Structural characterization, electrochemical, photoluminescence and thermal properties of potassium ion-mediated coordination polymer

Article abstract of DOI:10.1016/j.saa.2015.01.114

(Chemical Equation Presented). A polymeric potassium complex of p-nitrophenol was synthesized and characterized by analytical and spectroscopic techniques. Molecular structure of the complex was determined by single crystal X-ray diffraction study. X-ray

Full text of DOI:10.1016/j.saa.2015.01.114

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 142 (2015) 8–14
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Structural characterization, electrochemical, photoluminescence and
thermal properties of potassium ion-mediated coordination polymer
a
a
b
Gökhan Ceyhan a, , Muhammet Köse , Mehmet Tümer , Hakan Dal
⇑
a Chemistry Department, K.Maras Sütcü Imam University, 46100 K.Maras, Turkey
b Chemistry Department, Anadolu University, 26470 Eskißsehir, Turkey
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
A novel polymeric potassium
complex of p-nitrophenol is reported.
Molecular structure of the complex
was determined by X-ray diffraction
technique.
ꢀ
Electrochemical and thermal
properties of the complex were
investigated.
a r t i c l e i n f o
a b s t r a c t
Article history:
A polymeric potassium complex of p-nitrophenol was synthesized and characterized by analytical and
spectroscopic techniques. Molecular structure of the complex was determined by single crystal X-ray dif-
fraction study. X-ray structural data show that crystals contain polymeric K+ complex of p-nitrophenol.
Asymmetric unit consists of one p-nitrophenolate, one K+ ion and one water molecule. All bond lengths
and angles in the phenyl rings have normal Csp2–Csp2 values and are in the expected ranges. The p-nitro-
phenolate is close to planar with small distortions by some atoms. Each potassium ion in the polymeric
structure is identical and eight-coordinate, bonded to four nitro, two phenolate oxygen atoms from five p-
nitrophenolate ligands and two oxygen atoms from two water molecules. Electronic, electrochemical,
photoluminescence and thermal properties of the complex were also investigated.
Received 30 October 2014
Received in revised form 21 January 2015
Accepted 30 January 2015
Available online 9 February 2015
Keywords:
p-Nitrophenol
Potassium complex
X-ray structure
Coordination polymer
Electrochemical
Photoluminescence
Ó 2015 Published by Elsevier B.V.
Introduction
substrate can be measured with a spectrophotometer at around
405 nm and used as a proxy measurement for the amount of the
p-Nitrophenol is a product of the enzymatic cleavage of several
substrates such as p-nitrophenyl acetate (used as a substrate for
carbonic anhydrase) and p-nitrophenyl-b-D-glucopyranoside and
other sugar derivatives which are used to assay various glycosidase
enzymes. Amounts of p-nitrophenol produced by a particular
enzyme (alkaline phosphatase) in the presence of its corresponding
enzyme activity in the sample. p-Nitrophenol shows two poly-
morphs in the crystalline state. The alpha-form is colorless pillars
and unstable at room temperature. The beta-form is yellow pillars
and stable at room temperature, and gradually turns red upon irra-
diation of sunlight. Usually, p-nitrophenol exists as a mixture of
these two forms [1]. Potassium complexes of p-nitrophenyl
compounds have been reported in literature [2–6]. Molecular
structure of potassium complex of p-nitrophenyl sulfate (PNPS)
was structurally characterized by X-ray diffraction study.
The crystal structure of the compound [K(PNPS)] contains
⇑
Corresponding author. Tel.: +90 3442801861; fax: +90 3442801881.
E-mail address: gceyhan@ksu.edu.tr (G. Ceyhan).
http://dx.doi.org/10.1016/j.saa.2015.01.114
1386-1425/Ó 2015 Published by Elsevier B.V.

G. Ceyhan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 142 (2015) 8–14
9
p-nitrophenylsulphate anions and potassium cations. Each K+ ions
Table 2
Hydrogen-bond geometry for the complex (Å, °).
is 8-coordinate with approximate square antiprism geometry [2].
