ZnII and Hg11 complexes with 2,3-substituted-5,6- di(1H-tetrazol-5-yl)pyrazine ligands: Roles of substituting groups and synthetic conditions on the formation of complexes

Article abstract of DOI:10.1021/cg900934u

In our continuing efforts to explore the effects of substituting groups of bridging ligands on the structure and properties of their complexes, two structurally related bis(tetrazolate) ligands, 2,3-diethyl-5,6-di(1H-tetrazol-5- yl)pyrazine (H₂L¹) and 2,3-diphenyl-5,6-di(1H-tetrazol-5- yl)pyrazine (H₂L²), have been designed, and seven Zn ¹¹ and Hg¹¹ complexes with the two ligands, [Zn ₂(L¹J₂(H₂O)₄](H ₂O)₄ (1), ([Zn₂(L₁J ₂](H₂O)_0.5}_∞ (2), [Zn ₆(L²)₆(H₂O)₁₂] (3), [Zn(L²]_∞, (4), [Hg(L¹)Br] _∞ (5), {[Hg₄(L²)₄(H ₂O)}₆](H₂O)}_∞ (6), and [Hg₃(L²)₂(H₂O)_0.5Br ₂]_∞, (7), have been synthesized and characterized. 1 has a dinuclear structure in which Zn is four-coordinated to furnish a distorted tetrahedral geometry, and in the crystal structure the dinuclear units are further assembled to form a three-dimensional (3D) framework by hydrogen bonds. 2 possesses a 3D framework with (4,12²] topology in which the Zn¹¹ center is four-coordinated by N atoms of the ligand. 3 has a hexanuclear structure comprised of two trinuclear motifs as basic building units each of which has three types of coordination environments around the Zn ¹¹ ions, and the hexanuclear units are interlinked by O-H...N hydrogen-bonding to generate a two-dimensional (2DJ framework. 4 takes a 3D (4,8,10) topology, in which Zn^II ions act as three-connected nodes and the L² ligand takes a chelating-bridging mode being similar to that in 1.5 possesses a 2D (4,8,8) layer structure with one kind of Hg ^II center four-coordinated by one Br anion, two N atoms from two L¹ ligands, and one weakly coordinated N atom from another L ¹ ligand. 6 has two kinds of one-dimensional chain structures with two kinds of Hg ions,and one kind of these chains is further assembled into 2D sheets via hydrogen-bonding interaction. 7 has a 2D layer structure with one kind of Hg¹¹ center coordinated by a Br anion, the other one being seven-coordinated by six N atoms from four L² ligands and one weakly coordinated O atom from a water molecule. In this work, 1,3,5, and 6 were synthesized by the conventional method at room temperature, while 2, 4, 7 were prepared under hydrothermal conditions. These results show that the substituting groups of ligands and the reaction conditions have great influences on the formation of these complexes. In addition, the luminescent properties of complexes 1-7 have been briefly studied.

Full text of DOI:10.1021/cg900934u

DOI: 10.1021/cg900934u
ZnII and HgII Complexes with 2,3-Substituted-5,6-di(1H-tetrazol-
5-yl)pyrazine Ligands: Roles of Substituting Groups and Synthetic
Conditions on the Formation of Complexes
2010, Vol. 10
564–574
Ying Tao, Jian-Rong Li, Ze Chang, and Xian-He Bu*
Department of Chemistry, Nankai University, Tianjin 300071, China
Received August 7, 2009; Revised Manuscript Received September 9, 2009
ABSTRACT: In our continuing efforts to explore the effects of substituting groups of bridging ligands on the structure and
properties of their complexes, two structurally related bis(tetrazolate) ligands, 2,3-diethyl-5,6-di(1H-tetrazol-5-yl)pyrazine
(H2L1) and 2,3-diphenyl-5,6-di(1H-tetrazol-5-yl)pyrazine (H2L2), have been designed, and seven ZnII and HgII complexes
with the two ligands, [Zn2(L1)2(H2O)4](H2O)4 (1), {[Zn2(L1)2](H2O)0.5}¥ (2), [Zn6(L2)6(H2O)12] (3), [Zn(L2)]¥ (4), [Hg(L1)Br]¥
(5), {[Hg4(L2)4(H2O)6](H2O)}¥ (6), and [Hg3(L2)2(H2O)0.5Br2]¥ (7), have been synthesized and characterized. 1 has a dinuclear
structure in which ZnII is four-coordinated to furnish a distorted tetrahedral geometry, and in the crystal structure the
dinuclear units are further assembled to form a three-dimensional (3D) framework by hydrogen bonds. 2 possesses a 3D
framework with (4,122) topology in which the ZnII center is four-coordinated by N atoms of the ligand. 3 has a hexanuclear
structure comprised of two trinuclear motifs as basic building units each of which has three types of coordination
environments around the ZnII ions, and the hexanuclear units are interlinked by O-H N hydrogen-bonding to generate
3 3 3
a two-dimensional (2D) framework. 4 takes a 3D (4,8,10) topology, in which ZnII ions act as three-connected nodes and the L2
ligand takes a chelating-bridging mode being similar to that in 1. 5 possesses a 2D (4,8,8) layer structure with one kind of HgII
center four-coordinated by one Br anion, two N atoms from two L1 ligands, and one weakly coordinated N atom from
another L1 ligand. 6 has two kinds of one-dimensional chain structures with two kinds of HgII ions, and one kind of these
chains is further assembled into 2D sheets via hydrogen-bonding interaction. 7 has a 2D layer structure with one kind of HgII
center coordinated by a Br anion, the other one being seven-coordinated by six N atoms from four L2 ligands and one weakly
coordinated O atom from a water molecule. In this work, 1, 3, 5, and 6 were synthesized by the conventional method at room
temperature, while 2, 4, 7 were prepared under hydrothermal conditions. These results show that the substituting groups of
ligands and the reaction conditions have great influences on the formation of these complexes. In addition, the luminescent
properties of complexes 1-7 have been briefly studied.
Introduction
Up to now, numerous tetrazole-based ligands have already
been studied.11-14 Therefore, we can estimate that bis- or
multi-tetrazole ligands which have more complicated coordi-
nation chemistry may serve as good building blocks for the
construction of functional coordination compounds.
