Cobalt(II) complexes with bis(N-imidazolyl/benzimidazolyl) pyridazine: Structures, photoluminescent and photocatalytic properties

Article abstract of DOI:10.1016/j.jssc.2016.04.037

Six new Co^II complexes [Co(L¹)₄(OH)₂] (1), {[Co(L¹)(H₂O)₄]·2ClO₄}_∞ (2), {[Co(L¹)(H₂O)₄]·SiF₆}_∞ (3), {[Co(L¹)₃]·2ClO₄}_∞ (4), [Co(L²)Cl₂]_∞ (5) and {[Co(L²)₂]·SiF₆}_∞ (6) [L¹=3,6-bis(N-imidazolyl) pyridazine, L²=3,6-bis (N-benzimidazolyl) pyridazine] have been synthesized and characterized by elemental analysis, IR spectra and single crystal X-ray diffraction. Complex 1 has a mononuclear structure, while complexes 2 and 3 have 1-D chain structures. Considering the Co^II centers were linked by the L¹ ligands, the 3-D framework of complex 4 can be rationalized to be a {4^12.6^3} 6-c topological net with the stoichiometry uninodal net. 5 reveals a coordination 1-D zigzag chain structure consisting of a neutral chain [Co(L²)Cl₂]_n with the Co^II centers. Complex 6 has a rhombohedral grid with a (4, 4) topology. The TGA property, fluorescent property and photocatalytic activity of complexes 1-6 have been investigated and discussed.

Full text of DOI:10.1016/j.jssc.2016.04.037

Journal of Solid State Chemistry 239 (2016) 251–258
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Cobalt(II) complexes with bis(N-imidazolyl/benzimidazolyl)
pyridazine: Structures, photoluminescent and photocatalytic
properties
n
Jin-Ping Li, Jian-Zhong Fan, Duo-Zhi Wang
Key Laboratory of Material and Technology for Clean Energy, Ministry of Education, Chemistry and Chemical Engineering School of Xinjiang University,
Urumqi 830046, PR China
a r t i c l e i n f o
a b s t r a c t
II
1
1
1
Article history:
Received 23 January 2016
Received in revised form
Six new Co complexes [Co(L ) (OH) ] (1), {[Co(L )(H O) ] ꢀ 2ClO } (2), {[Co(L )(H O) ] ꢀ SiF } (3), {[Co
4
2
2
4
4
1
2
4
6 1
1
2
2
1
(L ) ] ꢀ 2ClO } (4), [Co(L )Cl ] (5) and {[Co(L ) ] ꢀ SiF } (6) [L ¼3,6-bis(N-imidazolyl) pyridazine,
3
4
1 2 1 1
2
6
2
L ¼3,6-bis (N-benzimidazolyl) pyridazine] have been synthesized and characterized by elemental ana-
lysis, IR spectra and single crystal X-ray diffraction. Complex 1 has a mononuclear structure, while
31 March 2016
Accepted 25 April 2016
Available online 30 April 2016
II
1
complexes 2 and 3 have 1-D chain structures. Considering the Co centers were linked by the L ligands,
the 3-D framework of complex 4 can be rationalized to be a {4^12.6^3} 6-c topological net with the
stoichiometry uninodal net. 5 reveals a coordination 1-D zigzag chain structure consisting of a neutral
Keywords:
II
Co complexes
2
II
2 n
chain [Co(L )Cl ] with the Co centers. Complex 6 has a rhombohedral grid with a (4, 4) topology. The
Crystal structure
Luminescent property
Photocatalytic activity
TGA property, fluorescent property and photocatalytic activity of complexes 1–6 have been investigated
and discussed.
&
2016 Elsevier Inc. All rights reserved.
1
. Introduction
supramolecular networks [12]. A large number of metal co-
ordination compounds of imidazole and benzimidazole with lu-
minescent properties and novel topologies have been reported
[13].
In recent years, the rational design and assembly of solid co-
ordination network (SCF) have been an attractive research field in
supramolecular chemistry and coordination chemistry owing to
their fascinating structural diversities as well as their potential
applications in many fields, such as catalysis, sensing, photo-
voltaics, ion exchange, microelectronics, nonlinear optics and so
on [1–6]. The construction of solid coordination network (SCF)
with desired structures and specific properties still remains a far-
reaching challenge because there are so many factors influencing
the formation and structure of the complexes [7,8], especially, the
structure of organic ligands and the coordination modes of metal
ions [9]. An effective and facile approach for the synthesis of such
complexes with specific structures and properties is carried out by
the utilization of well-designed organic ligands and metal ions
Furthermore, from the standpoint of property investigation,
CoII metal with d electronic configuration is often employed in
crystal engineering owing to excellent electrochemical property
7
[14], magnetic property [15], photoluminescent property [16]
when it is coordinated to organic ligands. However, the reports of
II
Co metal complexes about photocatalysts are still very limited
[17].
