O and O-H?O hydrogen bonds between the (HL¹)^- ligands and the π?π stacking interactions between the phenanthroline ligands. Thermal behavior, studied by TG and DTA in nitrogen atmosphere, indicates that phen is eliminated at higher temperature than (HL¹)^- and (HL²)^-. Several possible mechanisms for the fluorescence quenching of the metal complexes are proposed.

Full text of DOI:10.1016/S0022-2860(03)00240-0

Journal of Molecular Structure 654 (2003) 235–243
www.elsevier.com/locate/molstruc
Synthesis, crystal structure and properties of the zinc complexes
with unsymmetrical tridentate ligands
a
a
a,
b
*
Xueting Liu , Yongshu Xie , Qingliang Liu , Chenxia Du ,
Yu Zhub, Xiaolong Xua
aDepartment of Chemistry, University of Science and Technology of China, Hefei 230026, People’s Republic of China
bDepartment of Chemistry, Zhengzhou University, Zhengzhou 450052, People’s Republic of China
Received 10 May 2002; revised 30 March 2003; accepted 1 April 2003
Abstract
Two complexes of zinc (II) with mixed-ligand, [Zn2(phen)2(HL1)2] (ClO4)2 (1) and [Zn2(phen)2(HL2)2] (ClO4)2(2)
(H2L1yN–(2-hydroxybenzyl) ethanolamine and H2L2 ¼ N–(2-hydroxybenzyl) propanolamine), and another zinc complex
1
ZnL1 (3) were synthesized and characterized by elemental analysis, IR spectra, thermal analysis, fluorescence and H NMR.
The crystal structure of (1) has a centrosymmetric di-phenoxo-bridged dizinc (II) core and each zinc center is laid in a slightly
distorted trigonal bipyramidal geometry. A 2D supramolecular structure is formed approximately along bc plane in terms of the
action of multiple N–H· · ·O and O–H· · ·O hydrogen bonds between the (HL1)2 ligands and the p· · ·p stacking interactions
between the phenanthroline ligands. Thermal behavior, studied by TG and DTA in nitrogen atmosphere, indicates that phen is
eliminated at higher temperature than (HL1)2 and (HL2)2. Several possible mechanisms for the fluorescence quenching of the
metal complexes are proposed.
q 2003 Published by Elsevier Science B.V.
Keywords: Dinuclear zinc complex; Crystal structure; 2D supramolecular structure; Hydrogen bonds; p· · ·p Stacking interactions; Thermal
analysis
1. Introduction
enzymes in biological systems is not clear, one aspect
has been confirmed, i.e. the coordination environ-
ments of the zinc (II) atoms such as the distance
between two zinc cores are crucial to allow the
cooperation of both zinc centers in the active sites [4].
A variety of model compounds for binuclear zinc-
containing enzymes have been designed and syn-
thesized to understand their biological functions
[7–10].
Zn complexes [1–6] have attracted increasing
interest in the field of synthetic and biological
chemistry particularly due to the key role they play
in biological systems. Binuclear zinc coordination
moieties are found in various zinc enzymes such as
phosphatase [7–9] and metallo-b-lactamases [10].
Although the detailed mechanism of these zinc
To assemble 1D, 2D or 3D supramolecular
structures has become another interesting area in
coordination chemistry. Two important types of
*
Corresponding author. Tel.: þ86-551-360-3214.
E-mail address: qliu@ustc.edu.cn (Q. Liu).
0022-2860/03/$ - see front matter q 2003 Published by Elsevier Science B.V.
doi:10.1016/S0022-2860(03)00240-0

236
X. Liu et al. / Journal of Molecular Structure 654 (2003) 235–243
noncovalent interactions for building supramolecular
networks, hydrogen bonds and aromatic p· · ·p
stacking interactions, have recently attracted much
more attention [11–15], for example, the supramole-
cular assemblies of zinc complexes involving the
above two noncovalent interactions [16–19]. The
supramolecular structures of some complexes con-
taining fluorophores and some specific metal ions are
expected to apply as sensing and switching devices
through spectral changes [20].
Fig. 1. Structures of ligands H2L1·HCl and H2L2.
Tridentate ligands H2L1·HCl and H2L2 have
demonstrated to be promising in the construction of
the supramolecular networks connected by multiple
hydrogen bonds [21]. On the other hand, phen has the
potential applications to build the supramolecular
structures via p· · ·p stacking interactions [22] and to
prepare the efficient chemosensors due to the
intensive emission and the binding sites of two
amine groups [23].