Great progress in the area of coordination compounds has
been achieved for their potential applications in catalysis,
chirality, conductivity, luminescence, magnetism, and poro-
sity,1 as well as their intriguing structures and topologies.2,3
A
Recently, we have reported a ditopic tetrazolate-based
ligand, 2,3-di-(1H-tetrazol-5-yl)pyrazine (H2L) and its ZnII
complex.15a As a continuation of the study on tetrazolate-
based coordination complexes,15 two structurally related bis-
(tetrazolate) ligands based on 2,3-di-(1H-tetrazol-5-yl)pyra-
zine, 2,3-diethyl-5,6-di(1H-tetrazol-5-yl)pyrazine H2L1 and
2,3-diphenyl-5,6-di(1H-tetrazol-5-yl)pyrazine H2L2, have
been designed, and seven ZnII and HgII coordination com-
plexes with the two ligands, [Zn2(L1)2(H2O)4](H2O)4 (1),
careful choice or design of ligands with suitable shape, sym-
metry, and functionality is the key point for the construction of
functional coordination compounds, with desired structural
features and physical-chemical properties.4 Among the
ligands used in coordination chemistry field, much attention
has been focused on rigid polytopic ligands,5 especially N-
heterocyclic ligands; in particular those with pyridyl and nitrile
donor groups are often employed to produce extended frame-
works with high structural stability and special topologies.6
Tetrazole and its derivatives as multifunctional ligands7
have been used widely in areas such as coordination chemis-
try, medicinal chemistry, and material science.8 From the view
of structure, the tetrazolate ring which is the analogue of
carboxylic acid provided the ability to participate in mono-,
bi-, or multidentate types of coordination modes with metal
ions in different conditions. As carboxylic acid ligands, they
could form unusual extended structures through coordination
and hydrogen bonds,9 tetrazole-based ligands also provided
theabilitytoproduce attractivemetal-organicframeworks.10
{[Zn2(L1)2](H2O)0.5 ¥ (2), [Zn6(L2)6(H2O)12] (3), [Zn(L2)]¥
}
(4), [Hg(L1)Br]¥ (5), {[Hg4(L2)4(H2O)6](H2O)}¥ (6), and
[Hg3(L2)2(H2O)0.5Br2]¥ (7), have been synthesized and char-
acterized. The effects of substituting groups of ligands on the
structure and properties of their complexes have been dis-
cussed according to the results. Furthermore, the factors such
as synthetic conditions especially reaction temperature,16,17
which have great influence on the formation of coordination
architectures, have also been investigated.
Experimental Section
Materials and General Methods. The solvents and reagents for
synthesis were commercially available and used as received. The
*Corresponding author. Fax: þ86-22-23502458. E-mail: buxh@nankai.
edu.cn.
r
pubs.acs.org/crystal
Published on Web 09/30/2009
2009 American Chemical Society

Article
Crystal Growth & Design, Vol. 10, No. 2, 2010 565
Chart 1. The Three Structurally Related Ligands H2L, H2L1,
and H2L2
slowly evaporated for ca. 7 days. Yellow crystals were obtained and
washed with water, methanol, and dried in air. Yield: ∼30%. Anal.
Calcd C108H84N60O12Zn6: C, 46.22; H, 3.02; N, 29.94. Found: C,
46.53; H, 3.25; N, 29.76. IR (KBr, cm-1): 3165vs, 1617m, 1444w,
1395s, 1266w, 1166w, 1102w, 769w, 702m, 538w.
[Zn(L2)]¥ (4). Zn(NO3)2 6H2O (30 mg, 0.1 mmol), H2L2 (37 mg,
3
0.1 mmol), with 10 mL water and 1 mL methanol, and a drop of
hydrochloric acid was sealed in a 25 mL Teflon-lined stainless steel
vessel and heated to 140 ꢀC at a 10 ꢀC h-1 rate, kept at 140 ꢀC for 3
3
days and then cooled to room temperature at a rate of 10 ꢀC h-1
.
3
Yellow prism-shaped crystals of 4 were isolated and washed with
water, methanol and dried in air. Yield: ∼30%. Anal. Calcd
C
18H10N10Zn: C, 50.23; H, 2.34; N, 32.56. Found: C, 50.51; H,
2.65; N, 31.88. IR (KBr, cm-1): 3453vs, 2170w, 1637s, 1401s,
1115m, 1018w, 752w, 691m, 543w.
We tried to use ZnSO4 7H2O or ZnCl2 instead of Zn(NO3)2
3
3
6H2O under the same reaction condition to prepare the same
complex. The crystal obtained was too small to analyze by X-ray
single-crystal diffraction, but their IR spectra are completely con-
sistent with that of complex 4.
Scheme 1. The Route for Ligand Synthesis
[Hg(L1)Br]¥ (5). HgBr2 (72 mg, 0.2 mmol) and H2L1 (54 mg,
0.2 mmol) were dissolved in a mixture of ca. 5 mL distilled water and
5 mL methanol until it was pellucid. After filtration, it was slowly
evaporated for about 7 days. The resulted colorless block-shaped
crystals were washed by water, methanol, and dried in air. Yield:
40%. Anal. Calcd C10H11N10HgBr: C, 21.77; H, 2.01; N, 25.39.
Found: C, 22.22; H, 1.86; N, 25.46. IR (KBr, cm-1): 3454vs, 2170w,
1630s, 1524w, 1401s, 1176m, 1068m, 918w, 515w.
{[Hg4(L2)4(H2O)6](H2O)}¥ (6). A mixture of HgBr2 (72 mg, 0.2
mmol), H2L2(74 mg, 0.2 mmol) was dissolved in ca. 8 mL ammonia
and 5 mL methanol until it was pellucid, and then filtrated, slowly
evaporated for ca. 7 days. The resulted yellow block-shaped crystals
were washed by water, methanol and dried in air. Yield: ∼30%.
Anal. Calcd C72H54N40Hg4O7: C, 36.02; H, 2.27; N, 23.35. Found:
C, 36.26; H, 2.72; N, 23.26. IR (KBr, cm-1): 3444vs, 2170w, 1633s,
1400s, 1161w, 1117w, 1037w, 1018m, 764w, 700m, 527w.
ligands, 2,3-diethyl-5,6-di(1H-tetrazol-5-yl)pyrazine (H2L1) and
2,3-diphenyl-5,6-di(1H-tetrazol-5-yl)pyrazine (H2L2), were synthe-
sized by modified literature methods (see Scheme 1).18 Elemental
analyses (C, H, and N) were performed on a Perkin-Elmer 240C
analyzer and IR spectra were measured on a Tensor 27 OPUS
(Bruker) FT-IR spectrometer with KBr pellets. The X-ray powder
diffraction (XRPD) was recorded on a Rigaku D/Max-2500 dif-
fractometer at 40 kV, 100 mA for a Cu-target tube and a graphite
monochromator. Simulation of the XRPD spectra (see Supporting
Information, Figure S2) were carried out by the single-crystal data
and diffraction-crystal module of the Mercury (Hg) program avail-
able free of charge via the Internet at http://www.iucr.org. Emission
spectra in solid state at room temperature were taken on a Cary
Eclips fluorescence spectrophotometer. The thermogravimetric
analysis (TGA) was done on a standard TG-DTA analyzer under
air atmosphere at a heating rate of 10 ꢀC/min for all measurements.