Pyridazines are well established as potential bridging units in
binuclear complexes since they are capable of spanning two metal
ions via their two N atoms [18,19]. 3,6-bis(N-imidazolyl) pyr-
idazine as a kind of heterocyclic ligand has been reported, and Jin
and his cooperators [20,21] reported a series of chlorocadmate
complexes with imidazole derivatives under strong acidic condi-
[10]. Among the various organic ligands, the ligands of imidazole
II
tion. But in their articles, the Cd ions of all compounds were
derivatives have received considerable attention because these
compounds have a variety of pharmacological activities like fun-
gicides or anti-helminthics [11]. The complexes of bis(imidazole/
benzimidazole) ligands containing two imidazole rings capable of
acting as hydrogen bond donors are linked into high-dimensional
ꢁ
tetrahedrally coordinated by Cl , while 3,6-bis(N-imidazolyl)
pyridazine ligand has not taken part in coordination. In this work,
we focus our attention on the coordination chemistry of ligands
containing pyridazine, two structurally related neutral ligands,
1
3
,6-bis(N-imidazolyl) pyridazine (L ) and 3,6-bis(N-benzimidazo-
2
lyl) pyridazine (L ) (Chart 1) as an extension of our work, and six
Co metal-organic complexes were synthesized and structurally
characterized. In these Co complexes, because of the difference of
II
n
Corresponding author.
II
E-mail address: wangdz@xju.edu.cn (D.-Z. Wang).
http://dx.doi.org/10.1016/j.jssc.2016.04.037
0
022-4596/& 2016 Elsevier Inc. All rights reserved.

252
J.-P. Li et al. / Journal of Solid State Chemistry 239 (2016) 251–258
1
benzimidazole instead of imidazole. Yield 76%. m.p. 283–284 °C. H
NMR (400 MHz, DMSO-d ): : 9.130 (s, 2 H, imidazole-2), 8.653 (s,
2 H, pyridazine), 7.388–8.384 (m, 8 H, benzene);
(100 MHz, DMSO-d ): 152.30, 144.34, 142.26, 131.68, 124.53,
N N
N
N
6
δ
N
N
13
N N
C NMR
N
N
N
N
6
1
23.71, 122.51, 120.09, 114.64; HRMS: (ESI) calcd for C18
H
H
12
N
6,
þ
(
[MþH] ): 313.1196, found: 313.1187; Anal. Calcd for C18
12
N
6
L1
L2
(%): C, 69.21; H, 3.87; N, 26.91; Found (%): C, 69.34; H, 3.56; N,
ꢁ
1
2
2
7.41. IR (KBr, cm ): 3082m, 3058m, 2924w, 2854w, 2773w,
371w, 1921w, 1783w, 1739w, 1669w, 1609m, 1590m, 1558s, 1497s,
Chart 1. The ligands L1 and L2 studied in this work.
1
459s, 1359m, 1338m, 1308m, 1279m, 1238m, 1190s, 1163m, 1138m,
L1 and L2 ligands, the CoII centers of complexes 1–4 adopted oc-
tahedral coordination spheres, while they adopted tetrahedral
coordination sphere in complexes 5 and 6. Moreover, the fluor-
escent property and photocatalytic activity of complexes 1–6 have
been investigated and discussed.
1035m, 992m, 979m, 962m, 939m, 884m, 830m, 769s, 753s, 732s,
6
2
2
0
44m, 623m, 575m, 538m, 486m, 427m.
.3. Synthesis of complexes 1–6
.3.1. [Co(L1)
A mixture of Co(NO
.3 mmol) and 5 mL water, was placed in a Teflon-lined stainless
4
2
(OH) ] (1)
1
3
)
2
ꢀ 6H
2
O (87 mg, 0.3 mmol) and L (63 mg,
2
. Experimental section
steel vessel (25 mL) and heated to 140 °C for 3 days, then cooled to
ꢁ
1
room temperature at a rate of 10 °C ꢀ h . The red block crystals of
2.1. Materials and general methods
1
1
C
3
2
were obtained (ca. 30% yield based on L ). Anal. Calcd for
H34CoN24O : C, 51.01; H, 3.64; N, 35.69. Found: C, 50.85; H,
All the other reagents used for the syntheses were commer-
40 2
ꢁ
1
.60; N, 35.60. IR (cm , KBr pellets): 3386m, 3114m, 2525w,
416w, 2212w, 2080w, 1995w, 1911w, 1870w, 1806w, 1579m,
cially available and employed without further purification. Imi-
dazole, benzimidazole, and 3,6-dichloropyridazine were pur-
chased from J&K Scientific LTD, whose purities are 99%, 98% and
1522m, 1481s, 1377s, 1318s, 1241m, 1148m, 1099m, 1065m, 1032m,
967m, 931m, 917m, 838m, 737m, 652m, 615m, 492m, 419m.
97%, respectively. Elemental analysis of C, H and N were de-
termined with a Thermo Flash EA 1112-NCHS-O analyzer. IR
spectra were measured via KBr pellets using a Brucker Equinox 55
FT-IR spectrometer. NMR data were collected using an INOVA-400
1
2
.3.2. {[Co(L )(H
2
O)
4
] ꢀ 2ClO
4 1
} (2)
The pink block crystals of 2 suitable for X-ray analysis were
obtained by the similar method described for 1, except for using
Co(ClO O instead of Co(NO ꢀ 6h O (ca. 35% yield based on
ꢀ 6H
L ). Anal. Calcd for C10 CoN 12: C, 24.86; H, 3.34; N, 17.39.
