Synthesis, crystal structure and surface photo-electric property of a series of Co(II) coordination polymers and supramolecules

Article abstract of DOI:10.1016/j.ica.2011.09.040

Four new Co(II) coordination complexes, [Co(o-phta)(pz)₂] _n 1, [Co(PTA)₂(Imh)₂]·(HPTA) ·H₂O 2, {[Co(pdc)₂(H₂O)]·(ppz) ·2H₂O}_n 3, [K₂Co₂(ox)(btec) (CH₃OH)₂]_n 4, (H₂phta = o-phthalic acid, pz = pyrazole, HPTA = p-toluic acid, ppz = piperazine, Imh = imidazole, H₂pdc = pyridine-2,5-dicarboxylic acid, H₂(ox) = oxalic acid, H₄btec = 1,2,4,5-benzenetetracarboxylic acid), were hydrothermally synthesized and characterized by X-ray single crystal diffraction, IR, UV-Vis absorption spectrum, TG analysis and elemental analysis. The surface photovoltage properties of the four Co(II) complexes were investigated by the surface photovoltage spectroscopy (SPS). The structural analyses indicate that complexes 1 and 3 are 1D coordination polymers and complex 2 is a mononuclear molecular complex. Complexes 1, 2 and 3 are connected into 2D supramolecules by hydrogen bonds, respectively. Complex 4 is a coordination polymer with 3D structure, exhibiting a 4-nodal(4,5,6,12)-connected topology with a Schlaefli symbol of (4¹⁰)₂(4 ²⁴·6³²·8¹⁰)(4⁵· 6)₂(4⁹·6⁵·8). The results of SPS show the four complexes exhibit obvious photovoltaic responses in 300-800 nm, which indicates they all possess photo-electric conversion properties. By the comparative analysis of the SPS, it is found that structure of the complex, species of ligand and coordination micro-environment of the Co(II) ion affect the SPS. The relationships between SPS and UV-Vis absorption spectra are discussed.

Full text of DOI:10.1016/j.ica.2011.09.040

Inorganica Chimica Acta 379 (2011) 44–55
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Inorganica Chimica Acta
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Synthesis, crystal structure and surface photo-electric property of a series
of Co(II) coordination polymers and supramolecules
⇑
Jing Jin, Dan Li, Lei Li, Xiao Han, Shengmei Cong, Yuxian Chi, Shuyun Niu
School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 July 2011
Received in revised form 2 September 2011
Accepted 16 September 2011
Available online 22 September 2011
Four new Co(II) coordination complexes, [Co(o-phta)(pz)2]n 1, [Co(PTA)2(Imh)2]ꢀ(HPTA)ꢀH2O 2, {[Co(pd-
c)2(H2O)]ꢀ(ppz)ꢀ2H2O}n 3, [K2Co2(ox)(btec)(CH3OH)2]n 4, (H2phta = o-phthalic acid, pz = pyrazole, HPTA =
p-toluic acid, ppz = piperazine, Imh = imidazole, H2pdc = pyridine-2,5-dicarboxylic acid, H2(ox) = oxalic
acid, H4btec = 1,2,4,5-benzenetetracarboxylic acid), were hydrothermally synthesized and characterized
by X-ray single crystal diffraction, IR, UV–Vis absorption spectrum, TG analysis and elemental analysis.
The surface photovoltage properties of the four Co(II) complexes were investigated by the surface photo-
voltage spectroscopy (SPS). The structural analyses indicate that complexes 1 and 3 are 1D coordination
polymers and complex 2 is a mononuclear molecular complex. Complexes 1, 2 and 3 are connected into
2D supramolecules by hydrogen bonds, respectively. Complex 4 is a coordination polymer with 3D struc-
ture, exhibiting a 4-nodal(4,5,6,12)-connected topology with a Schläfli symbol of (410)2(424ꢀ632ꢀ810)(45ꢀ6)2
(49ꢀ65ꢀ8). The results of SPS show the four complexes exhibit obvious photovoltaic responses in 300–
800 nm, which indicates they all possess photo-electric conversion properties. By the comparative
analysis of the SPS, it is found that structure of the complex, species of ligand and coordination micro-
environment of the Co(II) ion affect the SPS. The relationships between SPS and UV–Vis absorption
spectra are discussed.
Keywords:
Co(II) coordination polymer
Synthesis
Structure
Surface photo-electric property
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
phthalocyanine complexes. In fact, some special functions of
transition metal complexes are associated with their electron
The extensive studies of transition metal complexes with the li-
gands of aromatic carboxylic acid indicate that they possess poten-
tial applications in materials, medicine synthesis, electrochemistry,
biochemistry and many other fields. Therefore, in recent years, the
studies on the design, synthesis, structural analysis and property of
carboxylic acid coordination polymers have been becoming a very
active comprehensive subject [1–6]. Cobalt complexes aroused
extensive attentions in the coordination chemistry due to the var-
iable oxidation states and coordination geometries of cobalt ions,
and cobalt complexes possess important academic significance
and wide applications in magnetism, catalysis, biochemistry, etc.
In the recent years, many cobalt complexes were reported. For
example, Pochodylo et al. [7] reported a 2D coordination polymer
{[Co3(tBuip)2 (HtBuip)2(bpmp)]ꢀbpmp}n with ferromagnetic prop-
erties. Ma et al. [8] reported the structure of [Co3(NCS)6(admtrz)4
(H2O)2]ꢀ2H2O and found that there is weak antiferromagnetic
interaction between the Co(II) ions. Losse et al. [9] reported a series
of cobalt complexes and studied the catalytic properties. Nas et al.