Zn(ClO4)2·6H2O and phen·H2O were used as received
without further purification.
IR spectra were recorded on a Bruker Vector-22
Spectrometer (KBr Disc.). Fluorescence spectra were
measured with 850 Hitachi Fluorescence Spectropho-
tometer. Thermal analysis (TG, DTA) measurements
were performed using Rigaku Thermoflex Thermal
Analyzer in a flowing nitrogen atmosphere with
heating rate of 10 8C min21. A sample size of 2–
Thus, the mixed-ligand Zn complexes containing
the tridentate ligand and phen may give some
supramolecular structures with interesting fluorescent
properties.
1
10 mg was used. The H NMR measurements were
carried out on a Bruker 300 Ultrashield NMR
Spectrometer in DMSO-d6.
Herein, we describe the studies of the syntheses,
IR, 1H NMR, fluorescence and thermal analysis of two
zinc complexes with mixed-ligand, [Zn2(HL1)2(-
phen)2](ClO4)2 (1), [Zn2(HL2)2(phen)2](ClO4)2 (2)
(H2L1yN–(2-hydroxybenzyl) ethanolamine and
H2L2yN–(2-hydroxybenzyl) propanolamine) and
another zinc complex ZnL1 (3). The synthesis of
ZnL2 was unsuccessful. For a better understanding,
the properties of the Zn complex Zn(phen)3(ClO4)2
(4) [24] and free ligands H2L1·HCl and H2L2 are also
reported.
2.2. Preparation of [Zn2(HL1)2(phen)2](ClO4)2 (1),
[Zn2(HL2)2(phen)2](ClO4)2 (2), ZnL1 (3) and
Zn(phen)3(ClO4)2 (4)
Preparation of [Zn2(HL1)2(phen)2](ClO4)2 (1).
To a stirred methanol solution of H2L1·HCl
(0.0814 g, 0.4 mmol), Zn(ClO4)2·6H2O (0.1490 g,
0.4 mmol) and phen·H2O (0.0793 g, 0.4 mmol)
were added followed by the addition of an aqueous
solution of NaOH (0.4 M, 0.1 ml, 0.4 mmol). The
resulting solution was allowed to reflux for 4 h,
then concentrated in vacuo, and the light yellow-
coloured solid was collected by filtration, washed
with methanol and dried. Yield: 0.16 g, 80%. Anal.
Calcd for C42H40Cl2N6O12Zn2: C, 49.34; H, 3.94;
N, 8.22%. Found: C, 49.02; H, 4.15; N, 8.09%.
The filtrate was left undisturbed at room tempera-
ture for a few days affording light yellow-coloured
crystals of (1) suitable for X-ray structural
determination.
It is interesting that complex (1) can be self-
assembled into a 2D supramolecular structure via the
intermolecular hydrogen bonds between the (HL1)2
ligands and p· · ·p interactions between the phenan-
throline rings.
2. Experimental
2.1. Materials and physical measurements
Synthesis of (2) is similar to that of (1). Yield:
0.18 g, 85%. Anal. Calcd for C44H44Cl2N6O12Zn2: C,
50.31; H, 4.22; N, 8.00%. Found C, 49.98; H, 4.25; N,
8.17%.
H2L1·HCl, H2L2 (Fig. 1) and complex (4) were
prepared by the methods reported earlier [21,25,24].

X. Liu et al. / Journal of Molecular Structure 654 (2003) 235–243
237
Preparation of (3). To a stirred methanol solution
of H2L1·HCl (0.0814 g, 0.4 mol), Zn(ClO4)2·6H2O
(0.0814 g, 0.4 mmol) were added followed by the
addition of NaOH (0.4 M, 0.1 ml, 0.4 mmol). The
resulting solution was allowed to reflux for 4 h, then
concentrated in vacuo, and the colourless solid was
collected by filtration, washed with methanol and
dried. Yield: 0.075 g, 82%. Anal. Calcd for
C9H11N1O2Zn: C, 46.96; H, 4.82; N, 6.09%. Found:
C, 46.49; H, 4.92; N, 5.94%.
were refined anisotropically. Hydrogen atoms were
included but not refined. The final cycle of full-matrix
least-squares refinement was based on observed reflec-
tions ðI . 2:00sðIÞÞ and variable parameters. All
calculations were performed using SHELX-97 soft-
ware package [26].
Crystallographic data for (1) are listed in Table 1.