In this study, polymeric potassium complex of p-nitrophenol
(KNP) was prepared and characterized by spectroscopic and ana-
lytical methods. Molecular structure of the complex was deter-
mined by single crystal X-ray diffraction study. Electronic and
electrochemical properties of the complex were also investigated.
D–HÁ Á ÁA
D–H
HÁ Á ÁA
2.00 (2)
1.97 (2)
DÁ Á ÁA
D–HÁ Á ÁA
O4–H4AÁ Á ÁO3*
0.79 (2)
0.84 (2)
2.7863 (13)
2.7781 (13)
172.7 (18)
160.1 (17)
O4–H4BÁ Á ÁO3**
Symmetry codes.
*
Àx, Ày, Àz.
**
x, y À 1, z.
Experimental
Table 3
General methods
Bond lengths and angles for the complex (Å, °).
K1–O4
K1–O3
2.6652 (10)
2.7683 (9)
2.7819 (10)
2.8308 (9)
2.8493 (9)
2.8704 (9)
2.8972 (10)
2.9813 (10)
2.8309 (9)
2.9813 (10)
2.8705 (9)
2.7819 (10)
O2–K1vii
2.8493 (9)
All starting materials and organic solvents were purchased from
commercial sources and used as received, unless noted otherwise.
IR spectrum was performed on a Perkin Elmer, Spectrum 400 (res-
olution; 0.5–4 cmÀ1). CHN analysis was performed using a CE-440
Elemental analyzer. The 1H- and 13C NMR were performed using a
BrukerAvance 400. Mass spectrum was recorded on a Thermo
Fisher Exactive Orbitrap mass spectrometer coupled to an Advion
TriVersa Nanomate injection system.
O2–K1iv
O2–N1
O1–N1
O3–C4
N1–C1
C1–C6
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
2.8972 (10)
1.2484 (14)
1.2430 (14)
1.2891 (14)
1.4187 (15)
1.3983 (17)
1.4006 (16)
1.3735 (17)
1.4293 (16)
1.4292 (16)
1.3693 (17)
K1–O4i
K1–O1ii
K1–O2iii
K1–O3iv
K1–O2v
K1–O1v
O1–K1ii
O1–K1iv
O3–K1i
O4–K1iv
X-ray structures solution and refinement for the polymeric complex
O4–K1–O3
146.88 (3)
135.11 (3)
77.05 (3)
73.16 (3)
126.34 (3)
85.21 (3)
74.97 (3)
76.12 (3)
147.90 (3)
96.75 (3)
77.20 (3)
130.91 (3)
58.85 (3)
73.39 (3)
152.11 (3)
72.63 (3)
89.17 (3)
111.82 (3)
143.95 (3)
85.11 (3)
88.25 (3)
107.77 (3)
72.57 (3)
69.23 (3)
144.549 (14)
118.04 (3)
O3iv–K1–O1v
O2v–K1–O1v
N1–O1–K1ii
N1–O1–K1iv
K1ii–O1–K1vi
N1–O2–K1vii
N1–O2–K1iv
K1vii–O2–K1iv
C4–O3–K1
C4–O3–K1i
K1–O3–K1i
K1–O4–K1iv
O1–N1–O2
O1–N1–C1
O2–N1–C1
C6–C1–C2
72.43 (3)
43.26 (3)
161.62 (8)
93.89 (7)
88.22 (2)
149.50 (8)
97.82 (7)
94.89 (3)
106.54 (7)
122.55 (7)
91.71 (2)
O4–K1–O4i
O3–K1–O4i
O4–K1–O1ii
O3–K1–O1ii
O4i–K1–O1ii
O4–K1–O2iii
O3–K1–O2iii
O4i–K1–O2iii
O1ii–K1–O2iii
O4–K1–O3iv
O3–K1–O3iv
O4i–K1–O3iv
O1ii–K1–O3iv
O2iii–K1–O3iv
O4–K1–O2v
O3–K1–O2v
O4i–K1–O2v
O1ii–K1–O2v
O2iii–K1–O2v
O3iv–K1–O2v
O4–K1–O1v
O3–K1–O1v
O4i–K1–O1v
O1ii–K1–O1v
O2iii–K1–O1v
X-ray diffraction data for the complex was collected at 100(2) K
on a Bruker ApexII CCD diffractometer using Mo-K
a radiation
(k = 0.71073 Å). Data reduction was performed using Bruker SAINT.