[10] reported the antibacterial biological activity of the Co(II)
behaviors. For instance, the electrons transfer between different
components of complexes can cause oxidation and reduction pro-
cesses, which may be correlated with catalytic function. The
change of electron arrangement, coupling and exchange may give
rise to different magnetic properties. The separation and transfer
of photogenerated charges under light-inducement may lead to
the voltage or current on the solid surface, which is photo-electric
conversion. Obviously, ascertaining surface electron behaviors of
complexes is very significant for deep research on properties and
exploiting applications of transition metal complexes. Surface
photovoltage spectroscopy (SPS) is a high sensitive detection tool
and it not only relates to the charge transition process under light
inducement but also reflects directly the separation and transition
of photogenerated charges. This technique has been successfully
applied in the study of the charge transfer in photo-stimulated sur-
face interactions, dye sensitization processes, photo-catalysis and
the process of charge transition between surfaces and inter-phases
of solid materials [11–17]. Recently, our group has reported the
surface electron behaviors and photo-electric conversion proper-
ties of transition metal complexes involving nickel, manganese,
iron and cobalt. Some preliminary results have been obtained
[18–27]. In order to compare and study photo-electric property
⇑
Corresponding author. Tel.: +86 411 82159044; fax: +86 411 82158977.
E-mail address: syniu@sohu.com (S. Niu).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.09.040

J. Jin et al. / Inorganica Chimica Acta 379 (2011) 44–55
45
of cobalt complexes with different aromatic carboxylic acid li-
gands, the four Co(II) coordination complexes were synthesized
in this paper and the influence of ligand and structure on surface
photo-electric properties was discussed by SPS.
2.2.2. [Co(PTA)2(Imh)2]ꢀ(HPTA)ꢀH2O 2
A solution of Co(NO3)2ꢀ6H2O (0.15 g, 0.50 mmol) in water
(10 mL) was added to an ethanol (5 mL) and water (10 mL) solu-
tion of HPTA (0.28 g, 2.0 mmol), and then a water (8 mL) solution
of Imh (0.07 g, 1.0 mmol) was added into the above solution. The
color of the solution turned to purple, and pH value is 5.0. The mix-
ture was then transferred into a Teflon-lined stainless steel vessel
that was sealed and heated to 110 °C for 5 days. Cooled to room
temperature, purple crystals of complex 2 were collected (0.12 g;
Yield, 40% based on Co). Anal. Calc. for C30H32N4O7Co: C, 58.16;
H, 5.21; N, 9.04; Co, 9.51. Found: C, 57.90; H, 5.22; N, 9.02; Co,
2. Experimental
2.1. Materials and apparatus
All chemicals were of A.R. grade without further purification.
Single-crystal X-ray diffraction data were collected with Bruker
Smart APEX II CCD diffractometer. SPS were performed on a
home-built surface photovoltage spectrophotometer in the 300–
800 nm. IR spectra were recorded as KBr pellets with a JASCO
FT-IR/480 spectrophotometer in the 4000–220 cmꢁ1 region and
UV–Vis diffuse reflectance spectra were recorded with a JASCO
V-570 UV–Vis–NIR spectrophotometer in the 200–2500 nm. The
elemental analyses were detected on a PE-240C Analyzer and
TLASMA-II ICP instrument. Thermogravimetric (TG) analyses were
performed under N2 atmosphere on a Perkin–Elmer Pyris Diamond
9.35%. IR (KBr, cmꢁ1): 3246(
2957, 2920( C–H); 2860, 2626(
m
O–H); 3151(
O–Hꢀ ꢀ ꢀO); 2514(
1557(masðCOO Þ); 1389(msðCOO Þ); 1610, 1594, 1500(mC C); 1329,
m
N–H); 3066, 3031(
m
Ar–H);
m
ꢁ
m
m
N–Hꢀ ꢀ ꢀO); 1678(
mC@O);
ꢁ
. . .
•
1309(dN–H); 1285, 1212(dC–H); 1176, 1137, 1170(mC–C
953, 849(dN–Hꢀ ꢀ ꢀO); 656, 623, 756, 695(dAr–H); 566, 526, 470(
417, 374( Co–N).
,
mC–O
,
m
C–N);
m
Co–O);
m
2.2.3. {[Co(pdc)2(H2O)]ꢀ(ppz)ꢀ2H2O}n
3
A solution of CoCl2ꢀ6H2O (0.12 g, 0.50 mmol) in water (10 mL)
was added to a solution of H2pdc (0.09 g, 0.50 mmol) and NaOH
(0.08 g, 2.0 mmol) in water (10 mL), then an ethanol (5 mL) solu-
tion of ppz (0.09 g, 0.50 mmol) was added into the above solution.
The color of the solution turned deep pink, and the pH value was
adjusted to 6.0. Then the mixture was transferred into a Teflon-
lined stainless steel vessel, and the vessel was sealed and heated
to 120 °C for 5 days. Cooled to room temperature, pink crystals of
complex 3 were collected (0.10 g; Yield, 36% based on Co). Anal.
