Complexes of unsymmetric bis-hydrazide ligands: Crystal structures and properties

Article abstract of DOI:10.1080/00958972.2012.708411

Two unsymmetric bis-aroyl-hydrazines, N-(2-hydroxybenzoyl) isonicotinohydrazide (L1) and N-(2-hydroxybenzoyl)nicotinohydrazide (L2), were synthesized through reactions of salicyl hydrazide with isonicotinoyl chloride and nicotinoyl chloride, respectively.

Full text of DOI:10.1080/00958972.2012.708411

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Complexes of unsymmetric bis-
hydrazide ligands: crystal structures
and properties
Ying-Xia Zhou a , Rui-Fang Yuan b , Cai-Ling Fan a , Li-E Liu c , Ben-
Lai Wu b & Hong-Yun Zhang b
a College of Sciences, Henan Agricultural University , Zhengzhou
450002 , People's Republic of China
b Department of Chemistry , Zhengzhou University , Zhengzhou
450052 , People's Republic of China
c College of Public Health , Zhengzhou University , Zhengzhou
450001 , People's Republic of China
Accepted author version posted online: 04 Jul 2012.Published
online: 27 Jul 2012.
To cite this article: Ying-Xia Zhou , Rui-Fang Yuan , Cai-Ling Fan , Li-E Liu , Ben-Lai Wu & Hong-Yun
Zhang (2012) Complexes of unsymmetric bis-hydrazide ligands: crystal structures and properties,
Journal of Coordination Chemistry, 65:17, 3133-3146, DOI: 10.1080/00958972.2012.708411
To link to this article: http://dx.doi.org/10.1080/00958972.2012.708411
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Journal of Coordination Chemistry
Vol. 65, No. 17, 10 September 2012, 3133–3146
Complexes of unsymmetric bis-hydrazide ligands:
crystal structures and properties
YING-XIA ZHOUy, RUI-FANG YUANz, CAI-LING FANy, LI-E LIUx,
BEN-LAI WU*z and HONG-YUN ZHANGz
yCollege of Sciences, Henan Agricultural University, Zhengzhou 450002,
People’s Republic of China
zDepartment of Chemistry, Zhengzhou University, Zhengzhou 450052,
People’s Republic of China
xCollege of Public Health, Zhengzhou University, Zhengzhou 450001,
People’s Republic of China
(Received 25 March 2012; in final form 21 May 2012)
Two unsymmetric bis-aroyl-hydrazines, N0-(2-hydroxybenzoyl)isonicotinohydrazide (L1) and
N0-(2-hydroxybenzoyl)nicotinohydrazide (L2), were synthesized through reactions of salicyl
hydrazide with isonicotinoyl chloride and nicotinoyl chloride, respectively. Reactions of metal
salts with L1 or L2 gave three new complexes, [Cd(L1)2(SCN)2]n (1), [Zn(L1)2Cl2] ꢀ H2O (2),
and [Zn(L2)2Cl2] (3). Complex 1 features a 1-D double-chain structure built by SCN– bridging
six-coordinate CdII centers while 2 and 3 are mononuclear ZnII complexes. In 1–3, isomeric
ligands L1 and L2 coordinate with metal ions in a terminal coordination mode. Ligands L1 and
L2 through O–Hꢀ ꢀ ꢀN and N–Hꢀ ꢀ ꢀO hydrogen-bonding interactions in 1–3 are crucial for the
structure extension into 3-D supramolecular structures of 1 and 2, or 2-D sheet of 3. Complexes
1–3 emit interesting blue-green luminescence. Thermal behaviors of 1–3 as well as the specific
rotation of 2 were also investigated.
Keywords: Bis-hydrazide ligand; d10 Metal complex; Crystal structure; Fluorescence;
Thermogravimetric analysis
1. Introduction
Hydrazine derivatives have been investigated because of their coordinative and
biological activities as well as their use in analytical chemistry as metal-extracting
agents [1–4]. Hydrazides based on –CONHNH2 and their derivatives contain trigonal
N- and O-donors, making them potential chelating ligands. Hydrazide derivatives and
complexes have supramolecular interactions because they include hydrogen-bonding
donors (amino-groups) and acceptors (carbonyl), and thus hydrogen-bonding plays an
important role in extending and stabilizing the structures of the resultant complexes [5].
Hydrazide derivatives which have heteroatoms and various conformers may provide
*Corresponding author. Email: wbl@zzu.edu.cn
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.708411