SHELXTL was used to solve and refine the structures [7]. The struc-
tures were solved by direct methods and refined on F2 using all the
reflections [8]. All the non-hydrogen atoms were refined using
anisotropic atomic displacement parameters and hydrogen atoms
bonded to carbon were inserted at calculated positions using a rid-
ing model. Hydrogen atoms bonded to water oxygen atom (O4)
were located from difference maps and refined with temperature
factors riding on the carrier atom. Details of the crystal data and
refinement are given Table 1. Hydrogen bond parameters are given
in Table 2 and bond lengths and angles are given in Table 3.
95.94 (3)
120.96 (10)
119.66 (10)
119.36 (10)
120.99 (11)
119.41 (10)
119.56 (11)
119.46 (11)
121.43 (11)
121.71 (11)
121.31 (10)
116.98 (10)
121.54 (11)
119.60 (11)
C6–C1–N1
C2–C1–N1
C3–C2–C1
Preparation of the polymeric complex (KNP)
C2–C3–C4
O3–C4–C5
O3–C4–C3
C5–C4–C3
C6–C5–C4
C5–C6–C1
p-Nitrophenol (1 mmol, 0.139 g) in acetone (10 ml) and K2CO3
(0.5 mmol, 0.069 g) in acetone (5 ml) were mixed and refluxed
Table 1
Crystallographic data.
Symmetry codes.
Identification code
K1
i
Àx, y + 1/2, Àz + 1/2.
ii
Àx + 1, Ày, Àz + 1.
Empirical formula
Formula weight
T/K
Crystal system
Space group
C6H6KNO4
195.22
100(2)
Monoclinic
P21/c
iii
Àx + 1, y À 1/2, Àz + 1/2.
Àx, y À 1/2, Àz + 1/2.
x À 1, Ày + 1/2, z À 1/2.
x + 1, Ày + 1/2, z + 1/2.
Àx + 1, y + 1/2, Àz + 1/2.
iv
v
vi
vii
Unit cell
a (Å)
b (Å)
10.4828 (2)
7.2887 (1)
11.2186 (2)
90
117.682 (1)
90
759.06 (2)
4
1.708
for 4 h at 358 K. An intense light brown coloration appeared imme-
diately. After one week, well-formed light brown crystals grew on
the walls. A single crystal of dimensions 0.33 Â 0.23 Â 0.16 mm3
was selected from mother liquor and mounted for X-ray diffraction
study at low temperature.
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
Yield: 88%, color: light brown, M.p.: 127 °C. Anal. (%) Found
Z
Calculated density (g/cm3)
Crystal size (mm3)
(Calculated for C6H6KNO4):
C 36.95(36.92), H 3.10(3.07), N
7.18(7.20). 1H NMR (d, ppm): 6.25–7.55 (4H, Ar–H). 13C NMR (d,
ppm): 115.20–149.10 (Ar–C). Mass Spectrum (LC/MS APCI):
m/z 196 [M+1]+ (40%), 195 [M]+ (100%). FTIR (KBr, cmÀ1): 2960
0.33 Â 0.23 Â 0.16
Abs. coeff. (mmÀ1
Refl. collected
)
0.670
6878
1894 [0.0204]
Ind. Refl. [Rint
]
m
(C–H)aromatic, 1455 m(NO2), 1345 m(phenolic C–O). UV–vis (kmax
R1, wR2 [I > 2
r
(I)]
0.0245, 0.0637
0.0274, 0.0655
1.064
max), nm). EtOH; 344(0.42 Â 103), 459(0.36 Â 103), MeOH;
R1, wR2 (all data)
(e
Goodness-of-fit on F2
319(1.19 Â 103),
449(0.61 Â 103),
DMF,
316(0.67 Â 103),
CCDC number
987883
448(0.35 Â 103), Ethylacetate; 349(0.19 Â 103), 454(0.13 Â 103).