Found: C, 24.58; H, 3.51; N, 17.45. IR (cm , KBr pellets): 3368m,
178m, 3131m, 2577w, 2385w, 2025w, 1925w, 1806w, 1646m,
582m, 1497s, 1455s, 1301s, 1256m, 1074s, 1048s, 967m, 927m,
NMR spectrometer and chemical shifts are reported in
TMS. High-resolution mass spectra (HRMS) were recorded on
δ
relative to
4
)
2
2
3
)
2
2
1
1
H16Cl
2
6
O
Thermo Q-Exactive. Solid state luminescent spectra of ligands L ,
ꢁ
1
2
L and complexes 1–6 were measured by Hitachi F-4500 Fluores-
3
1
8
cence Spectrophotometer with a Xe arc lamp as the light source
and bandwidths of 2.5 nm at room temperature. UV–vis absorp-
tion spectra were obtained using a Hitachi UV-3010 UV–vis spec-
trophotometer. The X-ray powder diffraction (XRPD) was recorded
on a Rigaku D/Max-2500 diffractometer at 40 kV, 100 mA for a Cu-
target tube and a graphite monochromator.
21m, 769m, 643m, 615m, 531m, 496m, 446m.
1
2
.3.3. {[Co(L )(H
2
O)
4
] ꢀ SiF
6
}
1
(3)
2
O (15 mg, 0.05 mmol) and L (10 mg,
1
A mixture of CoSiF
.05 mmol) in water (8 mL) and ethanol (8 mL) was refluxed for
h. The red block crystals of 3 were formed after several days with
the evaporation of the filtrate (ca. 45% yield based on L ). Anal.
6
ꢀ 6H
0
3
1
2
2
2
8
.2. Synthesis of ligands L and L
1
.2.1. 3,6-bis(N-imidazolyl) pyridazine (L1)
Imidazole (3.4 g, 49.9 mmol), sodium (1.2 g, 52.2 mmol) and
0 mL THF was added to a 250 mL three-necked flask. The reaction
Calcd for C10
5.14; H, 3.35; N, 17.60. IR (cm , KBr pellets): 3409s, 3173m,
155m, 3146m, 3064m, 2361w, 1919w, 1657m, 1574m, 1534s, 1489s,
463s, 1373m, 1326s, 1293m, 1254m, 1155m, 1109m, 1076m, 1053m,
038m, 970m, 937m, 868m, 844m, 761m, 716s, 649m, 617m.
6 6 4
H16CoF N O Si: C, 24.75; H, 3.32; N, 17.32. Found: C,
ꢁ
1
2
3
1
1
mixture was refluxed for 40 min.
chloropyridazine (3.7 g, 24.8 mmol) in 10 mL THF was added to the
mixture within 40 min. The mixture was refluxed for 4 h under N
A
solution of 3,6-di-
2
.
2
.3.4. {[Co(L1)
A buffer layer of acetonitrile/cholorform (10 mL, 1: 1) was
carefully layered over a cholorform solution (3 mL) of L (10 mg,
.05 mmol). Then
.05 mmol) in acetonitrile (3 mL) was layered on the buffer layer.
3
] ꢀ 2ClO
4 1
} (4)
The reaction mixture was poured into ice water after being cooled
1
to room temperature. The earthy yellow solid of L was obtained
1
1
after filtering. Pure ligand L was obtained by recrystallization
from ethanol as white crystals. Yield 80%. m.p. 281–282 °C. 1
H
0
0
a
solution of Co(ClO
4
)
2
ꢀ 6H
2
O
(22 mg,
NMR (400 MHz, DMSO-d
6
):
δ
:8.69 (s, 2 H, imidazole-2), 8.48 (s,
The system was left for about two weeks at room temperature, and
pink block crystals of 4 were obtained. (ca. 40% yield based on L ).
2
H, pyridazine), 8.11 (d, 2 H, J¼2.4 Hz, imidazole-5), 7.23(d, 2 H,
1
1
3
J¼2.4 Hz, imidazole-4); C NMR (100 MHz, DMSO-d
6
): 151.32,
Anal. Calcd for C30
Found: C, 40.39; H, 2.68; N, 28.17. IR (cm , KBr pellets): 3479m,
137m, 3083m, 3024m, 2603w, 2415w, 2213w, 2013w, 1909w,
806w, 1580m, 1490s, 1452s, 1370m, 1324m, 1305s, 1236m, 1095s,
036m, 969s, 930m, 835m, 749m, 654m, 620m, 492m.
24 2 8
H N18Cl O Co: C, 40.28; H, 2.70; N, 28.19.
135.46, 130.72, 121.60, 116.73. HRMS: (ESI) calcd for C10
H
8
N
6,
ꢁ
1
þ
(
5
[MþH] ): 213.0805, found: 213.0875; Anal. Calcd for C10
8 6
H N : C,
3
1
1
6.60; H, 3.80; N, 39.60; Found: C, 56.75; H, 3.75; N, 39.54. IR
ꢁ
1
(
cm , KBr pellets): 3176w, 3145m, 3109m, 3047m, 3018m, 2946m,
782w, 2621w, 2526w, 2408w, 2214w, 1991w, 1903w, 1795w,
727w, 1692w, 1645w, 1577s, 1519s, 1490s, 1459s, 1371s, 1321s,
277s, 1237s, 1163m, 1106m, 1059m, 1031s, 962m, 903m, 861s,
2
1
1
2
2
.3.5. [Co(L )Cl
A mixture of CoCl
.3 mmol) and 6 mL ethanol, was placed in a Teflon-lined stainless
2 1
] (5)
2
ꢀ 6H
O (71 mg, 0.3 mmol) and L2 (93 mg,
2
8
23s, 766s, 749s, 645s, 613m, 507w, 487m, 421m.