3134
Y.-X. Zhou et al.
additional coordinative properties [6, 7]. Herein, as part of our continuing study, two
unsymmetric pyridyl bis-hydrazides based on –CONHNHCO– were synthesized as
spacers in this article. In the search for molecular-based materials with new and
unusual properties, a marked increase in both interest and research activity has been
given to extended solids of metals with d10 configuration because of their various
coordination configurations and coordination numbers [8–14]. Therefore, three
complexes of bis-hydrazide with d10 metal ions (ZnII and CdII) were synthesized and
characterized.
2. Experimental
2.1. Materials and physical measurements
Reagent grade chemicals were purchased from Zhengzhou Zhongliang Chemical
Reagent Company and most were used without purification. The solvents were dried
using standard methods when required [15].
IR spectra were recorded with an FTS-40 infrared spectrometer as KBr pellets from
4000 to 400 cmꢁ1. Thermal decomposition experiments were carried out using an
NETZSCH TG 209 instrument in air from room temperature to 800ꢂC with a flow rate
of 20 mL ꢀ minꢁ1 and a heating rate of 10ꢂC ꢀ minꢁ1. Luminescence spectra in solid
samples were determined with a Fluoro Max-p spectrophotometer at room temperature
with slit width of 0.5 nm. 1H NMR spectra were recorded on a Bruker DPX-300
spectrometer operating at 300 MHz.
Data collection was on a Rigaku Raxis-IV X-ray diffractometer at 291(2) K using
graphite monochromated Mo-Ka radiation (ꢀ ¼ 0.071073 nm). All structures were
solved by direct methods and refined on F2 by full-matrix least squares using
SHELXTL [16]. Non-hydrogen atoms were located by direct phase determination and
subjected to anisotropic refinement. Hydrogen atoms of N and O were located from
difference Fourier maps and included in the final refinement by using geometrical
restraints, while the other hydrogen positions were generated geometrically and allowed
to ride on their parent. Details of the crystal structure determinations of 1–3 are listed in
table 1, and selected bond distances and angles are in table 2.
2.2. Syntheses of ligands
2.2.1. Synthesis of L1. Salicyl hydrazide was synthesized according to the reported
method [17]. A mixture of isonicotinic acid (3.94 g, 32 mmol) and thionyl chloride
(25 mL) in a round-bottomed flask was refluxed for 7 h with stirring. Excess thionyl
chloride was removed under reduced pressure until yellow crystals of isonicotinoyl
chloride were obtained. A solution of the prepared isonicotinoyl chloride and
chloroform (30 mL) was dropped into a solution of salicyl hydrazide (5.02 g,
33 mmol), triethylamine (6 mL), and chloroform (30 mL) with vigorous stirring at
0–5ꢂC. After addition, the resulting mixture was allowed to react for another 2 h at the
same temperature. Finally, white solid product of L1 was obtained by filtration,
washed with water, and recrystallized with ethanol. Yield: 61%; m.p.: 228–229ꢂC.