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G. Ceyhan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 142 (2015) 8–14
93.0
92
90
88
86
84
82
80
78
76
74
72
70
68
66
64
62
60
58
56
54
52
50
48.0
%T
4000.0 3600
3200
2800
2400
2000
1800
cm-1
1600
1400
1200
1000
800
600 450.0
Fig. 1. FT-IR spectrum of the K+ complex.
multiplets in the 6.25–7.55 ppm range can be attributed to the aro-
matic ring protons. In the 13C NMR spectrum, the aromatic ring
carbon atoms were observed in the range of 115.20–149.10 ppm.
In the mass spectrum of the complex KNP, the molecular ion peak
was observed at m/e 195. In the FT-IR spectrum of the complex, the
vibrations at 2960, 1455 and 1345 cmÀ1 can be assigned to the aro-
matic t(C–H), nitro t(NO2) and phenolic t(C–O) groups vibrations,
respectively Fig. 1. In order to investigate the solvent effect, the
electronic properties of the complex were studied in the different
solvents such as EtOH, MeOH, DMF and ethylacetate. The elec-
tronic spectra of the coordination complex are given in Fig. 2.
While the complex has maximum absorption band in the MeOH,
it has lowest band in the ethylacetate solvent. In all solvents, two
absorption bands were absorbed in the 459–316 nm range. These
Fig. 2. Electronic absorption spectra of the coordination polymer complex (KNP) in
the different solvents.
absorption bands can be attributed to the n–p and p–
p⁄ transitions
[9]. In ethanol, the absorption bands shifted to longer wavelength.
This situation shows that the polarity of the solvents effected the
transitions.
Results and discussion
Electrochemical properties of the coordination polymer com-
plex (KNP) were studied in DMF – 0.1 M NBu4BF4 as supporting
electrolyte at 293 K. In order to study the effects of the solvent
and the scan rates on electrochemical behaviors, two different sol-
vents (DMF and acetonitrile) and different scan rates (100, 150,
200, 250, 500, 750, 1000 mV/s) were used against an internal ferro-
cence–ferrocenium standard. The obtained data are given in
Table 4. The electrochemical curves of the complex KNP are shown
A novel polymeric potassium complex (KNP) was synthesized
by the reaction of p-nitrophenol and K2CO3 in acetone in high yield
and purity. The complex is stable at room temperature and soluble
in common organic solvents such as DMSO and DMF, EtOH, MeOH,
CH3CN, CH3Cl and CH2Cl2. Elemental analysis data are given in the
experimental section and are in well agreement with the theoret-
ical values. In the 1H NMR spectrum of the complex KNP, the
Table 4
The electrochemical data of the polymeric potassium complex (KNP).
Compound
KNP
Solvent
DMF
Concentration (M)
Scan rate (mV/s)
Epa (V)
Epc (V)
Ipa/Ipc
E1/2 (V)
DEp (V)
1 Â 10À3
100
250
500
750
1000
100
250
500
750
1000
À0.18, 0.41, 0.89
À0.25, 0.42, 0.87
À0.32, 0.36, 0.81
À0.35, 0.32, 0.76
À0.41, 0.28, 0.72
À1.25, À0.61, 0.20
À1,24, À0.62, 0.21
À1,23, À0.65, 0.20
À1,22, À0.67, .020
À1.21, À0.70, 0.23
0.49, À1,61
0.47, À1.61
0.45, À1.60
0.41, À1.61
0.37, À1.60
0.75, À0.62
0,74, À0.62
0.73, À0. 65
0.72, À0.67
0.70, À0.70
0.83
0.89
0.80
0.78
0.75
1.00
1.00
1.00
1.00
1.00
–
–
–
–
0.40
0.40
0.36
0.35
0.35
0.60
0.62
0.58
0.52
0.51
–
ACN
0.61
0.62
0.65
0.67
0.70
All the potentials are referenced to Ag+/AgCl; where Epa and Epc are anodic and cathodic potentials, respectively.
D
Ep = Epa À Epc. E1/2 = 0.5 Â (Epa + Epc).