0
2
2
.2.2. 3,6-bis(N-benzimidazolyl) pyridazine (L )
steel vessel (25 mL) and heated to 140 °C for 2 days, then cooled to
room temperature at a rate of 10 °C ꢀ h . The blue block crystals of
2
was synthesized similarly as L1 by using
–1
Ligand
L

J.-P. Li et al. / Journal of Solid State Chemistry 239 (2016) 251–258
253
2
5
were obtained (ca. 35% yield based on L ). Anal. Calcd for
Table 1
Crystal data and structure refinement summary for complexes 1–6.
C
18 2 6
H12Cl CoN : C, 48.89; H, 2.74 N, 19.01. Found: C, 48.85; H, 2.71;
ꢁ
1
N, 19.19. IR (cm , KBr pellets): 3849w, 3796w, 3730w, 3668w,
644w, 3441w, 3143m, 3100m, 3041w, 2839w, 2546w, 1957w,
920w, 1838w, 1802w, 1704w, 1652w, 1607m, 1589m, 1564m, 1510s,
466s, 1382m, 1320m, 1300m, 1239s, 1149m, 1036m, 1009m, 979w,
1
2
3
3
1
1
Formula
Formular wt
Crystal system
Space group
T/K
a/Å
b/Å
c/Å
a/deg
C
40
H
34CoN24
O
2
C
10
H
16
C
l2CoN
6
O
12
C
10 6 6 4
H16CoF N O Si
941.86
Orthorhombic
Aba2
293(2)
13.770(3)
13.780(3)
27.590(5)
90
542.12
485.24
Triclinic
P-1
Orthorhombc
C222(1)
296(2)
9.1632(19)
36.472(8)
9.159(2)
90
9
5
44w, 911w, 845w, 808w, 777s, 763s, 680w, 642m, 616m, 587m,
20m, 449m, 423m.
293(2)
7.635(2)
11.179(3)
11.545(3)
102.803(7)
107.065(7)
106.551(7)
851.4(4)
2
2
.3.6. {[Co(L2)
Crystals of 6 were obtained by the similar method described for
, except for using CoSiF O instead of CoCl ꢀ 6H O (ca. 25%
ꢀ 6H
24CoF 12Si: C, 52.37; H,
.93; N, 20.36. Found: C, 52.45; H, 2.99; N, 20.78. IR (cm , KBr
pellets): 3487w, 3150m, 3107m, 3081m, 2978w, 2795w, 2522w,
925w, 1790w, 1706w, 1572m, 1503s, 1479m, 1462m, 1441s, 1363m,
310m, 1295m, 1233s, 1158m, 1129m, 1054s, 914m, 851m, 837m,
2
] ꢀ SiF
6
}
1
(6)
5
6
2
2
2
b/deg
90
90
90
90
2
yield based on L ). Anal. Calcd for C36
2
H
6
N
g/deg
ꢁ
1
3
V/Å
5235.2(19)
4
1.198
3061.0(11)
4
1.176
Z
ꢁ
3
D/g cm
m/mm
1.862
1.174
1
1
ꢁ1
0.384
0.784
F(000)
1948
1100
474
7
80m, 746s, 679m, 611m, 519m, 448m, 418m.
Caution! Perchlorate complexes of metal ions in the presence
Messuredreflns
Obsd reflns
R /wR
19,691
4593
0.0696/0.1931
4
9418
2703
0.0656/0.2497
5
5410
3016
0.0871/0.2546
6
a
b
of organic ligands are potentially explosive. Only a small amount of
material should be used and handled with care.
Formula
Formular wt
Crystal system
Space group
T/K
a/Å
b/Å
c/Å
a/deg
C
30
H
24Cl
2
CoN18
O
8
C
18
H
12Cl
2
CoN
6
C
36
H
24CoF
6
N12Si
894.50
Trigonal
R-3c
293(2)
13.851(3)
13.851(3)
58.358(17)
90
90
120
9696(4)
6
0.919
0.392
2729
24,854
2762
442.17
825.69
2
.4. X-Ray crystallography
Orthorhombic
P2(1)2(1)2(1)
296(2)
9.9546(4)
12.1863(6)
15.0008(7)
90
Tetragonal
P4(2)/n
296(2)
12.5740(6)
12.5740(6)
11.2126(8)
90
The X-ray diffraction (XRD) data of complexs 1–6 was collected
on a Bruker APEX II Smart CCD diffractometer at 293(2) K with
Mo-K radiation ( scan modescan mode.
¼0.71073 Å) by
α
λ
ω-ϕ
Semi-empirical absorption corrections were applied to the data
using SADABS program. The program SAINT [22] was used for
integration of the diffraction profiles. The structures were solved
by direct methods using the SHELXS program of the SHELXTL
package and refined by full-matrix least-squares methods with
SHELXL [23]. Metal atoms in each complex were located from the
E-maps and other non-hydrogen atoms were located in successive
difference Fourier syntheses and refined with anisotropic thermal
b/deg
90
90
90
90
g/deg
3
V/Å
1819.74(14)
4
1.614
1.253
892
11,898
3292
0.0375/0.0943
1772.77(17)
2
1.547
0.597
838
10,340
1528
0.0509/ 0.1556
Z
ꢁ
3
D/g cm
m/mm
ꢁ1
F(000)
Messuredreflns
Obsd reflns
2
parameters on F . Hydrogen atoms of carbon were located at cal-
a
b
R /wR
0.0730/0.2138
culated positions and refined with fixed thermal parameters riding
on their parent atoms. Experimental details for the structure de-
termination are presented in Table 1.
a
R ¼ Σ(||F |ꢁ|F ||)/Σ|F |.