Unsymmetric bis-hydrazide
Table 1. Crystal data and structure refinement for 1–3.
3135
Complex name
1
2
3
Empirical formula
Formula weight
Temperature (K)
C28H22N8O6S2Cd
743.08
291(2)
0.71073
Monoclinic
P21/c
C26H24Cl2N6O7Zn
668.77
291(2)
0.71073
Orthorhombic
C2221
C26H22Cl2N6O6Zn
650.77
291(2)
0.71073
Monoclinic
C2/c
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions (A,
ꢂ
˚
)
a
b
c
16.591(2)
5.8816(8)
14.9320(19)
97.809(2)
1443.6(3), 2
1.709
748
0.44 ꢃ 0.37 ꢃ 0.19
2.48ꢁ25.0
ꢁ19 ꢄ h ꢄ 19,
ꢁ6 ꢄ k ꢄ 6,
ꢁ17 ꢄ l ꢄ 15
2524
7.6776(15)
11.806(2)
29.145(6)
8.668(2)
11.513(3)
26.406(6)
96.848(3)
2616.4(11), 4
1.652
1328
0.45 ꢃ 0.27 ꢃ 0.20
1.55ꢁ24.99
ꢁ9 ꢄ h ꢄ 10,
ꢁ13 ꢄ k ꢄ 13,
ꢁ31 ꢄ l ꢄ 26
2123
ꢂ
Volume (A ), Z
3
˚
2641.8(9), 4
1.681
1368
0.30 ꢃ 0.20 ꢃ 0.20
2.79ꢁ25.50
ꢁ9 ꢄ h ꢄ 9,
ꢁ14 ꢄ k ꢄ 14,
ꢁ34 ꢄ l ꢄ 34
2342
13,377 [R(int) ¼ 0.0474]
2342/0/207
1.059
0.0393
0.0798
Calculated density (Mg ꢀ m3)
F(000)
Crystal size (mm3)
ꢃ range for data collection (ꢂ)
Limiting indices
Reflections collected
Independent reflection
Data/restraints/parameters
Goodness-of-fit on F2
R1
6950 [R(int) ¼ 0.0179]
2524/0/205
1.071
0.0222
0.0559
5750 [R(int) ¼ 0.0332]
2123/0/187
1.107
0.0929
0.2431
wR2
ꢁ3
˚
Dꢄmin and Dꢄmax (e ꢀ A
)
0.303 and ꢁ0.288
0.310 and ꢁ0.242
1.193 and ꢁ0.695
ꢂ
˚
Table 2. Selected bond distances (A) and angles ( ) for 1–3.
1
2
3
Cd(1A)–N(1B)
Cd(1A)–N(1A)
Cd(1A)–N(2F)
Cd(1A)–N(2A)
Cd(1A)–S(1B)
Cd(1A)–S(1E)
2.285(2)
2.285(2)
2.3887(17) Zn(1)–Cl(1)
2.3887(17) Zn(1)–Cl(1A)
2.7240(7) N(1)–Zn(1)–N(1A)
Zn(1)–N(1A)
Zn(1)–N(1)
2.057(2) Zn(1)–N(1)
2.057(2) Zn(1)–N(1A)
2.2120(9) Zn(1)–Cl(1)
2.2120(9) Zn(1)–Cl(1A)
113.44(14) N(1)–Zn(1)–N(1A)
2.061(6)
2.061(6)
2.206(2)
2.206(2)
105.8(4)
110.3(2)
2.7240(7) N(1A)–Zn(1)–Cl(1A) 106.84(11) N(1)–Zn(1)–Cl(1A)
N(1A)–Cd(1A)–N(2F) 89.19(7)
N(1A)–Cd(1A)–N(2A) 90.81(7)
N(2F)–Cd(1A)–N(2A) 180.00(2)
N(1A)–Zn(1)–Cl(1)
Cl(1A)–Zn(1)–Cl(1) 120.74(5)
104.65(11) N(1)–Zn(1)–Cl(1)
105.57(18)
N(1A)–Zn(1)–Cl(1A) 105.57(18)
N(1)–Zn(1)–Cl(1)
N(1)–Zn(1)–Cl(1A)
C(3)–N(1)–Zn(1)
C(3)–N(1)–Zn(1)
104.65(11) N(1A)–Zn(1)–Cl(1) 110.3(2)
106.84(11) Cl(1A)–Zn(1)–Cl(1) 118.62(13)
118.3(3)
123.0(2)
N(1A)–Cd(1A)–S(1B)
N(2A)–Cd(1A)–S(1B)
N(2A)–Cd(1A)–S(1E)
91.63(5)
89.65(5)
90.35(5)
C(4)–N(1)–Zn(1)
C(1)–N(1)–Zn(1)
119.5(5)
122.4(5)
N(1F)–Cd(1A)–N(1A) 180.0(8)
N(1F)–Cd(1A)–S(1B)
S(1B)–Cd(1A)–S(1E)
88.37(5)
180.0
Symmetry codes: A ¼ ꢁx þ 1, ꢁy þ 1, ꢁz þ 1, B ¼ x, y þ 1, z , E ¼ ꢁx, ꢁy þ 1, ꢁz þ 1, and F ¼ ꢁx, y þ 1/2, ꢁz þ 1/2 for
1; A ¼ ꢁx þ 2, y, ꢁz þ 3/2 for 2; A ¼ ꢁx, y, ꢁz þ 1/2 for 3.
Elem. Anal. Found (%): C, 60.34; H, 4.35; N, 16.21. Calculated for C13H11N3O3 (257.1)
(%): C, 60.70; H, 4.31; N, 16.33. IR (KBr, cmꢁ1): 3421 (m), 3281 (m), 1626 (s), 1476
1
(m), 1306 (m), 749 (m). H NMR (300 MHz, DMSO-d6) ꢁ: 12.16 [1H, OH], 11.03 [2H,
NH], 7.53–8.86 [4H, py], 6.76–7.46 [4H, Ar].