3. Result and discussion
2.3. X-ray data collection and structural
determination
3.1. IR spectra
IR spectra, showing the characteristic absorptions
of the complexes and the ligands are listed in Table 2.
Two characteristic absorptions at 1421 and 853 cm21
for free phen, slightly shift to higher and lower
frequencies, respectively, in the complexes. The
strong unresolved broad band at 1050–1101 cm21
and the sharp band at 624 cm21 are assigned to the
vibrations of free ClO24 . The m2-bridging mode of
the phenoxo groups in (1) can be inferred from the
A single crystal of (1) was mounted on a glass-fiber.
All measurements were made on a Rigaku RAXIS-IV
imageplateareadetectorwithgraphitemonochromated
Mo Ka radiation. The data were collected at 18 8C and
corrected for Lorentz and polarization effects. The
correction for secondary extinction was applied. The
structure was solved by direct methods and expanded
using Fourier techniques. The non-hydrogen atoms
Table 1
Crystal data and structure refinement for (1)
Empirical formula
Formula weight
C21H20ClN3O6Zn
511.22
Temperature
291(2) K
˚
0.71073 A
Wavelength
Crystal system, space group
Unit cell dimensions
TRICLINIC, P-1
˚
a ¼ 9:910ð2Þ A
a ¼ 110:63ð3Þ (8)
b ¼ 108:55ð3Þ (8)
g ¼ 101:33ð3Þ (8)
˚
b ¼ 11:330ð2Þ A
˚
c ¼ 11:529ð2Þ A
3
˚
Volume
1076.7(4) A
Z; Calculated density
Absorption coefficient
F(000)
2, 1.577 Mg/m3
1.309 mm21
524
Crystal size
0.26 £ 0.25 £ 0.20 mm
2.05–27.54 (8)
u Range for data collection
Index ranges
212 # h # 11; 214 # k # 13; 0 # l # 14
3786/3786
Reflections collected/unique
Completeness to 2? ¼ 27:54
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices ½I . 2sðIފ
R indices (all data)
88.76%
0.7798 and 0.7272
Full-matrix least-squares on F2
3786/0/302
1.029
R1 ¼ 0:0771; wR2 ¼ 0:1973
R1 ¼ 0:0997; wR2 ¼ 0:2123
0.010(4)
Extinction coefficient
Largest diff. peak and hole
23
˚
0.946 and 20.987 e A

238
X. Liu et al. / Journal of Molecular Structure 654 (2003) 235–243
Table 2
Characteristic IR spectral data for Zn complexes and ligands
Compounds
n(N–H)
n(Ar–O)
Ring vibration
n(C–H)
Vibration(ClO24 )
(1)
(2)
3250(m)
3250(w)
3264(m)
1264(m)
1267(s)
1274(s)
1625(w), 1593(w), 1519(m), 1481(m),
1427(s), 850(s), 771(m), 726(s)
2925(w)
1090(s), 624(s)
1101(s), 624(m)
1624(w), 1595(w), 1520(w), 1482(s)1429(m),
849(m), 770(s), 727(s)
2939(w)
(3)
(4)
1597(s), 1482(s), 760(s)
2922(m), 2859(m)
1627(m), 1588(m), 1523(s), 1430(vs), 849(s), 726(s)
1590(m), 1503(s), 1421(s), 853(s), 738(s)
1592(s), 1458(s), 1439(s), 763(s)
1610(m), 1581(m), 1492(s), 762(s)
1050(s), 623(s)
Phen·H2O
H2L1·HCl
H2L2
3198(s)
1237(s)
1257(s)
2965(m), 2839(m)
2970(m), 2862(m)
n(C–O) vibration band at 1264 cm21, which is lower
than 1296 cm21, responsible for the nonbridging
mode in [Cu(HL1)2] [21]. For (2), the corresponding
vibration bands are very alike, as the similar structure
to (1).
decomposition of ClO24 . Compared to the first stage,
the loss rate of the second stage is relatively moderate.