0
C
2
0
2
b
C 0
| ꢁ|F | ) /Σw(F .
2)]1/2
2
wR ¼ [Σw(|F
0
3
3
.2. Description of the crystal structure
.2.1. [Co(L1)
3
. Results and discussion
4
(OH)
2
] (1)
3.1. Syntheses and general characterization
Single crystal X-ray diffraction analysis reveals that complex 1
crystallizes in the orthorhombic space group Aba2 and crystal-
lographic data and experimental details for structural analyses
were summarized in Table 1, the selected bond distances and
angles were listed in Table 1 of Supplementary 1. Complex 1 has a
In this work, our synthetic method of the ligands was different
from the reported in literature [21]. The yields of ligands were
1
2
higher than previous one. The structures of L and L determined
1
13
by H NMR, C NMR, IR, HRMS and elemental analysis. All the
II
mononuclear structure (Fig. 1a). The complex 1 contains one Co
complexes 1–6 were air stable at room temperature. Complexes 1,
and 5, 6 were synthesized by the hydrothermal method at 140 °C
without adding any base for adjusting the pH value. 3 was ob-
tained in mixed solvent by refluxing for 3 h after being cooled and
filtrated. Complex 4 was obtained in organic solvent at room
temperature. Complex 1 has a mononuclear structure. Complexes
1
II
cation, four neutral L ligands and two OHˉ anions. The Co center
2
1
is six coordinated by four N atoms from four independent L li-
gands and two O atoms from OHˉ anions to complete a distorted
octahedral geometry with the coordination angles varying from
86.5(2)° to 179.7(4)°. The Co-O bond lengths are 2.069(4) Å, and
the lengths of Co-N bonds are 2.128(6) Å and 2.130(6) Å, respec-
1
2
and 3 have 1-D chain structures. Complex 4 can be rationalized
tively. The equatorial plane is formed by four N atoms from four L
to be a {4^12.6 ^3 } 6-c topological net. Complex 5 reveals a co-
ordination 1-D zigzag chain. Complex 6 has a rhombohedral grid
with a (4, 4) topology.
ligands, and the axial positions are occupied by two O atoms from
two OHˉ anions. All the L ligands adopt monodentate coordina-
tion mode and two-coordinated OHˉ anions not only participated
in coordination but also are used to balance the charge.
As shown in Fig. 1b, such adjacent mononuclear structures are
linked by O(1)-H(1A) ꢀ ꢀ ꢀ N(6) hydrogen bonds to form a one-di-
mensional chain [O(1) ꢀ ꢀ ꢀ N(6) separation is 2.781(8) Å, see
Table 2 of Supplementary 1]. In addition, the C-H ꢀ ꢀ ꢀ N weak in-
teractions are observed between adjacent chains. The distances of
1
2
In the IR spectra of 1, 2 and 3, the bands of the coordinated H O
ꢁ
1
molecules appeared at about 3300 cm . The absorption bands at
ꢁ
1
1
4
074 and 615 cm indicate the existence of the ClO ˉ anions in 2,
and characteristic bands of the free ClO
4
ˉ anions appear at
ꢁ
1
ꢁ1
ꢁ1
1095 cm
and 620 cm
in 4. The bands at 970 and 1054 cm
were assigned to the free SiF
6

254
J.-P. Li et al. / Journal of Solid State Chemistry 239 (2016) 251–258
Fig. 2. View of the 1-D chain of 2 (H atoms omitted for clarity) (b) the 2-D su-
pramolecular sheet formed O-H···O hydrogen-bonds.
neighboring non-bonding Co ꢀ ꢀ ꢀ Co distance is 12.9558(5) Å. Be-
1
2þ
cause of such coordination mode, the [CoL (H
2
O)
4
]
unit has two
ꢁ
positive charge, the weaker coordination ability of ClO
does not show any bonding interaction with Co , and only acts as
4
anion
II
ꢁ
counter anion for charge balance. The ClO
4
anions are located in
the cavities of the sheet and formed O-H ꢀ ꢀ ꢀ O hydrogen-bonding
with the coordinated water molecules to develop a two-dimen-
sional sheet [O ꢀ ꢀ ꢀ O separations are at the range of 2.718(8)ꢁ
2.792(9) Å] (Fig. 2b). The hydrogen-bonding parameters (Å, °)
were listed in Table 2 of Supplementary 1.
1
3
.2.3. {[Co(L )(H
2
O)
4 6 1
] ꢀ SiF } (3)
1
Complex 3 was obtained when the reaction of L with
CoSiF was carried out in the mixed solvent (H O/
ꢀ 6H
CH CH OH) at room temperature. Because of the weak coordina-
tion ability of SiF
Fig. 1. View of (a) the coordination environment of CoΙΙ ions in 1 (H atoms omitted
O
6
2
2
for clarity) (b) the 1-D chain by the O–H ꢀ ꢀ ꢀ N hydrogen bonds of 1 (c) the 2-D
3
2
2
–
supramolecular sheet formed by C–H ꢀ ꢀ ꢀ N weak interactions of 1.