3136
Y.-X. Zhou et al.
2.2.2. Synthesis of L2. The synthesis of L2 is similar to that of L1 only with
isonicotinic acid being substituted by nicotinic acid. White solid product of L2 was
obtained. Yield: 67%; m.p.: 238–239ꢂC. Elem. Anal. Found (%): C, 60.92; H, 4.24; N,
16.50. Calculated for C13H11N3O3 (257.1) (%): C, 60.70; H, 4.31; N, 16.33. IR (KBr,
1
cmꢁ1): 3420 (m), 3217 (m), 1632 (s), 1530 (m), 1484 (m), 1303 (s), 706 (m). H NMR
(300 MHz, DMSO-d6) ꢁ: 12.16 [1H, OH], 11.03 [2H, NH], 7.65–9.05 [4H, py], 6.76–7.45
[4H, Ar].
2.3. Syntheses of complexes
2.3.1. Synthesis of [Cd(L1)2(SCN)2]n (1). A solution of L1 (0.10 mmol) in methanol
(5 mL) was mixed with a solution of CdSO4 ꢀ H2O (0.10 mmol) in water (5 mL), and then
a solution of KSCN (0.10 mmol) in methanol (5 mL) was added dropwise. The resulting
mixture was stirred for a half-hour and filtered. After keeping the filtrate at room
temperature for two weeks, pale yellow block crystals suitable for X-ray analysis were
formed. Yield: 0.032 g (36%). IR (KBr, cmꢁ1): 3282 (m), 1637 (s), 1528 (m), 1480 (m),
1066 (m), 764 (m).
.
2.3.2. Synthesis of [Zn(L1)2Cl2] H2O (2). A solution of L1 (0.2 mmol) in methanol
(5 mL) was added dropwise to a solution of ZnCl2 (0.2 mmol) in water (5 mL) with the
resulting mixture stirred for a half-hour. The solution was filtered and the filtrate was
kept at room temperature. After three weeks, yellow block crystals suitable for X-ray
analysis were formed. Yield: 0.037 g (36%). IR (KBr, cmꢁ1): 3404 (m), 3278 (m), 1635
(s), 1530 (m), 1487 (m), 1091(m), 756 (m).
2.3.3. Synthesis of [Zn(L2)2Cl2] (3). The synthesis process of 3 is similar to that of 2
only with the L1 being substituted by L2. Colorless block crystals of 3 suitable for X-ray
analysis were formed. Yield: 0.030 g (31%). IR (KBr, cmꢁ1): 3446 (m), 3253 (m), 1615
(s), 1567 (m), 1488 (m), 1099 (m), 742 (m).
3. Results and discussion
3.1. Description of the crystal structures
3.1.1. Crystal structure of [Cd(L1)2(SCN)2]n (1). Complex 1 is a 1-D two-stranded
chain and crystallizes in the monoclinic space group P21/c. The coordination
environment of CdII is shown in figure 1. Selected bond lengths and angles are given
in table 2. The centrosymmetric unit of 1 consists of one CdII atom, two SCNꢁ anions,
and two L1 ligands with CdII located at the inversion center i. The coordinated sphere
around every CdII is a distorted octahedron constructed by two nitrogen atoms from
two L1 ligands, two nitrogen atoms from two bridging SCNꢁ anions, and two sulfur
atoms from another two bridging SCNꢁ anions. In 1, N(1A), N(1D), S(1 C), S(1B),
˚
and Cd(1A) are coplanar with Cd–N and Cd–S being 2.285(2) and 2.7240(7) A,
respectively (table 2). N(2A), Cd(1A), and N(2D) are in a straight line with the angle