G. Ceyhan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 142 (2015) 8–14
11
process. On the other hand, in CH3CN solution, the complex has
five reversible redox process and, in this process, the nitro group
of the p-nitrophenol compound reduces to the primary amine
group and again oxidizes to the nitro group.
DSC study of the polymer complex was performed in the 20–
500 °C temperature range. The DSC curve of the complex KNP is
shown in Fig. 4. The melting point of the polymer complex is about
127 °C. The melting point is shown as a strong endothermic peak.
The peaks at about 245 and 280 °C temperatures are crystallization
peaks of the complex. The coordination polymer complex decom-
posed to the metal oxide (K2O) at the higher temperatures.
X-ray structure of the complex
X-ray structural data shows that crystals contains polymeric K+
complex of p-nitrophenol. Asymmetric unit consists of a p-nitro-
phenolate, a K+ ion and a water molecule (Fig. S1). All bond lengths
and angles in the phenyl rings have normal Csp2–Csp2 values and
are in the expected ranges (Table 3). The ligand (p-nitrophenolate)
is close to planar with small distortions by some atoms. Each
potassium ion in the polymeric structure is identical and eight-
coordinate, bonded to four nitro, two phenolate oxygen atoms
from five p-nitrophenolate ligands and two oxygen atoms from
two water molecules (Fig. 5). The same coordination contacts are
extended between the other symmetry-related molecules in their
respective planes to form a 2D coordination layers. Each oxygen
atoms of the ligand and water molecules bridge two potassium
ions in the structure. K–O distances range between 2.6652(10)
and 2.9813(10) Å. The K–O4 (water) distance is the shortest dis-
tance at 2.6652(10) Å.
The ligand p-nitrophenol is deprotonated and each phenolate
oxygen atom is involved in hydrogen bonding with water molecule
(O3Á Á ÁHO4) strengthening the polymeric structure (Figs. 6, S2 and
Table 2). Each water molecule bridge two potassium ions and
involved in two hydrogen bonding (as donor) with two phenolate
oxygen atoms (as acceptor) with distorted tetrahedral geometry.
Each potassium ions in the polymeric structure is linked ben-
zene rings (spacer) (Fig. 6). The shortest K–K distance in the chain
Fig. 3. (a and b) Cyclic voltammograms of the polymeric potassium complex (KNP)
in the presence of 0.1 M NBu4BF4 in the (a) DMF and (b) CH3CN solutions
(1 Â 10À3 M).
in Fig. 3a and b. In DMF and CH3CN solvents, the complex shows
three anodic and two cathodic peak potentials at all scan rates.
In DMF solution, the complex shows the quasi-reversible redox
is 4.047 Å (Fig. S2). There are
p–p edge to edge stacking interac-
Fig. 4. DSC curve of the polymeric potassium complex under nitrogen atmosphere in the 20–500 °C temperature range.

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G. Ceyhan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 142 (2015) 8–14
Fig. 5. Molecular structure of the complex showing coordination around potassium ions, hydrogen atom are omitted for clarity.
Molecular structures of Na+ and Mg2+ complexes of p-nitrophe-
nol have been reported [10–11]. It is informative to compare
molecular structure of the polymeric K+ complex of p-nitrophenol
with Na+ and Mg2+ analogous. The structure of Na+ complex of p-
nitrophenol contains p-nitrophenol molecules, p-nitrophenolate
anions and water molecules surrounding the sodium ion. One p-
nitrophenol molecule deprotonates for each sodium ion to balance
the charge. Each Na+ is six-coordinate bonding to two nitro group
oxygens of p-nitrophenol and p-nitrophenolate and four water
oxygen atoms (Fig. S3). Water molecules each serve to bridge
two Na+ ions resulting in a polymeric chain along the two fold axis
cations. The infinite polymeric chains [Na(p-nitrophenol)(p-nitro-
phenolate)(H2O)2]n are linked via hydrogen bonding between the
phenolate anions and phenol molecules. The structure of Mg2+
complex of p-nitrophenol [Mg(p-nitrophenolate)2(H2O)2]n is iso-
typic with that of the Na+ complex. In the structure of both Na
and Mg complexes of p-nitrophenol, phenolic oxygens do not
involve in coordination with metal ions but involves in hydrogen
bonding however in the structure of K+ complex phenolate oxygen
atoms coordinate to the K+ ions.