Calc. for C18H22N4O11Co: C, 40.84; H, 4.19; N, 10.58; Co, 11.13.
Found: C, 40.68; H, 4.20; N, 10.53; Co, 10.96%. IR (KBr, cmꢁ1):
TG/DTA instrument with a heating rate of 10 °Cminꢁ1
.
2.2. Synthesis of complexes 1, 2, 3 and 4
2.2.1. [Co(o-phta)(pz)2]n
1
A solution of Co(NO3)2ꢀ6H2O (0.15 g, 0.50 mmol) in water
(10 mL) was added to a methanol (2.5 mL) and water (7.5 mL) solu-
tion of H2-phta (0.20 g, 1.0 mmol), and then a methanol (5 mL) and
water (5 mL) solution of pz (0.14 g, 2.0 mmol) was added into the
above solution. The color of the solution turned to purple, and pH
value is 5.0. The mixture was then transferred into a Teflon-lined
stainless steel vessel that was sealed and heated to 160 °C for
4 days. Cooled to room temperature, purple crystals of complex 1
were collected (0.07 g; Yield, 39% based on Co). Anal. Calc. for
3389(
2514, 2465(
m
O–H); 3225(
mN–H); 3013 (mAr–H); 2817, 2756 (mC–H); 2601,
ꢁ
ꢁ
m
O–Hꢀ ꢀ ꢀO); 1581(masðCOO Þ); 1404(msðCOO Þ); 1602, 1543,
1476, 1458(mC C); 1354(dC–H); 1331, 1307(dN–H); 1169, 1092,
. . .
1033(mC–C
,
mC–O
,
•mC–N); 835, 759, 690(dAr–H); 570, 523, 453(
mCo–O);
415, 374(mCo–N).
C
14H12N4O4Co: C, 46.81; H, 3.37; N, 15.60; Co, 16.41. Found: C,
46.68; H, 3.38; N, 15.53; Co, 16.20%. IR (KBr, cmꢁ1): 3202
2.2.4. [K2Co2(ox)(btec)(CH3OH)2]n
4
(
m
N–Hꢀ ꢀ ꢀO); 3148, 3121(
m
N–H); 3073, 3014(
m
Ar–H); 2944(
m
C–H); 1604,
A
solution of CoCl2ꢀ6H2O (0.12 g, 0.50 mmol) and K2C2O4
ꢁ
ꢁ
1559(mC C); 1583(masðCOO Þ); 1399(msðCOO Þ); 1517, 1488(dN–H);
(0.18 g, 1.0 mmol) in water (5 mL) was added to a solution of
H4btec (0.13 g, 0.50 mmol) in methanol (5 mL). The color of the
solution turned to pink, and the pH value was adjusted to 6.0.
The mixture was transferred into a Teflon-lined stainless steel
. . .
•
1478, 1446(dC–H); 1167, 1142, 1085, 1070, 1047(mC–C
777, 752, 706, 654, 619, 607(dAr–H); 566, 482(
360( Co–N).
,
m
mC–O
Co–O); 455,
,
m
C–N);
m
Table 1
Summary of data collections and structure refinements for complexes 1–4.
1
2
3
4
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C
14H12CoN4O4
C30H32CoN4O7
619.53
293(2)
C18H22CoN4O11
529.33
293(2)
0.71073
monoclinic
P21/c
13.1739(15)
11.9326(13)
13.7668(16)
90
100.455(2)
90
2128.2(4)
4
1.652
C7H5CoKO7
299.14
293(2)
0.71073
monoclinic
P21/n
7.162(10)
14.312(19)
8.066(11)
90
102.251(18)
90
808.0(19)
4
2.459
359.21
293(2)
0.71073
monoclinic
P21/c
8.1825(19)
16.626(4)
11.621(3)
90
101.102(3)
90
1551.4(6)
4
0.71073
triclinic
ꢀ
P1
9.5393(17)
11.796 (2)
14.636(3)
76.228(2)
88.585(2)
77.190(2)
1559.1(5)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
Z
Dc (gcmꢁ3
F(000)
)
1.538
732
1.320
646
1092
596
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Reflections collected/unique
2728/0/208
1.076
5400/0/383
1.075
4013/0/307
1.063
1961/0/145
1.113
7644/2728
Rint = 0.0319
0.0386, 0.1118
0.0478, 0.1166
0.378 and ꢁ0.497
7836/5400
Rint = 0.0206
0.0446, 0.1257
0.0564, 0.1328
0.256 and ꢁ0.321
10851/4013
Rint = 0.0445
0.0552, 0.1523
0.0823, 0.1707
0.692 and ꢁ0.629
4916/1961
Rint = 0.0440
0.0740, 0.2308
0.1069, 0.2676
2.122 and ꢁ1.835
R1,wR2 [I > 2r(I)]
R1,wR2 (all data)
Largest difference in peak and hole (eÅꢁ3
)

46
J. Jin et al. / Inorganica Chimica Acta 379 (2011) 44–55
vessel, and the vessel was sealed and heated to 120 °C for 5 days.
Cooled to room temperature, pink crystals of complex 4 were col-
lected (0.06 g; Yield, 37% based on Co). Anal. Calc. for C7H5O7KCo:
C, 28.11; H, 1.69; Co, 19.70. Found: C, 27.98; H, 1.70; Co, 19.45%.