Unsymmetric bis-hydrazide
3137
Figure 1. View of the coordination environment of CdII in 1 (hydrogen atoms are omitted for simplicity)
Symmetry codes: A ¼ ꢁx þ 1, ꢁy þ 1, ꢁz þ 1, B ¼ x, y þ 1, z, E ¼ ꢁx, ꢁy þ 1, ꢁz þ 1, and F ¼ ꢁx, y þ 1/2,
ꢁz þ 1/2 for 1.
Figure 2. View of 1-D chain in 1 (hydrogen atoms are omitted for simplicity).
ꢂ
˚
N(2D)–Cd(1A)–N(2A) of 180.0(9) and the Cd–N bond distances of 2.3887(17) A; this
line is almost perpendicular to the plane N(1A)N(1D)S(1C)S(1B). The overall structural
feature of 1 is a two-stranded chain along the b-axis constructed from two SCNꢁ anions
simultaneously bridging two adjacent CdII atoms (figure 2). All CdII atoms are linear
with angle of Cd(1A)ꢀ ꢀ ꢀCd(1B)ꢀ ꢀ ꢀCd(1C) 180ꢂ (figure 2).
In the crystal structure of 1, there are intraligand hydrogen bonds with O(3)ꢀ ꢀ ꢀO(2)
˚
being 2.680(2) A between O–H and the oxygen from carbonyl near the benzene ring in
L1 (table 3 and figure 3). Besides these intraligand hydrogen bonds, the amino N–H
near the benzene ring of L1 with the oxygen from carbonyl near the pyridine ring of the
˚
adjacent chain form interchain hydrogen bonds with N(4)ꢀ ꢀ ꢀO(1) being 2.847(2) A,
and the O–H with the oxygen from carbonyl near the benzene ring of the

3138
Y.-X. Zhou et al.
ꢂ
˚
Table 3. Hydrogen bond distances (A) and angles ( ) for 1–3.
D–Hꢀ ꢀ ꢀA
d(D ꢀ ꢀ ꢀ A)
ff(DHA)
1
N(4)–H(4A)ꢀ ꢀ ꢀO(1F)
N(3)–H(3B)ꢀ ꢀ ꢀO(2E)
O(3)–H(3A)ꢀ ꢀ ꢀO(2)
2.847(2)
2.926(2)
2.680(2)
168.3
156.4
139.3
2
N(2)–H(2A)ꢀ ꢀ ꢀO(4B)
O(3)–H(3A)ꢀ ꢀ ꢀO(2C)
O(4)–H(4A)ꢀ ꢀ ꢀO(1)
N(3)–H(3B)ꢀ ꢀ ꢀO(3)
2.938(5)
2.878(4)
2.910(3)
2.626(5)
161.4
169.4
158.5
138.4
3
N(3)–H(3A)ꢀ ꢀ ꢀO(3)
N(2)–H(2A)ꢀ ꢀ ꢀO(2B)
O(3)–H(3B)ꢀ ꢀ ꢀO(1C)
2.599(8)
2.928(8)
2.705(8)
139.0
154.2
158.6
Symmetry codes: A ¼ ꢁx þ 1, ꢁy þ 1, ꢁz þ 1, B ¼ x, y þ 1, z, E ¼ ꢁx, ꢁy þ 1, ꢁz þ 1
and F ¼ ꢁx, y þ 1/2, ꢁz þ 1/2 for 1; A ¼ ꢁx þ 2, y, ꢁz þ 3/2, B ¼ x þ 1/2, yꢁ1/2, z,
and C ¼ x þ 1/2, y þ 1/2, z for 2; A ¼ ꢁx, y, ꢁz þ 1/2, B ¼ ꢁx þ 1/2, ꢁyꢁ1/2, ꢁz, and
C ¼ ꢁx þ 1/2, ꢁy þ 1/2, ꢁz for 3.
Figure 3. View of self-assembly of L1 through O–Hꢀ ꢀ ꢀN and N–Hꢀ ꢀ ꢀO hydrogen-bonding interactions in 1
(hydrogen atoms are omitted for simplicity). Symmetry codes: A ¼ ꢁx þ 1, ꢁy þ 1, ꢁz þ 1, B ¼ x, y þ 1, z.
˚
neighboring chain form interchain hydrogen bonds with N(3)ꢀ ꢀ ꢀO(2) being 2.926(2) A
(table 3 and figure 3). In this manner, the two-stranded chains are connected with
neighboring chains by two interchain hydrogen bonds to form a 3-D supramolecular
framework in 1 (figure 4).