Synthesis of Complexes. [Zn2(L1)2(H2O)4](H2O)4 (1). ZnCl2
(14 mg, 0.1 mmol) and H2L1 (27 mg, 0.1 mmol) were added in 10
mL of ammonia under stirring at room temperature for about 5
minutes, then the mixture was filtrated and slowly evaporated for
ca. 7 days at room temperature. The colorless block-shaped crystals
of 1 wereobtainedand washed with water, methanol, and dried in air.
Yield:∼30%. Anal. Calcd for C20H36N20O8Zn2: C, 29.46;H, 4.45; N,
34.35. Found: C, 29.83; H, 4.57; N, 33.94. IR (KBr, cm-1): 3416vs,
3166vs, 2170w, 1618m, 1401s, 1241w, 1163w, 1087w, 620m.
[Hg3(L2)2(H2O)0.5Br2]¥ (7). 7 was synthesized by the reaction of
HgBr2 (72 mg, 0.2 mmol), H2L2 (74 mg, 0.2 mmol), and 12 mL water
which was sealed in a 25 mL Teflon-lined stainless steel vessel, and
then heated to 150 ꢀC at a 10 ꢀC h-1 rate, at 150 ꢀC for 3 days and
3
then cooled to room temperature at a 5 ꢀC h-1 rate. The resulting
yellow block-shaped crystals were washed by water and by ethanol
3
and dried in air. Yield: ∼30%. Anal. Calcd for
C
144H84Br8Hg12N80O2: C, 28.76; H, 1.41; N, 18.64. Found: C,
28.53; H, 1.71; N, 18.27. IR (KBr, cm-1): 3416vs, 3160vs, 2170w,
1619m, 1400s, 1126w, 1019w, 772w, 693w, 620w, 528w.
Caution! Although we met no problems in handling tetrazoles
and their complexes during this work, they should be treated with
great caution owing to their potentially explosive nature.
X-ray Data Collection and Structure Determinations. X-ray sin-
gle-crystal diffraction data for complexes 1-6 were collected on a
Rigaku SCX-mini diffractometer at 293(2) K, while data for 7 on a
Bruker Smart 1000 CCD diffractometer at 293(2) K, with Mo KR
˚
radiation (λ=0.71073 A) in the ω scan mode. The program SAINT
was used for integration of the diffraction profiles. All the structures
were solved by direct methods using the SHELXS program of the
SHELXTL package and refined by full-matrix least-squares meth-
ods with SHELXL. Semiempirical absorption corrections were
carried out using SADABS program. Metal atoms in the complexes
were located from the E-maps, and other non-hydrogen atoms were
located in successive difference Fourier syntheses and refined with
anisotropic thermal parameters on F2. The hydrogen atoms of the
ligand were generated theoretically onto the specific atoms and
refined isotropically with fixed thermal factors. H atoms of water
were added by the difference Fourier maps and refined with con-
strained. Crystal data and structure refinement parameters details
for complexes 1-7 are given in Table 1, and the selected bond
lengths and angles are given in Tables 2-8.
{[Zn2(L1)2](H2O)0.5
}¥ (2). A mixture of ZnCl2 (56 mg, 0.4 mmol)
and H2L1 (27 mg, 0.1 mmol) with anhydrous methanol (ca. 12 mL)
and one drop of hydrochloric acid was sealed in a 25 mL Teflon-
lined stainless steel vessel and heated to 140 ꢀC at a 10.8 ꢀC h-1 rate,
kept the temperature for 3 days, and then cooled to room tempera-
3
ture with a 10.8 ꢀC h-1 rate. White block crystals were obtained and
3
washed by water and by ethanol and dried in air. Yield: ∼20%.
Anal. Calcd for C10H10.50N10O0.25Zn: C, 35.31; H, 3.11; N, 41.18.
Found: C, 35.82; H, 2.97; N, 41.33. IR (KBr, cm-1): 3416vs, 3134vs,
2169w, 1618m, 1402s, 1177m, 1113m, 1060m, 983m, 621m, 540w.
Results and Discussion
[Zn6(L2)6(H2O)12] (3). A mixture of ZnSO4 7H2O (58 mg,
Synthesis Consideration. As an extension of our previous
study15a of the metal complexes with 5,6-di-(1H-tetrazole-
5-yl)pyrazine ligand, we have designed some substituent to
3
0.2 mmol) and H2L2 (74 mg, 0.2 mmol) was dissolved in ca. 10
mL ammonia until it was pellucid, and then it was filtrated, and

566 Crystal Growth & Design, Vol. 10, No. 2, 2010
Table 1. Crystallographic Data and Structure Refinement Summary for Complexes 1-7
Tao et al.