Co(II) ion is four-coordinate with O1 and O4A atoms from two dif-
ferent o-phta groups, N1 and N3 atoms from two different pz mol-
ecules, displaying distorted tetrahedral structure. The bond lengths
of Co–O are 1.965(2) and 1.969(3) Å and those of Co–N are 2.005(3)
and 2.010(3) Å. Although the two carboxyl of o-phta group are
deprotonated, only one O atom of each COOꢁ group involves in
the coordination. And only one N atom of each pz molecule in-
volves in the coordination and N atoms of –NH groups do not in-
volve in the coordination. In the asymmetric unit, the angle
between planes of two pz rings is 107.28(13)°.
IR (KBr, cmꢁ1): 3559(
2856( C–H);
m
O–H); 3346(
m
OHꢀ ꢀ ꢀO); 3049(
m
Ar–H); 2923,
1496,
C–O); 869,
K–O).
ꢁ
ꢁ
m
1582(masðCOO Þ);
1436(mC C); 1335(dO–H); 1309(dC–H); 1163, 1141(mC–C, m
814, 782, 685(dAr–H); 587, 542, 499(
1393(msðCOO Þ);
1626,
. . .
•
mCo–O); 443, 317(
m
2.3. Determination of crystal structure
In the crystal, the o-phta groups link [Co(pz)2]2+ cations into a
1D chain along the c-axis (Fig. 2). In the 1D chain, the carboxyl O
atoms (O1 and O4) of o-phta group join in the connection of the
chain, but uncoordinated carboxyl O atoms (O2 and O3) did not
participate in the connection of the chain. The adjacent chains
are linked by the hydrogen bonds (N2–Hꢀ ꢀ ꢀO3, 2.876 Å) formed be-
tween the N atom (N2) of pz molecule and the uncoordinated car-
boxyl O atom (O3) of o-phta group along the b-axis (Fig. S1),
resulting in a 2D hydrogen-bonded layer in the bc plane (Fig. 3).
X-ray diffraction data of complexes were collected on the Bruker
APEX II CCD diffractometer with graphite-monochromated Mo K
a
radiation (k = 0.71073 Å) at 293(2) K. Empirical absorption correc-
tions were applied to the data. The structures were solved by the di-
rect methods and refined by full matrix least-squares method on F2.
All of the non-hydrogen atoms were refined anisotropically. The
hydrogen atoms of organic ligands were placed in calculated posi-
tions and refined isotropically with a riding model. All the structural
calculations and drawings were taken out with the SHELXL-97 crystal-
lographic software package. Further details of X-ray structural anal-
yses were given in Table 1. Selected bond lengths and angles were
summarized in Table S1 of the Supplementary Material.
3.2. The crystal structure of [Co(PTA)2(Imh)2]ꢀ(HPTA)ꢀH2O 2
Complex 2 is a mononuclear molecular complex (Fig. 4). It con-
sists of one Co(II) ion, two PTA groups, two Imh molecules, one free
HPTA molecule and one lattice water molecule. The Co(II) ion is
four-coordinate with two N atoms (N1 and N3) from two different
Imh molecules and two O atoms (O1 and O3) from two different
PTA groups, forming a distorted tetrahedral geometry. The bond
lengths of Co–O are 1.963(2) and 1.972(2) Å and those of Co–N
are 1.992(2) and 1.993(3) Å.
In the crystal, the adjacent molecules are linked by a lot of
hydrogen bonds (N–Hꢀ ꢀ ꢀO and O–Hꢀ ꢀ ꢀO) as follows: the hydrogen
bond (N2–Hꢀ ꢀ ꢀO2, 2.788 Å) between N atom of Imh and O atom
of PTA, the hydrogen bond (N4–Hꢀ ꢀ ꢀO5, 2.966 Å) between N atom
of Imh and O atom of free HPTA, the hydrogen bond (O6–Hꢀ ꢀ ꢀO7,
2.571 Å) between O atom of free HPTA and O atom of lattice water,
the hydrogen bond (O7–Hꢀ ꢀ ꢀO4, 2.757 Å, O7–Hꢀ ꢀ ꢀO2, 2.733 Å) be-
tween O atom of lattice water and O atom (O2 and O4) of PTA.
Those hydrogen bonds connect the molecules along the b-axis,
forming a hydrogen-bonded 1D chain (Fig. S2). Simultaneously,
the adjacent 1D chains are further connected by hydrogen bonds
(N4–Hꢀ ꢀ ꢀO5, 2.966 Å, O6–Hꢀ ꢀ ꢀO7, 2.571 Å, O7–Hꢀ ꢀ ꢀO4, 2.757 Å,
O7–Hꢀ ꢀ ꢀO2, 2.733 Å) along the a-axis (Fig. S3). As a result, a 2D
hydrogen-bonded layer is formed for 2 (Fig. 5).
3. Results and discussion
3.1. The crystal structure of [Co(o-phta)(pz)2]n
1
Complex 1 is a coordination polymer with 1D chain structure
bridged by o-phta groups. The asymmetric unit consists of one
Co(II) ion, one o-phta group and two pz molecules (Fig. 1). The
3.3. The crystal structure of {[Co(pdc)2(H2O)]ꢀ(ppz)ꢀ2H2O}n
3
Complex 3 is a coordination polymer bridged by pdc2ꢁ with 1 D
structure. The asymmetric unit comprises one Co(II) ion, two
pdc2ꢁ, one coordinated water molecule, one free ppz molecule
Fig. 1. The asymmetric unit of complex 1.