Unsymmetric bis-hydrazide
3139
Figure 4. View of 3-D supramolecular network of 1 (hydrogen atoms are omitted for simplicity).
Figure 5. The molecular structure of 2 (hydrogen atoms are omitted for simplicity). Symmetry code:
A ¼ ꢁx+2, y, ꢁz þ 3/2.
.
3.1.2. Crystal structure of [Zn(L1)2Cl2] H2O (2). Complex 2 is a monomer crystal-
lizing in the orthorhombic chiral space group C2221 with the Flack parameter of
0.058(1). The crystal structure unit of 2 is shown in figure 5. The crystallographic data
and selected bond lengths and angles are listed in tables 1 and 2, respectively. Complex
2 is a chiral structure, and its structural unit consists of one ZnII atom, two L1 ligands,
and two Clꢁ atoms with a two-fold axis passing through ZnII and halving the structural
unit. ZnII is ligated by two nitrogen atoms from L1 and two Clꢁ atoms, forming a
distorted tetrahedral coordination geometry. In 2, two L1 ligands form a distorted
V-shaped structure constructed from coordination between ZnII and nitrogen of
pyridine with the torsion angle C(3A)–N(1A)–Zn(1)–N(1) of ꢁ29.02ꢂ, and the two rings
of N(1)C(1)C(2)C(5)C(4)C(3) and C(8)C(9)C(10)C(11)C(12)C(13) from the same L1 are
twisted with dihedral angle of 13.6ꢂ. This distortion phenomenon also exists in 1 for the
bis-hydrazide group (–CONHNHCO–) bridging the pyridine ring and the benzene ring
is rotatable and flexible.

3140
Y.-X. Zhou et al.
Figure 6. View of self-assembly of L1 through O–Hꢀ ꢀ ꢀN and N–Hꢀ ꢀ ꢀO hydrogen-bonding interactions in 2
(hydrogen atoms are omitted for simplicity). Symmetry codes: A ¼ ꢁx þ 2, y, ꢁz þ 3/2 and B ¼ x þ 1/2, yꢁ1/2.
Every lattice water molecule among structural units of 2 is a tetrahedral supramo-
lecular connector, connecting with amido near the pyridine ring and oxygen atoms of
carbonyl near the pyridine ring from four different units through intermolecular
˚
˚
hydrogen bonds with N(2)ꢀ ꢀ ꢀO(4) being 2.938(5) A and O(4)ꢀ ꢀ ꢀO(1) being 2.910(3) A,
respectively. Another intermolecular hydrogen bond O(3)ꢀ ꢀ ꢀO(2) occurs between O–H
˚
and oxygen from carbonyl near the benzene ring of the neighboring unit at 2.878(4) A.
In addition, there is an intramolecular hydrogen bond between the amino N–H near the
˚
benzene ring and hydroxyl group from the same unit with N(3)ꢀ ꢀ ꢀO(3) being 2.626(5) A.
Figure 6 is a view of self-assembly of L1 through O–Hꢀ ꢀ ꢀN and N–Hꢀ ꢀ ꢀO hydrogen-
bonding interactions in 2. As a result, the structural units of 2 extend into a 3-D
supramolecular framework by the complicated hydrogen-bonding network (figure 7
and table 3). Through regular intermolecular hydrogen-bonding interactions homo-
chiral monomers of 2 recognize each other to form chiral crystals although the whole
complex is racemic mixtures of enantiopure crystals.
Vertical face-to-face distances between pyridine rings and benzene rings of the
˚
neighboring unit are 3.679 A, indicating the existence of ꢅ–ꢅ stacking interactions.