The structure of the K+ complex with the analogous complex of
the related ligand 4-(4-nitrophenyl)phenol was reported by Haase
et al. [12]. In general terms, the published structure of the poly-
meric complex [K(4-(p-nitrophenyl)phenolate)(H2O)]n (Fig. S4) is
very similar to that of the complex [K(p-nitrophenolate)(H2O)]n;
in both cases the K+ ion is 8-coordinate, both have similar K–O
bond distances. Both complexes show similar hydrogen bonding
Fig. 6. Polymeric chains showing hydrogen bonding within the chains and
interactions within the spacers.
p–p
tions observed within the structure. The N1–C3 edge of the nitro-
phenolate ring is stacked with the same section of an adjacent mol-
ecule under symmetry of operation of 1 À x, 1 À y, 1 À z; C3 and N1
are separated by a distance of 3.314 Å and centroid–centroid dis-
tance is 3.881 Å.
and p–p interactions.
The effect of different concentration on the photoluminescence
properties of the metal complex
Table 5
The effect of different concentration on the photoluminescence
properties of the polymeric potassium complex (KNP) was investi-
gated in the 1.0 Â 10À3–1.0 Â 10À7 M range in the DMF solution.
Obtained data are given in Table 5. At room temperature, the poly-
meric potassium complex exhibits similar emission spectra in the
UV–vis region. The emission and excitation spectra of the poly-
meric potassium complex (KNP) in the DMF are shown in Fig. 7a
and b. In the 1.0 Â 10À3 M concentration, the polymeric potassium
complex have highest emission peaks in the 628–666 nm range. In
the 1.0 Â 10À7 M concentration, the emission peaks of the poly-
meric potassium complex have both lowest intensity and also shift
The obtained absorption data from different concentrations of the DMF solution KNP
complex.
Concentration (M)
KNP
Excitation
k (nm)
Emission
A (abs)
k (nm)
A (abs)
1 Â 10À3
1 Â 10À4
1 Â 10À5
1 Â 10À6
1 Â 10À7
557.61
556.42
555.31
554.21
547.06
1000.00
832.66
536.61
372.20
330.10
613.23
622.46
625.19
634.72
637.61
497.45
260.57
132.23
61.21
39.52

G. Ceyhan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 142 (2015) 8–14
13
Fig. 7. (a and b) Photoluminescence of the polymeric potassium complex (KNP) (a) excitation, (b) emission in the DMF solution (1 Â 10À3–1 Â 10À7 M).
to the lower regions (628 nm). The quantity of the polymeric
potassium complex have the effect on the emission peaks. Similar
properties were shown also for excitation peaks of the polymeric
potassium complex. In the 1.0 Â 10À3 M concentration, the ligands
have highest excitation peaks in the 557–547 nm range. In the
1.0 Â 10À7 M concentration, the excitation peaks of the ligands
have both lowest intensity and also shift to the lower regions
(547 nm).
Conclusions
In conclusion, a novel polymeric complex was prepared from p-
nitrophenol and K2CO3. Molecular structure of the complex was
successfully characterized by X-ray diffraction study. Each potas-
sium ion in the complex is eight-coordinate, coordinated to four
nitro, two phenolate oxygen atoms from five p-nitrophenolate
ligands and two oxygen atoms from two water molecules. The

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G. Ceyhan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 142 (2015) 8–14
complex has an interesting thermal, electrochemical and electronic
properties. Thermal study shows that crystallization peaks of the
complex were found to be 245 and 280 °C. The redox processes
in the CH3CN solution were found to be reversible at all potentials.
can be found, in the online version, at http://dx.doi.org/10.1016/j.
saa.2015.01.114.
References
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CCDC 987883 contains the supplementary crystallographic data
for the complex. These data can be obtained free of charge via
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