Fig. 2. The 1D infinite chain of complex 1 along c-axis.

J. Jin et al. / Inorganica Chimica Acta 379 (2011) 44–55
47
Fig. 3. The 2D hydrogen-bonded layer of complex 1 on bc plane.
3.4. The crystal structure of [K2Co2(ox)(btec)(CH3OH)2]n
4
Complex 4 is a coordination polymer bridged by btec4ꢁ and
ox2ꢁ groups with 3D structure. The asymmetric unit consists of
one Co(II) ion, one K(I) ion, one-second of ox2ꢁ, one-second of
btec4ꢁ and one methanol molecule (Fig. 10). The central Co(II)
ion is six-coordinate with four O atoms from four different btec4ꢁ
and two O atoms from one ox2ꢁ, forming a slightly distorted octa-
hedral geometry (Fig. S6). O1A, O3A, O5 and O6A atoms construct
the equatorial plane and O2 and O4A atoms occupy the axial posi-
tion. The bond lengths of Co–O are 2.176(5)–2.240(5) Å. The K(I)
ion is seven-coordinate with two O atoms from one btec4ꢁ group,
one O atom from another btec4ꢁ group, two O atoms from two
ox2ꢁ group and left two O atoms from two methanol molecules
(Fig. S7). The bond lengths of K–O are 1.866(11)–3.248(6) Å. The
coordination mode of K(I) is rare. The Co(II) and K(I) ions are
bridged by btec4ꢁ and ox2ꢁ groups (Fig. 11). The btec4ꢁ is all depro-
tonated, and its eight O atoms all participate in coordination to
connect eight Co(II) ions and four K(I) ions (Fig. S8). Four O atoms
of ox2ꢁ all involve in the coordination, bridging two Co(II) ions and
four K(I) ions (Fig. S9).
Fig. 4. Molecular structure of complex 2.
and two lattice water molecules (Fig. 6). The central Co(II) ion is
six-coordinate with two N atoms and two O atoms from two differ-
ent pdc2ꢁ, one O atom from the coordinated water molecule, an-
In the crystal, the K(I) and Co(II) ions are connected into a 1D
chain by the btec4ꢁ group along the c-axis (Fig. S10). The adjacent
1D chains are connected by the ox2ꢁ groups along b-axis, so a 2D
layer is formed in the bc plane (Fig. 12).
other
O atom from a a slightly distorted
pdc2ꢁ forming
octahedral geometry (Fig. 7). The equatorial plane is made up of
O3, N3, O1 and N4 atoms, and the axial position is occupied by
O8 and O9 atoms. The bond lengths of Co–O are 2.058(3)–
2.132(3) Å and those of Co–N are 2.137(4) and 2.138(3) Å. The
two pdc2ꢁ anions bond to Co(II) ions in two different coordination
modes. The first one is that the pyridine N atom together with its
neighboring one O atom of COOꢁ group of pdc2ꢁ anion chelate
one Co(II) ion, and the other COOꢁ group coordinates to another
Co(II) ion in the type of unidentate coordination (Fig. S4). In the
second one, only the N atom and its neighboring COOꢁ group coor-
dinate to one Co(II) ion, but the other carboxyl does not join in the
coordination (Fig. S5).
TheCo(II) ions are also connectedinto 1D double chain by the car-
boxyl O atoms of btec4ꢁ groups by monodentate mode along the a-
axis (Fig. 13). As a result, a 3D structure is formed for 4 (Fig. 14). From
the topological view, in the 3D framework structure of complex 4,
the btec4ꢁ ligand connecting eight Co(II) ions and four K(I) ions
can be considered as a 12-connected node, ox2ꢁ ligand as a 6-con-
nected node, the Co(II) ion as a 5-connected node, the K(I) ion as a
4-connected node, respectively. As a result, the framework of 4
can be reduced to a 4-nodal(4,5,6,12)-connected topology with a
Schläfli symbol of (410)2(424ꢀ632ꢀ810)(45ꢀ6)2(49ꢀ65ꢀ8) (Fig. 15 and
Fig. S11). For comparison and more clarity, in the 3D framework
neglecting K(I) ion, the btec ligand can be regarded as an
In the crystal, firstly, the Co(II) ions are linked by pdc2ꢁ groups
adopting the first coordination mode to form a 1D chain along the
b-axis (Fig. 8). The adjacent 1D chains are linked by the hydrogen
bonds (O9–Hꢀ ꢀ ꢀO7, 2.690 Å, O9–Hꢀ ꢀ ꢀO5, 2.636 Å) formed between
coordinated water molecules and uncoordinated carboxyl O atoms
of two pdc2ꢁ along the c-axis. As a result, a 2D hydrogen-bonded
layer is formed in the bc plane (Fig. 9).
8-connected node, ox ligand as
a 2-connected node, Co(II)
ion as a 5-connected node. Therefore, the framework of 4 becomes
a
3-nodal (2,5,8)-connected net with a Schläfli symbol of
(412ꢀ612ꢀ84)(48ꢀ62)2(4)(Fig. 16 and Fig. S12), which, to the best of
our knowledge, is a new topology type.