Unsymmetric bis-hydrazide
3141
Figure 7. View of 3-D framework supported by hydrogen-bonding net in 2.
Figure 8. The molecular structure of 3. Symmetry code: A ¼ ꢁx, y, ꢁz þ 1/2.
The ꢅ–ꢅ stacking interactions and intermolecular hydrogen bonds mentioned above
play an important role in stabilization of the 3-D supramolecular framework of 2.
3.1.3. Crystal structure of [Zn(L2)2Cl2] (3). The structural unit of 3 consists of one
ZnII atom, two L2 ligands, and two Clꢁ atoms as shown in figure 8. The crystal
structure parameters and selected bond lengths and angles are listed in tables 1 and 2,
respectively. In 3, ZnII is four-coordinate by two nitrogen atoms from L2 and two Clꢁ
atoms, forming a distorted tetrahedron, similar to that of 2. In 3, the two rings of
N(1)C(1)C(2)C(3)C(5)C(4) and C(8)C(9)C(10)C(11)C(12)C(13) from the same L2 are
distorted with dihedral angle of 12.4ꢂ and torsion angle C(1)–N(1)–Zn(1)–N(1A) of
39.83ꢂ. Although 3 is similar to 2, in shape, 2 is V-like while 3 is linear. The structure of
3 is similar to that of [Zn(Py)2Cl2] [18]. The shape difference mainly originates from the
different bite angles of L1 and L2, which results in crystal packing as presented below.

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Y.-X. Zhou et al.
Figure 9. View of self-assembly of L2 through O–Hꢀ ꢀ ꢀN and N–Hꢀ ꢀ ꢀO hydrogen-bonding interactions in 3
(hydrogen atoms are omitted for simplicity). Symmetry codes: A ¼ ꢁx, y, ꢁz þ 1/2 and B ¼ ꢁx þ 1/2, ꢁyꢁ1/2.
Hydrogen bonds exist in 3 (table 3 and figure 9), also. There is an intramolecular
hydrogen bond between the amino N–H near the benzene ring and hydroxyl group
˚
from the same unit with N(3)ꢀ ꢀ ꢀO(3) being 2.599(8) A, similar to that in 2. The
N(2)ꢀ ꢀ ꢀO(2) intermolecular hydrogen bond between N–H near the pyridine ring of L2
˚
and carbonyl near the benzene ring of the neighboring unit is 2.928(8) A, and the
O(3)ꢀ ꢀ ꢀO(1) intermolecular hydrogen bond between O–H group and carbonyl near the
˚
pyridine ring of the neighboring unit is 2.705(8) A. These intermolecular hydrogen
bonds join the monomer units to give a 2-D sheet as shown in figure 10. In 3, there are
ꢅ–ꢅ stacking interactions between pyridine rings and benzene rings of neighboring
˚
layers with vertical face-to-face distances of 3.657 A. The ꢅ–ꢅ interaction stabilizes the
complexes.
As discussed above, 2 and 3 are 0-D and 1 shows a 1-D structure. The three
complexes propagate into metal–organic supramolecular architectures by various
intermolecular interactions, such as hydrogen-bonding and ꢅ–ꢅ stacking interactions.
The hydrogen bonds are the main forces sustaining the crystal framework. In 1, the
polymeric chains are connected into a 3-D supramolecular framework through
interchain hydrogen bonds occurring between L1 (shown in figure 3) while the
monomer units are extended into a 3-D supramolecular structure of 2 or 2-D sheet of 3
via complicated hydrogen-bonded self-assembly of L1 or L2 (shown in figures 6 and 9).

Unsymmetric bis-hydrazide
3143
Figure 10. View of 2-D framework of 3 connected by hydrogen bonds (hydrogen atoms are omitted for
simplicity).
Formation of the 3-D supramolecular structure of 2 is aided by water-mediated
hydrogen-bonding interactions.
It is familiar that ꢅ–ꢅ stacking interaction exists in metal complexes of aromatic
ligands, and the usual ꢅ–ꢅ interaction is an offset or slipped stacking, i.e. the rings are
parallel displaced, the ring normal, and the vector between the ring centroids form an
ꢂ
˚
angle of about 20 up to centroid–centroid distances of 3.8 A [19]. In 2 and 3, the ꢅ–ꢅ
stacking interactions exist and the ꢅ–ꢅ interactions also play an important role in
stabilizing the crystal packing.
3.2. Fluorescent properties of 1–3
The photoluminescence properties of 1–3 as well as L1 and L2 were investigated in the
solid state at room temperature. L1 displays weaker emissions centered at 470 and
517 nm, probably attributable to ꢅ*!ꢅ or ꢅ*!n transitions [20–23]. However, 1 and 2
give relatively strong fluorescence under the same experimental conditions. The
enhancement may be due to the introduction of the metal ions enhancing the rigidity of
L1 which causes increase in the conjugation of the whole molecule, thereby reducing the
non-radiative decay of the intraligand (ꢅ!ꢅ*) excited state [24, 25]. Spectral bands of 1
and 2 are blue-shifted compared with free L1. This may be related to the coordination
environment, hydration level, and crystal packing, which could result in an increase in
HOMO–LUMO energy gap of the complex [26–28]. Compared with free L2,