1
2
3
4
chemical formula
formula weight
crystal system
space group
C20H36N20O8Zn2
815.47
triclinic
P1
7.7062(15)
10.660(2)
11.619(2)
114.72(3)
104.23(3)
94.37(3)
822.9(3)
1
1.646
1.534
420
10451
3888
243
1.061
0.0500
0.1310
C10H10.50N10O0.25Zn
340.15
trigonal
R3
23.783(3)
23.783(3)
13.842(3)
90
90
120
6780.4(19)
18
1.499
1.642
3105
23713
3451
210
1.123
0.0744
0.1969
C108H84N60O12Zn6
2806.57
triclinic
P1
14.228(3)
14.449(3)
16.065(3)
83.85(3)
87.63(3)
70.23(3)
3090.0(11)
1
1.508
1.230
1428
24658
10892
838
1.101
0.0692
0.1533
C18H10N10Zn
431.75
tetragonal
I41/a
19.431(7)
19.431(7)
18.713(4)
90
90
90
7065(4)
16
1.624
1.420
3487
36546
4052
262
1.186
0.0836
0.1331
˚
a/A
˚
b/A
˚
c/A
R/o
β/o
γ/o
3
˚
V/A
Z
D/g cm-3
μ/mm-1
F(000)
reflns collected
unique reflns
parameters
GOF
R1 [I > 2σ(I)]
wR2 (all data)
5
6
7
chemical formula
formula weight
crystal system
space group
C10H11BrN10Hg
551.79
monoclinic
P21/n
10.064(2)
13.053(3)
12.178(2)
90
101.49(3)
90
1567.8(5)
4
2.338
12.379
1024
15936
3527
203
0.963
0.0411
0.0785
C72H54N40O7Hg4
2393.91
triclinic
P1
7.2484(14)
16.064(3)
17.506(3)
73.78(3)
79.86(3)
83.75(3)
1922.8(6)
1
2.067
8.044
1142
20459
8793
559
1.030
0.0482
0.0948
C144H84Br8N80O2Hg12
6013.27
orthorhombic
Pbcn
9.5499(19)
26.263(5)
15.567(3)
90
˚
a/A
˚
b/A
˚
c/A
R/o
β/o
γ/o
90
90
3
˚
V/A
Z
3904.4(14)
1
2.557
13.875
2763
28604
4670
281
1.056
0.0540
0.1615
D/g cm-3
μ/mm-1
F(000)
reflns collected
unique reflns
parameters
GOF
R1 [I > 2σ(I)]
wR2 (all data)
a
a
˚
Table 2. Selected Bond Distances (A) and Angles (deg) for Complex 1
˚
Table 4. Selected Bond Distances (A) and Angles (deg) for Complex 3
Zn(1)-O(1)
1.990(2)
2.015(2)
Zn(1)-N(8)
Zn(1)-O(2)
2.008(2)
2.062(3)
N(30)-Zn(1A)
Zn(1)-O(6)
Zn(1)-N(20)
Zn(2)-O(1)
Zn(2)-O(2)
Zn(3)-O(5)
2.022(5)
2.015(5)
2.044(4)
2.028(5)
2.047(5)
2.010(5)
Zn(1)-N(23)
Zn(2)-N(3)
Zn(2)-O(3)
Zn(3)-N(10)
Zn(3)-N(16)
Zn(3)-O(4)
1.998(4)
2.015(4)
2.040(5)
2.003(4)
2.018(4)
2.112(5)
Zn(1)-N(4A)
O(1)-Zn(1)-N(8)
115.57(10) O(1)-Zn(1)-N(4A) 114.55(10)
107.54(11)
103.50(10) N(4A)-Zn(1)-O(2) 97.59(11)
N(8)-Zn(1)-N(4A) 115.35(10) O(1)-Zn(1)-O(2)
N(8)-Zn(1)-O(2)
a Symmetry code: A -x, -y þ 1, -z.
N(23)-Zn(1)-O(6)
127.14(19) N(23)-Zn(1)-N(30A) 104.46(17)
N(23)-Zn(1)-N(20) 110.86(17)
97.08(18) N(30A)-Zn(1)-N(20) 109.16(18)
O(6)-Zn(1)-N(30A) 107.3(2)
O(6)-Zn(1)-N(20)
N(3)-Zn(2)-O(1)
O(1)-Zn(2)-O(3)
O(1)-Zn(2)-O(2)
N(10)-Zn(3)-O(5)
O(5)-Zn(3)-N(16)
O(5)-Zn(3)-O(4)
a
˚
Table 3. Selected Bond Distances (A) and Angles (deg) for Complex 2
109.20(18) N(3)-Zn(2)-O(3)
121.61(19)
101.86(19)
105.8(2)
N(3)-Zn(1A)
N(7)-Zn(1)
Zn(1)-N(3D)
1.972(5) N(6)-Zn(1)
2.031(5) N(10)-Zn(1B)
1.972(5)
2.031(5)
1.995(5)
109.3(2)
108.1(2)
N(3)-Zn(2)-O(2)
O(3)-Zn(2)-O(2)
110.14(19) N(10)-Zn(3)-N(16)
129.25(19) N(10)-Zn(3)-O(4)
112.50(18)
100.59(19)
92.01(19)
N(3D)-Zn(1)-N(10C) 126.0(2) N(3D)-Zn(1)-N(6) 108.0(2)
106.0(2)
N(16)-Zn(3)-O(4)
N(10C)-Zn(1)-N(6)
N(10C)-Zn(1)-N(7)
109.2(2) N(3D)-Zn(1)-N(7) 114.0(2)
102.7(2) N(6)-Zn(1)-N(7) 91.5(2)
a Symmetry code: A -x þ 2, -y, -z þ 2.
a Symmetry code: A -x þ y -2/3, -x þ 2/3, z - 1/3; B x - y þ 2/3, x þ
1/3, -z þ 4/3; C y - 1/3, -x þ y þ 1/3, -z þ 4/3; D -y þ 2/3, x - y þ 4/3,
z þ 1/3.
functionalized ligands and synthesis conditions on the con-
struction of their coordination complexes.
Complexes 1, 3, 5, and 6 were synthesized by the direct
reaction between the ligands and the metal salts at room
temperature, while complexes 2, 4, and 7 were prepared
under hydrothermal reaction at higher temperature. The
route for ligand synthesis and some coordination modes of
geometrically diversify and modify the ligands to explore the
structures of their complexes (Scheme 1). Therefore, two
ligands bearing substituting alkyl or phenyl groups have
been prepared aiming to explore the influence of modified/

Article
Table 5. Selected Bond Distances (A) and Angles (deg) for Complex 4
Crystal Growth & Design, Vol. 10, No. 2, 2010 567
a
˚
Scheme 2. Some Coordination Modes of 2,3-Substituted-5,6-di-
(1H-tetrazol-5-yl)pyrazine Ligands
Zn(1)-N(3A)
Zn(1)-N(6)
1.964(4)
2.015(4)
Zn(1)-N(7B)
Zn(1)-N(10)
2.003(4)
2.024(4)
N(3A)-Zn(1)-N(7B) 117.98(15) N(3A)-Zn(1)-N(6) 109.98(16)
N(7B)-Zn(1)-N(6) 110.40(15) N(3A)-Zn(1)-N(10) 123.51(16)
N(7B)-Zn(1)-N(10) 101.27(16) N(6)-Zn(1)-N(10) 90.12(15)
a Symmetry code: A y - 1/4, -x þ 3/4, z - 1/4; B -y þ 1/4, x þ 1/4, -z
þ 1/4; C -y þ 3/4, x þ 1/4, z þ 1/4; D y - 1/4, -x þ 1/4, -z þ 1/4.
a
˚
Table 6. Selected Bond Distances (A) and Angles (deg) for Complex 5
Hg(1)-N(8A)
Hg(1)-N(1)
Hg(1)-N(2B)
2.131(5)
2.573(5)
2.786(5)
Hg(1)-Br(1)
N(8A)-Hg(1C)
2.4305(9)
2.131(5)
N(8A)-Hg(1)-Br(1) 169.93(13) N(8A)-Hg(1)-N(1)
90.88(17)
Br(1)-Hg(1)-N(1) 98.26(12) N(8AA)-Hg(1)-N(2B) 89.52(17)
Br(1)-Hg(1)-N(2B) 93.00(13) N(1)-Hg(1)-N(2B) 100.20(15)
a Symmetry code: A x - 1/2, -y þ 1/2, z - 1/2; B -x þ 1, -y, -z þ 1;
C x þ 1/2, -y þ 1/2, z þ 1/2.