48
J. Jin et al. / Inorganica Chimica Acta 379 (2011) 44–55
Fig. 5. The 2D hydrogen-bonded layer of complex 2 on ab plane.
band transition (or sub-gap transition), while the electron transi-
tion between d orbitals of central metal ions is called impurity
transition.
3.5.1. The analysis and assignment of SPS and UV–Vis spectra of [Co(o-
phta)(pz)2]n
1
In the SPS of complex 1 (Fig. 17a), there is a wide and strong re-
sponse band with many overlapped bands within 300–800 nm.
Treated by program ORIGIN 7.0, the response band can be divided
into four response bands (kmax = 339, 375, 450, and 618 nm). In
the complex 1, the coordination micro–environment of Co(II) ions
is distorted Td geometry with CoN2O2 coordination mode, so the re-
sponse bands can be assigned as follows: the strong responses at
kmax = 339 and 375 nm are assigned to the band-to-band transition
arising from ligand-to-metal charge transfer transition (LMCT). Be-
cause there are different direct coordinated atoms (O and N) and
their electronegativity is different in the complex 1, the two LMCT
responses can be assigned to the O ? Co and N ? Co transitions,
respectively. The response bands (kmax = 450 and 618 nm) are as-
signed to the impurity transition responses corresponding to the
d ? d⁄ transitions of Co(II) ions (4A2 ? 4T1(P) and 4A2 ? 4T1(F)).
Another d ? d⁄ transition of Co(II) ions (4A2 ? 4T2) should appear
in the near infrared region and it beyonds the measurement scope
of SPS (300–800 nm), so it can not be observed.
Fig. 6. The asymmetric unit of complex 3.
3.5. The analysis and assignment of SPS and UV–Vis spectra of
complexes
There are six absorption bands in the UV–Vis absorption spec-
trum of complex 1 (Fig. 17b and Fig. S13). The band (kmax = 258 nm)
is assigned to
p ?
p⁄ transition of the ligand. The bands (kmax = 294
Seen from the UV–Vis absorption spectra of the four complexes
(Figs. 17b–20b), there are some wide and strong absorption bands.
These absorption bands nearly cover the entire UV–Vis region, and
the energies of the bands are in the range of bandgap energy of
semiconductor, so they can be seen as broad semiconductors. In
this paper, energy-band theory of semiconductor and crystal field
theory were combined to analyze and assign the SPS, i.e., 2s and
2p orbitals of direct coordinated atoms (O or N) form valence band,
and 330 nm) are assigned to the LMCT (O ? Co and N ? Co). The
bands at kmax = 520 and 572 nm are assigned to the d ? d⁄ transi-
tions of Co(II) ions (4A2 ? 4T1(P), 4A2 ? 4T1(F)), and the band at
kmax = 1130 nm is assigned to another d ? d⁄ transition of Co(II) ions
(4A2 ? 4T2) in the near infrared region. There is a good correspond-
ing relationship between SPS and UV–Vis spectra.
meanwhile conjugated
p
orbitals of the ligands also belong to va-
3.5.2. The analysis and assignment of SPS and UV–Vis spectra of
[Co(PTA)2(Imh)2]ꢀ(HPTA)ꢀH2O 2
lence band. Empty 4s and 4p orbitals of central metal ions as well
as p⁄ orbitals of ligands form conduction band and 3d orbitals of
the central metal ions are considered as impurity levels. The tran-
sition from valence band to conduction band is called band-to-
There is a wide and strong response band with many over-
lapped peaks in the SPS of complex
2 within 300–800 nm
(Fig. 18a). Treated by program ORIGIN 7.0, the response band can

J. Jin et al. / Inorganica Chimica Acta 379 (2011) 44–55
49
Fig. 7. The coordination environment of Co(II) ion in complex 3.
Fig. 8. The 1D infinite chain of complex 3 along b-axis.
Fig. 9. The 2D hydrogen-bonded layer of complex 3 on bc plane.

50
J. Jin et al. / Inorganica Chimica Acta 379 (2011) 44–55
be divided into four response bands. In the complex 2, the coordi-
nation micro-environment and coordination mode of Co(II) is sim-
ilar to those of complex 1. The strong responses at kmax = 357 and
385 nm are assigned to the band-to-band transition based on
LMCT. Because there are different direct coordinated atoms (O
and N) with different electronegativity, the two LMCT response
bands can be assigned to the O ? Co and N ? Co transitions,
respectively. The response bands (kmax = 501 and 649 nm) are as-
signed to the impurity transition responses corresponding to the
d ? d⁄ transitions of Co(II) ions (4A2 ? 4T1(P) and 4A2 ? 4T1(F)).
Another d ? d⁄ response band should appear in the near infrared
region.
There are six absorption bands in the UV–Vis absorption spec-
trum of complex 2 (Fig. 18b and Figs. S14 and S17). The band
Fig. 10. The asymmetric unit of complex 4.
(kmax = 262 nm) is assigned to p ?
p⁄ transition of the ligand. The
Fig. 11. The coordination environment of K(I) and Co(II) ions in complex 4.
Fig. 12. The 2D layer of complex 4 on bc plane.

J. Jin et al. / Inorganica Chimica Acta 379 (2011) 44–55
51
Fig. 13. The 1D infinite chain of complex 4 along a-axis.