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Y.-X. Zhou et al.
the fluorescence intensity of 3 is slightly enhanced and the emitting wavelength is close
to L2, which indicates that the coordination of ZnII and Clꢁ does not affect the rigidity
of L2. The energy transfer in neutral guest–host systems accords with the relative energy
level spacings of the luminescing donor and acceptor molecules [29]. The fluorescence
behaviors suggest that emissions of 1–3 are neither MLCT nor LMCT, and can be
mainly assigned to intraligand charge transfer (ILCT) because CdII and ZnII are
difficult to oxidize or reduce due to d10 configurations [30–32].
3.3. Thermogravimetric analysis
Thermogravimetric (TG-DSC) analysis was performed on polycrystalline samples for
1–3. There are three transitions in the decomposition of 1. The first starts at 200ꢂC and
ends at 360ꢂC, due to loss of two molecular fragments of salicyl hydrazide from the
structure (Found: 51.5%, Calcd: 48.3%). The second transition from 360ꢂC to 660ꢂC
(26.8%) containing an exothermic peak at 546ꢂC is related to loss of two molecular
fragments of isonicotinoyl chloride (Calcd: 28.5%). The third transition from 660ꢂC to
780ꢂC of 8.4% is related to loss of two SCNꢁ anions (Calcd: 6.9%). The total mass loss
to 800ꢂC is 86.7%, which agrees with the theoretical value (84.4%) calculated by taking
CdO as the final product.
There are three transitions in the decomposition of 2 or 3. The first from 200ꢂC to
460ꢂC is due to loss of one H2O molecule and two molecular fragments of salicyl
hydrazide. The second transition from 460ꢂC to 620ꢂC is due to loss of two molecular
fragments of isonicotinoyl chloride for 2 and nicotinoyl chloride for 3. During the third
weight loss process from 620ꢂC to 700ꢂC, 2 and 3 lost two HCl. The total weight loss of
decomposition is 89.5% for 2 (calculated by taking ZnO as the final product, 89.7%)
and 90.9% for 3 (calculated by taking ZnO as the final product, 90.0%).
3.4. Polarimetric analysis of 2
Polarimetric analysis of 2 was also investigated. A solution of 15 mg of 2 in 10 mL of
DMF was added to an optical tube, and polarimetric measurements were carried out on
26
589
an America AA-10 apparatus (26ꢂC, 589 nm). The observed value of ½ꢆŠ
is
0ꢂ dL ꢀ cmꢁ1 ꢀ gꢁ1. Although the single crystal of 2 is a chiral structure, the solution of 2
in DMF has no optical activity, showing that 2 is a racemic mixture.
4. Conclusions
Two isomeric ligands, L1 and L2, coordinate with d10 metal ions in terminal
coordination, and different coordination modes of the ligands and environments
around the metal ions offer distinctive supramolecular interaction sites for each
structural unit. Therefore, 1, 2, and 3 have specific unit structures and crystal-packing
modes.
For polymer 1 and monomers 2 and 3, hydrogen bonds and ꢅ–ꢅ interactions are the
main forces holding complex molecules together and sustaining the crystal framework.

Unsymmetric bis-hydrazide
3145
Coordination of metal ions and anions change rigidity of ligands, thus fluorescence
behaviors of complex were changed. The luminescence mechanisms of 1–3 are mainly
ILCT.
Supplementary material
The supplementary crystallographic data for the structural analyses of this article have
been deposited via the Cambridge Crystallographic Data Centre, CCDC Reference
Nos: 847487 (for 1), 847488 (for 2), and 847489 (for 3). Copies of these can be obtained
free of charge from: The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax: þ44-1223-336-033; E-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk/data_request/cif).
Acknowledgments
The authors acknowledge financial support from the National Natural Science
Foundation of China (20771094).
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