6
anion, the 1-D chain structure of complex 3
was similar to 2 (Fig. 3a). But complex 3 crystallizes in the triclinic
II
C(8) ꢀ ꢀ ꢀ N(9) and C(18) ꢀ ꢀ ꢀ N(3) are 3.416(5) and 3.415(4) Å, re-
spectively. Therefore, such chains are further assembled by the
C-H ꢀ ꢀ ꢀ N weak interactions between adjacent chains into an in-
finite 2-D supramolecular sheet (Fig. 1c).
space group P-1. The Co center lies in a slightly distorted octa-
1
hedral environment. Ligand L acts as a typical bridging ligand
II
coordinating to the Co ion, and the Co-N bond lengths are 2.110
(5) and 2.114(5) Å, respectively. The N-Co-N angel is 98.3(2)°,
which is smaller than that of 2, so the neighboring non-bonding
1
1
Co ꢀ ꢀ ꢀ Co distance (12.609 Å) connected by L is shorter than that
3
.2.2. {[Co(L )(H
2
O)
4
] ꢀ ClO
4 1
} (2)
2
–
in complex 2. Complex 3 as similar with 2, SiF
6
anions do not
Single crystal X-ray diffraction analysis reveals that complex 2
II
show any bonding interactions with Co centers, and only act as
counter anions for charge balance. The Co-O bond lengths are the
range of 2.077(5) to 2.147(4) Å in complex 3. It should be pointed
crystallizes in the orthorhombic space group C222(1). Complex 2
shows 1-D chain structure (Fig. 2a). The complex 2 contains one
Co cation, two L1 ligands, four coordinated H
two ClO
II
2
O molecules and
4
ˉ anions. Obviously, the structural difference of 1 and 2 is
1
II
out that N(5) and N(6) atoms of L are not coordinated to Co ion,
which present intermolecular O-H ꢀ ꢀ ꢀ N weak interaction with
1
attributable to the difference of coordination mode of ligand L .
The ligands L1 in complex 2 adopt bidentate bridging mode co-
coordinated H
2
O between the adjacent two chains [the O(2) ꢀ ꢀ ꢀ N
(
3
5) separation is 3.043(7) Å, the O(3) ꢀ ꢀ ꢀ N(6) separation is
II
II
ordinated to Co centers and extend to a 1-D chain. The Co ion
possesses a slightly distorted (CoN ) octahedral configuration,
which is coordinated by two N atoms originating from two distinct
2–
.066 Å] (Fig. 3b). Additionally, the uncoordinated SiF
6
anions
2 4
O
serving as counter anions locate at the cavities of the sheets and
form O-H ꢀ ꢀ ꢀ F hydrogen-bonding with the coordinated water
molecules to give a three-dimensional framework [O ꢀ ꢀ ꢀ F se-
parations are at the range of 2.637(7)– 3.146(10) Å, see also
Table 2 of Supplementary 1] (Fig. 3c).
1
L
ligands [The Co(1)-N(3) bond length is 2.155(7) Å] and four O
atoms from four distinct H O molecules [The Co(1)-O(1) bond
length is 2.172(6) Å. Co(1)-O(2) bond length is 2.069(7) Å]. The
2

J.-P. Li et al. / Journal of Solid State Chemistry 239 (2016) 251–258
255
Fig. 3. View of (a) 1-D supramolecular chain of 3 (H atoms omitted for clarity)
b) the 1-D chain by the C-H···N weak interactions of 3 (c) the three-dimensional
framework formed by O-H···F hydrogen-bonds of 3.
(
3
.2.4. {[Co(L1)
Complex 4 crystallizes in the trigonal space group R-3c. The
3
] ꢀ 2ClO
4 1
} (4)
II
complex 4 contains one crystallographically independent Co
center and three L1 ligands and two ClO
ˉ anions. The X-ray dif-
4
fraction analysis shows that complex 4 possesses 3-D network
1
structure (Fig. 4b). The same metal salt and ligand L were used to
prepared complexes 2 and 4, but obtained entirely different
structures. The main reason is that the solvent was different. The
II
1
Co center can be coordinated by six N atoms from six distinct L
ligands. which shows a slightly distorted octahedral geometry
(
II
Fig. 4a). The coordination angles around Co center are varying
from 89.62(9)° to 180.00(14)°, and the Co-N bond lengths are 2.162
ꢁ
(
2) Å. In addition, the uncoordinated ClO
4
anions were located in
the voids in the 3-D framework structure in order to keeping the
balance of charge instead of taking part in coordination (Fig. 4c).
II
1
Meanwhile, considering the Co centers linked by the L ligands,
the 3-D framework of complex 4 can be rationalized to be a
{
4 ^1 2.6 ^3 } 6-c topological net with the stoichiometry uninodal net
(Fig. 4d).
Fig. 4. View of (a) the coordination environment of CoΙΙ ions in 4 (b) the 3-D
2
3
.2.5. [Co(L )Cl
2
]
1
(5)
II
4
network of 4 (c) the ClO ˉ anions in 3-D network of 4 (d) topological view of 4 (Co
Single crystal X-ray diffraction analysis reveals that complex 5
acts as sixconnected node, just a Co center linked by L1 was considered) (H atoms
II
shows 1-D zigzag chain structure (Fig. 5). Complex 5 crystallizes in
the orthorhombic space group P2(1)2(1)2(1). The complex 5 con-
tains one Co center, two neutral L ligands and two Cl anions.
omitted for clarity).