Fig. 14. The 3D infinite structure of complex 4.
bands (kmax = 276 and 304 nm) are assigned to the LMCT (O ? Co
and N ? Co). The bands at kmax = 524 and 557 nm are assigned to
the d ? d⁄ transitions of Co(II) ions (4A2 ? 4T1(P), 4A2 ? 4T1(F)),
and the band at kmax = 1134 nm is assigned to another d ? d⁄ tran-
sition of Co(II) ions (4A2 ? 4T2) in the near infrared region. There is
a corresponding relationship between the SPS and UV–Vis spectra
in complex 2.
by program ORIGIN 7.0, the response band can be divided into four re-
sponse bands. The two response bands (kmax = 348 and 387 nm) are
assigned to the band-to-band transition responses based on LMCT.
Because there are different direct coordinate atoms (O and N) with
different electronegativity, the two LMCT response bands can be as-
signed to the O ? Co and N ? Co transitions, respectively. The re-
sponse bands (kmax = 453 and 548 nm) are assigned to the
impurity transition responses corresponding to the d ? d⁄ transi-
tions of Co(II) ions (4T1g(F) ? 4A2g, 4T1g(F) ? 4T1g(P)). In the complex
3, the Co(II) ion is six-coordinate with the coordination mode of
CoN2O4 and the distorted octahedral geometry. Therefore, the en-
ergy of d ? d⁄ response bands in complex 3 is higher than that in
complexes 1 and 2. However, the lowering in symmetry from a reg-
ular Oh to distorted Oh (CoN2O4) results in the splitting of the d ? d⁄
response bands in the 3.
It is noted that the wide d ? d⁄ response bands are extended to
700 nm and present splitting in the SPS of complexes 1 and 2,
which arise because the Co(II) ions in the complexes 1 and 2 are
distorted Td (CoN2O2) geometry. The decrease of symmetry of coor-
dination micro-environment of Co(II) ion results in the widening
and splitting of d ? d⁄ response bands.
3.5.3. The analysis and assignment of SPS and UV–Vis spectra of
{[Co(pdc)2(H2O)]ꢀ(ppz)ꢀ2H2O}n
3
There are six absorption bands in the UV–Vis absorption spec-
There is a wide and strong response band with many overlapped
trum of complex
3
(Fig. 19b and Fig. S15). The band
peaks in the SPS of complex 3 within 300–800 nm (Fig. 19a). Treated
(kmax = 256 nm) is assigned to
p ?
p⁄ transition of the ligand. The

52
J. Jin et al. / Inorganica Chimica Acta 379 (2011) 44–55
Fig. 17a. SPS of complex 1.
Fig. 15. The 4-nodal (4,5,6,12)-connected topology of complex 4 (red: btec node;
cyan: ox node; blue: Co node; green: K node).
Fig. 17b. UV–Vis spectrum of complex 1.
Fig. 16. The 3-nodal (2,5,8) connected topology of complex 4 (K(I) node is omitted
for clarity; red: btec node; cyan: ox node; blue: Co node).
bands (kmax = 334 and 352 nm) are assigned to the LMCT (O ? Co
and N ? Co). The bands at kmax = 456, 518, and 1172 nm are as-
signed to the d ? d⁄ transitions of Co(II) ions (4T1g(F) ? 4A2g
,
4
4T1g(F) ? 4T1g(P), T1g(F) ? 4T2g). The SPS and the UV–Vis is also
closely related.
Fig. 18a. SPS of complex 2.
3.5.4. The analysis and assignment of SPS and UV–Vis spectra of
[K2Co2(ox)(btec)(CH3OH)2]n
There is a wide and strong response band with several over-
lapped peaks in the SPS of complex within 300–800 nm
4
(Fig. 20a). Treated by program ORIGIN 7.0, the response band can
be divided into three response bands. The strong response at
kmax = 339 nm is assigned to the band-to-band transition based
4

J. Jin et al. / Inorganica Chimica Acta 379 (2011) 44–55
53
Fig. 20a. SPS of complex 4.
Fig. 18b. UV–Vis spectrum of complex 2.
Fig. 19a. SPS of complex 3.
Fig. 20b. UV–Vis spectrum of complex 4.
of Co(II) ions (4T1g(F) ? 4A2g 4T1g(F) ? 4T1g(P). In the complex 4,
,
the coordination mode of Co(II) is CoO6 with octahedral geometry.
Therefore, there is only one response band of LMCT (O ? Co) in the
SPS, and the two d ? d⁄ transition response bands are not split.
There are five absorption bands in the UV–Vis absorption spec-
trum of complex
(kmax = 260 nm) is assigned to
4
(Fig. 20b and Fig. S16). The band
p
?
p⁄ transition of the ligand. The
bands (kmax = 320 nm) are assigned to the LMCT (O ? Co). The
bands at kmax = 486, 560, and 1154 nm are assigned to the d ? d⁄
transitions of Co(II) ions (4T1g(F) ? 4A2g
,
4T1g(F) ? 4T1g(P),
4T1g(F) ? 4T2g). The SPS and the UV–Vis is also basically same.
3.6. Comparison and analyses of SPS of complexes
(1) There are obvious photovoltage response bands in the SPS of
complexes 1–4, which indicates that they all possess certain
photo-electric conversion properties. But the changes of
structure, the coordination micro-environment and the
coordination number of central metal ion can lead to the dif-
ference of the intensity and width of the SPS response bands.
(2) The SPS are associated with the UV–Vis absorption spectra.