Theremovalofligandphenoughttobecompletedinthe
third stage between 600 and 730 8C, in which there is a
verysteepmassloss.Acontinuousweightloss,owingto
the removal of metallic zinc, occurs above 730 8C,
much lower than the temperature reported for
[Zn(sac)2(ea)2] [27]. Thermal analytical data in Table
3 show that ligand phen exhibits higher stability than
ligand (HL1)2 and ClO24 anion, as the initial decompo-
sition temperatures are taken as a measure of thermal
stability. However, at very high temperature, the
exothermic elimination feature of phen can consider-
ably speed up its-self decomposition. For complex (2),
the decomposition takes place at 251 8C and also
undergoes whole exothermic decomposition in three
stages corresponding to the elimination of (HL2)2,
3.2. Thermal analysis
Thermal behavior of the Zn complexes and the free
ligands was studied by TG and DTA. The thermal
analytical data are listed in Table 3. The complex (1)
startsdecompositionat256 8Candthenundergoesthree
stages of mass loss. In the first stage, the elimination of
(HL)2 beginsat256 8Candendsat505 8C,inwhichone
strong exothermic peak at 360 8C and two small rapid
masslossesintheTGcurvecanbeobserved.Thesecond
stage between 505 and 600 8C is assigned to the
Table 3
Thermal analytical data for Zn complexes and free ligands
Complexes
Stages
Temperature
DTAmax (8C)a
Mass loss (%)
Total mass loss
(%)
Solid residue
range (8C)
Found
Calcd
Found
Calcd
(1)
(2)
1
2
3
1
2
3
1
1
2
1
256–505
505–600
600–730
251–570
570–633
633–750
100–630
80–240
360(2)
520(2)
675(2)
30.4
17.8
37.2
32.5
19.5
35.3
35.5
19.0
34.3
71.7
17.9
82.1
85.4
34.3
87.3
Zn
275(2) 324(2) 510(2)
608(2)
709(2)
19.7
34.5
72.9
18.5
81.2
98.4
89.7
27.1
87.6
28.3
Zn
Zn
(3)
H2L1·HCl
350(2) 495(2) 570(2)
120(þ)
240–710
96–686
585(2)
155(þ) 184(þ) 241(þ) 677(þ)
99.7
98.4
100
100
None
None
H2L2
100
a
(þ), Endothermic; (2), exothermic.

X. Liu et al. / Journal of Molecular Structure 654 (2003) 235–243
239
Table 4
collected in Table 4. It is known that phenolic
derivatives, heterocyclic derivatives possess
the fluorescence and the formation of metal chelates
commonly promotes the fluorescence by strengthen-
ing rigidity and minimizing internal vibrations [30].
Generally, metal cation Zn can give rise to com-
plexes’ exhibiting fluorescence emission [31]. As
expected, all Zn complexes in Table 4 show red-shift
features, compared to free ligands H2L1·HCl, H2L2
and phen [32]. However, when the ligands coordinate
to metal ion Zn2þ, we can see obvious puzzling
fluorescence quenching. This may be explained as
following: first, the CHEF (chelation-enhanced fluor-
escence) effect follows the order Hþ . Zn2þ [33], i.e.
the Zn complexes of the ligands are less emissive than
the protonated ligands. This explanation should be
only suitable for H2L1·HCl, not for H2L2, because
H2L2 is not protonated; second, the chelated metal Zn
ion is proximate to the chromophores (HL1)2 and
(HL2)2, which can result in fluorescence quenching
[34]. In other words, the coordination of Zn to
phenoxo O and ethanolamine N may make it closer to
the phenoxo and ethanolamine, so that the energy-
transfer between them, takes place easier. Third,
although Zn2þ with d10, has not any the charge
transfer, its linking to phen and (HL1)2 (or (HL2)2)
fragments may result in electron transfer between
ligands in binuclear Zn complexes (1) and (2), and
then the fluorescence quenching [35]. Finally, the
considerably weak emission intensity of (1) and (2)
may be also attributed to the steric constraint between
the rigid phen ligands and (HL1)2 (or (HL2)2), which
strengthens the vibronic interaction-induced quench-
ing [36]. Obviously, the above explanations, except
the first one, are related to the conformation of
Spectroscopic data of Zn complexes and ligands: wavelength of
fluorescence maximum lF/nm, wavelength of excitation lex/nm,
emission intensity F
Complexes (or ligands)
lF
lex
F
(1)
(2)
560
306
0.39
556
333a
387
319
319
294
0.26
5.1
(3)
(4)
H2L1·HCl
H2L2
271
310
5.2
262.5
271.5
10
15.6
a
An additional band appeared at 430 nm with F of 1.8 and
overlapped with the 333 nm band.
ClO24 and phen sequentially. Comparing the thermal
decomposition temperatures for ligand phen in (1)
(600 8C) and (2) (633 8C) with those reported for free
phen (432 8C) [28] and phen coordinated in [Zn(H2-
O)4(phen)](NO3)2·H2O(ca.320 8C)[29],wecandrawa
conclusion that ligand phen have higher thermal
stability in (1) and (2).