˚
Table 7. Selected Bond Distances (A) and Angles (deg) for Complex 6
a
Hg(2)-N(18)
Hg(2)-O(2)
Hg(2)-N(14A)
Hg(1)-O(1)
Hg(1)-N(8C)
Hg(1)-N(5D)
2.126(5)
2.526(6)
2.767(5)
2.116(5)
2.479(5)
2.734(5)
Hg(2)-O(3)
Hg(2)-N(11B)
Hg(2)-N(19)
Hg(1)-N(1)
Hg(1)-N(9)
2.142(5)
2.587(5)
2.828(5)
2.126(5)
2.610(5)
N(18)-Hg(2)-O(3)
O(3)-Hg(2)-O(2)
O(3)-Hg(2)-N(11B)
171.10(18) N(18)-Hg(2)-O(2)
93.69(19) N(18)-Hg(2)-N(11B)
82.31(18) O(2)-Hg(2)-N(11B)
92.34(19)
105.52(17)
76.26(18)
73.98(18)
N(18)-Hg(2)-N(14A) 97.12(17) O(3)-Hg(2)-N(14A)
O(2)-Hg(2)-N(14A) 130.26(18) N(11B)-Hg(2)-N(14A) 144.63(17)
N(18)-Hg(2)-N(19)
O(2)-Hg(2)-N(19)
65.83(17) O(3)-Hg(2)-N(19)
133.87(15) N(11B)-Hg(2)-N(19)
113.78(18)
71.96(15)
N(14A)-Hg(2)-N(19) 93.86(16)
Each ZnII center was coordinated by two N atoms of two
distinct tetrazolate rings from two different L1 ligands and
two O atoms from water molecules to furnish a distorted
tetrahedral geometry, and it is connected to the adjacent ZnII
a Symmetry code: A -x þ 2, -y, -z; B -x þ 1, -y, - z; C -x, -y þ 1,
-z þ 1; D -x þ 1, -y þ 1, -z þ 1.
a
˚
Table 8. Selected Bond Distances (A) and Angles (deg) for Complex 7
center by two L1 ligands (Zn1 Zn1A=6.967 A), which
˚
3 3 3
Hg(1)-N(1)
Hg(1)-N(9A)
Hg(2)-N(7)
Hg(2)-N(2A)
2.097(7) Hg(1)-N(5)
2.783(7) Hg(1)-O(1W)
2.120(7) Hg(2)-Br(1)
2.618(7) Hg(2)-N(8B)
2.773(6)
2.88(2)
adopt the same coordination mode II (Scheme 2), either
tetrazolate ring of L1 ligand monodentate coordinates
through its 1-position N atom. In 1, the Zn-N bond
2.3685(12)
2.637(7)
˚
distances are in the 2.008(2)-2.015(2) A range, the
N(7)-Hg(2)-N(2A)
103.8(3) N(7)-Hg(2)-N(8B) 83.9(3)
O-Zn-N
angle
is
97.59(11)-115.57(10)ꢀ,
and
N(2A)-Hg(2)-N(8B) 82.3(2)
Br(1)-Hg(2)-N(2A) 102.11(18)
Br(1)-Hg(2)-N(8B) 105.85(17)
N(1D)-Hg(1)-N(5) 118.6(2)
O1-Zn1-O2 and N8-Zn1-N4A are 107.54(11)ꢀ and
115.35(10)ꢀ, respectively. Moreover, the two tetrazolate
rings in each ligand are not parallel and a dihedral angle of
79.8ꢀ is formed (see Supporting Information, figure S1). Also
different torsional degrees of each tetrazolate ring with the
pyrazine plane lead to dihedral angles of 79.4 and 4.9ꢀ,
respectively. Furthermore, each dinuclear unit is connected
with the neighboring dimers via two kinds of hydrogen
N(7)-Hg(2)-N(8C)
N(1)-Hg(1)-N(5)
N(5)-Hg(1)-N(9A)
83.9(3)
69.0(2)
81.39(19) N(5)-Hg(1)-O(1W) 140.84(13)
N(9A)-Hg(1)-O(1W) 67.55(14)
a Symmetry code: A x þ 1/2, -y þ 3/2, -z þ 1; B -x, y, -z þ 1/2;
C -x - 1/2, -y þ 3/2, z - 1/2; D -x, y, -z þ 3/2.
the ligands are shown in Schemes 1 and 2, respectively. The
structural differences between each pair of complexes with
the same ligands, 1 and 2, 3 and 4, and 6 and 7 might also be
attributed to the different preparing conditions in synthetic
procedures. Thermogravimetric analyses (TGA) experi-
ments were carried out (see Supporting Information, Figure
S3). From the experimental results, we can find that the four
obtained ZnII complexes are stable until 340 ꢀC (for 2 and 4
even above 400 ꢀC), whereas the three HgII complexes
decompose at a lower temperature of about 256, 292,
269 ꢀC, respectively.
bonds O-H N and O-H O to form a 3D supramole-
3 3 3 3 3 3
cular framework (Figure 1b).
{[Zn2(L1)2](H2O)0.5 ¥
(2). 2 has a 3D framework with a
}
(4,122) topology. Figure 2a illustrates the coordination en-
vironment of the ZnII ions. In the structure, each L1 ligand
coordinates to three ZnII atoms in the coordination mode III
(Scheme 2). ZnII ion in 2 is four-coordinated by two N atoms
from two tetrazolate rings of two different L1 ligands, and
two N atoms from two tetrazolate rings from the third L1
ligand. That is, each tetrahedral ZnII ion is coordinated by
two 1-position N atoms of two ligands and two N atoms of
one ligand in chelating mode. The bond distance of Zn-N is
Description of Crystal Structures. [Zn2(L1)2(H2O)4]-
(H2O)4 (1). 1 crystallizes in the triclinic P1 space group and
shows a centrosymmetric dinuclear structure (Figure 1a).
˚
from 1.972(5) to 2.031(5) A, and the range of the N-Zn-N

568 Crystal Growth & Design, Vol. 10, No. 2, 2010
Tao et al.