II
2
ꢁ

256
J.-P. Li et al. / Journal of Solid State Chemistry 239 (2016) 251–258
II
topology (Fig. 6c). The complex 6 contains a Co center, two
2
2–
neutral L ligands, one uncoordinated SiF
6
. Compared with
II
complexes 1–4, the Co centers adopt a distorted tetrahedral co-
ordinated geometry in complexes 5 and 6. The reason is that the
steric hindrance of benzimidazole-ring is larger than that of imi-
dazole-ring.
In complex 6, the Co center is coordinated to four N atoms
from four distinct L ligands [The Co-N bond lengths are 1.996
II
2
(
5) Å] to complete a distorted tetrahedral coordinated geometry
Fig. 5. View of the 1-D zigzag chain structure of 5 (H atoms omitted for clarity).
and the coordination angles 108.50(7) and 111.43(15)°, respec-
tively (Fig. 6a and Table 1 of Supplementary 1). Each L ligand links
two Co ions and in turn each Co ion connects four ligands
forming a layer structure with (4, 4) foursquare grid units.
Meanwhile, all the Co ions are located in one plane (Fig. 6b). From
Fig. 6b, we can see that each (4, 4) grid unit is constructed by four
ligands acting as four edges and four Co ions as four vertexs. All
the lengths of the edges are equal (the edges are 12.574 Å) and the
orthogonal distance is 17.782 Å. The uncoordinated SiF6
serving as counter anions are located in the cavities of the sheets.
In complex 6, the both dihedral angles between planes A and B, C
and B are 29.8°, while the dihedral angles between planes A and C
are 59.6° (Fig. 6a). The two kinds of dihedral angles are larger than
those in complex 5.
2
In complex 5, the CoII center adopts a distorted tetrahedral
II
II
coordinated geometry coordinated to two N atoms from two dis-
2
ꢁ
tinct L ligands and two Cl anions. The Co-N bond lengths are
.021(3) and 2.031(3) Å, respectively. The Co(1)-Cl(1) bond length
II
2
is 2.2279(12) Å, Co(1)-Cl(2) bond length is 2.2389(11) Å. The
neighboring non-bonding Co ꢀ ꢀ ꢀ Co distance is 12.819(7) Å, which
is shorter than the length of 2, longer than that of 3. In the 1-D
II
2
ꢁ
anions
2
zigzag chain, the angle of Co ꢀ ꢀ ꢀ Co ꢀ ꢀ ꢀ Co linked by the L ligands
is 71.620(4)°. The bond angle of N-Co-N is 105.59(14)°. The angles
ꢁ
N-Co-Cl are ranging from 101.37(10)° to 114.11(10)°. The Cl an-
ions not only take part in coordination but also serve as counter
anions. All the L2 ligands are equivalent in complex 5. The pyr-
idazine ring and two benzimidazole rings are not on the same
plane in the one L2 ligand. The both dihedral angles between
planes A and B, C and B are 15.6°, the dihedral angle between
planes A and C is 24.8° (Fig. 5).
3.3. Thermal stabilities and powder X-ray diffraction of the
complexes
To examine the thermal stabilities of complexes 1–6, the TGA
analyses of complexes 1–6 were carried out from room tempera-
3
.2.6. {[Co(L2)
Complex 6 crystallizes in the tetragonal with space group P4
2)/n. Complex 6 is a rhombohedral grid (Fig. 6b) with a (4, 4)
2
] ꢀ SiF
6 1
} (6)
ꢁ
1
ture to 1000 °C at the rate of 10 °C ꢀ min in nitrogen atmosphere,
(
as shown in Fig. S1 of Supplementary 2. The TGA study of
Fig. 6. View of (a) the coordination environment of CoΙΙ ions in 6 (b) 2-D (4,4) network. structure of 6 (H atoms omitted for clarity).

J.-P. Li et al. / Journal of Solid State Chemistry 239 (2016) 251–258
257
complexes 1-6, the weight loss is observed owing to the direct
decomposition of coordinated water molecule and organic ligands,
and continues to lose weight up to 1000 °C, indicating the con-
tinuous expulsion of organic moieties even at the upper limit of
the measurement range. The TGA curve indicates the weight loss
of 1 can be divided into two steps. The first step shows a slow
weight loss from 25 °C to 145 °C, then the removal of organic li-
gands occurs within the range of 255–975 °C. The TGA curve of 2
displays a weight loss of 15.36% (Calcd. 13.28%) in the range of 25–
heterogeneous system for purifying water by thoroughly decom-
posing organic pollutants [29]. In this work, we take the advantage
of complexes 1–6 degrading methylene blue (MB), whose char-
acteristic absorption band is 664 nm. The photocatalytic reactions
were performed as follow process: 50 mg of the title complexes
was dispersed in 50 mL aqueous solution of MB (10 mg ꢀ L ) un-
der stirring in the dark for 30 min to ensure the equilibrium of the
mixed solution. Then the mixed solution was exposed to UV ir-
radiation from an Hg lamp (300W) and kept under continuous
stirring during irradiations for 6 h. Samples of 4 mL were taken
every 30 min for analysis. The final results show that the de-
gradation rate (deduct the self-degradation) of MB is 25.1% for 1,
ꢁ
1
162 °C corresponded to the loss of four coordinated water mole-
cules. A weight loss is observed, which can be attributed to the
decomposing of the organic ligands from 162 °C to 984 °C. The
TGA curve of complex 3 shows that 3 is stable up to 93 °C and
above that loss of organic ligands is observed. The TGA curve of
complex 4 shows that a fast weight loss from 50 °C to 830 °C.