For free ligand H2L1·HCl, the thermal decompo-
sition consists of two stages. The first endothermic
stage, can be reasonably assigned to the elimination of
HCl, while the second one is the decomposition of
H2L1. Unlike H2L1·HCl and other Zn complexes,
ligand H2L2 displays several unexpected endothermic
peaks in the DTA curve. As shown in Table 3, free
ligands H2L1·HCl and H2L2 complete their decompo-
sition above 710 and 686 8C, respectively.
3.3. Fluorescence of binuclear Zn complexes (1), (2)
and mononuclear Zn complexes (3), (4)
The excitation, emission wavelength and emission
intensity of the Zn complexes and the ligands are
Table 5
1H NMR spectra data (d; in ppm) for the ligands and the complexes
Compounds
Phenyl protons
Phen protons
Aliphatic protons
(1)
(2)
6.40–6.98
6.39–6.98
8.07–9.20
8.07–9.10
2.62(C2–H), 3.85(C1–H), 4.27(C3–H)
1.63(C30 –H), 2.70(C20 –H), 3.80(C10 –H),
4.48(C40 –H)
(3)
H2L1·HCl
H2L2
6.49–7.00
7.5–8.0
2.72(C2–H), 3.82(C1–H), 4.26(C3–H)
3.11(C2–H), 4.19(C1–H), 3.79(C3–H)
2.15(C30 –H), 2.9(20), 3.5(C10 –H), 3.86(C40 –H)
6.78–7.24
Phen [37]
Zn(phen)23þ [38]
7.88–9.26
7.62–8.84

240
X. Liu et al. / Journal of Molecular Structure 654 (2003) 235–243
phenyl protons of ligands (HL1)2 and (HL2)2 and
also the signals of C1 and C2 protons shift upfield, but
downfield for C3 proton. For (HL2)2, the situation
becomes more complicated, i.e. the signals of C-20
and C-30 protons shift upfield, while C-10 and C-40
protons exhibit signals downfield. A doublelet of (3)
in the 6.49–7.00 range, can be assigned as phenyl
protons (C6H4, 4H), which have higher d values in
literature [39]. It is interesting that 1H NMR spectra of
(1) show a triplelet in the 6.40–6.98 range. This may
be associated with the diphenxo-bridged complexa-
tion mode of (1). Contrary to those of the phenyl
protons, 1H NMR signals of the coordinated phen shift
a little downfield as its coordination (Table 5).
3.5. Description of the structure (1)
Fig. 2. View of complex (1) showing the numbering scheme at the
20% probability level with the H atoms omitted for clarity.
A perspective view of complex (1) shows the atom
numbering scheme in Fig. 2. Selected bond lengths
and bond angles are listed in Table 6. Two zinc metal
centers are both pentacoordinated and bridged by two
phenoxo O atoms, resulting in a centrosymmetric
structure. For each zinc (II) core, the Addison
distortion index t [40] is 0.807 (t ¼ 0 for a square
pyramid, and t ¼ 1 for a trigonal bipyramid), which
suggests that the coordination geometry is a slightly
distorted trigonal bipyramid. The axial positions (for
Zn1) are occupied by N3 from phen and O (1)#1 from
another (HL1)2, and the equatorial positions are
occupied by N1, N2, O1 from another (HL1)2, phen
and (HL1)2, respectively. Unlike phenoxo O atom,
the alkoxyl O atom is left uncoordinated. The coplanar
complexes. As shown in Table 4, the spectroscopic
data of binuclear Zn complexes (1) and (2) are very
close, possibly due to the similar structures of two
complexes.