Figure 1. View of (a) the dinuclar structure of 1 (symmetry code:
A -x, -y þ 1, -z), and (b) 3D H-bonding framework of 1.
angle is 91.5(2)-126.0(2)ꢀ. In one L1 ligand, the two tetra-
zolate rings form a dihedral angles of 55.7ꢀ, and the dihedral
angle of each tetrazolate ring with the pyrazine ring is 30.4
and 44.2ꢀ, respectively.
In this framework, each L1 ligand adopts the same co-
ordination mode III with each tetrazolate ring adopting a
μ
1,4-bridging mode. Each asymmetric unit generates a hex-
Figure 2. View of (a) the local coordination geometry around ZnII
centers in 2 (symmetry code: A -x þ y - 2/3, -x þ 2/3, z - 1/3; B x
- y þ 2/3, x þ 1/3, -z þ 4/3; C y - 1/3, -x þ y þ 1/3, -z þ 4/3; D -y
þ 2/3, x - y þ 4/3, z þ 1/3), (b) hexagonal subunit in 2, (oxygen
atoms omitted for clarity), (c) 2D hexagonal sheet along c axis, (d)
3D (4,122) topology in 2 along the c axis, ZnII as three-connected
nodes.
agonal-grid-like subunit (Figure 2b) through 1,4-position N
atoms of one tetrazolate ring. Each hexagonal subunit is
connected to six adjacent same units via the 1,4-position N of
another bridging tetrazole ring in the same ligand and is
further interlinked into a 3D framework (Figure 2c). In this
way, this 3D framework could be simplified to pcu net with
the hexagonal subunit as a node.
and one O atom from one water molecule. Meanwhile, Zn2
coordinates to one N atom (N3) and three O atoms, while
Zn3 coordinates to two N atoms (N10, N16) from two
different ligands and two O atoms from water molecules.
The Zn-N bond distances are in the range of 1.998(4)-2.044
From another topological point of view (see Figure 2d),
this 3D network has a (4,122) topology, with ZnII ions and
ligands as three-connected nodes, respectively. In our pre-
vious work using the 2,3-di(1H-tetrazol-5-yl)pyrazine (H2L)
ligand,15a a robust guest-free 3D zeolite-like chiral me-
tal-organic framework has been obtained, which possesses
chiral open channels with nitrogen-rich walls and is a good
porous material,20 while 2 is almost nonporous due to the
ethyl group filling in the pores.
˚
˚
(4) A and the Zn-O distance is from 2.010(5) to 2.112(5) A.
The N-Zn-N angles are in the range of 104.46(17)-112.50
(18)ꢀ, and N-Zn-O 92.01(19)-129.25(19)ꢀ, and O-Zn-O
105.8(2)-109.3(2)ꢀ, respectively (see Table 4).
In 3, L2 ligands adopt the coordination mode II (Scheme 2)
in which each tetrazolate ring is monodentate. Two basic
trinuclear building units are interlinked together through
1-position N atom ligated to Zn1 of one tetrazolate ring
connected with adjacent Zn1 to form a hexanuclear cluster
(Figure 3b). The two tetrazolate rings have a dihedral angle
of 78ꢀ, while the two terminal phenyl groups are not parallel
and form a dihedral angle of 65.7ꢀ. Additionally, there
[Zn6(L2)6(H2O)12] (3). 3 crystallizes in the P1 space group
and exhibits a discrete hexanuclear structure of which the
trinuclear motif can be viewed as a basic building unit. In each
trinuclear unit, there are three types of coordination environ-
ment around the ZnII ions. As illustrated in Figure 3a, three
crystallographically independent ZnII ions exhibit the same
tetrahedral coordination geometry. Zn1 is ligated by three N
atoms (N20, N23, and N30) from three different L2 ligands

Article
Crystal Growth & Design, Vol. 10, No. 2, 2010 569
Figure 4. View of (a) the coordination geometry of ZnII in 4 (two
phenyl groups of the ligand omitted for clarity. Symmetry code:
A y - 1/4, -x þ 3/4, z - 1/4; B - y þ 1/4, x þ 1/4, -z þ 1/4), (b)
tetragonal subunit in 4, (c) 2D quadrilateral infinite layer of 4
extended in the ab plane, and (d) (4,8,10) topology net with the ZnII
as three-connected nodes.
Figure 3. View of (a) the coordination geometry of ZnII in 3, (b) the
hexanuclear structure in 3, and (c) 2D H-bonding structure of 3.
are several intramolecular O-H N/O hydrogen bonds
3 3 3
between coordinated water molecules and adjacent N atoms
of different hexanuclear units, leading to the formation of a
2D supramolecular network (Figure 3c).
this 3D framework could be simplified to a dia net with the
hexagonal subunit as a node. From another topological
point of view, it can be simplified to a (4,8,10) topology with
ZnII centers as three-connected nodes (Figure 4d).
[Zn(L2)]¥ (4). 4 crystallizes in the I41/a space group and
has a 3D framework. The asymmetric unit contains one
crystallographically independent ZnII center and one L2
ligand. Figure 4a shows that each tetrahedral ZnII ion is
coordinated by four N atoms from three independent L2
ligands, with one coordinated to the ZnII center in chelating
mode to form a seven-membered ring and another two in
monodentate mode. The Zn-N distances are from 1.964(4)
[Hg(L1)Br]¥ (5). 5 crystallizes in a P21/n space group and
takes a 2D layer structure. As shown in Figure 5a, the
coordination polyhedron of the HgII ion can be viewed as
distorted tetrahedron formed by one terminal Br anion and
three N atoms from tetrazolate rings of three different
ligands (including one weak coordination with the bond
to 2.024(4) A, which is in the normal range.21 The coordina-
˚
tion angles around ZnII centers vary from 90.12(15) to
123.51(16)ꢀ. The dihedral angle of the two tetrazolate rings
in L2 is 57.6ꢀ, and that of the two phenyl groups is 61ꢀ.
Each L2 ligand links three ZnII centers with a coordination
mode III as same as 2 (Scheme 2). Each tetrazolate ring
adopts a μ1,4-bridging mode. Compared with 2, each asym-
metric unit generates tetragonal-grid-like subunit
(Figure 4b) through the 1,4-position N atoms of one tetra-
zolate ring along the c axis, and the adjacent tetragonal
subunit is connected to each other via the other 1,4-position
N atoms of another tetrazolate ring in the same ligand and
further interlinked to a 3D network (Figure 4c). In this way,
˚
distance Hg-N2 of 2.786(5) A) (see Table 6).
The ligand takes only one kind of bridging mode IV
(Scheme 2), in which the tetrazolate rings adopts μ1-μ1,2
mode coordinating to the HgII center, and remarkably, one
of the two tetrazolate rings in each L1 ligand is protonated.