And the number and the relative intensity of the response
bands in SPS are similar to those of the absorption bands
in UV–Vis spectra except limit of measurement scope of SPS.
Fig. 19b. UV–Vis spectrum of complex 3.
on LMCT of O ? Co. The response bands (kmax = 457 and 536 nm)
are assigned to the impurity transitions between d orbitals of
Co(II)(d7) ions, which are corresponded to the d ? d⁄ transitions

54
J. Jin et al. / Inorganica Chimica Acta 379 (2011) 44–55
(3) The species and number of direct coordination atoms of
calcd. 37.90%), corresponding to the removal of two organic pz
molecules. The second weight loss of 42.4% (calcd. 45.69%) in the
temperature range of 300–700 °C can be assigned to the release
of o-phta ligand. The TG curve of polymer 3 shows two steps of
weight loss. It first loses the coordinated and lattice water mole-
cules in the temperature range of 100–160 °C (obsd. 10.75%; calcd.
10.21%). Subsequently, a plateau region is observed from 160 to
300 °C. It keeps losing weight from 300 to 750 °C, ascribing to
the removal of ppz and bdc molecules. For polymer 4, it is ther-
mally stable up to 100 °C. Above this temperature, the TG curve
exhibits two weight-loss stages. The first weight loss of 10.13% be-
tween 100 and 300 °C is attributable to loss of the methanol mol-
ecules (calcd. 10.71%). The second weight loss occurred from 300 to
500 °C, attributed to the decomposition of organic ligand and the
collapsion of the structure [28]. From the observed weight loss
(29.78%), it corresponds to loss of the four CO2 molecules from
decomposition of btec4ꢁ ligands (calcd. 29.42%), therefore, the lat-
ter step of weight loss mainly is decomposition of organic ligand
and release of CO2.
complexes directly affect the results of the SPS. Firstly, the
different direct coordination atoms with different electro-
negativity result in the splitting of the band-to-band
responses bands based on LMCT. Secondly, the different spe-
cies of direct coordination atoms can decrease the symmetry
of coordination environment of the central metal ions, lead-
ing to the splitting, shifting and broadening of d ? d⁄ impu-
rity response bands. For example, there is one species of
coordinated atoms (i.e., O atom) in complex 4, so there is
one LMCT response band and the d ? d⁄ transition response
bands are not split and broadened. However, in the other
three complexes, the coordination modes of Co(II) ions are
CoN2O2 (1), CoN2O2 (2) and CoN2O4(3), respectively. So there
are two LMCT response bands (O ? Co and N ? Co), and the
splitting and broadening of the two d ? d⁄ response bands
are observed in SPS of complexes 1–3.
(4) The different coordination numbers of Co(II) (d7) ions lead to
the different symmetries of coordination environments,
which causes the d ? d⁄ transition response obviously dif-
ferent. The Co(II) ion is four-coordinate (ꢂTd geometry) in
complexes 1 and 2, and the d ? d⁄ transition response bands
are red shifted than those in complexes 3 and 4 (six-coordi-
nate, ꢂOh geometry). This arises because the energy differ-
ence between d orbitals in Td field (Dt) are less than that
in Oh field (Do). The phenomenon is obvious in both of SPS
and UV–Vis spectra.
(5) It is worthy of attention that if the Co(II) ion is four-coordi-
nate and the species of direct coordination atom is not
unique, the d ? d⁄ transition response bands will show
red-shifting, splitting and widening. This is very beneficial
for improving the photo-electric conversion efficiency due
to expanding the utilizing scope of visible-light.
4. Conclusions
Four Co(II) coordination complexes were synthesized and struc-
tures were determined by single-crystal X-ray diffraction. The
photo-electric properties were discussed by SPS. By comparison
and analysis, it is obvious: (1) Four complexes can be seen as broad
semiconductors and they all possess certain photo-electric conver-
sion ability. (2) The change of structure of complexes, the species
and number of direct coordination atoms and the symmetry of
coordination environment of the central metal affect the response
bands of SPS. (3) The decrease of symmetry of coordination envi-
ronment of the central metal can lead to shifting, splitting and wid-
ening of the response bands of SPS. This is favorable for improving
the photo-electric conversion efficiency and extending the utiliza-
tion scope of the visible-light.
3.7. TG analyses
Acknowledgement
The thermogravimetric analyses of complexes 1–4 were per-
formed under N2 atmosphere for numerous single crystal samples
in the temperature 25–900 °C (Fig. 21). The TG data show that
polymers 1, 3 and 4 are stable before 200 °C, displaying a good
thermal stability. But, complex 2 begins to decompose at 100 °C,
which shows that its thermal stability is not good like that of poly-
mers 1, 3 and 4. This may be because complex 2 is not a coordina-
tion polymer. The TG curve of polymer 1 shows that it is stable up
to 220 °C, and then loses weight from 220 to 300 °C (obsd. 37.01%,
The research was supported by National Natural Science Foun-
dation of China (20571037) and the Educational Foundation of Lia-
oning Province in China (2007T092).
Appendix A. Supplementary material
CCDC 830390, 830391, 830392 and 830393 contain the supple-
mentary crystallographic data for complexes 1, 2, 3 and 4, respec-
tively. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif, or email: deposit@ccdc.cam.ac.uk. Supplemen-
tary data associated with this article can be found, in the online
version, at doi:10.1016/j.ica.2011.09.040.
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