Complexes 5 and 6 lose weight at about 397 °C and 230 °C to
16.8% for 2, 28.5% for 4, 15.4% for 5, 10.1% for 6. The curves of ab-
sorbance of the MB solution degraded by 1–6 of under UV light are
shown Fig. S1 of Supplementary 4. The absorption spectra of the
MB solution during the decomposition reaction under UV irra-
diation is shown Fig. S3 of Supplementary 4. When no catalyst was
added, the degradation rate of MB is 54.8% within 6 h under UV
irradiation. However, complex 3 can restrain the photodegradation
of dyes. The results indicate that complexes 1, 2 and 4–6 show
photocatalytic activity for the degradation of MB. The photo-
973 °C and 980 °C, respectively, which demonstrates that com-
plexes 5 and 6 are stable up to 230 °C. So the thermal stabilities of
complexes 5 and 6 are better than complexes 1–4, which indicates
their thermostabilities are enhanced by aromatic ring.
To confirm whether the crystal structures are truly re-
presentative of the bulk materials, X-ray powder diffraction
2
catalytic activity of TiO have been reported in literature [30].
Compared with TiO2, the degradation ability of the complexes is
weaker than that of TiO2.
(
XRPD) experiments were carried out for complexes 1–6. The
XRPD experimental and computer-simulated patterns of the cor-
responding complexes are shown in Fig. S2 of Supplementary 2.
Although the experimental patterns have a few unindexed dif-
fraction lines and some are slightly broadened in comparison with
those simulated from the single crystal modes. It still can be
considered favorably that the bulk synthesized materials and the
as-grown crystals were homogeneous for 1–6.
The possible photocatalytic mechanism for the above de-
gradation reactions is proposed as follows, (Fig. S2 of Supple-
mentary 4). Generally, the catalyst can be photo-activated by a
photon with irradiation energy equal to or higher than its band
ꢁ
gap energy (Eg), electrons (e ) in the valence band (VB) of title
complexes are excited to the conduction band (CB) at the photo-
þ
catalytic surface which generate same amount of holes (h ) in the
3.4. Luminescent property of the complexes
ꢁ
VB. Then O
2
ꢁ
may be reduced into O
2
by the combination of
electrons (e ), which may further turn into hydroxyl radicals
OH). Meanwhile, interaction of holes (h ) with hydroxyl (OH )
may generate the OH active radicals. As we all know, the OH
active works as a strong oxidizing agent to decompose MB effec-
tively and complete the photocatalytic process [31].
The solid-state photoluminescence property of complexes 1–6
1
2
þ
ꢁ
as well as the ligands L and L were investigated at room tem-
(·
1
perature (Supplementary 3). The free ligand L exhibits blue
·
·
fluorescent emission band at 403 nm upon excitation at 247 nm,
which can be originated from ligand center electronic transitions,
that is, the n-
π
* or
π
- * transition in nature according to the
π
reported literature [24]. Upon excitation with 250 nm light, com-
plexes 1–4 display fluorescent emission bands at 403, 403, 406
and 395 nm, respectively. The results reveal that the peaks of the
4. Conclusion
1
emission spectra for 1–3 are very close to that of the free ligand L ,
In conclusion, we have successfully synthesized and char-
which can probably be attributed to the intraligand electronic
transition [25]. The slightly blue shift of emission peak occurs in
complex 4, which is probably due to the coordination environment
II
acterized a series of new Co complexes with two structurally
1
related ligands, 3,6-bis(N-imidazolyl) pyridazine (L ) and 3,6-bis
2
(
N-benzimidazolyl) pyridazine (L ). The influences of the structure
II
around Co center. Since the photoluminescence behavior is clo-
II
of ligands on the resultant structures of Co complexes are briefly
discussed. Some intra-molecular and/or inter-molecular weak in-
teractions, such as hydrogen bonding, also play important role in
the formation of these complexes, especially in the aspects of
linking the discrete subunits and low-dimensional entities into
high-dimensional supramolecular networks. Moreover, the fluor-
sely associated with the metal ions and the ligands coordinated
around it [26].
2
1
The conjugate aromatic rings of L are larger than that of L , so
2
the ligand L presented emission bands at 469 nm excited bands at
370 nm. Complexes 5 and 6 display fluorescent emission bands at
4
46 and 408 nm upon excitation at 370 and 250 nm, respectively.
1
2
escence property of ligands L , L and part of complexes display
blue fluorescent emission at room temperature. The photocatalytic
activity of complexes 1–6 proved that they may be photocatalysts
for degradation of organic dyes in a certain extent. This approach
Complexes 5 and 6 reveal similar blue shifts of the emission peak,
which also attributed to intraligand electronic transition [27] and
2
decrease of planarity of L . The decreased degree in 6 is larger than
that in 5. The luminescent differences between 5 and 6 may be
probably assigned to the differences of coordination environment
and the solvent molecules. The enhance of luminescence efficiency
can be attributed to the ligand coordination to the metal center,
which enhances the rigidity of the ligand and thus reduces the loss
of energy through a radiationless pathway [28].
II
may be useful for the construction of a variety of new Co metal
complexes that have the potential of fluorescent or photocatalytic
activity.
Acknowledgments
3.5. Photocatalytic activity
This work was financially supported by the National Natural
Most of the photocatalytic reactions taken place in the
Science Foundation of China (No. 21361026).

258
J.-P. Li et al. / Journal of Solid State Chemistry 239 (2016) 251–258
Appendix A. Supporting information
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