Each ligand bonds to three HgII ion to form 2D layers as
˚
shown in Figure 5b with Hg Hg separation of 4.735 A.
3 3 3
From the topological point of view, this 2D network has a
(4, 8, 8) topology with HgII centers and ligands serving as
three-connected nodes (Figure 5c).
{[Hg4(L2)4(H2O)6](H2O)}¥ (6). Complex 6 crystallizes in
the P1 space group. In the asymmetric unit, there are two

570 Crystal Growth & Design, Vol. 10, No. 2, 2010
Tao et al.
˚
coordination Hg1-N5D=2.734(5) A), and an O atom from
coordinated water (see Table 7). The ligand adopts the
coordination mode V (see Scheme 2). It further forms a 1D
chain by linking the μ1,4 bridging tetrazolate ring (Figure 6c).
Additionally, two kinds of hydrogen-bonding interactions
between the coordination water molecule and N atom of the
tetrazolate ring, lattice water and coordinated water lead to
the formation of a 2D layer supramolecular network
extended in the ab plane. However, there exists another kind
of HgII ion (Figure 6b), in which each Hg2 ion exhibits a
distorted tetragonal-bipyramidal geometry with four N
atoms from three different ligands (including two weak
˚
coordination Hg2-N14A 2.767, Hg2-N19 2.830 A) and
two O atoms from water molecules, where the ligand also
takes the same coordination mode V (Scheme 2). Each L2
ligand is coordinated to one Hg2 ion, a tetrazole N atom and
a pyrazine N atom to form a five-membered ring in one side.
The bond distances of Hg-N are from 2.126(5) to 2.610(5)
˚
A, and the range of N-Hg-N angle is 65.83(17)-144.63-
(17)o. Furthermore, the distances of Hg2-N14 and
Hg2-N19 are longer than others, which can be considered
as weak coordination. Each ligand is bonded to three metal
ions and each metal ion is linked to four other metal ions by
three ligands, forming a 1D chain (Figure 6d). Interestingly,
the Hg1 related 2D layer vertical to the bc plane exists with
Hg2 related 1D chain along the a axis. So we can see the 1D
and 2D alternate structural feature extended to the bc plane.
(Figure 6e).
[Hg3(L2)2(H2O)0.5Br2]¥ (7). 7 has a 2D layer structure and
crystallizes in Pbcn space group. The unit cell consists of two
Hg2 and one Hg1, two L2 ligands, half O atom from water
molecule, and two terminal Br anions in the asymmetric unit.
Hg1 is seven-coordinated to two N1 atoms of two tetrazolate
2
˚
rings from two L ligands (Hg-N1=2.097(7) A), and weakly
coordinated to two N5, two N9, and one O atom from water
molecule (Hg1-N5=2.774, Hg1-N9=2.784, Hg1-O=2.878
A), while Hg2 is four-coordinated with a tetrahedral coordina-
˚
tion geometry, ligated to three ligands through three tetrazole
˚
N atom N2, N7 (Hg2-N2=2.618(7), Hg2-N7=2.120(7) A)
˚
(with one weak coordination Hg2-N8 = 2.636 A) and a
˚
terminal Br anion (Hg2-Br=2.37(12) A), in which the ligand
in VI coordination mode (Scheme 2). The bond angles of
N-Hg-N are in the range of 82.3(2)-171.2(4)ꢀ (Figure 7a).
Each L2 ligand links two Hg1 ions through one 3-position
N atom in one tetrazolate ring and two chelating N atom
from a pyrazine N atom and the other tetrazolate 1-position
N atom. Additionally, each L2 ligand also connects three
Hg2 ions via 1-position and 2-position N atoms in one
tetrazolate ring and additional 2-position N atom in the
other tetrazolate ring in one L2 ligand, all of which take only
one kind of bridging mode VI (Scheme 2). In this way, each
asymmetric unit is interlinked via 1-position N atoms of
tetrazolate rings to form a 1D chain and further extends the
structure via 2-position N atoms along the ab plane to form a
2D sheet (Figure 7b).
Comparison of Complexes Structure. Complexes 1 and 2
are based on the same L1 ligand and metal ion but forming
quite different structures: 1 has a centrosymmetric dinuclear
structure, while 2 is a 3D framework with (4,122) topology.
Similarly, the structures of complexes 3 and 4 with the L2
ligand are also quite different: 3 has a discrete hexanuclear
structure, but 4 has a 3D architecture with (4,8,10) topology.
These two pairs of complexes were obtained with a respective
ligand under different reaction conditions (at different
Figure 5. View of (a) the coordination environment of HgII in 5
(symmetry code: A x - 1/2, -y þ 1/2, z - 1/2; B -x þ 1, -y, -z þ 1),
(b) 2D sheet structure in 5, and (c) (4,8,8) topology net with HgII
ions as three-connected nodes.
kinds of independent units. As shown in Figure 6a, the
coordination polyhedron of the Hg1 atom can be viewed
as trigonal bipyramidal geometry formed by four N
atoms from three different L2 ligands (including a weak

Article
Crystal Growth & Design, Vol. 10, No. 2, 2010 571
Figure 6. View of (a) the coordination geometry of Hg1 in 6 (symmetry code: A -x þ 2, -y, -z; B -x þ 1, -y, -z; C -x, -y þ 1, -z þ 1; D -x
þ 1, -y þ 1, -z þ 1), (b) the coordination geometry of Hg2 in 6, (c) 1D chain of Hg1 in 6, (d) 1D chain of Hg2 in 6, and (e) the interlaced 1D
chain of Hg1 and 2D sheet of Hg2 in 6 extended in the bc plane.
temperatures). The results show that the reaction condition
plays an important role on the complex formation. Com-
plexes 1 and 3 were both prepared by conventional condi-
tions at room temperature, while 2 and 4 are synthesized by
hydrothermal method. The results indicate that hydrother-
mal method generally tends to form relatively compact
crystal packing.16b In fact, complexes 5, 6, 7 also show the
same tendency.
From the nature of ligands, we can see that the substituting
alkyl and/or phenyl groups of the ligands are quite important
factors that affect the structure in the metal coordination
sphere and might be used as a tool to control the structure of
coordination frameworks.15c,22 Complexes 2 and 4 were
obtained under the same condition, but their structures
are different: in 2, each asymmetric unit generates a hexago-
nal-grid-like subunit and further forms a 3D structure
with (4,122) topology, while in 4, the asymmetric units
are extended to a tetragonal-grid-like subunit and forms
a 3D framework with (4,8,10) topology. To some extent,
it is obvious that the dimensionality and topology of the
structure depend strongly upon the terminal groups of the
ligands.