3.4. 1H NMR spectra of H2L1·HCl, H2L2 and their Zn
complexes (1), (2), and (3)
1H NMR spectral data of the free ligands and the
zinc complexes are listed in Table 5. Upon the
complexiation of Zn (II) ion, 1H NMR signals of
Table 6
˚
Selected bond lengths (A) and angles (8) for (1)
Zn(1)–O(1)
1.967(4)
3.1365(2)
2.055(5)
2.123(4)
122.63(2)
119.6(2)
90.25(2)
105.08(2)
78.2(2)
Zn(1)–N(3)
O(1)–Zn(1)#1
Zn(1)–N(2)
2.170(5)
2.123(4)
2.089(5)
Zn(1)–Zn(1)#1
Zn(1)–N(1)
Zn(1)–O(1)#1
O(1)–Zn(1)–N(1)
N(1)–Zn(1)–N(2)
N(1)–Zn(1)–O(1)#1
O(1)–Zn(1)–N(3)
N(2)–Zn(1)–N(3)
O(1)–Zn(1)–Zn(1)#1
N(2)–Zn(1)–Zn(1)#1
O(1)#1–Zn(1)–Zn(1)#1
O(1)–Zn(1)–N(2)
117.31(2)
79.94(2)
92.97(2)
93.1(2)
O(1)–Zn(1)–O(1)#1
N(2)–Zn(1)–O(1)#1
N(1)–Zn(1)–N(3)
O(1)#1–Zn(1)–N(3)
N(1)–Zn(1)–Zn(1)#1
N(3)–Zn(1)–Zn(1)#1
171.06(2)
109.95(2)
146.28(2)
41.79(1)
108.84(1)
38.14(1)
Symmetry transformations used to generate equivalent atoms: #1 2x þ 1; 2y þ 2; 2z þ 2:

X. Liu et al. / Journal of Molecular Structure 654 (2003) 235–243
241
Table 7
Hydrogen-bonds for (1) (A and 8)
diphenoxo-bridged Zn complexes [42], but longer
˚
than the corresponding value [Zn· · ·Zn 3.0540(18) A]
˚
˚
[43] and shorter than that [Zn· · ·Zn 3.443(3) A] of
D–H
d
/DHA
d
A[symmetry operations]
phenoxy-bridged binuclear Zn complex where the
other bridging ligand is benzoato O atom [44]. Each
Zn (1) and Zn (1)#1 are shown to be laid
approximately in the coordinated phen mean planes.
A prominent feature of the complex (1) is the
formation of 2D supramolecular network. Along bc
plane, each complex molecule is surrounded by four
such molecules. Approximately along c axis, there
exist multiple hydrogen bonds between N–H, O–H
groups of (HL1)2 ligands and perchlorate anions
(Table 7), i.e. N1–H1F and uncoordinated O2–H2A
groups act as hydrogen donors; the perchlorate anions
act as hydrogen acceptors. Along b axis, the distance
between two phen mean planes of adjacent
(H· · ·A)
(D· · ·A)
N1–H1F 2.263
O2–H2A 1.979
N1–H1F 2.263
O2–H2A 1.979
145.17 2.910
167.38 2.785
145.17 2.910
167.38 2.785
O6 [1 2 x; 3 2 y; 2 2 z]
O5 [1 2 x; 3 2 y; 2 2 z]
O6 [x; 1 þ y; 1 þ z]
O5 [x; 1 þ y; 1 þ z]
structure of N1, N2, O1, Zn1 can be evidenced by the
sum of three neighboring angles (359.5(6)8): N1–
Zn1–O1, N1–Zn1–N2, N2–Zn1–O1. The average
˚
Zn1–O bond length for Zn1–phenolate is 2.045(4) A,
comparable to the corresponding value of the complex
˚
[Zn2(C25H17N2O2PS)2Cl2] (2.050(5) A) [41]. The
˚
Zn1· · ·Zn (1)#1 separation of 3.137 A is almost
˚
molecules is approximately 3.5 A, indicating that
˚
equal to the value [Zn· · ·Zn 3.13 A] reported for
Fig. 3. 2D supramolecular network of complex (1) approximately along the bc plane.

242
X. Liu et al. / Journal of Molecular Structure 654 (2003) 235–243
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the neighboring molecules are connected via p· · ·p
interactions. From above discussion, it can be
concluded that (1) was self-assembled into a 2D
supramolecular structure approximately along bc
plane via intermolecular N–H· · ·O and O–H· · ·O
hydrogen bonds and p· · ·p stacking interactions
between the phenanthroline rings (Fig. 3).
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In conclusion, two mixed-ligand zinc (II) com-
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complex (3) have been synthesized. Crystal structure
of (1) reveals that it has a centrosymmetric structure
with two zinc atoms bridged by two phenoxo O atoms.
It is interesting for (1) to assemble into a 2D ordered
supramolecular structure via hydrogen bonds and
p· · ·p stacking interactions. Complex (2) has a similar
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Acknowledgements
This work was financially supported by the
National Science Foundation of China (No.
30270321) and the Natural Science Foundation of
Anhui Province (No. 01045408).
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