In contrast to our previous work with 2,3-di-(1H-tetrazol-
5-yl)pyrazine (H2L),15a the introduction of the two substitut-
ing ethyl groups into this ligand results in the almost full
filling in the pore, so it could not get a similar 3D porous
structure. On the other hand, when using two phenyl groups
instead of the two ethyl ones, a much larger hindrance in the
ligands leads to the formation of the tetragonal-grid-like unit
containing less coordinating ligands and metal ions. In
addition, the free rotation of the terminal groups of the
ligand was expected to exert some dynamic features on the

572 Crystal Growth & Design, Vol. 10, No. 2, 2010
Tao et al.
Figure 7. View of (a) the coordination environment of HgII in 7
(symmetry code: A x þ 1/2, -y þ 3/2, -z þ 1; D -x, y, -z þ 3/2; E
-x - 1/2, -y þ 3/2, z þ 1/2; F x - 1/2, -y þ 3/2, -z þ 1), (b) 2D
layer structure with HgII centers in 7.
framework. The dinuclear structure of 1 is interlinked into a
3D supramolecular framework via hydrogen-bonding,
whereas the hexanuclear structure of 3 are just linked into
a 2D network through hydrogen-bonding. So what we can
find is that increasing the hindrance of terminal groups of the
bis(tetrazole)ligand might cause dramatic changes in the
complex network. Therefore, the above studies indicate that
substituting groups of ligands have a great influence on
complex formation.
Luminescent Properties. Luminescent coordination com-
pounds have attracted great attention because of their
potential applications as chemical sensors, photochemistry,
and electroluminescence (EL) displays.23 The synthesis of
metal-organic complexes by conjugated organic spacers
and metal centers can be an efficient method for obtaining
new luminescence materials, especially for d10 or d10-d10
systems.24,25 2,3-Substituted-5,6-di(1H-tetrazol-5-yl)- pyra-
zine may be a good candidate for enhanced emissive materi-
als, tunable, in principle, by the coordination to different
metal ions.26 Photoluminescent measurements of the two
ligands and seven complexes were carried out in the solid
state at room temperature.
Figure 8. (a) The emission spectra of ligands H2L1 and H2L2 in the
solid state, (b) the emission spectra of H2L1, 1, 2, 5 in the solid state,
and (c) the emission spectra of H2L2, 3, 4, 6, 7 in the solid state all at
room temperature.
two ligands can be assigned to the π*-n transition. The
relative intensities of the emission spectra of H2L2 are much
stronger than that of H2L1 and show stronger luminescence
upon the irradiation of UV light as shown in the insert
pictures. We can conclude that the phenylation of coordi-
nated tetrazolates results in higher energetic emission than
Figure 8a shows a comparison of the two free ligands that
were substituted with two ethyl or phenyl groups, respec-
tively. H2L1 emits at a maximum 460 nm upon excitation
around 360 nm, and H2L2 has a emission maxima at ca.
502 nm upon excitation at 443 nm. The emission bands of the

Article
Crystal Growth & Design, Vol. 10, No. 2, 2010 573
ethylation. That is probably responsible not only for changes
in the ligand σ-donor strength, but also for remarkable
variations in the tetrazole π-interannular conjugation.27
The luminescence properties of the free ligand H2L1 and
their complexes in the solid state at room temperature were
investigated. In Figure 8b, as disscussed above, H2L1 ex-
hibits an intense blue emission band at 460 nm upon excita-
tion at 360 nm. The emission bands of complexes 1, 2, 5
displays strong/weak fluorenscence-emission bands at 362,
378, 392 nm (λex=331, 300, 287 nm), respectively. In the light
of the close emission energy, the emission of the complexes is
tentatively attributed to the intraligand transition (n-π*,
π-π*) of 2,3-substituted-5,6-di(1H-tetrazol-5-yl)pyrazine
modified by metal coordination. The enhancement of lumi-
nescence in ZnII complexes may be attributed to the ligation
of the ligand to the metal center. To some extent, the
coordination enhances the “rigidity” of the ligand and thus
reduces the loss of energy through a radiationless pathway.28
Heavy atom in the fluorophore increases the rate of inter-
system crossing (ISC) by strengthening spin-orbit cou-
pling.29 Thus, the decrease of fluorescence yield (radiative
transition S1 f S0) in most cases can be explained by an
increase in the probability of the completing S1 f Tn
radiationless transition of the fluorophore, and it is particu-
larly effective if the excited states involved are of the π-π*
type and that S1 f S0 decay is slow.30
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The solid-state fluorescence spectra of the free ligand H2L2
and their complexes 3, 4, 6, and 7 at ambient temperature are
depicted in Figure 8c. Complexes 3 and 4 present an emission
band at 461 and 510 nm upon excitation at 413 and 446 nm,
respectively, while 6 and 7 have emission peaks at 396, 385
nm (λex =290, 280 nm). The emission may originate from
intraligand πL-πL* transitions emission (LLCT). On the
basis of H2L2, the HgII complex also exhibits much lower
intensity due to a heavy atom effect. Compared with the
strong emission of ZnII complexes, HgII complexes experi-
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luminescent properties. Moreover, the phenomena that the
relative intensity of the free ligand is higher than that of ZnII
complexes might be assigned to the strong conjugation and
intermolecular interaction between the molecule segment of
the free ligand. These results indicate that the fluorescent
properties might be tuned by attaching different 2,3-substi-
tuted groups.
In conclusion, two structurally related bis(tetrazolate)
ligands bearing different substituting groups, 2,3-diethyl-
5,6-di(1H-tetrazol-5-yl)pyrazine (H2L1) and 2,3-diphenyl-
5,6-di(1H-tetrazol-5-yl)pyrazine (H2L2), have been desig-
ned, and seven ZnII and HgII coordination complexes with
the two ligands have been synthesized by hydrothermal or
conventional methods. These results indicate that the sub-
stituting groups of ligands and the reaction conditions have
great influences on the formation of these complexes.
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Acknowledgment. This work was supported by the NNSF
of China (Nos. 20531040 and 50673043), the 973 Program of
China (2007CB815305) and the Natural Science Fund of
Tianjin, China (07JCZDJC00500).
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Supporting Information Available: Crystallographic data files
(CIF), the synthesis of ligands, the conformation of ligands (Figure
S1), the XRPD diagram for complexes 1-7 (Figure S2), TGA plots
for all complexes (Figure S3), hydrogen bonds for 1 (Table S1) and 3
(Table S2). This information is available free of charge via the
Internet at http://pubs.acs.org.
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